Abstract:
A tissue expansion system includes driver assembly having a syringe pump and a controller held in a common enclosure. The driver assembly is connected to both an inflatable bladder and an inflation medium source. Fluid is delivered from the driver assembly to the inflatable bladder through a pressure sensor. The pump is actuated to deliver predetermined incremental volumes of the inflation medium to the inflatable bladder at spaced apart time intervals. Pressure is monitored and the pumping is interrupted if the pressure exceeds a predetermined high threshold value. Pumping is recommenced when the pressure falls below a lower threshold value until the total incremental delivery volume has been reached.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to medical methods and devices. More particularly, the present invention relates to methods and systems for expanding tissue by delivering incremental volumes of an inflation medium to an implanted expandable bladder while monitoring inflation pressure. 
     Tissue defects in the skin and other tissues occur from a variety of causes including surgery, burns, traumatic injury, and congenital deformities. Such defects are often characterized by tissue “deficits” where there is insufficient or poor quality skin or tissue present to cover or fill the affected body region in a normal or desired profile or pattern. 
     Tissue deficit may be treated by stimulating skin expansion and/or tissue growth in the region of the defect. For example, “tissue expanders” may be implanted beneath a region of skin or within a volume of tissue which suffer from the deficit. By gradually inflating or otherwise expanding such tissue expander, the growth of skin and/or tissue can be promoted. 
     Presently, most tissue expanders are in the form of an implantable balloon with a valve that allows a physician to periodically inflate the balloon to increase its volume over successive office visits. As the patient will typically visit the doctor only about once per week, such periodic inflations often require relatively large volumes of inflation medium which can cause not only patient discomfort, but also tissue ischemia, concavities to underlying structures such as bone, and induce encapsulation of the implant causing capsular contracture and stiffening of tissue around the expander. 
     In order to address such shortcomings, a number of “continuously” expanding devices have been proposed. For example, in U.S. Patent Publication 2010/0010531, a device is described which allows the patient to periodically trigger a gas source within the implanted expander. Allowing the patient to control expansion, however, has its own drawbacks, and the patient will seldom follow an optimum inflation protocol to achieve the desired tissue expansion. Moreover, the use of a gas as the inflation medium is also disadvantageous. 
     A particular improvement in this field is found in U.S. Patent Publication No. 2013/0079807, commonly assigned with the present application, which describes a tissue expansion system including a pump, a controller, an inflatable bladder, and a pressure sensor. The pump is adapted for substantially continuous operation in response to a pressure within a subcutaneously inflatable bladder during expansion. Delivery is based solely on monitored pressure, which can sometimes result in overly rapid treatment. 
     For these reasons, it would be desirable to provide improved and alternative tissue expansion devices. In particular, it would be desirable to provide such devices which continuously and automatically deliver an inflation medium to an implanted expander over time in a more optimal and controlled pattern. It would be further desirable if such expanders and their supporting systems were adapted for patient convenience and comfort to further promote their use. It would be further desirable if such expanders were operated based on parameters in addition to pressure and the other parameters described above. At least some of these objectives will be met by the inventions described here and below. 
     2. Description of the Background Art 
     U.S. Patent Publication No. 2013/0079807, commonly assigned with the present application, describes a tissue expansion system including a pump, a controller, and inflatable bladder, and a pressure sensor. The pump is adapted for substantially continuous operation in response to a pressure within a subcutaneously the inflatable bladder during expansion. Other relevant patents and publications include U.S. Pat. Nos. 6,668,836; 6,432,081; 5,549,672; 5,496,368; 5,005,591; 5,092,348; 4,955,905; and U.S. Patent Publications 2011/152913; 2010/010531; 2008/051822; and 2004/147953. See also Logan and Hayden (1989) ISA, Paper #89-0207, pp. 27-33. 
