Patent Publication Number: US-2021187175-A1

Title: Blockage and leak detection in multiple dressing reduced pressure wound therapy systems

Description:
TECHNICAL FIELD 
     Embodiments of the present disclosure relate to methods and apparatuses for dressing and treating a wound with negative or reduced pressure therapy or topical negative pressure (TNP) therapy. In particular, but without limitation, embodiments disclosed herein relate to negative pressure therapy devices, methods for controlling the operation of TNP systems, and methods of using TNP systems. 
     BACKGROUND 
     Many different types of wound dressings are known for aiding in the healing process of a human or animal. These different types of wound dressings include many different types of materials and layers, for example, pads such as gauze pads and/or foam pads. Topical negative pressure (“TNP”) therapy, sometimes referred to as vacuum assisted closure, negative pressure wound therapy, or reduced pressure wound therapy, is widely recognized as a beneficial mechanism for improving the healing rate of a wound. Such therapy is applicable to a broad range of wounds such as incisional wounds, open wounds and abdominal wounds or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  illustrates a reduced pressure wound therapy system (a TNP system) according to some embodiments. 
         FIG. 2  illustrates a pump assembly having a canister according to some embodiments. 
         FIG. 3A  illustrates an electrical component schematic of a pump assembly according to some embodiments. 
         FIG. 3B  illustrates a block diagram of certain components of a pump assembly according to some embodiments. 
         FIGS. 4A and 4B  illustrate TNP systems including a pump assembly and canister and illustrating flexible suction adapters being applied to multiple wounds according to some embodiments. 
         FIG. 5  illustrates another embodiment of multiple dressing TNP system. 
         FIG. 6  illustrates a TNP system that includes a pump assembly as well as an inlet manifold branching attachment, pressure sensor and a plurality of fluid flow paths, wound dressings positioned over wounds according to some embodiments. 
         FIG. 7  illustrates a wound dressing according to some embodiments. 
         FIG. 8  illustrates a cross section of a fluidic connector connected to a wound dressing according to some embodiments. 
         FIG. 9  illustrates a process for providing negative pressure wound therapy according to some embodiments. 
         FIG. 10  illustrates a process for providing negative pressure wound therapy according to some embodiments. 
         FIG. 11  illustrates pressure versus time graph according to some embodiments. 
         FIG. 12  illustrates pressure versus time graphs for different dressing sizes according to some embodiments. 
         FIG. 13  illustrates a process for providing negative pressure wound therapy according to some embodiments. 
         FIGS. 14A-14D  illustrate graphs of peak-to-trough pressure signals according to some embodiments. 
         FIG. 15  illustrates pressure versus time graphs when a leak condition is detected according to some embodiments. 
       SUMMARY 
       A negative pressure wound therapy apparatus can include a negative pressure source configured to couple, via a plurality of fluid flow paths, to a plurality of wound dressings and provide negative pressure to the plurality of wound dressings. The plurality of fluid flow paths can include a first fluid flow path configured to fluidically connect a first wound dressing to the negative pressure source, the first wound dressing with a first fluid retention capacity and a second fluid flow path configured to fluidically connect a second wound dressing to the negative pressure source, the second wound dressing with a second fluid retention capacity. The apparatus can include at least one pressure sensor configured to measure pressure associated with the plurality of fluid flow paths and a controller configured to operate the negative pressure source. The controller can be further configured to receive a plurality of pressure measurements from the at least one pressure sensor, determine from at least some of the plurality of pressure measurements first and second fluid retention capacities of the first and second wound dressings, determine a blockage threshold based at least in part on the determined first and second fluid retention capacities, detect presence of a blockage in at least one of the first or second fluid flow paths based at least in part on comparing at least some of the pressure measurements associated with flow of fluid in at least one of the first or second fluid flow paths to the blockage threshold, and provide an indication of the blockage in response to determining that the blockage threshold is satisfied. 
       The apparatus of any of the preceding paragraphs can include one or more of the following features. Blockage can indicate that at least one of the first or second wound dressings contains an amount of fluid that is greater than a capacity threshold but less than the first or second fluid retention capacity. The controller can be further configured to determine the first and second fluid retention capacities of the first and second wound dressings based on a duration of time for achieving a negative pressure setpoint following activation of the negative pressure source. The controller can be further configured to deactivate the negative pressure source when the negative pressure setpoint has been achieved. The duration of time can be inversely proportional to a combined first and second fluid retention capacities of the first and second wound dressing. The controller can be further configured to detect a combined first and second fluid retention capacities of the first and second wound dressing. The controller can be further configured to determine a rate of pressure change in the first and second fluid flow paths based on at least some of the pressure measurements and determine the first and second fluid retention capacities of the first and second wound dressings based on the rate of pressure change. The rate of pressure change can be inversely proportional to dressing capacity. 
       The apparatus of any of the preceding paragraphs can include one or more of the following features. The controller can be configured to determine at least one peak-to-trough pressure measurement and detect presence of the blockage based on comparing the at least one peak-to-trough pressure measurement to the blockage threshold. The blockage can be caused by at least one of the first or second dressing being substantially filled with exudate. The controller can be further configured to determine a leak threshold based at least in part on the determined first and second fluid retention capacities, detect presence of a leak in at least one of the first or second fluid flow paths based at least in part on comparing at least some of the pressure measurements associated with flow of fluid in at least one of the first or second fluid flow paths to the leak threshold, and provide an indication of the leak in response to determining that the leak threshold is satisfied. The apparatus can be canisterless. 
       A method of operating a negative pressure wound therapy apparatus can include, by a controller of the negative pressure wound therapy apparatus, operating a negative pressure source of the negative pressure wound therapy apparatus, wherein the negative pressure source is configured to couple, via a plurality of fluid flow paths, to a plurality of wound dressings, the plurality of fluid flow paths including a first fluid flow path configured to fluidically connect a first wound dressing to the negative pressure source, the first wound dressing with a first fluid retention capacity and a second fluid flow path configured to fluidically connect a second wound dressing to the negative pressure source, the second wound dressing with a second fluid retention capacity. The method can further include, by the controller, receiving a plurality of pressure measurements from the at least one pressure sensor of the negative pressure wound therapy apparatus, determining from at least some of the plurality of pressure measurements first and second fluid retention capacities of the first and second wound dressings, determining a blockage threshold based at least in part on the determined first and second fluid retention capacities, detecting presence of a blockage in at least one of the first or second fluid flow paths based at least in part on comparing at least some of the pressure measurements associated with flow of fluid in at least one of the first or second fluid flow paths to the blockage threshold, and providing an indication of the blockage in response to determining that the blockage threshold is satisfied. 
       The method of any of the preceding paragraphs can include one or more of the following features. Blockage can indicate that at least one of the first or second wound dressings contains an amount of fluid that is greater than a capacity threshold but less than the first or second fluid retention capacity. The method can further include, by the controller, determining the first and second fluid retention capacities of the first and second wound dressings based on a duration of time for achieving a negative pressure setpoint following activation of the negative pressure source. The method can further include, by the controller, deactivating the negative pressure source when the negative pressure setpoint has been achieved. The duration of time can be inversely proportional to a combined first and second fluid retention capacities of the first and second wound dressing. The method can further include, by the controller, detecting a combined first and second fluid retention capacities of the first and second wound dressing. 
       The method of any of the preceding paragraphs can include one or more of the following features. The method can further include, by the controller, determining a rate of pressure change in the first and second fluid flow paths based on at least some of the pressure measurements and determining the first and second fluid retention capacities of the first and second wound dressings based on the rate of pressure change. The rate of pressure change can be inversely proportional to dressing capacity. The method can further include, by the controller, determining at least one peak-to-trough pressure measurement and detect presence of the blockage based on comparing the at least one peak-to-trough pressure measurement to the blockage threshold. Blockage can be caused by at least one of the first or second dressing being substantially filled with exudate. The method can further include, by the controller, determining a leak threshold based at least in part on the determined first and second fluid retention capacities, detecting presence of a leak in at least one of the first or second fluid flow paths based at least in part on comparing at least some of the pressure measurements associated with flow of fluid in at least one of the first or second fluid flow paths to the leak threshold, and providing an indication of the leak in response to determining that the leak threshold is satisfied. The negative pressure wound therapy apparatus can be canisterless. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     Embodiments disclosed herein relate to systems and methods of treating a wound with reduced pressure. As is used herein, reduced or negative pressure levels, such as −X mmHg, represent pressure levels relative to normal ambient atmospheric pressure, which can correspond to 760 mmHg (or 1 atm, 29.93 inHg, 101.325 kPa, 14.696 psi, etc.). Accordingly, a negative pressure value of −X mmHg reflects absolute pressure that is X mmHg below 760 mmHg or, in other words, an absolute pressure of (760−X) mmHg. In addition, negative pressure that is “less” or “smaller” than X mmHg corresponds to pressure that is closer to atmospheric pressure (for example, −40 mmHg is less than −60 mmHg). Negative pressure that is “more” or “greater” than −X mmHg corresponds to pressure that is further from atmospheric pressure (for example, −80 mmHg is more than −60 mmHg). Local ambient atmospheric pressure can be used as a reference point, and such local atmospheric pressure may not necessarily be, for example, 760 mmHg. 
     Embodiments of the present disclosure are generally applicable to use in topical negative pressure (TNP) or reduced pressure therapy systems. Briefly, negative pressure wound therapy assists in the closure and healing of many forms of “hard to heal” wounds by reducing tissue oedema, encouraging blood flow and granular tissue formation, or removing excess exudate and can reduce bacterial load (and thus infection risk). In addition, the therapy allows for less disturbance of a wound leading to more rapid healing. TNP therapy systems can also assist in the healing of surgically closed wounds by removing fluid. In some embodiments, TNP therapy helps to stabilize the tissue in the apposed position of closure. A further beneficial use of TNP therapy can be found in grafts and flaps where removal of excess fluid is important and close proximity of the graft to tissue is required in order to ensure tissue viability. 
     Negative Pressure System 
       FIG. 1  illustrates of a negative or reduced pressure wound treatment (or TNP) system  100  including a wound filler  130  placed inside a wound cavity  110 , the wound cavity sealed by a wound cover  120  according to some embodiments. The wound filler  130  in combination with the wound cover  120  can be referred to as wound dressing. A flow path  140 , such as a single or multi lumen tube or conduit, is connected to the wound cover  120  with a negative pressure wound therapy device, for example pump assembly  150 , configured to supply reduced pressure. The wound cover  120  can be in fluidic communication with the wound cavity  110 . In any of the system embodiments disclosed herein, as in the embodiment illustrated in  FIG. 1 , the pump assembly can be a canisterless pump assembly (meaning that exudate is collected in the wound dressing or is transferred via tube  140  for collection to another location). However, any of the pump assembly embodiments disclosed herein can be configured to include or support a canister. Additionally, in any of the system embodiments disclosed herein, any of the pump assembly embodiments can be mounted to or supported by the dressing, or adjacent to the dressing. 
     The wound filler  130  can be any suitable type, such as hydrophilic or hydrophobic foam, gauze, inflatable bag, and so on. The wound filler  130  can be conformable to the wound cavity  110  such that it substantially fills the cavity. The wound cover  120  can provide a substantially fluid impermeable seal over the wound cavity  110 . The wound cover  120  can have a top side and a bottom side, and the bottom side adhesively (or in any other suitable manner) seals with wound cavity  110 . The conduit  140  or lumen or any other conduit or lumen disclosed herein can be formed from polyurethane, PVC, nylon, polyethylene, silicone, or any other suitable material. 
     Some embodiments of the wound cover  120  can have a port (not shown) configured to receive an end of the conduit  140 . In other embodiments, the conduit  140  can otherwise pass through or under the wound cover  120  to supply reduced pressure to the wound cavity  110  so as to maintain a desired level of reduced pressure in the wound cavity. The conduit  140  can be any suitable article configured to provide at least a substantially sealed fluid flow pathway between the pump assembly  150  and the wound cover  120 , so as to supply the reduced pressure provided by the pump assembly  150  to wound cavity  110 . 
     The wound cover  120  and the wound filler  130  can be provided as a single article or an integrated single unit. In some embodiments, no wound filler is provided and the wound cover by itself may be considered the wound dressing. The wound dressing may then be connected, via the conduit  140 , to a source of negative pressure, such as the pump assembly  150 . The pump assembly  150  can be miniaturized and portable, although larger conventional pumps such can also be used. 
     The wound cover  120  can be located over a wound site to be treated. The wound cover  120  can form a substantially sealed cavity or enclosure over the wound site. In some embodiments, the wound cover  120  can be configured to have a film having a high water vapour permeability to enable the evaporation of surplus fluid, and can have a superabsorbing material contained therein to safely absorb wound exudate. It will be appreciated that throughout this specification reference is made to a wound. In this sense it is to be understood that the term wound is to be broadly construed and encompasses open and closed wounds in which skin is torn, cut or punctured or where trauma causes a contusion, or any other surficial or other conditions or imperfections on the skin of a patient or otherwise that benefit from reduced pressure treatment. A wound is thus broadly defined as any damaged region of tissue where fluid may or may not be produced. Examples of such wounds include, but are not limited to, acute wounds, chronic wounds, surgical incisions and other incisions, subacute and dehisced wounds, traumatic wounds, flaps and skin grafts, lacerations, abrasions, contusions, burns, diabetic ulcers, pressure ulcers, stoma, surgical wounds, trauma and venous ulcers or the like. The components of the TNP system described herein can be particularly suited for incisional wounds that exude a small amount of wound exudate. 
     Some embodiments of the system are designed to operate without the use of an exudate canister. Some embodiments can be configured to support an exudate canister. In some embodiments, configuring the pump assembly  150  and tubin  140  so that the tubin  140  can be quickly and easily removed from the pump assembly  150  can facilitate or improve the process of dressing or pump changes, if necessary. Any of the pump embodiments disclosed herein can be configured to have any suitable connection between the tubing and the pump. 
     The pump assembly  150  can be configured to deliver negative pressure of approximately −80 mmHg, or between about −20 mmHg and −200 mmHg. Note that these pressures are relative to normal ambient atmospheric pressure thus, −200 mmHg would be about 560 mmHg in practical terms. The pressure range can be between about −40 mmHg and −150 mmHg. Alternatively a pressure range of up to −75 mmHg, up to −80 mmHg or over −80 mmHg can be used. Also a pressure range of below −75 mmHg can be used. Alternatively a pressure range of over approximately −100 mmHg, or even 150 mmHg, can be supplied by the pump assembly 150. 
     The pump assembly  150  can provide continuous or intermittent negative pressure therapy. Continuous therapy can be delivered at above −25 mmHg, −25 mmHg, −40 mmHg, −50 mmHg, −60 mmHg, −70 mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120 mmHg, −140 mmHg, −160 mmHg, −180 mmHg, −200 mmHg, or below −200 mmHg. Intermittent therapy can be delivered between low and high negative pressure setpoints. Low setpoint can be set at above 0 mmHg, 0 mmHg, −25 mmHg, −40 mmHg, −50 mmHg, −60 mmHg, −70 mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120 mmHg, −140 mmHg, −160 mmHg, −180 mmHg, or below −180 mmHg. High setpoint can be set at above −25 mmHg, −40 mmHg, −50 mmHg, −60 mmHg, −70 mmHg, −80 mmHg, −90 mmHg, −100 mmHg, −120 mmHg, −140 mmHg, −160 mmHg, −180 mmHg, −200 mmHg, or below −200 mmHg. During intermittent therapy, negative pressure at low setpoint can be delivered for a first time duration, and upon expiration of the first time duration, negative pressure at high setpoint can be delivered for a second time duration. Upon expiration of the second time duration, negative pressure at low setpoint can be delivered. The first and second time durations can be same or different values. The first and second durations can be selected from the following range: less than 2 minutes, 2 minutes, 3 minutes, 4 minutes, 6 minutes, 8 minutes, 10 minutes, or greater than 10 minutes. In some embodiments, switching between low and high setpoints and vice versa can be performed according to a step waveform, square waveform, sinusoidal waveform, and the like. 
     The TNP system  100  moreover can include multiple wound dressings connected to the pump assembly  150 , such as described in greater detail with respect to  FIGS. 4A and 4B . The performance and wound healing capabilities (such as, fluid management) of the TNP system  100  with multiple wound dressings with the pump assembly  150  can be equivalent to or exceed that of a standard single wound dressing with single pump set-up. 
     In operation, the wound filler  130  is inserted into the wound cavity  110  and wound cover  120  is placed so as to seal the wound cavity  110 . The pump assembly  150  provides a source of a negative pressure to the wound cover  120 , which is transmitted to the wound cavity  110  via the wound filler  130 . Fluid (for example, wound exudate) is drawn through the conduit  140 , and can be stored in a canister. In some embodiments, fluid is absorbed by the wound filler  130  or one or more absorbent layers (not shown). 
