A control unit for maximal-rate continuous tissue expansion (CTE)

Subcutaneous or submuscular tissue expansion has become a major tool for the reconstructive plastic surgeon in the repair of difficult wounds and in breast reconstruction. This technique can provide additional or replacement tissue with good match in color, sensation, texture and adnexal characteristics. A major limitation of the technique is the time required for periodic tissue expansion to the required volume in the clinical setting, typically taking from a few weeks to several months. Conceptually, the maximum rate possible for safe clinical tissue expansion would result from continuous maintenance of tissue expander pressure just below capillary filling pressure (continuous tissue expansion, CTE). A control device with this capability would have important clinical and research applications. A self-contained portable control unit (patent pending) for CTE has been designed, fabricated, and testing initiated in a dog model. The 4-lb unit includes a 250-cc fluid reservoir, power pack, pressure transducer (Microswitch 160 PC), pump (Spalding 701A), feedback circuits and memory (2-lb power pack, 2-lb controller and reservoir). Preselected constant pressure (15-50 mmHg +/- 0.1 mmHg) can be maintained in a tissue expander with a maximal flow rate of 16 cc/hr for approximately 18 hours before change of the NiCad battery pack. A digital memory records pressure and volume infused and transfers this data to a Macintosh computer after completion of expansion. Verification of this prototype control unit is presently underway. Initial data suggests that the time required for complete filling of a subcutaneous tissue expander in a dog model can be reduced to approximately 72 hours. Several potential clinical applications and variations of this device are discussed.