Total arterial compliance: differences between spontaneously hypertensive rats and normotensive Wistar-Kyoto rats

Invasive hemodynamic measurements were performed on 14 normotensive Wistar-Kyoto (WKY) rats and 15 spontaneously hypertensive rats (SHRs) to test the hypothesis that SHRs have lower total arterial compliance than WKY rats. Ascending aortic pressure was measured with a catheter-tip manometer, and aortic flow was measured with an electromagnetic flow probe. Prolonged diastoles were produced by an electrocardiographically timed aortic occluder. The aortic decay time constant (Tau) for each prolonged diastole was calculated by an exponential fit of the initial linear segment of the log (pressure)-time curve. Tau is the product of resistance (R) and compliance (C) in the Windkessel model for the arterial system. Total arterial compliance was therefore determined from the relation Tau/R. The total arterial compliance index was calculated by correcting for body weight. Compliance was also estimated by the stroke volume/pulse pressure ratio. Compared with WKY rats, SHRs have higher mean pressure (111 +/- 19 [SD] mm Hg vs 71 +/- 14, P less than .0001), higher mean flow (0.50 +/- 0.10 mL/sec vs 0.38 +/- 0.04, P less than .001), and a shorter decay time constant (365 +/- 54 msec vs 475 +/- 54, P less than .001).(ABSTRACT TRUNCATED AT 250 WORDS)