Patent Description:
There is much prior art available relating to the provision of apparatus and methods of use thereof for the application of topical negative pressure (TNP) therapy to wounds together with other therapeutic processes intended to enhance the effects of the TNP therapy. Examples of such prior art include those listed and briefly described below.

TNP therapy (sometimes referred to as Vacuum Assisted Closure or negative pressure wound therapy) assists in the closure and healing of wounds by reducing tissue oedema; encouraging blood flow and granulation of tissue; removing excess exudates and may reduce bacterial load and thus, infection to the wound. Furthermore, TNP therapy permits less outside disturbance of the wound and promotes more rapid healing.

In International patent application, <CIT>, an apparatus, a wound dressing and a method for aspirating, irrigating and cleansing wounds are described. In very general terms, the application describes the treatment of a wound by the application of TNP therapy for aspirating the wound together with the further provision of additional fluid for irrigating and/or cleansing the wound, which fluid, comprising both wound exudates and irrigation fluid, is then drawn off by the aspiration means and circulated through means for separating the beneficial materials therein from deleterious materials. The materials which are beneficial to wound healing are recirculated through the wound dressing and those materials deleterious to wound healing are discarded to a waste collection bag or vessel.

In International patent application, <CIT>, an apparatus, a wound dressing and a method for cleansing a wound using aspiration, irrigation and cleansing are described. Again, in very general terms, the invention described in this document utilises similar apparatus to that in <CIT> with regard to the aspiration, irrigation and cleansing of the wound, however, it further includes the important additional step of providing heating means to control the temperature of that beneficial material being returned to the wound site/dressing so that it is at an optimum temperature, for example, to have the most efficacious therapeutic effect on the wound.

However, the above described apparatus and methods are generally only applicable to a patient when hospitalised as the apparatus used is complex, needing people having specialist knowledge in how to operate and maintain the apparatus, and also relatively heavy and bulky, not being adapted for easy mobility outside of a hospital environment by a patient, for example.

Some patients having relatively less severe wounds which do not require continuous hospitalisation, for example, but whom nevertheless would benefit from the prolonged application of TNP therapy, could be treated at home or at work subject to the availability of an easily portable and maintainable TNP therapy apparatus. To this end <CIT> describes a portable TNP therapy unit which may be carried by a patient and clipped to belt or harness. A negative pressure can thus be applied at a wound site.

However, this portable apparatus is still relatively bulky, and may require monitoring of the patient by a trained caregiver. Furthermore, such portable therapy units commonly have reduced capacity to deal with fluid flow rates into a wound cavity caused by leaks. This leads to a greater number of alarms being raised due to an inability to maintain the desired negative pressure at the wound site in the presence of leaks.

Another problem associated with portable apparatus is that on occasion an onboard power source such as a battery pack is used rather than a continuous connection to a power source such as a mains power source. It will be appreciated that such a battery pack has only a limited power resource and therefore TNP therapy can on occasion be halted prior to a desired moment in time because of power failure. <CIT> discloses a portable NPWT system which includes a dressing assembly for positioning over a wound to apply a negative pressure to the wound and a canister assembly. The canister assembly includes a control unit having a vacuum source and a controller and a collection canister in communication with the dressing assembly operable to receive fluid from the wound.

Another problem associated with therapy units which can be utilised by a patient alone without the need for skilled technical assistants is that from time to time warning lights or warning alarms may be initiated when a desired therapy can not be maintained or initiated. This can be distressing for a patient who may not understand the meaning of the cues.

A still further problem associated with the apparatus used to provide TNP therapy is that from time to time a motor associated with a pump which generates a negative pressure will start up or stop. The change in volume coming from the therapy unit can be a cause of concern to a patient.

The invention is as set forth in the appended claims.

It is an aim of certain embodiments of the present invention to at least partly mitigate one or more of the above-mentioned problems.

It is an aim of certain embodiments, not claimed in the present invention, to provide a method for controlling the provision of a desired negative pressure at a wound site to aid in wound closure and healing.

It is an aim of certain embodiments of the present invention to provide a pressure control apparatus that avoids the generation of unnecessary alarms in the presence of transient leaks.

It is an aim of certain embodiments of the present invention to provide a pressure control apparatus that helps extend battery power lifetime.

