Title

Cardiovascular and perceptual responses to dehydration, oral and intravenous saline rehydration, and subsequent exercise in the heat

Date of Completion

January 1995

Keywords

Biology, Animal Physiology|Education, Physical|Health Sciences, Recreation

Degree

Ph.D.

Abstract

Athletes strive to maintain adequate hydration during exercise in the heat by drinking, and more recently by saline infusion. The purpose of this investigation was to compare perceptual and cardiovascular responses to oral and intravenous saline rehydration at rest and during subsequent exercise in the heat. Eight unacclimatized males underwent four randomly assigned rehydration treatments following a 2-4 hour exercise-induced dehydration bout to reduce body weight by 4%. Rehydration treatments included 0.9% saline infusion (09IV), 0.45% saline infusion (45IV), no fluid (NF), and 0.45% saline oral ingestion (ORAL). Following rehydration and rest (2 h total), subjects walked at 50% VO2max for 90 min at 36$\sp\circ$C (EX). The following results were observed: (1) central RPE was significantly lower (p $<$ 0.05) in ORAL compared to all other trials, (2) Local RPE was higher than central RPE at all time points in each trial, (3) skin temperature and thirst had the highest correlations with overall RPE, (4) thirst was significantly lower (p $<$ 0.05) in ORAL during rest and EX compared to all other trials, (5) skin temperature was not different among trials, (6) plasma sodium was higher in 09IV and NF vs. 45IV and ORAL, (7) there was no difference in cardiac output and stroke volume among trials, (8) heart rate was significantly higher during ORAL and NF vs. 09IV and 45IV at 60EX, and (9) peak acceleration and velocity of blood flow in the ascending aorta was not different among trials. It was concluded that (1) ORAL results in more favorable perceptual ratings, (2) thirst may contribute to RPE during exercise in the heat in a hypohydrated state, (3) oropharyngeal and gastric mechanisms were responsible for lower thirst ratings during ORAL, (4) higher levels of plasma sodium in 09IV and ORAL contributed to higher thirst ratings in those trials, and (5) circulatory dynamics are generally not affected by the mode of rehydration. ^