Interstitial fluid pressure of ileum measured from chronically implanted polyethylene capsules.

Steady-state fluid pressure measurements were obtained from polyethylene capsules chronically implanted in the walls of cat ileum. Measurements were performed while ileal venous outflow pressure was maintained at 0, 10, 20, or 30 mmHg. The resulting mean steady-state capsule pressure ranged from -0.56 to 7.3 mmHg over the range of imposed venous outflow pressures. The data provide evidence that at an ileal venous outflow pressure in the range of 10 mmHg, comparable to a normal portal pressure, interstitial fluid pressure is positive, increasing as tissue hydration increases, and is a significant contributing force opposing increases in the transcapillary filtration force. Additionally, the qualitative response of implanted capsules to close intra-arterial infusion of normal saline (transcapillary filtration), Dextran 40 (transcapillary absorption), and histamine (transcapillary filtration-permeability changes), and during and after an arterial occlusion of 60-s duration (transcapillary absorption-filtration) were obtained. The results demonstrate that the implanted capsules appropriately track changes in interstitial fluid pressure when the state of tissue hydration is altered by an induced net transcapillary fluid filtration or absorption. Finally, total protein concentration of capsule fluid was not significantly different from lymph fluid derived from a lymphatic vessel draining the ileal segment.