It is an aim of certain embodiments of the present invention to provide a pressure control apparatus that reduces a number of pump motor start-up or power down operations.

According to a first aspect, not claimed in the present invention, there is provided apparatus for dressing a wound for the application of topical negative pressure at a wound site, comprising:.

According to a second aspect not claimed in the present invention there is provided a method of applying topical negative pressure (TNP) at a wound site, comprising the steps of:.

According to a third aspect, not claimed in the present invention, there is provided an apparatus for applying negative pressure to a wound, comprising:.

In some embodiments, the controller is further configured to: deactivate the source of negative pressure when the first desired negative pressure has not been generated under the dressing after activating the source of negative pressure for a first number of times exceeding a first threshold.

In some embodiments, the controller is further configured to: when the first number of times exceeds the first threshold, deactivate the source of negative pressure for a third time interval.

In some embodiments, the apparatus further comprises: a switch configured to signal to the controller to activate or deactivate the source of negative pressure; and the controller is further configured to, upon expiration of the third time interval or upon receiving a signal to activate the source of negative pressure from the switch, activate the source of negative pressure to generate the first desired negative pressure under the dressing.

In some embodiments, the apparatus further comprises: an indicator, wherein the controller is further configured to activate the indicator when the first number of times exceeds the first threshold.

In some embodiments, the controller is further configured to: deactivate the indicator upon expiration of the third time interval or receiving a signal to activate the source of negative pressure from the switch.

In some embodiments, the indicator indicates a leak in the seal.

In some embodiments, the controller is further configured to:.

In some embodiments, the first and second desired negative pressure are the same.

In some embodiments, the second desired negative pressure is less than the first desired negative pressure.

In some embodiments, the controller is further configured: to deactivate the source of negative pressure if the negative pressure under the dressing has reached the second desired negative pressure or if the negative pressure under the dressing has not reached the second desired negative pressure upon expiration of a fourth time interval.

In some embodiments, if the negative pressure under the dressing has not reached the second desired negative pressure upon expiration of the fourth time interval, the controller is further configured to, upon expiration of the second time interval, activate the source of the negative pressure to generate the first desired negative pressure under the dressing.

In some embodiments, the controller is further configured to: activate the source of the negative pressure to generate the first desired negative pressure under the dressing if the controller has activated the source of negative pressure to reach the second desired negative pressure for a second number of times less than a second threshold.

In some embodiments, the duty cycle comprises an amount, proportion, or percentage of time the source of negative pressure is active over a period of time.

In some embodiments, the controller is further configured to: calculate a number of duty cycles that exceed the first duty cycle threshold and deactivate the source of negative pressure when the number of duty cycles that exceed the first duty cycle threshold exceeds a second duty cycle threshold.

In some embodiments, the controller is further configured to calculate a number of consecutive duty cycles that exceed the first duty cycle threshold.

In some embodiments, the second duty cycle threshold comprises <NUM> minutes.

In some embodiments, the controller is further configured: to upon expiration of the third time interval or upon receiving the signal from the switch to active the source of negative pressure, activate the source of negative pressure to generate the first desired negative pressure under the dressing.

In some embodiments, the source of negative pressure comprises a pump.

In some embodiments, the apparatus further comprises: a pressure sensor configured to sense pressure under the dressing and to communicate the sensed pressure to the controller.

In some embodiments, the apparatus further comprises: a one-way valve coupled between an inlet and the source of negative pressure, wherein the inlet is in fluid communication with the dressing.

In some embodiments, the source of negative pressure comprises: a valve configured to connect the port to an external source of negative pressure.

In some embodiments, the controller is further configured to: activate or deactivate the source of negative pressure by operating the valve.

According to a fourth aspect, not claimed in the present invention, there is provided a method of applying negative pressure to a wound, comprising:.

In some embodiments, the method further comprises: deactivating the source of negative pressure when the first desired negative pressure has not been generated under the dressing after activating the source of negative pressure for a first number of times exceeding a first threshold.

In some embodiments, the method further comprises: deactivating the source of negative pressure for a third time interval when the first number of times exceeds the first threshold.

In some embodiments, the method further comprises: activating the source of negative pressure to generate the first desired negative pressure under the dressing upon expiration of the third time interval or upon receiving a signal to activate the source of negative pressure from a switch.