     Wound dressings that may be utilized with the pump assembly and other embodiments of the present application include Renasys-F, Renasys-G, Renasys AB, and Pico dressings available from Smith &amp; Nephew. Any of the dressings described herein can be used with Smith and Nephew&#39;s Renasys Soft Port connector or interface between the dressing and the pump assembly. For example, Renasys Soft Port connector can be positioned in the flow path  140  and serve as a port for the wound dressing. In other embodiments, other suitable wound dressings can be utilized. 
     Pump Assembly and Canister 
       FIG. 2  illustrates a pump assembly  230  having a canister  220  according to some embodiments. As is illustrated, the pump assembly  230  and the canister can be connected, thereby forming a TNP device or system. The pump assembly  230  can be similar to or the same as the pump assembly  150  in some embodiments. 
     The pump assembly  230  includes one or more indicators, such as visual indicator  202  configured to indicate alarms and visual indicator  204  configured to indicate status of the TNP system. The indicators  202  and  204  can be configured to alert a user, such as patient or medical care provider, to a variety of operating or failure conditions of the system, including alerting the user to normal or proper operating conditions, pump failure, power supplied to the pump or power failure, detection of a leak within the wound cover or flow pathway, suction blockage, no flow condition, canister full condition, or any other similar or suitable conditions or combinations thereof. The pump assembly  230  can include additional indicators. The pump assembly can use a single indicator or multiple indicators. Any suitable indicator can be used such as visual, audio, tactile, vibration, indicator, and so on. The indicator  202  can be configured to signal alarm conditions, such as canister full, power low, conduit  140  disconnected, seal broken in the wound seal  120 , and so on. The indicator  202  can be configured to display red flashing light to draw user&#39;s attention. The indicator  204  can be configured to signal status of the TNP system, such as therapy delivery is ok, leak detected, and so on. The indicator  204  can be configured to display one or more different colors of light, such as green, yellow, etc. For example, green light can be emitted when the TNP system is operating properly and yellow light can be emitted to indicate a warning. 
     The pump assembly  230  includes a display or screen  206  mounted in a recess  208  formed in a case of the pump assembly. The display  206  can be a touch screen display. The display  206  can support playback of audiovisual (AV) content, such as instructional videos. The display  206  can render a number of screens or graphical user interfaces (GUIs) for configuring, controlling, and monitoring the operation of the TNP system. The pump assembly  230  includes a gripping portion  210  formed in the case of the pump assembly. The gripping portion  210  can be configured to assist the user to hold the pump assembly  230 , such as during removal of the canister  220 . The canister  220  can be replaced with another canister, such as when the canister  220  as been filled with fluid. 
     The pump assembly  230  includes one or more keys or buttons  212  configured to allow the user to operate and monitor the operation of the TNP system. As is illustrated, there buttons  212   a ,  212   b , and  212   c  (collectively referred to as buttons  212 ) are included. Button  212   a  can be configured as a power button to turn on/off the pump assembly  230 . Button  212   b  can be configured as a play/pause button for the delivery of negative pressure therapy. For example, pressing the button  212   b  can cause therapy to start, and pressing the button  212   b  afterward can cause therapy to pause or end. Button  212   c  can be configured to lock the display  206  or the buttons  212 . For instance, button  212   c  can be pressed so that the user does not unintentionally alter the delivery of the therapy. Button  212   c  can be depressed to unlock the controls. In other embodiments, additional buttons can be used or one or more of the illustrated buttons  212   a ,  212   b , or  212   c  can be omitted. Multiple key presses or sequences of key presses can be used to operate the pump assembly  230 . 
     The pump assembly  230  includes one or more latch recesses  222  formed in the cover. In the illustrated embodiment, two latch recesses  222  can be formed on the sides of the pump assembly  230 . The latch recesses  222  can be configured to allow attachment and detachment of the canister  220  using one or more canister latches  221 . The pump assembly  230  includes an air outlet  224  for allowing air removed from the wound cavity  110  to escape. Air entering the pump assembly can be passed through one or more suitable filters, such as antibacterial filters. This can maintain reusability of the pump assembly. The pump assembly  230  includes one or more strap mounts  226  for connecting a carry strap to the pump assembly  230  or for attaching a cradle. In the illustrated embodiment, two strap mounts  226  can be formed on the sides of the pump assembly  230 . In some embodiments, various features are omitted or various additional features are added to the pump assembly  230 . 
     The canister  220  is configured to hold fluid (for example, exudate) removed from the wound cavity  110 . The canister  220  includes one or more latches  221  for attaching the canister to the pump assembly  230 . In the illustrated embodiment, the canister  220  includes two latches  221  on the sides of the canister. The exterior of the canister  220  can formed from frosted plastic so that the canister is substantially opaque and the contents of the canister and substantially hidden from plain view. The canister  220  includes a gripping portion  214  formed in a case of the canister. The canister  220  includes a substantially transparent window  216 , which can also include graduations of volume. The canister  220  includes a tubing channel  218  for connecting to the conduit  140 . In some embodiments, one or more of these features, such as the gripping portion  214 , are omitted or various additional features are added to the canister  220 . Any of the disclosed canisters may include or may omit a solidifier. 
     While  FIG. 2  illustrates a system with a canister, as discussed above with respect to different TNP system embodiments, a pump assembly may be canisterless. Further, some embodiments with a canister may be configured to operate in canisterless mode by detaching the canister. For example, the pump assembly  230  may operate in canisterless mode by detaching the canister  220  and essentially collecting exudate in the dressings or transferring the exudates to another location other than the canister  220 . 
     Electronics and Software 
       FIG. 3A  illustrates an electrical component schematic  300 A of a pump assembly, such as the pump assembly  230 , according to some embodiments. Electrical components can operate to accept user input, provide output to the user, operate the pump assembly and the TNP system, provide network connectivity, and so on. Electrical components can be mounted on one or more printed circuit boards (PCBs). As is illustrated, the pump assembly can include multiple processors. It may be advantageous to utilize multiple processors in order to allocate or assign various tasks to different processors. For example, one processor can be responsible for user activity, and another processor can be responsible for controlling the pump. This way, the activity of controlling the pump, which may necessitate a higher level of responsiveness (and corresponding to higher risk level), can be offloaded to a dedicated processor and, thereby, will not be interrupted by user interface tasks, which may take longer to complete because of interactions with the user. 
     The pump assembly can include a user interface processor or controller  310  configured to operate one or more components for accepting user input and providing output to the user, such as the display  206 , buttons  212 , etc. Input to the pump assembly and output from the pump assembly can controlled by an input/output (I/O) module  320 . For example, the I/O module can receive data from one or more ports, such as serial, parallel, hybrid ports, and the like. The processor  310  also receives data from and provides data to one or more expansion modules  360 , such as one or more USB ports, SD ports, Compact Disc (CD) drives, DVD drives, FireWire ports, Thunderbolt ports, PCI Express ports, and the like. The processor  310 , along with other controllers or processors, stores data in one or more memory modules  350 , which can be internal or external to the processor  310 . Any suitable type of memory can be used, including volatile or non-volatile memory, such as RAM, ROM, magnetic memory, solid-state memory, magnetoresistive random-access memory (MRAM), and the like. 
     In some embodiments, the processor  310  can be a general purpose controller, such as a low-power processor. In other embodiments, the processor  310  can be an application specific processor. The processor  310  can be configured as a “central” processor in the electronic architecture of the pump assembly, and the processor  310  can coordinate the activity of other processors, such as a pump control processor  370 , communications processor  330 , and one or more additional processors  380  (for example, processor for controlling the display  206 , processor for controlling the buttons  212 , etc.). The processor  310  can run a suitable operating system, such as a Linux, Windows CE, VxWorks, etc. 
     The processor  310 , alone or in combination with one or more other processors, can track and store various data, such as one or more of positioning data, therapy parameters, logs, device data, and so on. Data can be stored, for example, in the memory  350 . 
     The pump control processor  370  can be configured to control the operation of a negative pressure source or pump  390 . The pump  390  can be a suitable pump, such as a diaphragm pump, peristaltic pump, rotary pump, rotary vane pump, scroll pump, screw pump, liquid ring pump, pump (for example, diaphragm pump) operated by a piezoelectric transducer, voice coil pump, and the like. The pump control processor  370  can measure pressure in a fluid flow path, using data received from one or more pressure sensors, calculate the rate of fluid flow, and control the pump. The pump control processor  370  can control an actuator, such as a pump motor, so that a desired level of negative pressure is achieved in the wound cavity  110 . The desired level of negative pressure can be pressure set or selected by the user. In various embodiments, the pump control processor  370  controls the pump actuator (for example, pump motor) using pulse-width modulation (PWM). A control signal for driving the pump actuator can be a 0-100% duty cycle PWM signal. The pump control processor  370  can perform flow rate calculations and detect various conditions in a flow path. The pump control processor  370  can communicate information to the processor  310 . The pump control processor  370  can include internal memory or can utilize memory  350 . The pump control processor  370  can be a low-power processor. 
     A communications processor  330  can be configured to provide wired or wireless connectivity. The communications processor  330  can utilize one or more antennas  340  for sending and receiving data. The communications processor  330  can provide one or more of the following types of connections: Global Positioning System (GPS) technology, cellular connectivity (for example, 2G, 3G, LTE, 4G), Wi-Fi connectivity, Internet connectivity, and the like. Connectivity can be used for various activities, such as pump assembly location tracking, asset tracking, compliance monitoring, remote selection, uploading of logs, alarms, and other operational data, and adjustment of therapy settings, upgrading of software or firmware, and the like. The communications processor  330  can provide dual GPS/cellular functionality. Cellular functionality can, for example, be 3G functionality. The pump assembly can include a SIM card, and SIM-based positional information can be obtained. 
     The communications processor  330  can communicate information to the processor  310 . The communications processor  330  can include internal memory or can utilize memory  350 . The communications processor  330  can be a low-power processor. 
     Using the connectivity provided by the communications processor  330 , the device can upload any of the data stored, maintained, or tracked by the pump assembly. For example, the following information can be uploaded to a remote computer or server: activity log(s), which includes therapy delivery information, such as therapy duration, alarm log(s), which includes alarm type and time of occurrence; error log, which includes internal error information, transmission errors, and the like; therapy duration information, which can be computed hourly, daily, and the like; total therapy time, which includes therapy duration from first applying a particular therapy program or programs; lifetime therapy information; device information, such as the serial number, software version, power source level, etc.; device location information; patient information; and so on. The device can also download various operational data, such as therapy selection and parameters, firmware and software patches and upgrades, and the like. 
       FIG. 3B  illustrates a block diagram of certain components  300 B of a pump assembly, such as the pump assembly  230 , according to some embodiments. The components  300 B can include an inlet  395  (which can be similar to or the same as the inlet  252 ), the pump  390 , an exhaust  396 , a pressure sensor  397 , and the pump control processor  370 . The pump assembly of  FIG. 3B  can include some of the components of the pump assembly of  FIG. 3A . 
     The pump  390  can provide negative pressure in one or more fluid flow paths connecting the pump  390  (via the inlet  395 ) to one or more wound dressings placed over one or more wounds, such that the negative pressure is communicated through the inlet  395  to one or more fluid flow paths and the respective one or more wound dressings. 
     In some embodiments, the pump control processor  370  can determine the pressure at the inlet  395  or at any other location in the one or more fluid flow paths using data received from one or more pressure sensors, such as the pressure sensor  397  and control the pump  390  based on the determined pressure. The pump control processor  370  can, for instance, control one or more pump actuators, such as a pump motor of the pump  390 , so that a desired level of pressure is achieved at the wound. The desired level of pressure (or pressure setpoint) can be a pressure set or selected by the user or set automatically according to a mode of operation or setting for the pump assembly. 
     The components  300 B can further include one or more additional sensors (not shown), such as a tachometer  398 , positioned to detect or determine a level of activity of the pump  390  (for example, the pump motor) and provide indications responsive to the level of activity of the pump  390  to the pump control processor  370 . For example, a tachometer  398  can be separate from the pump  390  (for example, external to the pump) and positioned near or coupled to the pump  390 , and the tachometer  398  can detect a rotation (such as a partial rotation, complete rotation, or multiple partial or complete rotations) of the pump motor of the pump  390 . 
     In some implementations, one or more pressure sensors can be positioned in or fluidically connected to the one or more fluid flow paths to permit measurement of the pressure in the one or more fluid flow paths. The pressure measurements can be used to determine one or more of rate of change in pressure over time, minimum and maximum pressure, or peak-to-trough (or peak-to-peak) pressure differential. In some implementations, at least two pressure sensors can be positioned at different locations in the fluid flow path to provide differential pressure measurements. For example, a first pressure sensor can be positioned downstream of the wound dressing (such as at or near an inlet of the pump assembly) and a second pressure sensor can be positioned to detect pressure at or near the wound dressing or at or near a canister. This configuration can be accomplished by incorporating, in addition to one or more lumens forming a first fluid flow path connecting the pump assembly to the wound, a second fluid flow path that includes one or more lumens connecting the pump assembly to the wound dressing and through which the second pressure sensor can monitor pressure at or near the wound dressing or at or near the canister. The first and second fluid flow paths can be fluidically isolated from each other. When the at least two pressure sensors are used, the rate of change of pressure, peak-to-trough pressure, peak-to-peak pressure, maximum pressure, or the like in the first and second fluid flow paths can be determined and the difference in pressure detected between the first and second pressure sensors can be determined. These values, measured or derived, can be used separately or together to detect various operational conditions, such as leaks, blockages, canister full, presence of blood in the first fluid flow path or the second fluid flow path, etc. Additionally or alternatively, the values can be used to detect sizes of one or more connected wound dressings. Moreover, multiple redundant pressure sensors can be provided to protect against failure of one or more of the pressure sensors in some implementations. 
     Multiple Dressing Wound Therapy 
       FIGS. 4A and 4B  illustrate multiple dressing TNP systems  440   a ,  440   b  according to some embodiments. The multiple dressing TNP systems  440   a ,  440   a  may include a TNP device  434  capable of supplying negative pressure. The TNP device  434  can be similar to or the same as a combination of the pump assembly  230  and the canister  220 . 
     The TNP device  434  may be in fluidic connection with wound dressings  406   a ,  406   b  so as to supply negative pressure to wounds  430   a ,  430   b.  The fluidic connections between the wound dressings  406   a ,  406   b  and the TNP device  434  can be referred to as fluid flow paths (for example, the paths through which fluid aspirated from the wounds flow). For instance, one fluid flow path can include components providing fluidic connection from the TNP device  434  to the wound dressing  406   a . This fluid flow path can include the path from the first wound dressing  406   a  to an inlet of a branching attachment  444  in fluidic connection with the TNP device  434 . The multiple dressing TNP system  440   a  can include the wound dressings  406   a ,  406   b  (and corresponding fluid flow paths) in fluidic connection with the TNP device  434  via a plurality of connectors, such as Smith &amp; Nephew&#39;s Renasys Soft Port connectors. 
     Each of the wound dressings  406   a ,  406   b  and the corresponding fluid flow paths can include a variety of features or elements which match or are similar to features or elements of another wound dressing or fluid flow path the multiple dressing TNP systems  440   a ,  400   b . Moreover, for brevity and although not described in detail in some instances, features or elements described herein that are denoted with a common number but different letter may have similar or the same features as one another. 
     The multiple dressing TNP system  440   a  may include a Renasys Soft Port connector including a bridge  402   a  having a proximal end  403   a  and a distal end  405   a  and an applicator  420   a  at the distal end  405   a  of the bridge  402   a  forming a flexible suction interface or adapter. A connector  404   a  can be disposed at the proximal end  403   a  of the bridge  402   a  to provide fluidic connection between the wound dressing  406   a  and the TNP device  434 . A cap  436   a  may be provided with the multiple dressing TNP system  440   a  (and can in some cases, as illustrated, be attached to the connector  404   a ). The cap  436   a  can be useful in preventing fluids from leaking out of the proximal end  403   a  when the connector  404   a  is disconnected from the TNP device  434 . The wound dressings  406  may, in some implementations, collect the wound exudates and other fluids, and the TNP device  434  may not include a canister. In other implementations, multiple canisters are provided, for instance, one canister per wound dressing. The TNP device  434  can in one example be a Renasys Touch device, as manufactured by Smith &amp; Nephew. 
