Blood volume and plasma protein responses to heat acclimatization in humans

Abstract

The effects of heat acclimatization on intravascular volume and protein responses to acute heat stress and exercise were studied in six male subjects. Absolute values for hematocrit and hemoglobin concentration were lower after, than before, acclimatization, indicating hemodilution. Also, after acclimatization, the magnitude of the hemoconcentration response to exercise in the heat was significantly increased. There ws no change in the concentration of plasma protein during or after acclimatization compared with before acclimatization, but there was a net increase in the total intravascular protein content. It is suggested that the hemodilution associated with heat acclimatization may be explained in terms of an increase in the intravascular oncotic pressure following an exercise-induced augmentation of protein, occurring at the expense of the interstitial compartment. It is concluded that this hemodilution is unlikely to be primarily responsible for the cardiovascular adjustment accompanying heat acclimatization and that it should be regarded as a secondary feature of adaptation to heat.

Induction and decay of short-term heat acclimation

“…However, the blood volume (BV) expansion observed across EUH and DEH acclimation, indicated that resting [TP] p has increased and may well be a mechanism for the PV expansion that was evident. This is supported by previous research on the notion that PV expansion is mediated by elevated plasma protein content (Harrison et al 1981;Mack and Nadel 1996). There was an increased exercise-induced response of [TP] p in the present study that became more pronounced within the DEH compared to the EUH acclimation bouts ( (Figure 3) in the standardised exercising heat stress after the DEH regime.…”

“…It has been established that there are two mechanisms of PV expansion to account for such a change; increased renal electrolyte and water retention (Wyndham 1973;Costill et al 1975;Armstrong et al 1987;Convertino et al 1991) and elevated plasma protein content (Harrison et al 1981;Harrison 1985). Therefore, it has been suggested that both these mechanisms occur during heat acclimation and there interaction may contribute to PV expansion .…”

Effects on heat tolerance of physical training in water and on land

“…Plasma volume has been found to expand following physical training (16, 21) and heat acclimation (14,25). In the present study, resting values of plasma volume were not significantly increased in any of the groups although all three tended to demonstrate somewhat of a plasma volume expansion following training.…”

The Effect of One Session of Muscle Soreness-Inducing Weight Lifting Exercise on WBC Count, Serum Creatine Kinase, and Plasma Volume

“…The present study suggests that PV expansion can be elicited by one session of high resistance weight lifting exercise. Others have theorized that exercise PV expansion is from adaptations to hypovolemia, increased osmolality, and increased temperatures that occur during exercise (12)(13)(14)21). Indeed, weight lifting exercise has been found to reduce plasma volume during (-17.g0/0) (25) and immediately following (-14.3O/0) exercise (11).…”