In some embodiments, the method further comprises: indicating to a user when the first number of times exceeds the first threshold.

In some embodiments, the method further comprises: stopping the indication upon expiration of the third time interval or receiving a signal to activate the source of negative pressure from the switch.

In some embodiments, the indicating indicates a leak in the seal.

In some embodiments, the method further comprises:.

In some embodiments, the method further comprises: deactivating the source of negative pressure if the negative pressure under the dressing has reached the second desired negative pressure or if the negative pressure under the dressing has not reached the second desired negative pressure upon expiration of a fourth time interval.

In some embodiments, the method further comprises: if the negative pressure under the dressing has not reached the second desired negative pressure upon expiration of the fourth time interval, activating the source of the negative pressure to generate the first desired negative pressure under the dressing upon expiration of the second time interval.

In some embodiments, the method further comprises: activating the source of the negative pressure to generate the first desired negative pressure under the dressing if the source of negative pressure has been activated to reach the second desired negative pressure for a second number of times less than a second threshold.

In some embodiments, the method further comprises: calculating a number of duty cycles that exceed the first duty cycle threshold and deactivating the source of negative pressure when the number of duty cycles that exceed the first duty cycle threshold exceeds a second duty cycle threshold.

In some embodiments, the method further comprises: calculating a number of consecutive duty cycles that exceed the first duty cycle threshold.

In some embodiments, the method further comprises: upon expiration of the third time interval or upon receiving the signal from the switch to active the source of negative pressure, activating the source of negative pressure to generate the first desired negative pressure under the dressing.

In some embodiments, the method further comprises sensing pressure under the dressing.

In some embodiments, the method further comprises: activating or deactivating the source of negative pressure by operating a valve.

Certain embodiments of the present invention provide the advantage that the raising of alarms due to transient leaks into a wound chamber can be avoided, while also reducing the potential for drawing contaminants into a wound site through a leak into the wound chamber.

Certain embodiments of the present invention provide the advantage of extending the useful life of a battery powered source of negative pressure used to provide a desired negative pressure to a wound site.

Embodiments of the present invention will now be described hereinafter, by way of example only, with reference to the accompanying drawings in which:.

<FIG> illustrates an arrangement for applying negative pressure wound therapy to a wound site <NUM>. A packing material <NUM> is placed within a wound cavity, and then a drape <NUM> sealed to the surface of the skin around the wound site <NUM> forming a fluid tight seal around the perimeter of a wound chamber. A source of negative pressure, such as a pressure control apparatus <NUM> is coupled to the wound cavity via a tube <NUM>. A fluid collection canister (not shown) may be coupled between the pressure control apparatus <NUM> and the wound chamber to collect any wound exudate drawn from the wound site <NUM>. The use of the packing material <NUM> is optional, and it may be omitted in certain arrangements as appropriate.

Alternatively, a self contained wound dressing may be used in place of the drape, such a wound dressing absorbs wound exudate within the layers of the dressing removing the need for a separate fluid collection canister.

Further details regarding wound dressings that may be used in combination with the embodiments described herein are found in <CIT>.

It is envisaged that the negative pressure range for the apparatus in certain embodiments of the present invention may be between about -<NUM> mmHg and - <NUM> mmHg (note that these pressures are relative to normal ambient atmospheric pressure thus, -<NUM> mmHg would be about <NUM> mmHg in practical terms). Aptly, the pressure range may be between about -<NUM> mmHg and -<NUM> mmHg. Alternatively a pressure range of upto -<NUM> mmHg, upto -<NUM> mmHg or over -<NUM> mmHg can be used. Also aptly a pressure range of below -<NUM> mmHg could be used. Alternatively a pressure range of over -<NUM> mmHg could be used or over - <NUM> mmHg.

<FIG> illustrates a schematic representation of a pressure control apparatus <NUM> that can be used to apply negative pressure to a wound site <NUM>. The pressure control apparatus includes an inlet <NUM> coupled to a pressure sensor <NUM>, and also to an inlet of a pump <NUM> via a one-way check valve <NUM>. The pump is operated by an electric motor <NUM>, which draws power from a battery <NUM>. A controller <NUM> is coupled to the pressure sensor <NUM> and provides control signals for controlling the operation of the electric motor <NUM>. Indicators <NUM> are coupled to the controller <NUM> to allow audio and/or visual feedback of status signals to a user. An outlet of the pump <NUM> is coupled to an outlet <NUM> of the pressure control apparatus. A user can utilise a power button <NUM> to initiate or terminate operation.