     The bridge  402   a  can include upper and lower channel layers (not shown) for channeling wound exudate away from the wound  430   a  and for transmitting negative pressure or vented air to the wound  430   a . The upper and lower channel layers can be elongate layers extending from the proximal end  403   a  to the distal end  405   a  and may each include a porous material, such as open-celled foams like polyethylene or polyurethane. One or more of the upper and lower channel layers may include a fabric, such as a knitted or woven spacer fabric or a nonwoven material. Suitable materials may also include terry-woven or loop-pile materials. The fibers may not necessarily be woven, and can include felted and flocked fibrous materials. The upper channel layer is optional, and the multiple dressing TNP system  440   a  may instead be provided with an open upper channel. 
     The multiple dressing TNP system  440   a  can be the same as the multiple dressing TNP system  440   b  except that the multiple dressing TNP system  440   b  illustrates the flexible suction adapters placed over the wounds  430   a ,  430   b.    
     The applicator  420   a  can be placed over an aperture  435   a  formed in a drape  431   a  that is placed over the wound  430   a , which may in some cases be filled with a wound packing material such as foam or gauze. Subsequently, with the TNP device  434  connected via a lumen or tube  440  or an inlet manifold branching attachment or connector  444  and a tube  442   a  to the connector  404   a , the TNP device  434  can be activated thereby supplying negative pressure to the wound  430   a , as well as in a similar manner to the wound  406   b . Application of negative pressure may be applied until a desired level of wound healing is achieved. 
     Although two wounds and wound dressings are illustrated in the multiple dressing TNP systems  440   a ,  400   b,  the TNP device  434  can provide treatment to more than two wounds in some embodiments. Moreover, an air leak  424   a  (sometimes referred to as a fluid leak or a controlled air leak) may be disposed in a fluid flow path, such as, at the proximal end  403   a  of the bridge  402   a . As described herein, in some embodiments, the bridge  402   a , the proximal end  403   a , the connector  404   a , the distal end  405   a , the applicator  420   a , the air leak  424   a , the drape  431   a , the aperture  435   a , the cap  436   a , and the tube  442   a  can respectively be or function the same as a bridge  402   b , a proximal end  403   b , a connector  404   b , a distal end  405   b , an applicator  420   b , an air leak  424   b , a drape  431   b , an aperture  435   b , a cap  436   b , and a tube  442   b.    
     Branching Attachment 
     The TNP device  434  can be in fluidic connection with the wound dressings  406   a ,  406   b  via the tubes  440 ,  442   a ,  442   b , the bridges  402   a ,  402   b , and an inlet manifold branching attachment  444 . As illustrated in  FIGS. 4A-4B , the inlet manifold branching attachment  444  can connect the TNP device  434  to a plurality of fluid flow paths via dressing conduit attachment portions  445   a ,  445   b . The inlet manifold branching attachment  444  can further include any number of additional dressing conduit attachment portions to be fluidically connected to a negative pressure attachment portion  446  via a joint. In some embodiments, the manifold branching attachment  444  can be connected directly to the TNP device  434  without using the tube  440 . 
     The negative pressure attachment portion 446 can, in some implementations, include multiple different attachment portions. Each of the attachment portions can include a shaft extending away from the joint and an inlet distal the joint. The multiple inlets can be configured to fluidically connect to the TNP device  434 . For instance, the inlets can include male or female non-luer connectors to attach to a corresponding male or female connector of a conduit or the TNP device  434 . 
     The inlet manifold branching attachment  444  can include one or more incorporated valves, clamps, caps, air leaks, or other flow regulator mechanisms which may be configured to admit fluid into a fluid flow path or, alternatively, block or restrict flow or passage of fluid through a fluid flow path. In some embodiments, valves, air leaks, or other flow regulation mechanisms in the inlet manifold branching attachment  444  can be opened or closed electronically. A controller of the TNP device  434  can, for instance, communicate with the valves, air leaks, etc. to open or close each one individually or as a unit. This communication can be wired or wireless. 
     The dressing conduit attachment portions  445   a ,  445   b  can include shafts forming the top portions of a Y- (two wound), W- (three wound) or other shape of the inlet manifold branching attachment. The proximal ends of dressing conduit shafts and the distal end of the pump conduit shaft can meet at a joint. In some implementations, the joint can include a hinge that allows rotation of the shafts about the joint. The inlet manifold branching attachment  444  can further be a W-shaped connector in some implementations, and the inlet manifold branching attachment  444  can include three or more dressing conduit attachment portions and one negative pressure attachment portion. 
     The inlet manifold branching attachment can include rigid plastic or flexible plastic tubing and can also or alternatively be encased in a soft silicone sleeve to increase patient comfort and prevent the inlet manifold branching attachment  444  from becoming a pressure point. 
     The TNP device  434  can aspirate fluid from wounds  430   a ,  430   b  simultaneously when the inlet manifold branching attachment  444  attaches the TNP device  434  to the wound dressings  406   a ,  406   b . The performance and wound healing capabilities (such as, fluid management) of such a system can be equivalent to or exceed that of a standard single wound dressing with single pump set-up. 
     An integrated inlet manifold (not shown) can be used in place of the inlet manifold branching attachment  444  in some implementations. In implementations such as these, inlet manifolds can be incorporated (for example, directly attached) into the TNP device  434  such that the one or more fluid flow paths can fluidically connect to the TNP device  434  via one or more inlets of the integrated inlet manifolds. The integrated inlet manifolds can include a splitting attachment (similar to the Y-shaped or W-shaped branching attachment described herein) or can include one or more separately integrated inlets in fluidic connection with the TNP device  434 . 
       FIG. 5  illustrates another embodiment of multiple dressing TNP system  510 . The multiple dressing TNP system  510  includes a TNP apparatus  511 , a first fluid flow path  515 A, a first wound dressing  516 A, a second fluid flow path  515 B, a second wound dressing  516 B, a plurality of integrated inlet manifolds or connectors  520 A,  520 B. The TNP apparatus  511  can be a canisterless system. The plurality of integrated inlet manifolds  520 A,  520 B are integrated with the TNP apparatus  511  and are fluidically connected to the first wound dressing  516 A via the first fluid flow path  515 A and the second wound dressing  516 B via the second fluid flow path  515 B. 
     In some instances, a fluid flow path  515 A can be lengthy and in a location remote from the TNP apparatus  511 . As such, it can be desirable for the fluid flow paths to include one or more indicators  521 A,  521 B (collectively  521 ) which would be helpful to a user in identifying which fluid flow path  515 A is connected to a particular inlet of the plurality of integrated inlet manifolds  520 A,  520 B. 
     As shown, the first fluid flow path  515 A includes a plurality of first identifiers (stars)  521 A, and the second fluid flow path  515 A includes a plurality of second identifiers (triangles)  521 B. In both instances, at least one identifier  521  is located in close proximity to the inlet manifolds  520 A,  520 B and at least one identifier is located in close proximity to a wound dressing. In some examples, a fluid flow path can include more than two identifiers  521 . For example, identifiers  521  can be located across the length of the fluid flow path. Moreover, an identifier  521  can alternatively include a printed glyph, a printed icon, an embossed glyph, an embossed icon, a braille character, a color-coding and the like. In some examples, an electronically controlled indication (such as an LED, an indicator on a display, etc.) is associated with each fluid flow path. This facilitates the apparatus  511  in indicating an operating condition that may have occurred on the associated dressing. 
     In some embodiments, at least one pressure sensor can be positioned with an inlet manifold (either an integrated manifold or attachment manifold) to measure the combined pressure of the first and second fluid flow paths. The controller of the TNP apparatus  511  monitors the pressure measured by the pressure sensor and determines whether an operating condition has occurred in any of the fluid flow paths. In some aspects, the controller can be configured to provide a first indication associated with an operating condition in the first fluid flow path  515 A and a second indication associated with an operating condition in the second fluid flow path  515 B. 
     In some examples, a negative pressure therapy system includes more than two wound dressings. Accordingly, the number of fluids flow paths and inlets can correspond with the number of wound dressings. For instance, a negative pressure therapy system having four wound dressings can have at least four fluid flow paths and at least four inlets manifolds. In some examples, a single wound dressing can be configured to communicate with a TNP apparatus via more than one fluid flow path. In some examples, the negative pressure therapy system can include more inlets manifolds than fluid flow paths or wound dressings. In examples such as these, the additional inlets can be disregarded or plugged. 
       FIG. 6  illustrates a block diagram of multiple dressing TNP system, according to some embodiments. The system  510 B includes the TNP apparatus  511  of  FIG. 1 , as well as a first fluid flow path  515 A, a first wound dressing  516 A configured to be placed over a first wound  517 A, a second fluid flow path  515 B, a second wound dressing  516 B configured to be placed over a second wound  517 B, an inlet manifold branching attachment  518 , and a third fluid flow path  515 C. The TNP apparatus  511  can be used to treat the first wound  517 A using the first wound dressing  16 A that is in fluidic communication with the TNP apparatus  511  via the first fluid flow path  15 A, the inlet manifold branching attachment  518 , and the third fluid flow path  515 C. The TNP apparatus  511  can also be used to treat the second wound  517 B using the second wound dressing  516 B that is in fluidic communication with the TNP apparatus  511  via the second fluid flow path  515 B, the inlet manifold branching attachment  518 , and the third fluid flow path  515 C. 
     The inlet manifold branching attachment  18  is attached between the TNP apparatus  511  and the first and second wound dressings, thereby advantageously enabling the TNP apparatus  511  to generate and maintain negative pressure in or under both of the wound dressings simultaneously. In this example, the inlet manifolds are not incorporated into the TNP apparatus. Instead, an inlet manifold branching attachment  518 , such as a Y-shaped connector, is used to connect the first and second fluid flow paths  515 A- 515 B to the third fluid flow path  515 C. In other examples, inlet manifolds can be incorporated into the TNP apparatus  511  such that the first and second fluid flow paths connect directly to the TNP apparatus via integrated inlet manifolds. 
     A pressure sensor  512 F is positioned in the third fluid flow path  515 C, such as at or near an inlet of the TNP apparatus  511 , to measure pressure in the third fluid flow path  515 C. The controller of the TNP apparatus  511  can monitor the pressure measured by the pressure sensor  512 F and determine whether an operating condition (for example, a blockage, leakage, overpressure, or dressing full condition) has occurred in within the negative pressure therapy system  510 B. 
     In some instances, the controller can determine that an operating condition exists by comparing the measured pressure to an expected measured pressure (or flow). An “expected” pressure (or flow) can be the pressure measured by a pressure sensor in a negative pressure system operating in a normal state. The expected pressure can be equivalent or almost equivalent (for example, within 1, 2, 3, 4, 5, 10, 15, or 20 mmHg) to a pressure supplied by the negative pressure source (or a pressure selected by a user). In contrast, an “unexpected” pressure (or flow) can be any measured pressure other than the expected pressure (or flow). For instance, in some examples, a wound dressing experiencing a blockage, overpressure, or dressing full condition, can cause the pressure sensor to measure a higher (for example, more negative pressure) than expected pressure. In other examples, a wound dressing experiencing a leakage condition can cause the pressure sensor to measure a lower than expected pressure. In some examples, an operating condition can change the measured pressure (for example, cause a spike, dip, increase, or decrease in measured pressure). In some embodiments, measured pressure is compared to one or more thresholds in order to determine if it is expected or unexpected. 
     In some examples, the TNP apparatus  511  will only function (for example, provide negative pressure) when two or more wound dressings are connected. Additionally, some indicators or functionality of the TNP apparatus that is available when only a single wound dressing is connected may be disabled so as not to confuse the user. For example, in some instances the dressing full indicator may not be available for TNP systems having more than one connected wound dressing. Thus, the dressing full indicator(s) can be disabled or removed from the front panel so as not to confuse the user with unavailable functionality. 
     In any of the disclosed embodiments, the connected wound dressings may be of different sizes. For example, multiple large wound dressings or multiple small wound dressings may be connected to the TNP apparatus  434  or  511 . In some embodiments, the connected wound dressings may be of the same size. 
     Wound Dressings 
       FIG. 7  illustrates a perspective view of a wound dressing  700  in conjunction with a fluidic connector  710  according to some embodiments. The illustrated wound dressing can be used with any of the embodiment of negative pressure systems described herein. As is illustrated, the wound dressing  700  has an oval shaped absorbent layer  720  having multiple lobes  722 . In some embodiments, the absorbent layer  720  can have six lobes. In some examples, two or more lobes  722  (such as, six lobes) are provided on the wound dressing  700 ; the lobes  722 , and specifically, the gaps between the lobes  722 , aid the wound dressing  700  in conforming to nonplanar wounds. For example, it may be advantageous to use the dressing  700  to conform around joints such as elbows and knees. The dressing  700  can have a rectangular or square shaped backing layer  724 , and in some embodiments, the dressing  700  may come in different sizes as described herein. 
     In some examples, the dressing  700  may also have circular cutouts  728  in a central waisted portion, which may be located along a midline of the dressing  700  transverse to a longitudinal axis of the dressing  700 . Such cutouts  728  may be, in some embodiments, 10 mm, or approximately 10 mm, in diameter, or may be in the range of 5 mm to 25 mm, or approximately 5 mm to approximately 25 mm, in diameter. As illustrated, the circular cutouts  728  can be symmetrically arranged on opposite sides of a longitudinal midline of the dressing  700 , and may form an arc of greater than 180 degrees, sometimes between 180 and 270 (or about 180 to 270) degrees. 
     As illustrated, the fluidic connector  710  may include an elongate conduit, or a bridge  720  having a proximal end  730  and a distal end  740 , and an applicator  780  at the distal end  740  of the bridge  720 . In some examples, the bridge  720  provides a soft, fluidic connection between the tube  790  and the wound dressing  700  and can advantageously distance the tube  790  from wound dressing  700 , thereby reducing the potential for pressure points caused by the tube  790 . In some examples, the length of the bridge  720  can be 20, 30, 45, 60, or 70 centimeters (+/− a few centimeters). An optional coupling  760  can be disposed at the proximal end  730  of the bridge  720 . In some examples, a cap (not shown) can be attached to the coupling  760  and can be useful in preventing fluids from leaking out of the proximal end  730 . 
     A negative pressure system (such as the one illustrated in  FIG. 12 ) may be connected to the coupling  760  via a tube  790  (such as by connecting the tube  790  to one of the connectors  21 A or  21 B), or the system may be connected directly to the coupling  760  or directly to the bridge  720 . In some embodiments, as  FIG. 4A-4B and 5  illustrate, more than one wound dressings  700  can be coupled with a negative pressure source via a manifold branching attachment  444  or a plurality of integrated inlet manifolds or connectors  520 A,  520 B. In use, the dressing  700  is placed over a suitably-prepared wound, which may in some cases be filled with a wound packing material such as foam or gauze. The applicator  780  of the fluidic connector  710  has a sealing surface that is placed over an aperture in the dressing  700  and is sealed to the top surface of the dressing  700 . Either before, during, or after connection of the fluidic connector  710  to the dressing  700 , a system is connected via the tube  790  to the coupling  760 , or is connected directly to the coupling  760  or to the bridge  720 . The system is then activated, thereby supplying negative pressure to the wound. Application of negative pressure may be applied until a desired level of healing of the wound is achieved. In some embodiments, the system can be miniaturized and portable, although larger conventional pumps may also be used with the dressing  700 . In some embodiments, the system may be attached or mounted within, onto, or adjacent the dressing  700 . 
     In some embodiments, a source of negative pressure (such as a pump) and some or all other components of a TNP system, such as power source(s), sensor(s), connector(s), user interface component(s) (such as button(s), switch(es), speaker(s), screen(s), etc.) and the like, can be integral with the wound dressing  700 . The wound dressing  700  can include a cover layer for positioning over the layers of the wound dressing. The cover layer can be the upper most layer of the dressing. In some embodiments, the wound dressing  700  can include a second cover layer for positioning over the layers of the wound dressing and any of the integrated components. The second cover layer can be the upper most layer of the dressing or can be a separate envelope that encloses the integrated components of the topical negative pressure system. 
     As shown in  FIG. 7 , the fluidic connector  710  includes an enlarged distal end, or head  740  that is in fluidic communication with the dressing  700  as will be described in further detail below. In one embodiment, the enlarged distal end has a round or circular shape. The head  740  is illustrated here as being positioned near an edge of the dressing  700 , but may also be positioned at any location on the dressing. For example, some embodiments may provide for a centrally or off-centered location not on or near an edge or corner of the dressing  700 . In some embodiments, the dressing  700  may include two or more fluidic connectors  710 , each having one or more heads  740 , in fluidic communication therewith. In some embodiments, the head  740  may measure 30 mm along its widest edge. The head  740  forms at least in part the applicator  780 , described above, that is configured to seal against a top surface of the wound dressing. 
