PRESSURE-FLOW RELATIONSHIPS IN IN-VITRO MODEL OF COMPARTMENT SYNDROME

Compartment syndrome is a condition in which an increase in intramuscu lar pressure decreases blood flow to skeletal muscle. According to the Starling resistor (i.e., vascular waterfall) model of blood flow, the decrease in flow could occur through an increase in arterial resistan ce (Rart) or an increase in the critical closing pressure (Pcrit). To determine which explains the decrease in flow, we pump perfused a cani ne gastrocnemius muscle placed within an airtight box, controlled box pressures (Pbox) so that flow ranged from 100 to 50%, and measured Pcr it, Rart, arterial compliance, small venular pressure (measured by the double-occlusion technique), and venous pressure. An increase in Pbox limited flow mainly through an increase in Pcrit (75-85%), with only small changes in Rart (15-25%) and no change in arterial compliance. I ncreases in Pbox also produced a vascular waterfall in the venous circ ulation, but small venular transmural pressure always remained less th an control levels. We conclude that increases in Pbox mostly limit blo od flow through increases in Pcrit and that Rart plays a minor role. T ransmural pressure across the small venules decreases with increases i n intramuscular pressure, which contradicts the currently held belief that compartment syndrome is due to a cycle of swelling-ischemia swell ing.