The pump <NUM> shown is a diaphragm pump which may be highly efficient and capable of providing the required negative pressure. It will be appreciated that other types of pump such as peristaltic pumps, or the like can be used. In some arrangements, the one-way check valve <NUM> may form part of the pump <NUM>, and may not exist as a separate element of the apparatus.

While the apparatus of the invention has been described as being battery powered, it will be understood that an apparatus, not part of the invention, could alternatively draw electrical power from a mains power supply and the battery power cell removed. In some arrangements, the apparatus may be capable of being powered from either a mains power supply or a rechargeable battery that may be recharged from the mains power supply.

In operation, the inlet <NUM> is coupled to a wound chamber formed over a wound site <NUM> , for example via the length of tube <NUM>. The electric motor <NUM> drives the pump <NUM> under the control of the controller <NUM> to provide a negative pressure at the inlet <NUM>. The negative pressure can then be communicated to the wound chamber in order to provide a desired negative pressure at the wound site. The check valve <NUM> maintains the level of negative pressure at the inlet <NUM> when the pump <NUM> is not active and helps avoid leaks.

Upon initially connecting the pressure control apparatus <NUM> to the wound chamber, the pressure at the wound site will be equal to atmospheric pressure, and an initial pump-down must be performed to establish the desired negative pressure at the wound site. This may require the pump <NUM> to be operated for an extended period of time until the desired negative pressure is achieved.

The pressure at the inlet <NUM> is indicative of the pressure experienced at the wound site, and this pressure is measured by the pressure sensor <NUM>. The controller <NUM> receives the pressure value measured at the pressure sensor <NUM>, and once the measured pressure reaches the desired negative pressure, the controller deactivates the pump <NUM>. The controller <NUM> then continues to monitor the pressure at the pressure sensor.

If during the initial pump-down phase, the controller <NUM> determines that the desired negative pressure has not been achieved within a certain time (for example <NUM> minutes or <NUM> minutes or <NUM> minutes or <NUM> minutes or the like), then leaks may be present into the wound chamber, and this condition is signalled via the indicators <NUM> to show that the wound chamber has not been correctly sealed, or some other error or fault is present.

Once the desired negative pressure has been established, the controller <NUM> monitors the pressure at the inlet of the pressure control apparatus. From time to time, leaks of fluid may occur into the wound chamber, reducing the level of negative pressure experienced at the wound site, or in other words increasing the absolute pressure at the wound site. The pressure value measured at the pressure sensor <NUM> and provided to the controller <NUM> will therefore increase as fluid leaks into the wound chamber. When the measured negative pressure value drops below a certain defined pressure level, the controller <NUM> will reactivate the pump <NUM> in order to re-establish the desired negative pressure at the wound site. The desired negative pressure and the defined pressure level at which the controller reactivates the pump provide hysteresis limits between which the pressure should be maintained to apply topical negative pressure to the wound site.

However, if a leak forms that allows fluid, for example air, to leak into the wound chamber with a flow rate greater than the maximum pump capacity <NUM>, it will not be possible for the pressure control apparatus <NUM> to maintain the desired negative pressure at the wound site. If the pressure control apparatus <NUM> continued to attempt to re-establish the desired negative pressure in the presence of such a leak, the battery power cell <NUM> would become depleted. Furthermore, continued operation of the pump in the presence of a large leak can draw contaminants into the wound site, and lead to excessive drying of the wound site which is undesirable. Therefore, the controller <NUM> is configured to deactivate the pump <NUM> if the desired negative pressure is not re-established after operation of the pump <NUM> for a predetermined period of time. For example sometime between around <NUM> minutes and <NUM> hours.

The formation of leaks into the wound chamber may occur due to a range of factors. One common cause of such leaks is movement of a patient being treated with the pressure control apparatus <NUM>. For example, a leak may form when a patient moves from a lying to a sitting position, or during the normal range of movement when walking. Such leaks may be transient, and have been found to regularly reseal as the patient continues to move or returns to their previous position. Thus, there is a risk that the pump <NUM> may be deactivated due to the detection of a leak that subsequently reseals. However, once the leak reseals, operation of the pressure control apparatus would be able to re-establish the desired negative pressure within the wound chamber.

