AJP - Gastrointestinal and Liver Physiology, Vol 260, Issue 2 325-G332, Copyright © 1991 by American Physiological Society
Index of contractility: quantitative analysis of hepatic venous distensibility
W. W. Lautt, C. V. Greenway and D. J. Legare
Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
The low-pressure resistance vessels of the splanchnic circulation are
passively distensible, and changes in regional blood pressures can lead to
large changes in vascular resistance. The relationship between distending
blood pressure (Pd) and vascular resistance (R) is described as a constant,
the index of contractility (IC) where IC = R x Pd3. IC was derived in an
isolated blood-perfused liver and was confirmed in vivo for both pre- and
postsinusoidal resistance sites. IC does not change passively in response
to wide changes in blood flow or hepatic outflow pressure. IC is
dramatically altered in response to active vasoconstriction. In vivo, the
presinusoidal IC rose from a control level of 12.2 +/- 4.2 to 92.7 +/- 20.6
IC units (mmHg4.ml-1.min.kg body wt) in response to 1.25
micrograms.kg-1.min-1 norepinephrine intraportal; the postsinusoidal IC
rose from 20.4 +/- 2.3 to 59.6 +/- 14.2 IC units. IC reflects resistance
changes secondary to active contractile responses independent of the
passive consequences of the distensible nature of the resistance sites. We
suggest that these concepts can be applied to any vascular bed with
distensible resistance vessels.