       FIG. 8  illustrates a cross-section through a wound dressing  800  similar to the wound dressing  700  as shown in  FIG. 7  along with fluidic connector  810  according to some embodiments. The wound dressing  800 , which can alternatively be any wound dressing embodiment disclosed herein or any combination of features of any number of wound dressing embodiments disclosed herein, can be located over a wound site to be treated. The dressing  800  can be used with any of the negative pressure system embodiment described herein. The dressing  800  may be placed as to form a sealed cavity over the wound site. In some embodiments, the dressing  800  includes a top or cover layer, or backing layer  820  attached to an optional wound contact layer  822 , both of which are described in greater detail below. These two layers  820 ,  822  can be joined or sealed together to define an interior space or chamber. This interior space or chamber may include additional structures that may be adapted to distribute or transmit negative pressure, store wound exudate and other fluids removed from the wound, and other functions that will be explained in detail below. Examples of such structures, described below, include a transmission layer  826  and an absorbent layer  821 . 
     As used herein the upper layer, top layer, or layer above refers to a layer furthest from the surface of the skin or wound while the dressing is in use and positioned over the wound. Accordingly, the lower surface, lower layer, bottom layer, or layer below refers to the layer that is closest to the surface of the skin or wound while the dressing is in use and positioned over the wound. 
     As illustrated in  FIG. 8 , the wound contact layer  822  can be a polyurethane layer or polyethylene layer or other flexible layer which is perforated, for example via a hot pin process, laser ablation process, ultrasound process or in some other way or otherwise made permeable to liquid and gas. The wound contact layer  822  has a lower surface  824  and an upper surface  823 . The perforations  825  can include through holes in the wound contact layer  822  that enable fluid to flow through the layer  822 . The wound contact layer  822  helps prevent tissue ingrowth into the other material of the wound dressing. The perforations can be small enough to meet this requirement while still allowing fluid to flow therethrough. For example, perforations formed as slits or holes having a size ranging from 0.025 mm to 1.2 mm are considered small enough to help prevent tissue ingrowth into the wound dressing while allowing wound exudate to flow into the dressing. In some configurations, the wound contact layer  822  may help maintain the integrity of the entire dressing  800  while also creating an airtight seal around the absorbent pad in order to maintain negative pressure at the wound. 
     Some embodiments of the wound contact layer  822  may also act as a carrier for an optional lower and upper adhesive layer (not shown). For example, a lower pressure sensitive adhesive may be provided on the lower surface  824  of the wound dressing  800  whilst an upper pressure sensitive adhesive layer may be provided on the upper surface  823  of the wound contact layer. The pressure sensitive adhesive, which may be a silicone, hot melt, hydrocolloid or acrylic based adhesive or other such adhesives, may be formed on both sides or optionally on a selected one or none of the sides of the wound contact layer. When a lower pressure sensitive adhesive layer is utilized may be helpful to adhere the wound dressing  800  to the skin around a wound site. In some embodiments, the wound contact layer may include perforated polyurethane film. The lower surface of the film may be provided with a silicone pressure sensitive adhesive and the upper surface may be provided with an acrylic pressure sensitive adhesive, which may help the dressing maintain its integrity. In some embodiments, a polyurethane film layer may be provided with an adhesive layer on both its upper surface and lower surface, and all three layers may be perforated together. 
     A layer  826  of porous material can be located above the wound contact layer  822 . This porous layer, or transmission layer,  826  allows transmission of fluid including liquid and gas away from a wound site into upper layers of the wound dressing. In particular, the transmission layer  826  can ensure that an open air channel can be maintained to communicate negative pressure over the wound area even when the absorbent layer  821  has absorbed substantial amounts of exudates. The layer  826  can remain open under the typical pressures that will be applied during negative pressure wound therapy as described above, so that the whole wound site sees an equalized negative pressure. The layer  826  may be formed of a material having a three dimensional structure. For example, a knitted or woven spacer fabric (for example Baltex 7970 weft knitted polyester) or a non-woven fabric could be used. 
     In some embodiments, the transmission layer  826  includes a 3D polyester spacer fabric layer including a top layer (that is to say, a layer distal from the wound-bed in use) which is a 84/84 textured polyester, and a bottom layer (that is to say, a layer which lies proximate to the wound bed in use) which is a 10 denier flat polyester and a third layer formed sandwiched between these two layers which is a region defined by a knitted polyester viscose, cellulose or the like monofilament fiber. Other materials and other linear mass densities of fiber could of course be used. 
     Whilst reference is made throughout this disclosure to a monofilament fiber it will be appreciated that a multistrand alternative could of course be utilized. The top spacer fabric thus has more filaments in a yarn used to form it than the number of filaments making up the yarn used to form the bottom spacer fabric layer. 
     This differential between filament counts in the spaced apart layers helps control moisture flow across the transmission layer. Particularly, by having a filament count greater in the top layer, that is to say, the top layer is made from a yarn having more filaments than the yarn used in the bottom layer, liquid tends to be wicked along the top layer more than the bottom layer. In use, this differential tends to draw liquid away from the wound bed and into a central region of the dressing where the absorbent layer  821  helps lock the liquid away or itself wicks the liquid onwards towards the cover layer where it can be transpired. 
     To improve the liquid flow across the transmission layer  826  (that is to say perpendicular to the channel region formed between the top and bottom spacer layers, the 3D fabric may be treated with a dry cleaning agent (such as, but not limited to, Perchloro Ethylene) to help remove any manufacturing products such as mineral oils, fats or waxes used previously which might interfere with the hydrophilic capabilities of the transmission layer. In some embodiments, an additional manufacturing step can subsequently be carried in which the 3D spacer fabric is washed in a hydrophilic agent (such as, but not limited to, Feran Ice 30 g/l available from the Rudolph Group). This process step helps ensure that the surface tension on the materials is so low that liquid such as water can enter the fabric as soon as it contacts the 3D knit fabric. This also aids in controlling the flow of the liquid insult component of any exudates. 
     A layer  821  of absorbent material is provided above the transmission layer  826 . The absorbent material, which includes a foam or non-woven natural or synthetic material, and which may optionally include a super-absorbent material, forms a reservoir for fluid, particularly liquid, removed from the wound site. In some embodiments, the layer  821  may also aid in drawing fluids towards the backing layer  820 . 
     The material of the absorbent layer  821  may also prevent liquid collected in the wound dressing  800  from flowing freely within the dressing, and can act so as to contain any liquid collected within the dressing. The absorbent layer  821  also helps distribute fluid throughout the layer via a wicking action so that fluid is drawn from the wound site and stored throughout the absorbent layer  821 . This helps prevent agglomeration in areas of the absorbent layer  821 . The capacity of the absorbent material must be sufficient to manage the exudates flow rate of a wound when negative pressure is applied. Since in use the absorbent layer experiences negative pressures the material of the absorbent layer is chosen to absorb liquid under such circumstances. A number of materials exist that are able to absorb liquid when under negative pressure, for example superabsorber material. The absorbent layer  821  may typically be manufactured from ALLEVYN™ foam, Freudenberg 18-224-4 or Chem-Posite™ 11C-450. In some embodiments, the absorbent layer  821  may include a composite having superabsorbent powder, fibrous material such as cellulose, and bonding fibers. In some embodiments, the composite is an airlaid, thermally-bonded composite. 
     In some embodiments, the absorbent layer  821  is a layer of non-woven cellulose fibers having super-absorbent material in the form of dry particles dispersed throughout. Use of the cellulose fibers introduces fast wicking elements which help quickly and evenly distribute liquid taken up by the dressing. The juxtaposition of multiple strand-like fibers leads to strong capillary action in the fibrous pad which helps distribute liquid. In this way, the super-absorbent material is efficiently supplied with liquid. The wicking action also assists in bringing liquid into contact with the upper cover layer to aid increase transpiration rates of the dressing. 
     An aperture, hole, or orifice  827  can be provided in the backing layer  820  to allow a negative pressure to be applied to the dressing  800 . The fluidic connector  810  can be attached or sealed to the top of the backing layer  820  over the orifice  827  made into the dressing  800 , and communicates negative pressure through the orifice  827 . A length of tubing may be coupled at a first end to the fluidic connector  810  and at a second end to a negative pressure system (not shown) to allow fluids to be removed from the dressing. Where the fluidic connector is adhered to the top layer of the wound dressing, a length of tubing may be coupled at a first end of the fluidic connector such that the tubing, or conduit, extends away from the fluidic connector parallel or substantially to the top surface of the dressing. The fluidic connector  810  may be adhered and sealed to the backing layer  820  using an adhesive such as an acrylic, cyanoacrylate, epoxy, UV curable or hot melt adhesive. The fluidic connector  810  may be formed from a soft polymer, for example a polyethylene, a polyvinyl chloride, a silicone or polyurethane having a hardness of 30 to 90 on the Shore A scale. In some embodiments, the fluidic connector  810  may be made from a soft or conformable material. 
     The absorbent layer  821  can include at least one through hole  828  located so as to underlie the fluidic connector  810 . The through hole  828  may in some embodiments be the same size as the opening  827  in the backing layer, or may be bigger or smaller. As illustrated in  FIG. 8  a single through hole can be used to produce an opening underlying the fluidic connector  810 . It will be appreciated that multiple openings could alternatively be utilized. Additionally should more than one port be utilized according to certain embodiments of the present disclosure one or multiple openings may be made in the absorbent layer  821  and the obscuring layer in registration with each respective fluidic connector. Although not essential to certain embodiments of the present disclosure, the use of through holes in the super-absorbent layer may provide a fluid flow pathway which remains unblocked in particular when the absorbent layer is near saturation. 
     The aperture or through-hole  828  can be provided in the absorbent layer  821  beneath the orifice  827  such that the orifice is connected directly to the transmission layer  826  as illustrated in  FIG. 8 . This allows the negative pressure applied to the fluidic connector  810  to be communicated to the transmission layer  826  without passing through the absorbent layer  821 . This ensures that the absorbent layer does not inhibit the negative pressure applied to the wound site as it absorbs wound exudates. In other embodiments, no aperture may be provided in the absorbent layer  821 , or alternatively a plurality of apertures underlying the orifice  827  may be provided. In further alternative embodiments, additional layers may be provided over the absorbent layer  821  and beneath the backing layer  820 . 
     The backing layer  820  can be gas impermeable, but moisture vapor permeable, and can extend across the width of the wound dressing  800 . The backing layer  820 , which may for example be a polyurethane film (for example, Elastollan SP9109) having a pressure sensitive adhesive on one side, is impermeable to gas and this layer thus operates to cover the wound and to seal a wound cavity over which the wound dressing is placed. In this way an effective chamber is made between the backing layer  820  and a wound site where a negative pressure can be established. The backing layer  820  can be sealed to the wound contact layer  822  in a border region around the circumference of the dressing, ensuring that no air is drawn in through the border area, for example via adhesive or welding techniques. The backing layer  820  protects the wound from external bacterial contamination (bacterial barrier) and allows liquid from wound exudates to be transferred through the layer and evaporated from the film outer surface. The backing layer  820  can include two layers; a polyurethane film and an adhesive pattern spread onto the film. The polyurethane film can be moisture vapor permeable and may be manufactured from a material that has an increased water transmission rate when wet. In some embodiments, the moisture vapor permeability of the backing layer increases when the backing layer becomes wet. The moisture vapor permeability of the wet backing layer may be up to about ten times more than the moisture vapor permeability of the dry backing layer. 
     The absorbent layer  821  may be of a greater area than the transmission layer  826 , such that the absorbent layer overlaps the edges of the transmission layer  826 , thereby ensuring that the transmission layer does not contact the backing layer  820 . This provides an outer channel of the absorbent layer  821  that is in direct contact with the wound contact layer  822 , which aids more rapid absorption of exudates to the absorbent layer. Furthermore, this outer channel ensures that no liquid is able to pool around the circumference of the wound cavity, which could seep through the seal around the perimeter of the dressing leading to the formation of leaks. As illustrated in  FIG. 8 , the absorbent layer  821  may define a smaller perimeter than that of the backing layer  820 , such that a boundary or border region is defined between the edge of the absorbent layer  821  and the edge of the backing layer  820 . 
     As shown in  FIG. 8 , one embodiment of the wound dressing  800  includes an aperture  828  in the absorbent layer  821  situated underneath the fluidic connector  810 . In use, for example when negative pressure is applied to the dressing  800 , a wound facing portion of the fluidic connector may thus come into contact with the transmission layer  826 , which can thus aid in transmitting negative pressure to the wound site even when the absorbent layer  821  is filled with wound fluids. Some embodiments may have the backing layer  820  be at least partly adhered to the transmission layer  826 . In some embodiments, the aperture  828  is at least 1-2 mm larger than the diameter of the wound facing portion of the fluidic connector  810 , or the orifice  827 . 
     In particular for embodiments with a single fluidic connector  810  and through hole, the fluidic connector  810  and through hole can be located in an off-center position as illustrated in  FIG. 7 . Such a location may permit the dressing  800  to be positioned onto a patient such that the fluidic connector  810  is raised in relation to the remainder of the dressing  800 . So positioned, the fluidic connector  810  and the filter  814  may be less likely to come into contact with wound fluids that could prematurely occlude the filter  814  so as to impair the transmission of negative pressure to the wound site. 
     Turning now to the fluidic connector  810 , some embodiments include a sealing surface  816 , a bridge  811  (corresponding to bridge  720 ) in  FIG. 7 ) with a proximal end  730  and a distal end  740 , and a filter  814 . The sealing surface  816  can form the applicator previously described that is sealed to the top surface of the wound dressing. In some embodiments a bottom layer of the fluidic connector  810  may include the sealing surface  816 . The fluidic connector  810  may further include an upper surface vertically spaced from the sealing surface  816 , which in some embodiments is defined by a separate upper layer of the fluidic connector. In other embodiments the upper surface and the lower surface may be formed from the same piece of material. In some embodiments the sealing surface  816  may include at least one aperture  829  therein to communicate with the wound dressing. In some embodiments the filter  814  may be positioned across the opening  829  in the sealing surface, and may span the entire opening  829 . The sealing surface  816  may be configured for sealing the fluidic connector to the cover layer of the wound dressing, and may include an adhesive or weld. In some embodiments, the sealing surface  816  may be placed over an orifice in the cover layer. In other embodiments, the sealing surface  816  may be positioned over an orifice in the cover layer and an aperture in the absorbent layer  820 , permitting the fluidic connector  810  to provide air flow through the transmission layer  826 . In some embodiments, the bridge  811  may include a first fluid passage  812  in communication with a source of negative pressure, the first fluid passage  812  including a porous material, such as a 3D knitted material, which may be the same or different than the porous layer  826  described previously. The bridge  811  can be encapsulated by at least one flexible film layer  808 ,  810  having a proximal and distal end and configured to surround the first fluid passage  812 , the distal end of the flexible film being connected to the sealing surface  816 . The filter  814  is configured to substantially prevent wound exudate from entering the bridge. 
     Some embodiments may further include an optional second fluid passage positioned above the first fluid passage  812 . For example, some embodiments may provide for an air leak disposed at the proximal end of the top layer  808  that is configured to provide an air path into the first fluid passage  812  and dressing  800 . 
     The fluid passage  812  can be constructed from a compliant material that is flexible and that also permits fluid to pass through it if the spacer is kinked or folded over. Suitable materials for the fluid passage  812  include without limitation foams, including open-cell foams such as polyethylene or polyurethane foam, meshes, 3D knitted fabrics, non-woven materials, and fluid channels. In some embodiments, the fluid passage  812  may be constructed from materials similar to those described above in relation to the transmission layer  826 . Advantageously, such materials used in the fluid passage  812  not only permit greater patient comfort, but may also provide greater kink resistance, such that the fluid passage  812  is still able to transfer fluid from the wound toward the source of negative pressure while being kinked or bent. 
     In some embodiments, the fluid passage  812  may include a wicking fabric, for example a knitted or woven spacer fabric (such as a knitted polyester 3D fabric, Baltex 7970®, or Gehring 879®) or a nonwoven fabric. These materials selected can be suited to channelling wound exudate away from the wound and for transmitting negative pressure or vented air to the wound site, and may also confer a degree of kinking or occlusion resistance to the fluid passage  812 . In some embodiments, the wicking fabric may have a three-dimensional structure, which in some cases may aid in wicking fluid or transmitting negative pressure. In certain embodiments, including wicking fabrics, these materials remain open and capable of communicating negative pressure to a wound area under the typical pressures used in negative pressure therapy, for example between 40 to 150 mmHg. In some embodiments, the wicking fabric may include several layers of material stacked or layered over each other, which may in some cases be useful in preventing the fluid passage  812  from collapsing under the application of negative pressure. In other embodiments, the wicking fabric used in the fluid passage  812  may be between 1.5 mm and 6 mm; or the wicking fabric may be between 3 mm and 6 mm thick, and may include either one or several individual layers of wicking fabric. In other embodiments, the fluid passage  812  may be between 1.2-3 mm thick, for example, thicker than 1.5 mm. Some embodiments, for example a suction adapter used with a dressing which retains liquid such as wound exudate, may employ hydrophobic layers in the fluid passage  812 , and only gases may travel through the fluid passage  812 . Additionally, and as described previously, the materials used in the system can be conformable and soft, which may help to avoid pressure ulcers and other complications which may result from a wound treatment system being pressed against the skin of a patient. 