According to embodiments of the invention, the controller <NUM> is configured to deactivate the pump <NUM> after the pump has operated for a certain period of time without the desired level of negative pressure being reached in the wound chamber. That is a timeout event occurs. The controller then waits for a further period of time before a retry attempt is made to re-establish the desired negative pressure at the wound site using the pump <NUM>. If the leak has resealed while the pump has been temporarily deactivated, the retry attempt to re-establish the desired negative pressure will be successful, and operation of the pressure control apparatus <NUM> can continue as normal. However, if the leak is still present a further timeout event will occur and the pump will be deactivated for the further period of time.

This cycle of deactivating the pump <NUM> and then attempting to re-establish the desired negative pressure may be repeated a number of times in order to provide an opportunity for any leaks to reseal. However, once a timeout event occurs the negative pressure at the wound site will start to degrade, and therefore there will be a break in the negative pressure wound therapy applied to the wound site. While a short break in therapy may not be a concern, an extended period in which the negative pressure is not applied should preferably be avoided. Furthermore, if a leak path into the wound chamber exists for an extended period of time, the potential for contaminants reaching the wound site increases. Thus, if a number, N, of unsuccessful attempts are made to re-establish the desired negative pressure it can be assumed that the leak is permanent, and not transient, and the controller <NUM> disables operation of the pressure control apparatus <NUM> and provides a signal via an audio and/or visual cue to a user that attention is required. This allows a patient or caregiver to arrange for any dressings or drapes to be changed to thereby reform the wound chamber and allow the negative pressure wound therapy to be continued. Aptly N is an integer between <NUM> and <NUM> inclusive.

Alternatively, the pump <NUM> and motor <NUM> may be omitted, and the negative pressure may be provided via an external source of negative pressure, such as by connection to a vacuum line or vacuum reservoir. <FIG> provides a schematic representation of a further pressure control apparatus <NUM> for use with an external source of negative pressure, and which can be used to provide negative pressure to a wound site <NUM>. Pressure control apparatus <NUM> includes a controllable valve <NUM> coupled between an inlet <NUM> and an outlet <NUM>. The outlet <NUM> is coupled to the external source of negative pressure. Controller <NUM> provides control signals to the valve <NUM> to control the coupling of the external source of negative pressure to the inlet <NUM>, and thereby to the wound chamber. The pressure at the inlet <NUM> is monitored by a pressure sensor <NUM>, coupled to the inlet, and this monitored pressure is supplied to the controller <NUM>.

The operation of the pressure control apparatus <NUM> of <FIG> is similar to that of the pressure control apparatus <NUM>, except that pressure is controlled by operating the valve <NUM> to couple the wound chamber to the external source of negative pressure. Controller <NUM> is able to control the level of negative pressure at the inlet <NUM> by controlling the valve <NUM>. By monitoring the pressure at the inlet via the pressure sensor <NUM>, the controller <NUM> can control the valve to provide the desired negative pressure at the wound site.

Unlike the pressure control apparatus of <FIG>, an extended attempt to provide the desired negative pressure in the presence of a leak will not lead to depletion of a battery power cell. However, longterm it is still undesirable to continue to apply a negative pressure in the presence of a leak due to the possibility of drawing contaminants into the wound chamber, and of drying out the wound site due to the flow of air through the chamber. Thus, the controller <NUM> of <FIG> implements the same control flow as described above with respect to the pressure control apparatus <NUM>. That is, controller <NUM> is configured to de-couple the inlet <NUM> from the external source of negative pressure by closing the valve if the desired negative pressure is not established at the wound site within a predetermined period of time. A number of attempts may then be made to re-establish the desired negative pressure in order to provide the opportunity for transient leaks into the wound chamber to reseal.

Thus, the pressure control apparatus of <FIG> and <FIG> are able to control the application of negative pressure to a wound site, and advantageously reduce the number of alarms due to transient leaks of fluid into the wound chamber. When a leak forms that allows air into the wound chamber at a flow rate above a certain level, the pressure control apparatus is configured to disable the provision of negative pressure to the wound chamber for a predetermined period of time, providing an opportunity for the leak to reseal. Then, if the leak is transient and reseals, the desired negative pressure may then be re-established at a subsequent attempt. This avoids the need to indicate an alarm condition for transient leaks, and also avoids the problem of drawing contaminants and excessive amounts of air into the wound chamber. This also avoids a pump motor being repeatedly energised and de-energised which avoids concerning noise level changes and helps improve pump motor longevity.

