Polycythemia and hydration: effects on thermoregulation and blood volume during exercise-heat stress.
We studied the effects of autologous erythrocyte infusion on thermoregulation and blood volume during exercise in the heat. Specifically, we wanted to determine whether heat-acclimated subjects, as well as hypohydrated subjects, would have a thermoregulatory advantage from acute polycythemia during exercise in the heat. Five heat-acclimated males attempted four heat stress tests (HSTs): two pre- and two postinfusion. Autologous erythrocyte infusion was accomplished with 500 ml of a NaCl-glucose-phosphate solution containing approximately 60% hematocrit. One HST, both pre- and postinfusion, was done while subjects were euhydrated, and one HST was done while subjects were hypohydrated (-5% of body wt). After 30 min of rest in a 20 degrees C antechamber, the HST consisted of a 120-min exposure (2 repeats of 15 min rest and 45 min walking) in a hot (35 degrees C, 45% relative humidity) environment. The findings concerning acute polycythemia in heat-acclimated subjects are summarized: 1) polycythemia increased (P less than 0.05) sweating rate and reduced (P less than 0.01) core temperature during exercise-heat stress for both euhydrated and hypohydrated subjects; 2) the erythrocyte infusion caused an increased (P less than 0.05) plasma volume and increased (P less than 0.01) blood volume; 3) the increased plasma volume was associated with an increased (P less than 0.05) total circulating protein mass; 4) the increased total circulating protein mass tended to better maintain plasma volume when hypohydrated; and 5) heat acclimation may increase extravascular protein mass. Therefore, it is concluded that erythrocyte infusion provides a thermoregulatory advantage during exercise in the heat for heat acclimated subjects when both euhydrated and hypohydrated.
US Army Research Institute of Environmental Medicine, Natick 01760-5007.
M N
MN
Sawka
R R
RR
Gonzalez
A J
AJ
Young
S R
SR
Muza
K B
KB
Pandolf
W A
WA
Latzka
R C
RC
Dennis
C R
CR
Valeri
D000064:Acclimatization; D001798:Blood Proteins / Q000032:analysis; D001803:Blood Transfusion; D001810:Blood Volume; D001831:Body Temperature; D001833:Body Temperature Regulation; D017707:Erythrocyte Transfusion; D006358:Hot Temperature; D006801:Humans; D008297:Male; D005082:Physical Exertion; D011086:Polycythemia / Q000503:physiopathology*; D012016:Reference Values; D013312:Stress, Physiological / Q000503:physiopathology*; D013546:Sweating
D001798:Blood Proteins