     SUMMARY OF THE INVENTION 
     In a first aspect of the present invention, a method for expanding tissue comprises locating an expandable bladder underneath a region of skin, subcutaneous tissue, or muscle to be expanded by introducing saline or another incompressible inflation medium. Preselected, incremental volumes of the incompressible inflation medium are delivered into the inflatable bladder at spaced-apart time intervals where delivery of one incremental volume is completed and delivery of a subsequent preselected incremental volume is commenced after a time delay, typically between 10 minutes and 3 hours, usually from 30 minutes to 2 hours, and typically about once an hour. By making the incremental volumes small, typically from 1 cc to 10 cc, and spacing the incremental inflation as just noted, the tissue expansion occurs at a slow, controlled rate and the tissue is allowed to yield or remodel between active expansion steps. As an additional protection against over stressing the tissue being expanded, pressure of the pumped inflation medium is monitored while each preselected incremental volume of inflation medium is being pumped into the bladder. Pumping is stopped if the monitored pressure exceeds an upper threshold level, typically in the range from 40 mmHg to 50 mmHg. Pumping of the incremental volume will also be terminated when the preselected incremental volume has been delivered to the bladder. If the pumping was stopped because the monitored pressure exceeded the upper threshold level, pumping the incremental volume will be recommenced when the monitored pressure falls back below a lower threshold level, typically in the range from 25 mmHg to 35 mmHg, and pumping of that incremental volume will continue until the preselected incremental volume has been reached or the monitored pressure once again exceeds the upper threshold level. The steps above will be repeated if the monitored pressure once again exceeds the upper threshold level before the preselected incremental volume has been delivered, and delivery of a plurality of subsequent incremental volumes will then begin at the preselected time intervals set forth above until a preselected cumulative volume of the inflation medium has been delivered to the expandable bladder. In the exemplary embodiments, the time required for delivery of each incremental volume of inflation medium will typically be only a small fraction of the time interval between successive incremental deliveries. For example, if the time interval between successive deliveries is on the order of one hour, the time necessary to driver one incremental volume will usually be under one minute. Thus, even if the high pressure threshold is exceeded more that once and pumping is interrupted, there will almost always be sufficient time to complete the delivery of each incremental volume during the time period between delivery of successive incremental volumes. 
     Usually, the successive incremental volumes and the time intervals between successive deliveries will be the same and within the ranges set forth above. Alternatively, either or both of the successive incremental volumes and the time intervals between successive deliveries may vary and be different at different times in the inflation delivery protocol. 
     In specific embodiments of the methods of the present invention, locating the expandible bladder may comprise placing the expandable bladder beneath skin in a subcutaneous, subfascial or submuscular plane, located beneath a region of skin or tissue to be expanded. For example, this may be in a subpectoral pocket following mastectomy. The expandable bladder will usually be initially inflated with a volume of saline, typically in the range from 50 cc to 100 cc. 
     In other embodiments, the expandable bladder may be placed beneath skin, fascia or muscle located adjacent to a defect which, for example may be a burn scar. The expandable bladder will usually be initially inflated with a volume of saline, typically in the range from 20 cc to 100 cc. In these cases, the bladder may be removed after the skin has been expanded to create a flap and the flap is used to cover the defect. 
     In all these cases, the pumping may be performed with a constant speed positive displacement pump so that the predetermined incremental volume is provided by a predetermined incremental run time for the pump, and the preselected cumulative volume of the inflation medium is provided by a preselected cumulative run time of the pump. 
     In a second aspect of the present invention, a system for expanding tissue comprises an expandable bladder adapted to be located beneath a region of skin to be expanded. A syringe pump is configured to draw inflation medium from a source and to deliver said inflation medium to the expandable bladder. A pressure sensor is adapted to monitor pressure of the inflation medium being delivered by the syringe pump, and a delivery line connects the syringe pump to the inflatable bladder. A first one-way valve in the delivery line allows fluid from the syringe pump to flow to the inflatable bladder but blocks reverse flow from the bladder to the syringe. A refill line connects the syringe pump to the source, and a second one-way valve in the refill line allows fluid flow from the source to the syringe and blocks reverse flow from the syringe to the source. A controller operates the syringe pump to deliver inflation medium to the inflatable bladder and to draw inflation medium from the source, where said controller drives the syringe pump periodically over a plurality of incremental time periods to deliver a plurality of incremental volumes of the incompressible inflation medium. The controller receives pressure data from the pressure sensor, and the controller stops the pump when a monitored pressure exceeds an upper threshold level and restarts the pump when the monitored pressure falls below a lower threshold value. The controller usually operates the syringe pump for a predetermined incremental run time to deliver the incremental volume to the inflatable bladder. 