     The filter element  88  can be impermeable to liquids, but permeable to gases, and is provided to act as a liquid barrier and to ensure that no liquids are able to escape from the wound dressing  800 . The filter element  814  may also function as a bacterial barrier. Typically the pore size is 0.2μm. Suitable materials for the filter material of the filter element  814  include 0.2 micron Gore™ expanded PTFE from the MMT range, PALL Versapore™ 200R, and Donaldson™ TX6628. Larger pore sizes can also be used but these may require a secondary filter layer to ensure full bioburden containment. As wound fluid contains lipids, an oleophobic filter membrane can be used, for example 1.0 micron MMT-332 prior to 0.2 micron MMT-323. This prevents the lipids from blocking the hydrophobic filter. The filter element can be attached or sealed to the port or the cover film over the orifice. For example, the filter element  814  may be molded into the fluidic connector  810 , or may be adhered to one or both of the top of the cover layer and bottom of the suction adapter  810  using an adhesive such as, but not limited to, a UV cured adhesive. 
     It will be understood that other types of material could be used for the filter element  814 . More generally a microporous membrane can be used which is a thin, flat sheet of polymeric material, this contains billions of microscopic pores. Depending upon the membrane chosen these pores can range in size from 0.01 to more than 10 micrometers. Microporous membranes are available in both hydrophilic (water filtering) and hydrophobic (water repellent) forms. In some embodiments of the present disclosure, filter element  814  includes a support layer and an acrylic co-polymer membrane formed on the support layer. The wound dressing  800  according to certain embodiments of the present disclosure can use microporous hydrophobic membranes (MHMs). Numerous polymers may be employed to form MHMs. For example, the MHMs may be formed from one or more of PTFE, polypropylene, PVDF and acrylic copolymer. All of these optional polymers can be treated in order to obtain specific surface characteristics that can be both hydrophobic and oleophobic. As such these will repel liquids with low surface tensions such as multi-vitamin infusions, lipids, surfactants, oils and organic solvents. 
     MHMs block liquids whilst allowing air to flow through the membranes. They are also highly efficient air filters eliminating potentially infectious aerosols and particles. A single piece of MHM is well known as an option to replace mechanical valves or vents. Incorporation of MHMs can thus reduce product assembly costs improving profits and costs/benefit ratio to a patient. 
     The filter element  814  may also include an odor absorbent material, for example activated charcoal, carbon fiber cloth or Vitec Carbotec-RT Q2003073 foam, or the like. For example, an odor absorbent material may form a layer of the filter element  814  or may be sandwiched between microporous hydrophobic membranes within the filter element. The filter element  814  thus enables gas to be exhausted through the orifice. Liquid, particulates and pathogens however are contained in the dressing. 
     Similar to the embodiments of wound dressings described above, some wound dressings include a perforated wound contact layer with silicone adhesive on the skin-contact face and acrylic adhesive on the reverse. Above this bordered layer sits a transmission layer or a 3D spacer fabric pad. Above the transmission layer, sits an absorbent layer. The absorbent layer can include a superabsorbent non-woven (NW) pad. The absorbent layer can over-border the transmission layer by approximately 5 mm at the perimeter. The absorbent layer can have an aperture or through-hole toward one end. The aperture can be about 10 mm in diameter. Over the transmission layer and absorbent layer lays a backing layer. The backing layer can be a high moisture vapor transmission rate (MVTR) film, pattern coated with acrylic adhesive. The high MVTR film and wound contact layer encapsulate the transmission layer and absorbent layer, creating a perimeter border of approximately 20 mm. The backing layer can have a 10 mm aperture that overlies the aperture in the absorbent layer. Above the hole can be bonded a fluidic connector that includes a liquid-impermeable, gas-permeable semi-permeable membrane (SPM) or filter that overlies the aforementioned apertures. 
     One or more wound dressing, such as one or more absorbent layers  821 , can, over the course of a negative pressure therapy, become saturated with exudate. As exudate accumulates in the one or more wound dressings  800 , the effectiveness of the treatment may become compromised. Other compromising operating conditions, such as leakages, blockages, high pressure, or low vacuum, may also develop. Some disclosed embodiments provide systems or methods for the detection and notification of one or more of such operating conditions. 
     As described herein, the wound dressings may have various sizes including small dressings to large dressings. For example, in case of a rectangular wound dressing (such as the dressing  700 ), a small wound dressing can be 5 centimeters by 5 centimeters and a large wound dressing can be 15 centimeters by 10 centimeters. Depending on the shape of the wound dressing(s), different size representations can be used including, for example, radius for circular wound dressings. In some instances, the wound dressings can be categorized into certain standardized sizes, such as small, medium, large, extra-large, etc. For example, Pico dressings available from Smith &amp; Nephew are available in the following sizes: 10 cm×20 cm (45 cm 3  volume), 10 cm×30 cm (75 cm 3  volume), 10 cm×40 cm (105 cm 3  volume), or 25 cm×25 cm (240 cm 3  volume) among others. 
     In some cases, each wound dressing may have associated parameters or operational profiles. The TNP system may download, store, or access various parameters or profiles associated with the particular dressing, such as an expected rate of pressure change when operating a pump with a known capacity in a sealed condition. For instance, with a large dressing it can take longer for a pump to reduce pressure down to a negative pressure setpoint than it would take the pump to reduce pressure down to the setpoint in a smaller dressing. This can be due to the larger amount of fluid that would have to be evacuated from a larger dressing that has larger volume that a smaller dressing. 
     Delivery of Wound Therapy 
     A pump assembly, such as the pump assembly  200  or  511 , can control a vacuum pump to deliver negative pressure therapy to a wound according to a selected or programmed protocol. Pump control can be performed by one or more processors, such as the pump control processor  370  alone or in combination with the processor  310 . 
     For example, the user can select continuous operation at a desired pressure (or negative pressure setpoint). The pump assembly can activate the vacuum pump to reduce or draw down the pressure at the wound (for example, under the dressing) to reach the setpoint. As explained herein, in some embodiments, the drawdown can be performed by increasing the negative pressure at the wound limited by a maximum change in negative pressure per unit time called compression, until the setpoint (or another selected pressure value as explained below) has been achieved. Wound drawdown can be defined as the period of time immediately after therapy has been initiated during which the wound has not yet achieved the setpoint. As explained below, at the end of this period when the setpoint is achieved, the flow rate in the fluid flow path should be below a leak (or high flow) threshold and above a low vacuum threshold, otherwise an appropriate alarm will be activated. 
     As another example, the user can select intermittent operation between two desired pressures (or high and low pressure setpoints illustrated in, for example,  FIG. 11 ). The pump assembly can activate the vacuum pump to reduce or draw down the pressure at the wound to reach the low (or more negative) pressure setpoint. Subsequently, the pump assembly can allow pressure at the wound to increase to reach the high (or more positive) pressure setpoint. As explained herein, decreasing and increasing negative pressure can be performed in accordance with the compression setting. 
     As yet another example, compression can be used anytime there is a change in the pressure setpoint (which can include stopping delivery of negative pressure). In some embodiments, different compression settings can be used for setpoint changes that result in decreasing or increasing pressure at the wound. In various embodiments, compression setting can be adjusted while a pressure setpoint is being achieved. 
       FIG. 9  illustrates a process  900  for providing negative pressure wound therapy according to some embodiments. The process  900  can be executed by one or more processors, such as the processor  310  or the pump control processor  370 , alone or in combination, and utilize one or more other components described herein or other systems not shown. The process  900  can be periodically executed, such as for example every 100 milliseconds (or 10 times per second) or at any other suitable frequency. Alternatively or additionally, the process  900  can be continuously executed. 
     The process  900  can begin in block  902 , which it can transition to when therapy is initiated or when the setpoint is changed while therapy is being delivered. In block  902 , the process  900  compares wound pressure, which can be determined as explained below, to the setpoint. For example, the process  900  can subtract the wound pressure from the setpoint or vice versa. If the wound pressure is below the setpoint, the process  900  can transition to block  904 . Conversely, if the wound pressure exceeds or is equal to the setpoint, the process  900  can transition to block  906 . 
     In block  904  (pressure ramp up), the process  900  can increment a pump ramp setpoint by an amount that depends on the compression setting as explained herein. The vacuum pump will then attempt to draw down (or make more negative) the wound pressure to reach the current value of the pump ramp setpoint. For example, a suitable pump drive signal, such as voltage or current signal, can be generated and supplied to the pump motor so as to increase the speed of the pump motor to achieve wound draw down. For purposes of efficiency, the pump motor can be driven using PWM or any other suitable method. The process  900  can continue incrementing the pump ramp setpoint until it reaches the setpoint selected by the user. The process  900  can transition to block  908  when the wound pressure has nearly reached or reached the setpoint, which can correspond to reaching steady state pressure under the wound dressing. For example, the process  900  can transition to block  908  when the wound pressure is within a ramp up threshold pressure of the setpoint, such as within 2 mmHg of the setpoint or within any other suitable value. In some embodiments, the pump ramp setpiont can be adaptively set to a higher negative pressure than the setpoint. For example, as is explained below, the device can detect presence of one or more leaks which result in a higher level of flow. Because this can cause loss of pressure at the wound, the device can compensate such loss of pressure by increasing the pump ramp setpoint above the setpoint. For instance, the device can set the pump ramp setpoint to be 1%, 2%, 5%, etc. more negative than the setpoint. In certain embodiments, the pump ramp setpoint can be adaptively set to a lower negative pressure (or more positive pressure) than the setpoint. 
     In block  906  (pressure ramp down), the process  900  can set the pump ramp setpoint to the setpoint selected by the user (or to another set value as explained above). The process  900  can deactivate the pump so that the wound pressure is allowed to decay, such as due to one or more leaks in the fluid flow path, to reach or almost reach the setpoint. This can be performed in accordance with the compression setting, such as for example, deactivating the pump for a first period of time and then activating the pump for a second period of time so that pressure at the wound increases according to the compression setting. At this point, the process  900  can transition to block  908 . For example, the process  900  can transition to block  908  when the wound pressure is within a ramp down threshold pressure of the setpoint, such as within 9 mmHg of the setpoint or within any other suitable value. In some cases, the ramp down threshold pressure can be the same as the ramp up threshold pressure. In some embodiments, the pump ramp setpoint can be adaptively set to a lower negative pressure than the setpoint. For example, as is explained below, the device can detect presence of one or more leaks which result in a higher level of flow. Because this can cause loss of pressure at the wound, the device can compensate such loss of pressure by decreasing the pump ramp setpoint below the setpoint. For instance, the device can set the pump ramp setpoint to be 1%, 2%, 9%, etc. less negative than the setpoint. In certain embodiments, the pump ramp setpoint can be adaptively set to a higher negative pressure (or more positive pressure) than the setpoint. 
     In block  908  (steady state), the pump ramp setpoint can be set to the setpoint selected by the user (or another suitable value). The process  900  can control the vacuum pump to maintain the desired negative pressure at the wound. One or more conditions, such as high vacuum, low vacuum, leak, and the like can be detected in block  908  as is explained below. If the user changes the setpoint to be more negative or more positive or if delivery of therapy is paused, the process  900  can transition to block  902 . 
     In some embodiments, the pump assembly controls the vacuum pump to draw down the wound (for example, as is explained herein in connection with block  904 ) by utilizing compression. Using compression can be beneficial for avoiding rapid changes in wound pressure, which can minimize patient pain or discomfort, reduce noise produced as a result of operating the pump, maintain efficient delivery of negative pressure, maintain efficient use of power (for example, battery power), and the like. Compression can be executed by the process  900 , which in turn can be implemented by the reduced pressure control processor  370  alone or in combination with the processor  310 . Compression can correspond to the maximum desired increase or decrease in negative pressure at the wound per unit of time. Compression can be determined based on the negative pressure setpoint in the continuous mode or low and high negative pressure setpoints in the intermittent mode and selected compression setting (for example, low, medium, or high). 
     In some embodiments, the pump assembly monitors various parameters or resulting profiles (for example, see  FIGS. 12, 13, and 14A-14D ), such as pressure in the fluid flow path(s), rate of change in pressure, rate of flow in the fluid flow path(s), pressure profiles, or the like, in order to control the pump in connection with delivery of negative pressure wound therapy. Parameters monitoring and pump control can be performed by one or more processors, such as the reduced pressure control processor  370  alone or in combination with the processor  310 . Monitoring pressure parameters or profiles can be used to ensure that therapy is properly delivered to the wound, to detect wound dressing sizes, leakages, blockages, high pressure, and low vacuum, canister full, or the like. 
     In additional or alternative embodiments, multiple pressure sensors can be placed in different locations in the fluid flow path(s) to facilitate detection of one or more of the conditions described herein. For example, in addition to or instead of the pressure sensor being placed in the pump inlet, one or more pressure sensors can be placed in the wound or under the dressing to directly determine the wound pressure. Measuring pressure at different locations in the fluid flow path, such as in the canister and at the wound, can facilitate detection of wound dressing sizes, blockages, leaks, canister full condition, leaks, or the like. 
     As described with respect to  FIG. 12 , some of the parameters or profiles can indicate sizes of one or more attached wound dressings. Additionally, the parameters or profiles can indicate blockage ( FIGS. 13 and 14A-14D ) or leak conditions ( FIG. 15 ). In some embodiments, these conditions can be detected by the process  900  while the process in in block  908 . Similarly, one or more condition detection can be disabled or enabled based on which of the blocks  902 ,  904 ,  906 , or  908  the TNP system is currently operating in or is transitioning to. 
     Pump System Control 
       FIG. 10  illustrates a process  1000  of operation of a TNP apparatus or pump system according to some embodiments, such as the system  511 . The process  1000  can be executed by one or more processors as disclosed herein. For example, the process  1000  can provide a suitable balance between uninterrupted delivery of therapy or avoidance of inconveniencing the user by, for example, frequently or needlessly pausing or suspending therapy and a desire to conserve power, limit noise and vibration generated by the negative pressure source, etc. As is illustrated in  FIG. 10 , the operation of the pump system can, in some embodiments, be grouped into three general modes: initialization  1002 , operational  1010 , which includes maintenance  1050 , and end of life  1090 . As is illustrated in  FIG. 10 , categories  1002 ,  1010 , and  1050  can each include multiple states and transitions between states. 
     In some embodiments, so long as a power source is not connected or removed, or the pump system has not been activated (for example, by pulling an activation strip, triggering a switch or button, or the like), the pump system can remain in an inactive state. While remaining in this state, the pump system can remain inactive. When the power source is connected or the pump system has been activated from the inactive state, such as being activated for the first time, the pump system can transition to an initialization mode  1002 , where a bootloader  1001  can initiate a sequence of startup procedures as shown in block  1004 . The bootloader  1001  can be stored on any suitable non-volatile memory such as, for example, read only memory (ROM), erasable programmable read only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and the like. In some embodiments, one or more processors can execute the bootloader  1001  upon startup. The startup procedures can include power on selftest(s) (POST) and other tests or procedures that can be performed as shown in startup block  1004 . As shown in  FIG. 10 , the bootloader  1001  can initiate one or more of the POST(s) or one or more of the other tests. In some embodiments, the startup procedures can advantageously prepare or ensure that the pump system will deliver negative pressure wound therapy safely during operation. 
     Power on self-test(s) can include performing various checks to ensure proper functionality of the system, such as testing one or more components of the system including, but not limited to, memory such as memory  350  (for example, performing a check, such as a cyclic redundancy check (CRC check), of the program code to determine its integrity, testing the random access memory, etc.), reading the pressure sensor such as pressure sensors or monitors  397 , to determine whether the pressure values are within suitable limits, reading the remaining capacity or life of the power source (for example, battery voltage, current, etc.) to determine whether it is within suitable limits, testing the negative pressure source, and the like. Other tests or procedures can include waiting for automatic test equipment (ATE), initializing a watch dog timer (WDT), checking whether the pump system has previously entered a non-recoverable error (NRE), and determining whether the pump system has reached the end of its allotted operational lifespan (also referred to as its end of life (EOL)), and the like. For example, in some embodiments, the WDT can advantageously be used as a countermeasure to a firmware execution hanging conditions, the check for a previous NRE can advantageously prevent the reuse of a device that has transitioned to an NRE state, and the check of whether the device has reached its end of life can advantageously prevent the reuse of a device that has transitioned to an EOL state. 
