Distensibility of portacaval shunts in portal hypertensive cats: index of contractility model.

Complete shunting of portal blood flow through portacaval shunts was obtained using a constrictor around the portal vein to gradually produce a total occlusion. After 4 weeks, acute experiments were conducted in anesthetized cats. Blood from the femoral artery was shunted through a pump to supply and control the entire portal blood flow. As shunted portal blood flow was varied over a wide range, the portal shunt resistance showed distensibility. Decreasing portal venous pressure from 15.0 +/- 0.9 to 11.1 +/- 0.6 mmHg (1 mmHg = 133.3 Pa) resulted in elevations of resistance of 58%. The relation between the resistance (R) and the distending pressure (Pd) was a constant, the index of contractility (IC), where IC = R.Pd3. In steady state, the IC was 485 +/- 55 mmHg4.mL-1.min.kg and did not change passively in response to changes in portal blood flow. In conclusion, portacaval shunts are passively distensible, and resistance is altered as a cubic function of the distending pressure. Because resistance is altered both actively and passively, the IC should prove useful to differentiate these alternatives for evaluation of changes in portal hypertensive therapy.