Plastic and reconstructive surgery relies greatly on the use of free skin grafts, expansion of contiguous tissue or pediculed flaps of various shapes and sizes. In the repair of skin, the amount of skin available is often not sufficient for grafting and reconstruction. The requirement for additional skin or tissue has led to the development of various types of tissue expander devices. These devices are generally designed to cause gradual expansion of the skin and its subcutaneous tissue by applying progressively increasing pressure over a predetermined time period. An example of naturally occurring tissue expansion is seen in the extension of the skin over the pregnant female abdomen. A similar condition occurs when obese individuals undergo weight loss resulting in the development of folds of excess tissue.
Typically, the expander devices now commercially available and in use employ some form of elastic envelope or balloon which is surgically implanted under the skin and subcutaneous tissue in the area of the desired expansion. Ordinarily, a reservoir and connecting tube are implanted under the subcutaneous layers in communication with the envelope, and the envelope is slowly inflated by injecting a sterile saline solution into the reservoir using a syringe and hypodermic needle. The solution passes from the reservoir into the envelope through the connecting tube so as to inflate the envelope and cause it to exert pressure on the surrounding tissue which in turn expands to accommodate the increase in volume of the envelope. Periodic sterile injections of additional saline are typically performed at intervals of several days apart, this process being repeated until the desired degree of expansion has been achieved. When expansion has been completed, the envelope is surgically removed and the expanded tissue is then available for the desired plastic or reconstructive surgery. Representative tissue expander devices are set forth and described in a number of patents including U.S. Pat. No. 4,217,889 to C. Radovan; U.S. Pat. No. 4,666,447 to G. M. Smith et al; U.S. Pat. No. 4,615,704 to E. E. Frisch; U.S. Pat. No. 4,651,717 to E. R. Jakubczak; U.S. Pat. No. 4,662,357 to D. L. Pierce et al and U.S. Pat. No. 4,685,447 to A. A. Iversen et al.
Notwithstanding the development and availability of numerous types of tissue expander devices, a problem which is especially prevalent in connection with the use of these devices is that of closely controlling expansion of the tissue to avoid undue pain as well as tissue necrosis. For example, the aforementioned patent to Radovan et al describes the problems associated with too rapid expansion of tissue and which may lead to lack of blood flow in the surrounding expanded tissue which if not corrected results in tissue necrosis and loss of tissue viability. Similarly, wound dehissence may occur requiring a further healing period before expansion can be resumed. Presently, in the course of each filling or inflation procedure, the envelope is inflated until the tissue becomes "tight" or "firm" and this degree of tightness is based on the subjective opinion of the clinician; or, the clinician may gauge the degree of inflation by monitoring the pain experienced by the patient. However, this is not a reliable method as patients have widely variable thresholds of pain.
Pressure measuring devices have been utilized in the past for monitoring fluid pressure in the body. For example, U.S. Pat. No. 4,571,749 and U.S. Pat. No. 4,731,083 to R. E. Fischell disclose pressure measuring devices for a urinary sphincter. Similarly, U.S. Pat. No. 3,744,063 to D. M. McWhorter et al is directed to a method and apparatus for pressure monitoring an artificial sphincter. U.S. Pat. No. 3,863,584 to A. S. Borsanyi is concerned more with measuring the fluid pressure of plasma, blood or other fluids in the body while isolating the gauge from direct contact with the fluid. To the best of my knowledge, no one has recognized the ability to monitor tissue expansion by providing a reproducible method of measuring the pressure exerted on the tissue during or after the filling procedure. By closely monitoring the pressure and providing for a precise means of measuring actual pressure, it is possible to achieve an optimum inflation rate or degree of inflation which will overcome and avoid the previously noted problems associated with tissue expander devices. In this connection, it is hiqhly desirable that the pressure monitor be capable of directly sensing the fluid or liquid pressure condition of the tissue expander envelope but at the same time be isolated from the liquid such that the sterility of the fluid path is not compromised. That is to say that the liquid contents of the expander must be protected from any bacteria or particulate matter that may be carried by the liquid to or from the monitor itself. In this way, even though the tissue expander fill kit and tissue expander are disposable, the pressure gauge or monitor may be reusable.