AJP - Heart and Circulatory Physiology, Vol 232, Issue 4 361-H367, Copyright © 1977 by American Physiological Society
Capillary filtration measurement by strain gauge. II. Effects of mannitol infusion
M. A. Katz
Maintenance of normal partition of extracellular fluid into vascular and
interstitial compartments is a tightly controlled system. One means of
studying control of this system is to induce filtration by fluid loading,
and to measure associated changes capillary filtration coefficients (CFC)
and Starling pressures in a particular vascular bed. We therefore measured
responses of the dog hindlimb to isotonic mannitol infusions. Using
strain-gauge plethysmography to measure CFC, the Johnson zero-flow
technique to measure isogravimetric capillary hydrostatic pressure, and
chronically implanted capsules to measure muscular interstitial hydrostatic
pressure, we infused isotonic mannitol into anesthetized dogs for 30 min at
20 ml/min and 30 ml/min. There was a sustained 75% increase in CFC in
intact hindlimbs, no change in hydrostatic capillary or interstitial
pressure, and a 4-5 mmHg rise in filtration pressure due to dilution of
serum protein. The most likely mechanism for increased CFC is capillary
recruitment, since distension of capillaries requires large increases in
hydrostatic pressure. Interstitial fluid compliance appears high. These
studies indicate capillary intermittency may be an important mechanism in
the disposition of fluid loads.
