Alterations in red cell volume following exercise and dehydration.

in red cell volume following exercise and dehydration. J. Appl. Physiol. 37(6): 912-916. * 1974.-In vitro and in vivo studies were con-ducted to demonstrate the changes in red cell size (MCV) follow-ing alterations in plasma osmolality and to determine the effects of exercise and dehydration on MCV. By altering the osmolality of the diluent used by the model S Coulter counter, it was possible to determine the relationship between MCV and the osmolality of the medium supporting the blood cells. The %AMCV was found to be accurately described by changes in the mean corpuscu-lar hemoglobin concentration (MCHC). Selected hematological measurements made on three subjects before and after submaximal and maximal bicycle exercise showed considerable individual variations in MCV that appeared unrelated to changes in plasma osmolality (r =- 0.12). Dehydration (2 and 4y0 body weight losses), however, induced marked shrinkage of the red cells that was highly related to the increase in plasma osmolality (r =- 0.91). It was concluded that calculations of the percentage change in plasma volume during exercise and dehydration based on the change in venous hematocrit are subject to error unless corrections are made for changes in MCV. plasma volume; hematocrit; hemoglobin; mean corpuscular hemoglobin concentration CALCULATIONS of the change in plasma volume (%APV) during exercise and dehydration are frequently determined from venous hematocrit (Hct,). Such computations make two major assumptions: I> that the volume of circulating red corpuscles is constant, and 2) that the relationship be-tween Hct, and whole-body hematocrit (Hctg) remains unaffected by exercise and dehydration. Previous studies suggest that the first assumption is valid (1, 4, 11, 13). Costill and Saltin (3) have recently reported no change in the ratio of Hctv to HctB following dehydration (- 4 %), but no information is available to describe this relationship during intense exercise. Different results have been reported with regard to the effect of dehydration and exercise on