     In some embodiments, the bootloader  1001 , which can be executed by the one or more processors, can also initiate the operational mode  1010 . For example, as shown in  FIG. 10 , the bootloader can execute initialization of the operational mode  1010  after the initialization mode  1002  has been performed. In some embodiments, one or more indicators can indicate to the user (for example, by blinking or flashing once) that the pump system is undergoing POST test(s). In some embodiments, during the initialization mode  1002 , all indicators can continuously remain on. In some cases, the one or more indicators can be one or more LEDs. 
     In some embodiments, the one or more indicators can blink or flash intermittently or continuously to indicate to the user that the system has passed the POST(s) or other tests and procedures. In some embodiments, one or more indicators positioned on external surface of the TNP device can include an “OK” indicator which can indicate normal operation of the pump system  100 , a “leak” indicator which can indicate the existence of a leak in the pump system  100  or components attached thereto, a “dressing full” indicator which can indicate that a wound dressing is at or near capacity, and a “power source critical” indicator which can indicate that the power source is at or near a critical level. In some embodiments, the one or more indicators can be individually or cooperatively illuminated to indicate to the user that the pump system has passed POST(s) or other tests and procedures. For example, in some embodiments, the one or more indicators can be cooperatively illuminated to indicate that the system has passed the one or more tests such that the “OK” LED flashes once, the “leak” LED flashes once, the “dressing full” LED flashes once, and the “power source critical” LED flashes once. Similarly, if a previous non-recoverable error is discovered during startup or subsequently encountered during pump operation, the one or more indicators can be cooperatively illuminated such that the “OK” LED is solid, the “leak” LED is solid, the “dressing full” LED is solid, and the “power source critical” LED is solid. Any suitable individual or cooperative LED arrangement is envisioned in certain embodiments. In various embodiments, in addition to or instead of providing the visual indication using the one or more indicators, other indications can be provided, including audible, tactile, and the like. 
     In some embodiments, if one or more of the POST test(s) or other tests or procedures fail, the pump system can transition to a retry state  1006 . The retry state  1006  can include a delay or require user input before retrying the POST test(s) or other tests or procedures. In some embodiments, the retry state  1006  can be executed until each test or procedure that is part of the initialization mode passes or otherwise does not fail. In some embodiments, if one or more of POST test(s) fail after one or more retries, the pump system can transition to a non-recoverable error state. While in this state, the pump system can deactivate therapy, and indicators can indicate to the user that an error was encountered. In some embodiments, all indicators can remain active. Based on the severity of error, in some embodiments, the pump system can recover from the error and continue operation (or transition to the non-recoverable error state  1094 ). As is illustrated, the pump system can transition to the non-recoverable error state  1094  upon encountering a fatal error during operation. Fatal errors can include program memory errors, program code errors (for example, encountering an invalid variable value), controller operation errors (for example, watchdog timer expires without being reset by the controller), component failure. 
     With continued reference to  FIG. 10 , in some embodiments, when initialization has been successfully completed in state  1004 , the pump system can transition to the operational mode  1010 . This transition can be indicated to the user by deactivating or activating one or more indicators. In some embodiments, when the pump system transitions into the operational mode  1010 , the pump system can first enter a standby or paused state  1012 . While the pump system remains in the standby state  1012 , the user can be provided an indication, such as by deactivating or activating indicators (for example, an OK indicator or a dressing indicator). In some embodiments, the user can be provided an indication of the standby state  1012  by deactivating all indicators. In some embodiments, therapy can be suspended while the pump system remains in the standby state  1012 . For example, the source of negative pressure such as sources of negative pressure  1010 ,  1019 ,  1218 , can be deactivated (or turned off). In some embodiments, indication can be provided to the user by deactivating the source of negative pressure. 
     In some embodiments, the pump system can be configured to make a transition from the standby state  1012  to an initial pump down (“IPD”) state  1014  (where the pump system is configured to deliver therapy) in response to receiving a signal from the user. For example, the user can press a button (see  FIGS. 2  (illustrating  212   b ) or 5) to start, suspend, or restart therapy. In some embodiments, the pump system can monitor the duration of time the pump system remains in the standby state  1012 . This can be accomplished, for example, by maintaining a timer (in firmware, software, hardware or any combination thereof), which can be reset and started when the pump system transitions into the standby state  1012 . The pump system can automatically make the transition from the standby state  1012  to the IPD state  1014  when the time duration exceeds a threshold (for example, times out). In some embodiments, such threshold can be a preset value, such as between 1 minute or less and 1 hour or more. In some embodiments, the threshold can be set or changed by the user. In some embodiments, the threshold can be varied based on various operating conditions or on any combination thereof. For example, as the pump system nears the end of life (as is explained below), the threshold can be decreased used over the lifespan of the pump system. This can advantageously ensure that a power source, such as one or more batteries, is used more efficiently over the lifespan of the pump system by reducing the amount of time spent in the standby state  1012  and utilizing more of the power source by activating the pump sooner. In some embodiments, the pump system can monitor the entire amount of time spent in the standby state and store this information in memory. 
     During the IPD state  1014 , the pump system can activate the source of negative pressure to begin therapy and reduce pressure in the system or some portion thereof, such as a fluid flow path between a source of negative pressure and a wound dressing. In some embodiments, the pump system can reduce pressure in the system to a desired pressure, such as a low pressure setpoint or threshold. The pump system can intermittently or continuously monitor the pressure in the pump system or some portion thereof. For example, the pump system can monitor the pressure in the pump system or some portion thereof at a preset sampling rate of approximately 100 ms. In some embodiments, the sampling rate can be between approximately 20 ms and approximately 500 ms, between approximately 50 ms and 250 ms, between approximately 80 ms and 150 ms, approximately 100 ms, any value or subrange with these ranges, or any other sampling rate as desired. In some embodiments, the pump system can also calculate the rate of pressure change to estimate the amount of time until the pump system reaches a desired pressure, such as the low pressure threshold. In some cases, as described herein, the pump system can determine in the IPD state  1014  sizes of one or more dressings connected to the pump system. 
     In some embodiments, one or more indicators can blink or flash intermittently or continuously to indicate to the user that the pump system is in the IPD state. For example in some embodiments, the one or more indicators can include an “OK” indicator which can indicate normal operation of the pump system  100 , a “leak” indicator which can indicate the existence of a leak in the pump system  100  or components attached thereto, a “dressing full” indicator which can indicate that a wound dressing is at or near capacity (or “canister full” indicator which can indicated that a canister is at or near capacity), and a “power source critical” indicator which can indicate that the power source capacity is at or near a critical level. In some embodiments, the one or more indicators can be individually or cooperatively illuminated to indicate to the user that the system is in the IPD state. For example, in some embodiments, the one or more indicators can be cooperatively illuminated to indicate that the system is in the IPD state such that the “OK” LED is flashing, the “leak” LED is flashing, the “dressing full” LED is off, and the “power source critical” LED does not change (on, off, or flashing). Any suitable individual or cooperative LED arrangement is envisioned in certain embodiments. Once a desired negative pressure setpoint is reached during the IPD state, the one or more indicators can be individually or cooperatively illuminated to indicate that the desired negative pressure has been reached. For example, in some embodiments, the one or more indicators can be cooperatively illuminated to indicate that the negative pressure has been reached such that the “OK” LED is flashing, the “leak” LED is off, the “dressing full” LED is off, and the “power source critical” LED does not change (on, off, or flashing). In some embodiments, this same illumination pattern can also be used to indicate that the pump system is functioning properly, such as during the IPD state to indicate that the pump system is functioning properly during the IPD state, in addition to flashing to indicate that the negative pressure has been reached during the IPD state. In various embodiments, in addition to or instead of providing the visual indication using the one or more indicators, other indications can be provided, including audible, tactile, and the like. 
     In some embodiments, the user can pause therapy by activating the switch (for example, pressing the button), thereby causing the pump system to make a transition from the IPD state  1014  to the standby state  1012 . In some embodiments, the pump system can be configured so that the user can only pause therapy, whereas disconnecting the power source (for example, removing power source) stops therapy. As such, in some embodiments, the pump system can potentially time out while in the standby state  1012  and resume operation thereby reducing any energy expended while in the standby state  1012 . After being paused by the user, the pump system can transition from the standby state  1012  to the IPD state  1014  upon receiving a user input such as a button press. In some embodiments, after being paused by the user, the pump system can automatically make the transition from the standby state  1012  to the IPD state  1014  when the time duration exceeds a threshold. The threshold can be the same or different than the threshold of the standby state  1012  described above when the pump system enters the standby state  1012  after startup  1004 . 
     When the pump system transitions into and remains in the standby state  1012 , the user can be provided an indication. For example, in some embodiments, all indicators can be deactivated. In some embodiments, the pump system can deactivate an indicator (for example, an OK indicator) and cause another indicator (for example, a dressing indicator) to flash or blink. In some embodiments, one or more indicators can blink or flash intermittently or continuously to indicate to the user that the system is in the standby state. For example, in some embodiments, the one or more indicators can include an “OK” indicator which can indicate normal operation of the pump system  100 , a “leak” indicator which can indicate the existence of a leak in the pump system  100  or components attached thereto, a “dressing full” indicator which can indicate that a wound dressing is at or near capacity, and a “power source critical” indicator which can indicate that the power source capacity is at or near a critical level. In some embodiments, the one or more indicators can be individually or cooperatively illuminated to indicate to the user that the system is in the standby state. For example, in some embodiments, the one or more indicators can be cooperatively illuminated to indicate that the system is in the standby state such that the “OK” LED is off, the “leak” LED is off, the “dressing full” LED is off, and the “power source critical” LED is off. In some embodiments, this same illumination pattern can also be used to indicate that the pump system has completed its course of negative pressure wound therapy or to indicate that the power source, such as one or more batteries, has been depleted, in addition to indicating that the pump is in the standby state. Any suitable cooperative LED arrangement is envisioned in certain embodiments. In various embodiments, in addition to or instead of providing the visual indication using the one or more indicators, other indications can be provided, including audible, tactile, and the like. In some embodiments, therapy can be suspended while the pump system remains in the standby state  1012 . For example, the source of negative pressure can be deactivated (or turned off), which provides the indication to the user that the pump system is in the standby state  1012 . Similarly, the pump system can indicate various current operating states or transition into states with the one or more indicators. 
     With continued reference to  FIG. 10 , in some embodiments, the pump system can transition from the initial pump down state  1014  into a leak state  1016  when a number of retry cycles exceeds a retry limit or when a duty cycle of the pump (explained below) is determined to exceed a duty cycle limit. In some embodiments, exceeding a retry limit or duty cycle limit can reflect the presence of a leak in the system. In some embodiments, the pump system can transition from the IPD state  1014  to the leak state  1016  when a threshold pressure is not reached within a desired amount of time. The inability for the threshold pressure to reach the threshold pressure within a desired amount of time can reflect the presence of a leak in the system. Additionally or alternatively, in some embodiments, an indicator (for example, a leak indicator or dressing indicator) can blink or flash intermittently or continuously to indicate to the user the presence of a leak in the system. In some embodiments, one or more indicators can blink or flash intermittently or continuously to indicate to the user the presence of a leak. 
     After entering the leak state  1016 , the pump system can transition from the leak state  1016  to the IPD state  1014  upon receiving a user input such as a button press. This can advantageously give the user some time to mitigate or remove the leak, such as by checking the connections of the wound dressing or checking the seal of the wound dressing around the wound. In some embodiments, the pump system can monitor the duration of time the pump system remains in the leak state  1016 . This can be accomplished, for example, by maintaining a timer (in firmware, software, hardware or any combination thereof), which can be reset and started when the pump system transitions into the leak state  1016 . In some embodiments, after entering the leak state  1016 , the pump system can automatically make the transition from the leak state  1016  to the IPD state  1014  when the time duration exceeds a threshold. The threshold can be the same or different than the other time thresholds described herein, such as that of the standby state  1012  to the IPD state  1014 . The threshold can be the same or different depending on the state or mode prior to transitioning to the leak state  1016  (for example, the IPD state  1014  or the maintenance mode  1050 ). In some embodiments, such threshold can be a preset value, such as between 1 minute or less and 1 hour or more. In some embodiments, the threshold can be set or changed by the user. In some embodiments, the threshold can be varied based on various operating conditions or on any combination thereof. For example, as the pump system nears the end of life (as is explained below), the threshold can be decreased provided the power source has sufficient capacity remaining. This can advantageously ensure that the power source is more efficiently used over the lifespan of the pump system by reducing the amount of time spent in the leak state  1016  and utilizing more of the power source by activating the pump sooner. The pump system can transition into other modes or states, such as the maintenance mode  1050 , after activating the switch or automatically after exceeding the threshold. In some embodiments, the pump system can transition to the IPD state  1014  or the maintenance mode  1050  depending on operating conditions, such as the pressure at the time of the transition. 
     As noted above, in some embodiments, the pump system can be configured to operate in a canisterless system, in which the wound dressing retains exudate aspirated from the wound. Such dressing can include a filter, such as a hydrophobic filter, that prevents passage of liquids downstream of the dressing (toward the pump system). In other embodiments, the pump system can be configured to operate in system having a canister for storing at least part of exudate aspirated from the wound. Such canister can include a filter, such as a hydrophobic filter, that prevents passage of liquids downstream of the dressing (toward the pump system). In yet other embodiments, both the dressing and the canister can include filters that prevent passage of liquids downstream of the dressing and the canister. 
     With continued reference to  FIG. 10 , in some embodiments, the pump system can be configured to transition from the initial pump down state  1014  into a blockage state  1018 , which can be associated with dressing filter blocked or canister full state, when the system determines that the filter, such as a wound dressing filter, has been blocked (for example, caused by the wound dressing being filled with exudate to capacity or nearly to capacity) or canister is full or substantially full, which can cause a canister filter to be blocked as described herein. In some embodiments, an indicator (for example, a filter blocked or canister full indicator) can blink or flash intermittently or continuously to indicate to the user the presence of a blockage. In some embodiments, one or more indicators can blink or flash intermittently or continuously to indicate to the user the presence of a blockage. Further details on filter block or canister full detection are disclosed in connection with  FIGS. 13, 14A-14D, and 15 . 
     After entering the filter blocked or canister full state  1018 , the pump system can transition from the state  1018  to the IPD state  1014  upon receiving a user input, such as a button press. This can advantageously give the user an opportunity to mitigate or remove the blockage, such as by changing the wound dressing (or the canister). In some embodiments, the pump system can monitor the duration of time the pump system remains in blockage state  1018 . This can be accomplished, for example, by maintaining a timer (in firmware, software, hardware or any combination thereof), which can be reset and started when the pump system transitions into blockage state  1018 . In some embodiments, after entering the state  1018 , the pump system can automatically make the transition from the state  1018  to the IPD state  1014  when the time duration exceeds a threshold. The threshold can be the same or different than the other time thresholds described herein, such as that of the standby state  1012  to the IPD state  1014  or the leak state  1016  to the IPD state  1014 . The threshold can be the same or different depending on the state or mode prior to transitioning to the blockage state  1018  (for example, the IPD state  1014  or the maintenance mode  1050 ). In some embodiments, such threshold can be a preset value, such as between 1 minute or less and 1 hour or more. In some embodiments, the threshold can be set or changed by the user. In some embodiments, the threshold can be varied based on various operating conditions or on any combination thereof. For example, as the pump system nears the end of life (as is explained herein), the threshold can be decreased provided the power source has sufficient capacity remaining. This can advantageously ensure that the power source is more efficiently used over the lifespan of the pump system by reducing the amount of time spent in the blockage state  1018  and utilizing more of the power source by activating the pump sooner. The pump system can transition into other modes or states, such as the maintenance mode  1050 , after activating the switch or automatically after exceeding the threshold. In some embodiments, the pump system can transition to the IPD state  1014  or the maintenance mode  1050  depending on operating conditions, such as the pressure at the time of the transition. 
     With continued reference to  FIG. 10 , in some embodiments, during the IPD state  1014 , once the pump system has detected that the pressure within the pump system or some portion thereof, such as a fluid flow path between a source of negative pressure and a wound dressing, is at or around the low pressure threshold, the pump system can transition into a maintenance mode  1050  and, in particular, to the monitor state  1052 . For example, the low pressure threshold can be approximately −90 mmHg. In some embodiments, the low pressure threshold can be between approximately −50 mmHg and approximately −250 mmHg, between approximately −105 mmHg and approximately −125 mmHg, between approximately −80 mmHg and −105 mmHg, approximately −94 mmHg, any value or subrange within these ranges, or any other value as desired. As described with respect to  FIG. 12 , in some embodiments, one or more sizes of the one or more attached wound dressings can be determined in block  1014  based on the amount of time for the initial pump down, calculated rate of pressure change during the transition from the IPD state  1014  to the maintenance mode  1050 , or the like. 
