Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration.

Calculation of pcrccntage changes in volumes of blood, plasma, and red cells in dehydration. (Hct) and hemoglobin (Hb) were Inade in six men before and after running long enough to cause a 4y0 decrease in body weight. Subscripts B and A were used to denote before dehydration and after dehydration , respectively. Relations were derived between BVn, and HctA with which one can calculate the percentage decreases in BV, CV, and PV, as well as the concentration of hemoglobin in red cells, g. 100 ml-l (MCHC). When subjects reach the same level of dehydration the water loss from the various body compartments may vary reflecting difference in salt losses in sweat. Changes in PV calculated from the increase in plasma protein concentration averaged-7.5(z compared with-12.2 y0 calculated from changes in Hb and Hct. The difference could be accounted for by a loss of 6v10 plasma protein from the circulation. hematocrit; hemoglobin; exercise; sweat; body temperature WHEN MAN is acutely dehydrated plasma volulne (PV) decreases: Adolph has postulated that only protein-free filtrate leaves the bloodstream and that the increase in concentration of protein in plasma can be used to calculate the percentage decrease in PV (1). However, Dill et al. (3) have shown that this postulate is not valid for all subjects, at least in desert walks of 1 h or more. On the other hand, the protein of red cells, hemoglobin, cannot leave the red cells let alone the blood. This suggests using measurement of concentration of hemoglobin in blood and percentage of red cells in blood before and after dehydration to estimate percentage changes in volumes of plasma and of red cells. METHODS Six trained men ran on a motor-driven treadmill for 2 h at from 60 to 75% Of VOz max. The ambient temperature was 22.2 =i= 0.4OC and the relative humidity 40-45 $& Venous blood was drawn from the antecubital vein of the reclining subject before exercise and 30 min after the run. The hematocrit (Hct) was measured in triplicate with a microhematocrit centrifuge and corrected for 4?& plasma trapped with the packed red cells. Hemoglobin (Hb) was measured by the cyanmethemoglobin method. Standard Hb curves were established with a standard supplied by Hycel, Inc. Percentage changes in blood volume (BV), red cell volume (CV), and plasma volume (PV) were calculated from values for Hb and Hct in each of the six men before and after losing …