Technique for continuous measurement of compliance in isolated vascular segments

A method has been developed that provides an on-line (1/s) measurement of elastance [E = 1/compliance (C)] in a perfused isolated vessel segment in situ. Values of E can be obtained as a function of perfusion pressure (P) or in response to drug interventions. Noncompliant stainless steel tubes are used as inflow and outflow cannulas. Segment P is obtained from a short small-bore stainless steel catheter and miniature pressure transducer. During constant flow through the inflow cannula, an adjustable outflow resistance is used to set the segment P. Simultaneous activation of solenoid pinch valves, for 200 ms, compresses in-line Silastic tubing next to each cannula and serves to simultaneously 1) isolate the segment and 2) inject a small volume into the segment (delta V). This delta V results in a step increase in segment P (delta P). delta V is not significantly altered by changing the volume of air in the in-line windkessel reservoir (when air volume is greater than or equal to 100 ml), mean perfusion pressure (over a range of 50-150 mmHg) or compliance of the test cell. Therefore, delta P alpha E, and 1/delta P alpha C. Since this recorded variable is linearly related to C, actual C can be continuously recorded on a recorder after a simple two-point calibration process. C as determined by this method was found to be linearly related (r = 0.997) to calculated C of a test cell air bubble (range: 0.1 less than C less than 0.7 microliter/mmHg; resolution: 0.001 microliter/mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)