     During the maintenance mode  1050 , the pump system can advantageously monitor and maintain the pressure within the pump system or some portion thereof, such as a fluid flow path between a source of negative pressure and a wound dressing, within a target pressure range (or operating range). For example, in some embodiments, during the maintenance mode  1050 , the pump system can maintain the pump system or some portion thereof between a high pressure threshold and a low pressure threshold. For example, the high pressure threshold can be approximately −70 mmHg. In some embodiments, the high pressure threshold can be between approximately −40 mmHg and approximately −200 mmHg, between approximately −60 mmHg and approximately −100 mmHg, between approximately −70 mmHg and −80 mmHg, approximately −71 mmHg, approximately −67 mmHg, any value or subrange within these ranges, or any other value as desired. The low pressure threshold can be approximately −90 mmHg. In some embodiments, the low pressure threshold during the maintenance mode  1050  can be the same as the low pressure threshold during the IPD state  1014 . In some embodiments, the low pressure threshold during the maintenance mode  1050  can be different from the low pressure threshold during the IPD state  1014 . As shown in the illustrated embodiment, the maintenance mode  1050  can include a monitor state  1052  and a maintenance pump down (“MPD”) state  1054 . 
     In some embodiments, one or more indicators can blink or flash intermittently or continuously to indicate to the user that the system is in the MPD state. During the monitor state  1052 , the pump system can monitor the pressure in the pump system or some portion thereof, such as a fluid flow path between a source of negative pressure and a wound dressing, to ensure that the pressure within the pump system or the monitored portion thereof is maintained between a high pressure threshold and a low pressure threshold. The source of negative pressure can be deactivated during the monitor state  1052 . The pump system can intermittently or continuously monitor the pressure in the pump system or some portion thereof. For example, the pump system can monitor the pressure in the pump system or some portion thereof at a preset sampling rate of approximately 1 second. In some embodiments, the sampling rate can be between approximately 50 ms and approximately 5 seconds, between approximately 200 ms and 2 seconds, between approximately 500 ms and 2 seconds, approximately 1 second, any value or subrange with these ranges, or any other sampling rate as desired. In some embodiments, the sampling rate during the monitor state  1052  can be less than the sampling rate during the IPD state  1014  to advantageously reduce power usage and extend the life of the power source. A lower sampling rate can be used in some embodiments as the rate of pressure change during the monitor state  1052  (for example, when the source of negative pressure is deactivated) can be less than the rate of pressure change when the source of negative pressure is activated. In some embodiments, the pump system can also calculate the rate of pressure change to estimate the amount of time until the pump system reaches a desired pressure, such as a low pressure threshold. 
     In some embodiments, one or more indicators can blink or flash intermittently or continuously to indicate to the user that the system is in the monitor state. The pump system can stay in the monitor state  1052  until the pump system detects that the pressure in the pump system or some portion thereof, such as a fluid flow path between a source of negative pressure and a wound dressing, is at or around a high pressure threshold. Upon detecting that the pump system or some portion thereof is at or around the high pressure threshold, the pump system can transition to the MPD state  1054 . During the MPD state  1054 , the pump system can activate the source of negative pressure to begin therapy and reduce pressure in the system or some portion thereof until the pressure is at or near the low pressure threshold. In some embodiments, the low pressure threshold can be the same or similar to the low pressure threshold discussed in connection with the IPD state  1014 . In some embodiments, the low pressure threshold can be different from that in the IPD state  1014 . 
     The pump system can continually monitor the pressure in the pump system at a preset sampling rate. In some embodiments, the sampling rate can be the same or similar to the low pressure threshold discussed in connection with the IPD state  1014 . In some embodiments, the sampling rate can be different from the sampling rate during the IPD state  1014 . In some embodiments, the pump system can also calculate the rate of pressure change to estimate the amount of time until the pump system reaches a desired pressure, such as the low pressure threshold. When the pump system detects that the pressure in the pump system or some portion thereof is at or around the low pressure threshold, the pump system can transition back to the monitor state  1052 . 
     With reference to  FIG. 10 , in some embodiments, the user can pause therapy by activating the switch (for example, pressing the button), thereby causing the pump system to make a transition from the maintenance mode  1050  to the standby state  1012 . After being paused by the user, the pump system can transition from the standby state  1012  to the IPD state  1014  upon receiving a user input such as a button press. In some embodiments, after being paused by the user, the pump system can automatically make the transition from the standby state  1012  to the IPD state  1014  when the time duration exceeds a threshold. The threshold can be the same or different than the thresholds discussed above, such as the threshold when the pump system enters the standby state  1012  from the IPD state 1014 from a button press. In some embodiments, such threshold can be a preset value, such as between 1 minute or less and 1 hour or more. In some embodiments, the threshold can be set or changed by the user. In some embodiments, the threshold can be varied based on various operating conditions or on any combination thereof. For example, as the pump system nears the end of life (as is explained below), the threshold can be decreased provided the power source has sufficient capacity remaining. In some embodiments, the pump system can transition into the maintenance mode  1050  after activating the switch or automatically after exceeding the threshold. In some embodiments, the pump system can transition to the IPD state  1014  or the maintenance mode  1050  depending on operating conditions, such as the pressure at the time of the transition. 
     When the pump system transitions into and remains in the standby state  1012 , the user can be provided an indication. For example, in some embodiments, all indicators can be deactivated. In some embodiments, the pump system can deactivate an indicator (for example, an OK indicator) and cause another indicator (for example, a dressing indicator) to flash or blink. In some embodiments, therapy can be suspended while the pump system remains in the standby state  1012 . For example, the source of negative pressure can be deactivated (or turned off), which provides the indication to the user that the pump system is in the standby state  1012 . 
     With continued reference to  FIG. 10 , in some embodiments, the pump system can transition from the maintenance mode  1050  into a leak state  1016  when a threshold pressure is not reached within a desired amount of time. The inability for the threshold pressure to reach the threshold pressure within a desired amount of time can reflect the presence of a leak in the system. In some embodiments, the pump system can transition from the maintenance mode  1050  to the leak state  1016  when a number of retry cycles exceeds a retry limit or when the duty cycle of the pump is determined to exceed a duty cycle limit. In some embodiments, exceeding a retry limit or duty cycle limit can reflect the presence of a leak in the system. Additionally, as will be described in further detail with respect to  FIG. 15 , the pump system may transition into the leak state  1016  when the pump system detects peak-to-trough pressure measurements to be below a threshold for a period of time. In some embodiments, an indicator (for example, a leak indicator or dressing indicator) can blink or flash intermittently or continuously to indicate to the user the presence of a leak in the system. 
     With continued reference to  FIG. 10 , in some embodiments, the pump system can be configured to transition from the maintenance mode  1050  into the blockage state  1018  when the system determines that the filter, such as the wound dressing filter (or the canister filter), has been blocked (for example, caused by the wound dressing or canister being filled with exudate to capacity or nearly to capacity). In some embodiments, an indicator (for example, a filter blocked indicator) can blink or flash intermittently or continuously to indicate to the user the presence of a blockage. 
     With continued reference to  FIG. 10 , in some embodiments, the pump system can be configured to monitor the remaining capacity or life of the power source (for example, by periodically reading or sampling the power source voltage, current, etc.). The pump system can be configured to indicate to the user the remaining capacity. For example, if the power source is determined to have a normal remaining capacity (for example, as a result of comparison to a threshold, such as 2.7V, 2.6V, 2.5V, etc.), an indicator (for example, a power source indicator) can be deactivated. If the power source is determined to have low remaining capacity, the pump system, can provide an indication to the user by, for example, causing an indicator (for example, a power source indicator) to blink or flash. In some embodiments, an indicator (for example, a power source indicator) can be configured to be blinking or flashing intermittently or continuously regardless of the state the pump system is in or only in particular states. 
     In some embodiments, when the remaining capacity of the power source is determined to be at or near a critical level (for example, as a result of comparison to a threshold, such as 2.4V, 2.3V, 2.2V, etc.), the pump system can transition into an under voltage or power source critical state  1092 . In some embodiments, the pump system can remain in this state until the capacity of the power source is increased, such as by replacing or recharging the power source. The pump system can deactivate therapy while remaining in the power source critical state  1092 . In addition, the pump system can be configured to indicate to the user that the power source is at or near the critical level by, for example, deactivating all indicators. In some embodiments, when the pause/resume button is pressed after the pump system has transitioned to the under voltage state  1092 , the pump system can be configured to indicate that the device has not yet reached its end of life (EOL) by, for example, flashing a power source indicator LED. 
     With continued reference to  FIG. 10 , in some embodiments, the pump system can be configured to provide therapy for a predetermined period of time, such as approximately 1 day, 2-10 days, up to 30 days, etc. following a first activation. In some embodiments, such period of time can be a preset value, changed by the user, or varied based on various operating conditions or on any combination thereof. The pump system can be disposed upon the expiration of such period of time. Once the pump system has been activated, the pump system can monitor the duration it has remained active. In some embodiments, the pump system can monitor the cumulative duration the system has remained active. This can be accomplished, for example, by maintaining a timer (in firmware, software, hardware or any combination thereof), that reflects such duration. 
     When the duration reaches or exceeds a threshold (for example, 10 days), the pump system can transition to an end of life (EOL) state  1090 . The pump system can deactivate therapy while remaining in state  1090  and to indicate to the user that the end of the pump system&#39;s usable life has been reached. For example, the pump system can deactivate all indicators or deactivate the button. In some embodiments, when the pump system is disposable, transitioning to the end of life state  1090  means that the pump system can be disposed of. The pump system can disable reactivation of the pump system once the end of life has been reached. For example, the pump system can be configured to not allow reactivation even if the power source is disconnected and reconnected later, which can be accomplished by storing an indication, value, flag, etc. in the read only memory. 
     In some embodiments, the pressure during the IPD or MPD state can be sampled after a preset period of time as elapsed from when the IPD or MPD state was initiated. After this time period elapses, the pressure can be sampled in consecutive samples, and two or more of the consecutive samples can be averaged. In some embodiments, sampling of the pressure can be synchronized with the drive signal. For example, sampling of the pressure within the pump system or some portion thereof, such as a fluid flow path between a source of negative pressure and a wound dressing, can be performed when the drive signal is approximately at an amplitude that is substantially at an offset (explained below) or at a zero value. In some embodiments, two or more groups of consecutive pressure samples can be averaged to minimize measurement errors due to pressure fluctuations caused by operation of the motor. In some embodiments, averaging two or more groups of consecutive pressure samples can compensate for the time needed to detect the zero value when the pressure samples are synchronized at a zero value. Movement of the pump assembly can highly influence pressure within the pump system, such as a manifold of the pump system. By synchronizing sampling of the pressure with the offset or zero value of the drive signal, any measurement errors due to pressure fluctuations caused by operation of the motor can be reduced. In some embodiments, sampling of the pressure can be synchronized with the local maxima or local minima of the drive signal. In some embodiments, sampling of the pressure can be synchronized with certain portions of the drive signal, such as portions of the drive signal with a negative rate of change or a positive rate of change. 
     In some embodiments, the pressure can be sampled one or more times at or around the one or more selected sampling amplitudes such as the offset or zero value, local maxima, or local minima. This can beneficially reduce the likelihood of sampling errors and compensate for the delay elapsed between detection of the one or more selected sampling amplitudes and sampling of the pressure. For example, in some embodiments, the pump system can take 8 consecutive samples at approximately each offset or zero value. Accordingly, the pump system can take 16 samples over a single period of the drive signal. In some embodiments, the pump system can average some or all of the samples taken over a period. 
       FIG. 11  illustrates a graph  1100  of pressure versus time according to some embodiments. Graph  1100  illustrates pressure changes during the IPD state  1110 , monitor state  1120 , and MPD state  1130 , one or more of which can correspond to states  1014 ,  1052 , and  1054  in  FIG. 10 . As shown in graph  1100 , during the IPD state  1110 , the pump system can sample the pressure at two or more points in time represented on the graph as points  1112 ,  1114  corresponding to pressures P 1  at time t 1  and P 2  at time t 2  respectively. The rate of change of pressure between these two points can be calculated according to: (P 2 −P 1 )/(t 2 −t 1 ). 
     In some circumstances, an abrupt pressure drop, for example from point  1112  to point  1114 , is indicative of a transient blockage, such as a kinked conduit in the fluid flow path, dressing full, canister full, or the like. As described herein, the pump system can detect such blockage condition by determining that the rate of change of pressure exceeds a threshold. 
     Dressing Capacity or Size Determination 
     In some embodiments, such as in a multiple dressing TNP system or pump assembly, capacity(ies) or size(s) of one or more dressings, such as one or more dressings  700 , can be determined by one or more processors. In some cases, dressing size(s) can be determined based on determining the amount of time for initial pump down (such as, in IPD  1014  state) or reaching the negative pressure setpoint after therapy is initiated. For example, achieving the negative pressure setpoint in a system with a large dressing will take longer than in a system with a small dressing. For example, as illustrated in  FIG. 12 , a small dressing pressure profile  1202  is associated with IPD of t 1 , while a large dressing pressure profile  1204  is associated with IPD of t 2 . Since the time required to pump down a smaller volume for a given pump is shorter, t 1  is smaller than t 2 . As explained herein, in some cases, the TNP system can use a look up a table that associates IPD time to dressing sizes to determine the dressing size(s). As described herein, the pump system can determine sizes for combinations of two or more wound dressings. 
     When multiple dressings are present, multiple pressure sensors can be used to monitor pressure in multiple fluid flowpaths or a single pressure sensor can be used to measure combined pressure in the multiple fluid flowpaths. In some cases, dressing size(s) can be determined in based on time to reestablish the negative pressure setpoint (such as, MPD state  1054 ). 
     Additionally or alternatively, in some cases, the TNP system can determine sizes of one or more wound dressings based on a rate of pressure change. The rate of pressure change can be measured as differential change between two pressures known at two times divided by the differential of the corresponding two times (for example, (P 2 −P 1 )/(t 2 −t 1 ) as disclosed herein). As described herein, a large wound dressing includes more volume than a small wound dressing. Thus, when measuring the rate of pressure change, the large wound dressing would exhibit smaller rate of pressure change than the small wound dressing. Since the volume of a given wound dressing can be obtained beforehand from a manufacturer, associated pressure change can be determined during calibration and used during provision of therapy. For example, a look up table associating a rate of pressure change with wound dressing sizes can be stored in memory of the TNP system. Alternatively or additionally, a manufacturer can measure the volume of manufactured wound dressings and provide the volume measurement along with the wound dressing with which a similar look up table can associate a detected rate of pressure change and identify wound dressing size. 
       FIG. 12  illustrates, for a given pump having a known aspirating capacity, a rate of pressure change determined when aspirating fluid with the pump using a small wound dressing will be larger in magnitude than if a larger wound dressing was used (for example, compare pressure change of −20 mmHg/sec  1202  with a small dressing with pressure change of −16 mmHg/sec  1204  with the larger dressing). Based on the rate of pressure change, the TNP system, for instance, via one or more processors, can determine a size of a coupled wound dressing. 
     In some embodiments, the TNP system may use a look up table for associating detected rate of pressure change with one or more known sizes of different wound dressings. For example, as  FIG. 12  illustrates, a rate of pressure change of −20 mmHg/sec can be associated with a small wound dressing, while a rate of pressure change of −16 mmHg/sec may be associated with a large wound dressing. Using the look up table, the TNP system may determine which wound dressing is currently coupled with the system. 
     As illustrated with  FIGS. 4A-4B and 5 , a TNP system may be concurrently coupled with more than one wound dressings in a configuration where one negative pressure source can provide negative pressure to multiple wound dressings. In some embodiments, for a given size wound dressing, having another wound dressing of similar size (for example, two small wound dressings or two large wound dressings) can manifest a rate of pressure change that is approximately half in magnitude to a single wound dressing (for example, compare  1202  to  1206  or  1204  to  1208  in  FIG. 12 ). 
     In some cases, using the look up tables which can include associations with such multiple wound dressing configurations, or identifying a configuration that would best match a measured rate of pressure change with a combination of a plurality of known size wound dressings and their associated rates of pressure change, the TNP system may determine sizes of multiple coupled wound dressings. In some embodiments, where two different size wound dressings are coupled to the TNP system (for example, small and large  1210  in  FIG. 12 ), the TNP system may associate the determined rate of change with a combination of known wound dressing sizes. 