     In specific embodiments of the methods of the present inventions, the controller is programmed to deliver inflation medium until the pressure reaches an upper threshold value in the range from 40 mmHg to 50 mmHg, with pumping of the particular incremental volume being recommenced when the monitored pressure falls below the lower threshold level in the range from 25 mmHg to 35 mmHg. The preselected incremental volume of inflation medium is usually in the range from 1 cc to 10 cc, and the preselected time interval is in often the range from 10 minutes to 3 hours, more usually being in the range from 30 minutes to 2 hours, and typically being one hour. 
     The controller in preferred systems will be programmed or otherwise configured to pump inflation medium into the bladder and to terminate pumping of the incremental volume when said the incremental volume has been delivered to the bladder or when said the monitored pressure exceeds the upper threshold level. If the pumping was stopped because the monitored pressure exceeded the upper threshold level, the controller will recommence pumping of the incremental volume when the monitored pressure falls back below the lower threshold level and will continue pumping until the entire incremental volume has been reached or the monitored pressure once again exceeds the upper threshold level. The controller will repeat the stopping and recommencing if the monitored pressure once again exceeds the upper threshold level before the entire incremental volume has been delivered. After completing the delivery of each successive incremental volume, the controller will initiate delivery of the next successive incremental volume of inflation medium at a preselected time intervals until a preselected cumulative volume of the inflation medium has been delivered to the expandable bladder. 
     INCORPORATION BY REFERENCE 
     All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIG. 1  is a block flow diagram illustrating the system components of an exemplary system constructed in accordance with the principles of the present invention. 
         FIG. 2  is a perspective, partially disassembled view of a driver assembly which forms a portion of the exemplary system of  FIG. 1 . 
         FIGS. 3A and 3B  are front and rear views of the driver assembly of  FIG. 2 . 
         FIGS. 4A and 4B  are detailed views taken along the line  4 A- 4 A and line  4 B- 4 B of  FIG. 3B . 
         FIG. 5  is an exploded view of the exemplary system of the present invention showing the individual system components. 
         FIG. 6  is a logic diagram illustrating an exemplary operation protocol for the systems of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring in particular to  FIG. 1 , an exemplary system  10  constructed in accordance with the principles of the present invention comprises a driver assembly  12  which includes a controller  14 , a syringe  16 , and a motor  18 . Typically, the motor will drive a lead screw  20  as shown in  FIGS. 2 and 3A  in order to advance a carriage  22  which is coupled to a plunger  24  of the syringe. The plunger  24 , in turn, may either be advanced in a distal direction (to the right in  FIG. 2 ) in order to deliver inflation medium from a barrel  26  of the syringe or may be retracted in a proximal direction in order to draw new inflation medium into the barrel, as will be described in more detail below. 
     Referring now to  FIGS. 1, 2, and 5 , a connector  28  at a distal end of the syringe barrel  26  may be removably connected to a Y-fitting  32  which has two ports which are connected to a first one-way valve  34  and a second one-way valve  48 , respectively. The first one-way valve  34 , in turn, is removably connected to a connecting tube  38  which connects, at its distal end, to a pressure sensor  36 . Pressure sensor  36 , in turn, is connected to cable  30  which provides a pressure signal to the controller  14  within the delivery assembly  12 . The pressure sensor  36  is further removably connected to a catheter  40  which in turn delivers inflation medium to the expandable and inflatable bladder  42 . The first one-way valve  34  is oriented so that it allows flow from the syringe  16 , which is caused by advancement of the plunger  24 , to pass through the fitting  32 , through the fitting  34 , to the tube  38 , through the pressure sensor  36 , and finally through the catheter  40  into the inflatable bladder. The one-way valve  34  will prevent any backflow from the bladder  42  or elsewhere back into the syringe  16 , thus reducing the risk of contamination. 
