Journal of Applied Physiology, Vol 64, Issue 4 1580-1583, Copyright © 1988 by American Physiological Society
Evaluation of Starling forces in the equine digit
D. Allen Jr, R. J. Korthuis and S. Clark
University of Georgia, College of Veterinary Medicine, Department of Large Animal Medicine, Athens 30602.
A pump-perfused extracorporeal digital preparation was used to evaluate
blood flow, arterial pressure, venous pressure, isogravimetric capillary
filtration coefficient, capillary pressure, and vascular compliance in six
normal horses. From these data, pre- and postcapillary resistances and pre-
and postcapillary resistance ratios were determined. Vascular and tissue
oncotic pressures were estimated from plasma and lymph protein
concentrations, respectively. By use of the collected and calculated data,
tissue pressure in the digit was calculated using the Starling equation. In
the isolated equine digit, isogravimetric capillary pressure averaged 36.7
mmHg, plasma and lymph oncotic pressures averaged aged 19.12 and 6.6 mmHg,
respectively, interstitial fluid pressure averaged 25.6 mmHg, and the
capillary filtration coefficient averaged 0.0013 ml.min-1.mm-1.100 g-1. Our
results indicate that digital capillary pressure in the laterally recumbent
horse is much higher than in analogous tissues in other species such as dog
and human. However, the potential edemagenic effects of this high digital
capillary pressure are opposed by at least two mechanisms: 1) a high tissue
pressure and 2) a low microvascular surface area for fluid exchange and/or
a low microvascular permeability to filtered fluid.
