AJP - Heart and Circulatory Physiology, Vol 247, Issue 3 361-H370, Copyright © 1984 by American Physiological Society
Segmental and total microvascular resistances during hemorrhagic hypotension in rabbit omentum
J. C. Firrell, H. H. Lipowsky, S. Usami and S. Chien
Single input-output microvascular modules in the rabbit omentum were
studied to quantitate total modular resistance (RT) and the changes in
resistance of successive serial segments (Rseg) during hemorrhagic
hypotension (55 mmHg for 1 h). RT was calculated from the pressure drop
between input and output vessels and the total flow through the module.
Changes in Rseg were estimated from alterations in single microvessel
hindrance (1/diam4) for selected microvessels within a module together with
a correction for flow redistribution within each segment derived from
changes in the proportion of total flow. Mean RT increased to 2.1 times
control within the first 10 min of systemic hypotension and gradually
declined over 1 h. Response of Rseg varied in different generations of
microvessels (arterioles and venules subdivided by size). Rseg for
arterioles and venules less than 30 microns, but not that for arterioles
and venules greater than 30 microns, showed comparable or greater changes
than RT. Calculated differences between RT and the summed Rseg of measured
segments suggest that the unmeasured Rseg in capillaries and blood
rheological parameters may have significantly influenced changes in RT
during hemorrhagic hypotension.