Controller <NUM>, <NUM> may be implemented as a microcontroller, or an application specific integrated circuit, or the like, and may execute instructions to provide the above described control functions. For example, a suitable microcontroller would be one from the STM8L MCU family from ST Microelectronics, for example ST Microelectronics STM8L151G4U6, or one from the MC9S08QE4/<NUM> series from Freescale, such as the Freescale MC9S08QE4CWJ.

The operation of the controller <NUM> may be described as a finite state machine. The operation of the controller is described below with reference to <FIG> which shows a state diagram <NUM> describing the operation of the controller <NUM> for the pressure control apparatus shown in <FIG>.

<FIG> illustrates one embodiment of controller <NUM>. The controller comprises a memory <NUM>, which may hold program code for implementing the control functions. The memory is coupled to a microcontroller <NUM> able to execute the instructions. The microcontroller is coupled to inputs <NUM> and outputs <NUM> through which the microcontroller is able to monitor the operation of the system and provide control signals to other parts of the pressure control apparatus.

Referring again to <FIG> upon activation <NUM> of the pressure control apparatus <NUM> which may occur when an activation strip is pulled for the first time or a user button is pressed or the like, the controller <NUM> performs a power-on self test (POST) <NUM> to ensure that the pressure control apparatus is operating correctly. If the power-on self test is failed the pressure control apparatus should not be used. Therefore, after a failed POST, the controller transitions to a non-recoverable error state <NUM> and the error is signalled to the user via indicators <NUM>. If the POST is passed, the controller <NUM> transitions to an operational state <NUM> via a standby state, and performs an initial pump down <NUM> when a user indicates via a button, in which the pump <NUM> is operated until a desired negative pressure is established in the wound chamber. Alternatively, the controller may wait on a user input before performing the initial pump-down in state <NUM>.

Once the desired negative pressure has been successfully established, the controller transitions to the monitor pressure state <NUM>. However, if after a predetermined period of time the desired pressure has not been established and the initial pump down state <NUM> is unable to establish the desired negative pressure (indicative of a leak), a timeout occurs. On the first timeout, the controller will transition to a wait state <NUM>, in which the controller waits for a period of time before transitioning back to the initial pump down state <NUM>. Further timeouts may occur from the initial pump-down state <NUM>, and the controller maintains a count of the number of retry attempts made. Once the desired negative pressure has been established, the number of retry attempts may be reset.

If a timeout occurs and the number of retry cycles is greater than a predefined maximum number of retry attempts allowed, the controller transitions to a paused state <NUM>. While in the paused state <NUM> the controller will transition from the paused state <NUM> to the initial pump down state <NUM> in response to a user input, or after a maximum pause time.

In the monitor pressure state <NUM>, the controller monitors the pressure measured at the pressure sensor <NUM> and, if the pressure drops out of the desired pressure range, the controller transitions to a maintenance pump-down state <NUM>. In the maintenance pump-down state <NUM>, the suction pump is activated either for a predetermined period of time, for example between around <NUM> and <NUM> seconds, or until the desired negative pressure is re-established in the wound chamber, whichever occurs sooner.

It is noted that some hysteresis is built into the desired pressure range, such that the pressure value, a minimum desired negative pressure, that triggers a transition from the monitor pressure state <NUM> to the maintenance pump-down state <NUM> is lower than the desired negative pressure established in the wound chamber by operation of the pump during the maintenance pump-down state <NUM>. For example, taking the operating pressure ranges discussed above, the desired negative pressure may be -<NUM> mmHg and the minimum desired negative pressure may be -<NUM> mmHg. Alternatively, the controller may act to maintain the pressure within a certain percentage range of the desired negative pressure, for example a <NUM>% hysteresis may be used.

If the desired negative pressure is reached before the suction pump has been operating for the predetermined period of time, the controller transitions back to the monitor pressure state <NUM>.