     The second one-way valve  48 , in contrast, is oriented to cause inflation medium from a refill source  52  connected by a connecting tube  50  to flow back into the syringe barrel  26  when the plunger is retracted in order to draw the medium into the syringe. A needle  54  which is connectable to the tubing  15  is configured to be inserted into the source of saline or other inflation medium  52  so that the syringe maybe refilled between successive activations to deliver the inflation medium to the inflatable bladder  42 . The controller  14  will be programmed to allow convenient refilling performed by the user. A cover  56  is provided to maintain sterility of the needle between successive uses. Another cover  57  is provided to cover and maintain sterility of the syringe during use. 
       FIGS. 3A and 3B  illustrate certain control and other features present on the driver assembly  12  of the systems of the present invention. A battery cover  62  can be removed to replace batteries as shown also in FIG.  2 . A touch screen or other display  70  may be provided on the enclosure of the driver as a user interface. The display  70  will include, either virtually or mechanically, a power switch  72 , a status light  74 , a ready light  76 , an incrementing key  78 , a decrementing key  80 , a run/stop key  82 , and a syringe operation indicator  84 . 
     The syringe maybe removed and replaced on the top of the driver assembly  12 . In particular, the syringe is held in place by a securing strap  92 . The plunger  24  is engaged by a slot  90  in the carriage  22 , as best seen in  FIG. 4B . Similarly, the syringe barrel flange  88  is held in another slot  88 , as best seen in  FIG. 4A . The position of the plunger maybe monitored, when the top  57  is in place, with a travel indicator  86  on the display panel  70 . The carriage  22  maybe released from the lead screw  20  by a carriage release button  94 . 
     Referring now to  FIG. 6 , the inflation control system  10  of the present invention may be used by first connecting the catheter  40  to the pressure sensor  36  which in turn has been coupled to the driver  12 , as described above. After making sure that the syringe  10  has a sufficient volume of inflation medium, the drive  12  may be turned on using switch  82  which will initiate the sequence of operations illustrated in  FIG. 6 . Initially, the pressure from sensor  36  is checked. If the pressure exceeds the high pressure threshold level P H , the driver will be stopped and an alert or alarm raised since high pressure should not be present at this point in the protocol. Assuming that the initial pressure check is successful, the controller  14  will initiate power to the motor  18  in order to rotate the lead screw  20  which advances the carriage  22  which in turn drives the plunger  24  at a relatively low rate, typically the volumetric flow ranges set forth about. The pressure sensor  36  will monitor pressure while the syringe is delivering fluid, and the controller  14  will allow continued delivery for so long as the pressure does not exceed the high threshold value P H , again typically within the ranges set forth above. Assuming that no high pressure is detected, the syringe will be driven for a time sufficient to transfer the desired incremental volume V i  to the bladder  42 . Typically the volume will be from about 1 cc to 10 cc and it will take from 5 seconds to 60 seconds to complete the delivery. 
     If, however, the pressure sensor detects a pressure above the high threshold level P H , the controller will stop the pump and continue to monitor the pressure. For so long as the pressure remains above a low pressure threshold P L , which is typically 5 to 10 mmHg lower than the high pressure threshold P H , the pump will remain stopped. As soon as the pressure falls below this lower pressure threshold P L , the pump will be restarted and the inflation medium will continue to be delivered for so long as the pressure remains below the high pressure threshold P H . Pumping will continue until the entire incremental volume V i  has been delivered, at which time the pumping is stopped and not restarted until after the passage of a preselected time interval until the scheduled delivery of the successive incremental volumes V i+1, i+2 , . . . , typically in the time ranges set forth above. Such successive incremental volume deliveries will continue until the total cumulative volume V T  of inflation medium has been delivered to the inflatable bladder. Such total volume may take days or even weeks. In some instances, it may be desirable to divide the delivery of the total volume of inflation medium into stages, for example 2, 3, 4, 5, or even more stages, where the time between successive stages is greater than the normal time between the delivery of the incremental volumes.