     In some embodiments, detecting the rate of pressure change during the initial pump down can provide high degree of confidence of the detected rate of pressure change. Since detection of the wound dressing sizes is preferably performed at the start of the therapy and may not need to be redetermined unless the wound dressings are switched out, entire or partial duration of initial pump down can be advantageous for detecting wound dressing sizes. However, as described herein, in some embodiments detecting the rate of pressure change can be performed over a shorter time frame (for example, at times between t 1  time  1112  and t 2  time  1114  in  FIG. 11 ). 
     Blockage Detection 
     In some embodiments, a TNP system or pump assembly can detect and provide indication of a blockage, which can include canister pre-full or full, dressing pre-full or full, or other type of blockage in one or more fluid flow paths. As explained herein, for example, this determination can be made in when the process  900  of  FIG. 9  is in standby state (block  908 ). As another example, this determination can be made when the process  1000  of  FIG. 10  is in the maintenance mode states (block  1050 ). During operation, the pump generates pressure pulses or signals that are propagated through the fluid flow path(s). The pressure signals, which can be detected by one or more pressure sensors, are illustrated by the pressure curve  1302  of  FIG. 13  according to some embodiments. As is illustrated in region  1304 , pressure in a fluid flow path varies or oscillates around a particular negative pressure setpoint  1308  during normal operation of the system. Magnitude of pressure variation can be inversely proportional to the volume of the fluid flow path. Region  1306  illustrates pressure pulses in the flow path in presence of a blockage. Such blockage may be caused by, for example, the canister or dressing becoming full or a canister or dressing filter becoming occluded or blocked. 
     As is illustrated in region  1306 , presence of a blockage causes a reduced volume to be seen upstream of the canister or dressing, and the amplitude of the pressure pulses changes (for example, increases). The frequency of a pressure signal can also change (for example, slows down or decreases). These changes in the one or more parameters of the pressure signal can be caused by the pump evacuating fluid from a reduced volume in the fluid flow path, with the reduction being due to the blockage. Observed changes in one or more parameters of the pressure signal can be used to identify the type of blockage present, such as distinguish between canister full, dressing full, or other types of blockages in the fluid flow path. The observed in the one or more parameters of the pressure signal can additionally or alternatively be used to identify remaining capacity of one or more wound dressings in a multiple dressing system, such as the one illustrated in  FIGS. 4A-4B and 5 . Changes in the amplitude or frequency of the pressure signal can be measured using a variety of techniques, such as by measuring peak-to-trough change (for example, peak  1314  to trough  1316 ). 
     In some cases, peak-to-trough value(s) for detecting blockage in one or more fluid flow paths can be measured after the pump system reaches the negative pressure setpoint  1308  (such as, for example in the steady state  908 ). Before reaching the pressure setpoint  1308 , too much fluid may be evacuated by the TNP system to provide meaningful peak-to-trough measurements. Before reaching the negative pressure setpoint, peak-to-trough measurements may be too small to meaningfully determine presence of a blockage condition. 
     In certain embodiments, the changes in the pressure pulse signal can be magnified or enhanced by varying the pump speed, varying the cadence of the pump, such as by adjusting PWM parameters, turning the pump off and on, or the like. Such adjustments of pump operation are not required but can be performed over short time duration and the changes can be small such that the operation of the system remains relatively unaffected. 
     Blockage condition can be detected by collecting a one or more pressure sensor readings. For example, a single pressure sensor can be used to determine pressure in one or more fluid flow paths. One or more processors (as described herein) can use the one or more pressure sensor readings to determine one or more peak-to-trough values and compare the determined value(s) to one or more thresholds. The one or more thresholds can be determined or selected based on dressing sizes in a multiple dressing system, which can be detected as described herein. The one or more thresholds can be associated with expected pressure variations during normal operation, such as in the region  1304  of  FIG. 13 . For example, in a two dressing system, the combined volume of two small dressings can correspond to a threshold of T 1 , while the combined volume of two large dressings can correspond to a threshold of T 2 . T 2  can be smaller than T 1  because the combined volume of two large dressings is greater than the combined volume of two small dressings. The processor can compare determine peak-to-trough value(s) to the particular threshold (corresponding to the detected dressing sizes) and indicate presence of blockage if the threshold is satisfied (such as, exceeded as illustrated in the region  1306  of  FIG. 13 ). 
     In some cases, one or more thresholds can be determined or selected to permit detection of a dressing pre-full condition. For example, a threshold can be determined to detect and alert a user to at least one of the dressings in a multiple dressing system being 50% full, 75% full, or the like. This can be advantageous to filling of at least one of the dressings with wound fluid to capacity and resulting blockage of the dressing filter, which can lead to adverse effects including, but not limited to one or more of, pooling of exudate, infection, or maceration. 
     In some cases, peak-to-trough measurement can be performed over a time duration (for example, 2 seconds or any other suitable duration which may be vary between sample periods). A number of readings of the plurality of readings, such as 25 sample periods out of 30 or any other suitable number, can be checked to determine if each indicates that the a blockage is present. If it is determined that the peak-to-trough pressure for a particular sample period satisfies the threshold, then the particular sample period indicates that the blockage is present. 
     One or more thresholds can additionally or alternatively can be determined based on the negative pressure setpoint. For example, a greater negative pressure setpoint can be associated with a greater expected variation of pressure and a higher threshold as compared to a smaller negative pressure setpoint. 
     Blockage determination can be performed on a sliding window basis. For example, a sliding window of 25 out of 30 sample periods can be analyzed and if 25 sample periods are determined to indicate blockage, blockage can be indicated. Assuming that, for example, the sample period is 2 seconds, using a sliding window of 25 out of 30 sample periods effectively results in determining whether change in pressure pulse amplitude exceeds the threshold for 60 seconds. This can prevent generation of unnecessary or undesirable blockage alarms. 
     Alternatively or additionally, blockage can be detected if a single sample period indicates blockage. However, using a plurality of sample periods can mitigate the effects of one or more transient conditions in the fluid flow path or one or more errant pressure readings. Alternatively or additionally, blockage detection can be performed by measuring the frequency of detected pressure signal and comparing the measured frequency to one or more suitable thresholds. 
     As described herein, multiple pressure sensors can be placed in the fluid flow path to facilitate detection of one or more of the above-described conditions. For example, in addition to or instead of the pressure sensor being placed in the pump inlet, a pressure sensor can be placed in the wound or under the dressing to directly determine the wound pressure. Measuring pressure at different locations in the fluid flow path, such as in the canister and at the wound, can facilitate detection of blockages, leaks, or the like. 
       FIGS. 14A-14D  illustrate graphs of pressure signals according to some embodiments. Curve  1402 A can correspond to a signal observed when the canister and/or one or more dressings are relatively empty. For example, a canister may be configured to hold up to 750 mL fluid volume, and curve  1402 A can correspond to the empty volume of 515 mL. As is illustrated, the bounce in the pressure signal magnitude curve  1402 A is relatively small as the curve is substantially flat. The bounce of the pressure signal can be measured using a variety of techniques, such as by measuring peak-to-trough change and selecting the largest such change as being indicative of the largest bounce. Curve  1402 A can correspond to the voltage reading, current reading, etc. 
       FIG. 14B  illustrates a magnitude curve  1402 B of the pressure signal in the flow path as sensed by one or more pressure sensors over a period of time. Curve  1402 B can correspond to a signal observed when the canister and/or one or more dressings are relatively full. For example, the canister may be configured to hold up to 750 mL volume, and curve  1402 B can correspond to the empty volume of 60 mL. As is illustrated, the bounce in the pressure signal magnitude curve  1402 B is larger than that in curve  1402 A.  FIG. 14C  illustrates a magnitude curve  1402 C of the pressure signal in the flow path as sensed by one or more pressure sensors over a period of time. Curve  1402 C can correspond to a signal observed when the canister and/or one or more dressings are almost full. For example, the canister may be configured to hold up to 750 mL volume, and curve  1402 C can correspond to the empty volume of 30 mL. As is illustrated, the bounce in the pressure signal magnitude curve  1402 B is larger than that in curves  1402 A and  1402 B. 
       FIG. 14D  illustrates a magnitude curve  1402 D of the pressure signal in the flow path as sensed by one or more pressure sensors over a period of time. Curve  1402 D can correspond to a signal observed when the canister and/or one or more dressings are nearly full. For example, the canister may be configured to hold up to 750 mL volume, and curve  1402 D can correspond to the empty volume of 15 mL. As is illustrated, the bounce in the pressure signal magnitude curve  1402 D is larger than that in curves  1402 A,  1402 B, and  1402 C. 
     Table 2 illustrates the largest magnitude bounces or peak-to-trough changes (for example, in voltage as indicated by Vp-p) measured for the curves  1402 A,  1402 B,  1402 C, and  1402 D according to some embodiments. With reference to the first row (row  1 ), column A corresponds to curve  1402 A and indicates the largest change of 0.010 V, column B corresponds to curve  1402 D and indicates the largest change of 0.078 V, column C corresponds to curve  1402 C and indicates the largest change of 0.122 V, and column D corresponds to curve  1402 D and indicates the largest change of 0.170 V. These increasing bounce values confirm that the bounce in the pressure signal magnitude increases as the canister fills up or a blockage develops. Level of exudate in the canister (or the one or more dressings) can be detected by comparing the determined pressure magnitude bounce to one or more thresholds, which can be determined experimentally for canisters or dressings of various sizes as descrbed herein. For example, canister (or one or more dressings) pre-full condition may be set to the canister having 30 mL or less empty volume. Using Table 1, a pre-full threshold can be set to approximately 0.12 V peak-to-trough bounce. In some embodiments, measures other than or in addition to peak-to-trough can be used, such as average bounce, etc. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Pressure Magnitude Bounce at 40 mmHg 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pressure Magnitude 
                 D 
                 C 
                 B 
                 A 
               
               
                   
                 (V p-p ) 
                 15 mL 
                 30 mL 
                 60 mL 
                 515 mL 
               
               
                   
                 at 40 mmHg 
                 volume 
                 volume 
                 volume 
                 volume 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 60 
                 mL/min 
                 0.170 
                 0.122 
                 0.078 
                 0.010 
               
               
                 2 
                 150 
                 mL/min 
                 0.174 
                 0.120 
                 0.074 
                 0.012 
               
               
                 3 
                 450 
                 mL/min 
                 0.178 
                 0.118 
                 0.068 
                 0.008 
               
               
                 4 
                 1000 
                 mL/min 
                 0.124 
                 0.082 
                 0.050 
                 0.012 
               
               
                   
               
            
           
         
       
     
     In some embodiments, signal processing techniques can be utilized on the detected pressure signal(s). For example, sensed pressure values can be processed, such as low-pass filtered (for example, via averaging), to remove noise. As another example, detected pressure signal can be converted into frequency domain, for example by using the Fast Fourier Transform (FFT). The signal can be processed and analyzed in frequency domain. 
     As is illustrated in  FIGS. 14A-14D , the bounce or ripple in the observed pressure magnitude increases as the canister or one or more dressings fill up, which reduces the volume “seen” by the pump. As explained herein, because larger dressings have larger volume “seen” by the pump, the larger dressings can cause smaller peak-to-peak measurements than smaller dressings. By detecting sizes of one or more dressings, the pump system can adopt accurate blockage detection threshold values for different dressing sizes. 
     Disclosed embodiments of blockage detection can be used in a TNP system that operates substantially without an external leak or external flow of gas (such as, atmospheric air) into one or more fluid flow paths. For example, disclosed embodiments of blockage detection can be used with a Pico TNP system available from Smith &amp; Nephew operating with single or multiple dressings. 
     Leak Detection 
     A TNP system can perform leak detection similarly to blockage detection described herein. For example, leak detection can be performed during initial pump down (such as, in the IPD state  1014  of  FIG. 10 ) or in maintenance mode (such as, in the maintenance mode states  1050  of  FIG. 10 ). 
       FIG. 15  illustrates pressure versus time graphs when a leak condition is detected according to some embodiments. A TNP system or pump assembly (via one or more processors as described herein) can perform leak check test, which may result in detection of a leak or low vacuum. If at any point during a time period that follows initiation of therapy, such as 45 seconds or any other suitable duration after therapy has been started, the pump system transitions from the initial pump down state, such as the IPD state  1014 , to a monitoring state, such as the maintenance mode states  1050 , the leak check test has passed and suitable seal is deemed to have been achieved. That is, if pressure at the wound has reached desired negative pressure setpoint  1602  within the period of time, it is determined that the one or more fluid flow paths are suitably sealed and no significant leaks are present (for example, the one or more dressings have been properly placed and proper connections between one or more of pump assembly, canister, or dressing(s) have been made). 
     The pump system can detect a leak condition from the peak-to-trough measurements similarly to performing blockage detection as described herein. With reference to  FIG. 15 , a pressure profile  1604  of a suitably sealed pump system reaches the pressure setpoint  1602 . Once the pressure setpoint  1602  is reached, subsequent pressure measurements may oscillate, as the pressure profile  1602  illustrates, about the pressure setpoint as described herein. 
     When there exists a leak in one or more fluid flow paths, the pressure profile can follow a leak pressure profile  1606 . As illustrated in  FIG. 15 , the leak pressure profile  1606  does not reach the pressure setpoint  1602 . Additionally, the profile  1606  may show peak-to-trough variations  1608  that have relatively small magnitudes (for example, as compared to the blockage peak-to-trough variations in region  1306  of  FIG. 13 ). Still, comparing peak-to-trough measurements  1608  against suitable one or more thresholds, such as the threshold  1612  can ignore variations  1610  from suitably sealed pump systems, but detect small variations  1608  from leaking pump systems, existence of a leak condition can be performed. 
     In some cases, after leak check test has passed, a suitable seal can be deemed to have been achieved until therapy is paused. After therapy is restarted, leak check test can be performed. 
     Additional embodiments of blockage or leak detection are described in U.S. Pat. No. 8843327, U.S. Patent Publication No. 2016/0184496, International Patent Publication Nos. WO 2016/103033, WO 2016/103035, WO 2016/103032, and WO 2016/103031, and International Application No. PCT/EP2018/056494 (published as WO 2018/167199), each of which is incorporated herein by reference in its entirety. 
     Terminology 
     Depending on the embodiment, certain operations, acts, events, or functions of any of the processes described herein can be performed in a different sequence, can be added, merged, or left out altogether (such as not all are necessary for the practice of the processes). Moreover, in certain embodiments, operations, acts, functions, or events can be performed concurrently, such as through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. 
     The processing of the various components of the illustrated systems can be distributed across multiple machines, networks, and other computing resources. In addition, two or more components of a system can be combined into fewer components. Various components of the illustrated systems can be implemented in one or more virtual machines, rather than in dedicated computer hardware systems or computing devices. Likewise, the data repositories shown can represent physical or logical data storage, including, for example, storage area networks or other distributed storage systems. Moreover, in some embodiments the connections between the components shown represent possible paths of data flow, rather than actual connections between hardware. While some examples of possible connections are shown, any of the subset of the components shown can communicate with any other subset of components in various implementations. 
     Any patents and applications and other references noted above, including any that may be listed in accompanying filing papers, are incorporated herein by reference. Aspects of the disclosure can be modified, if necessary, to employ the systems, functions, and concepts of the various references described herein to provide yet further implementations. 
     Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of protection. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the processes illustrated or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the steps described above may be removed, others may be added. For example, the actual steps or order of steps taken in the disclosed processes may differ from those shown in the figure. Depending on the embodiment, certain of the steps described above may be removed, others may be added. For instance, the various components illustrated in the figures may be implemented as software or firmware on a processor, controller, ASIC, FPGA, or dedicated hardware. Hardware components, such as processors, ASICs, FPGAs, and the like, can include logic circuitry. Furthermore, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. 
     Although the present disclosure includes certain embodiments, examples and applications, it will be understood by those skilled in the art that the present disclosure extends beyond the specifically disclosed embodiments to other alternative embodiments or uses and obvious modifications and equivalents thereof, including embodiments which do not provide all of the features and advantages set forth herein. Accordingly, the scope of the present disclosure is not intended to be limited by the described embodiments, and may be defined by claims as presented herein or as presented in the future. 
     Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, or steps. Thus, such conditional language is not generally intended to imply that features, elements, or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, or steps are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Likewise the term “and/or” in reference to a list of two or more items, covers all of the following interpretations of the word: any one of the items in the list, all of the items in the list, and any combination of the items in the list. Further, the term “each,” as used herein, in addition to having its ordinary meaning, can mean any subset of a set of elements to which the term “each” is applied. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. 
     Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z. 
     Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree. 
     Any of the embodiments described herein can be used with a canister or without a canister. Any of the dressing embodiments described herein can absorb and store wound exudate. 
     The scope of the present disclosure is not intended to be limited by the description of certain embodiments and may be defined by the claims. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.