However, if the pump operates for the predetermined period of time without the desired negative pressure being re-established in the wound chamber, normally due to a leak into the wound chamber, the pressure control apparatus will signal the presence of a leak. If the pressure is within the hysteresis limits, i.e. between the minimum desired negative pressure and the desired negative pressure, this signifies the presence of a high leak, having a flow rate similar to the capacity of the pump. In this situation, the pump continues to operate until the desired negative pressure is re-established, or until the pressure at the wound site is no longer held within the hysteresis limits.

If in the presence of a large leak, the desired negative pressure is restored before a maximum maintenance time is reached, the controller will transition back to the monitor pressure state <NUM>, but will signal the presence of a leak. However, if the suction pump is operated for more than the maximum maintenance time to restore the desired negative pressure, the controller will transition to the paused state <NUM>, while signalling the presence of a leak.

If during the maintenance pump-down state <NUM>, the pressure in the wound chamber is not maintained within the hysteresis limits, a catastrophic leak has occurred, and the controller transitions to the wait state <NUM>.

In some embodiments, if after a predetermined period of time, the desired pressure has not been established and the maintenance pump down state <NUM> is unable to establish the desired negative pressure before the maximum maintenance time is reached, a timeout occurs. On the first timeout, the controller will transition to the wait state <NUM>, in which the controller waits for a period of time before transitioning back to the initial pump down state <NUM>. Further timeouts may occur from the maintenance pump-down state <NUM>, and the controller maintains a count of the number of retry attempts made. Once the desired negative pressure has been established in the maintenance pump down state <NUM>, the number of retry attempts may be reset. If a timeout occurs and the number of retry attempts is greater than a predefined maximum number of retry attempts allowed, the controller transitions to the paused state <NUM>, as described above.

Thus, if the leak is such that it is over a prescribed limit and the pump duty cycle (DC) as defined, in some embodiments, as pump on time divided by pump off time is over a predetermined limit then the pump shall continue to operate within the hysteresis limits for a particular time duration. For example, around <NUM> minutes as shown in <FIG>. Thus, in the monitor pressure loop if the duty cycle is less than a predetermined limit then all is okay. If the duty cycle is greater than a particular limit but less than a time out time the pump continues to run for up to <NUM> minutes. If DC is greater than time out then a paused state <NUM> is entered.

At any time while in the operational state <NUM>, the controller may be placed in the pause state <NUM> in response to a user input. Once the battery voltage reaches a low voltage cut off level or the lifetime of the pressure control apparatus has been reached, the controller de-activates the pressure control apparatus and an End of Life state is reached.

The controller <NUM> described with respect of the pressure control apparatus <NUM> of <FIG> operates in a similar manner as described above except that the initial pump-down and maintenance pump-down states are replaced with valve activation states in which the inlet <NUM> is coupled to the external source of negative pressure connected to the outlet <NUM> via controllable valve element <NUM>. Alternatively, the POST state <NUM> may be omitted.

The pressure control apparatus may be configured to be re-useable and be provided with a switch to allow the apparatus to be turned on and off as required. Such a re-usable apparatus may include rechargeable power cells, and may provide a low power indication in order to allow the power cells to be replaced/recharged.

In a disposable single use pressure control apparatus, activation may be provided by pulling an activation strip and it may not be possible to deactivate the apparatus once activated until the apparatus is to be discarded.

Claim 1:
A battery powered pressure control apparatus for applying topical negative pressure at a wound site, the apparatus comprising:
a pump (<NUM>) having an electric motor (<NUM>) configured to draw power from a battery;
an inlet (<NUM>) for operatively coupling to a wound chamber formed over the wound site;
a pressure sensor (<NUM>) coupled to the inlet (<NUM>); and
a controller (<NUM>);
wherein the controller (<NUM>) is coupled to the pressure sensor (<NUM>) and is configured to provide control signals for controlling the operation of the electric motor (<NUM>) to thereby provide negative pressure at the inlet (<NUM>); and
one or more indicators (<NUM>) coupled to the controller and configured to allow audio and/or visual feedback of status signals to a user;
characterized in that the controller (<NUM>) is further configured to disable the operation of the apparatus and provide a signal via an audio and/or visual cue to a user that attention to a non-transient leak is required if an unsuccessful attempt is made to establish a desired negative pressure at the wound site.