JT Lightfoot, JJ McDermott, J Weir, A Faulkner. Repeated exposures to central hypovolemia do not change plasma volume regulation . American Physiology Society - Experimental Biology 95 (Atlanta, GA).
We measured various plasma volume regulating hormones to determine if plasma volume alterations were responsible for the increase in tolerance to repeated central hypovolemic exposures. Twenty two subjects were randomly assigned to two groups: an Experimental group (EXP; n=12) that received a presyncopal limited central hypovolemic challenge (LBNP) every day for 10 days and a Control group (CON; n=10) that received LBNP once and then 10 days later. Immediately before and after LBNP on days 1 & 10, we measured plasma volume (Evans Blue dye) and the plasma concentrations of ADH, ANF, renin, and aldosterone using RIA. LBNP tolerance increased in the EXP group 12.5% (D1 = 239±15 vs. D10 = 269±11 mm Hg*min LTI) with no change in the CON group. There was no change in plasma volume, hematocrit, hemoglobin, or blood volume after 10 days of LBNP. Furthermore, there was no change in either resting or LBNP ADH, ANF, renin, or aldosterone responses. We conclude that repeated central hypovolemia does not alter plasma volume or its regulating mechanisms.
Funded by American Heart Association, Florida Affliate 90GIA/649.