Nathalie Koulmann

Influence of Variations in Body Hydration on Cognitive Function

Abstract Eight healthy men, unacclimated to heat, were submitted to variations in body hydration. The subjects were kept euhydrated, dehydrated by controlled passive hyperthermia or exercise on a treadmill up to a weight loss of 2.8%, or hyperhydrated using a solution containing glycerol, with a total ingested volume equal to 21.4 ml/kg of body weight. On completion of a 90-min recovery period, the subjects were assigned a pedaling exercise on an arm-crank ergometer. Psychological tests were administered 30 min after the phase of hydration variation and 15 min after the arm crank exercise. Both dehydration conditions impaired cognitive abilities (i.e., perceptive discrimination, psycho-motor skills, and short-term memory) as well as subjective estimates of fatigue, without any relevant differences between them. Short-term memory was significantly greater following hyperhydration when compared to euhydration (P < .05). Following arm crank exercise, further effects of dehydration were found for tracking per...

Plasma volume changes during and after acute variations of body hydration level in humans

Abstract This study examined plasma volume changes (ΔPV) in humans during periods with or without changes in body hydration: exercise-induced dehydration, heat-induced dehydration and glycerol hyperhydration. Repeated measurements of plasma volume were made after two injections of Evans blue. Results were compared to ΔPV calculated from haematocrit (Hct) and blood haemoglobin concentration ([Hb]). Eight well-trained men completed four trials in randomized order: euhydration (control test C), 2.8% dehydration of body mass by passive controlled hyperthermia (D) and by treadmill exercise (60% of their maximal oxygen uptake, V˙O2max) (E), and hyperhydration (H) by glycerol ingestion. The Hct, [Hb], plasma protein concentrations and plasma osmolality were measured before, during and after the changes in body hydration. Different Hct and [Hb] reference values were obtained to allow for posture-induced variations between and during trials. The ΔPV values calculated after two Evans blue injections were in good agreement with ΔPV calculated from Hct and [Hb]. Compared to the control test, mean plasma volume declined markedly during heat-induced dehydration [−11.4 (SEM 1.7)%] and slightly during exercise-induced dehydration [−4.2 (SEM 0.9)%] (Pu2009<u20090.001 compared to D), although hyperosmolality was similar in these two trials. Conversely, glycerol hyperhydration induced an increase in plasma volume [+7.5 (SEM 1.0)%]. These results would indicate that, for a given level of dehydration, plasma volume is dramatically decreased during and after heat exposure, while it is better maintained during and after exercise.

Use of bioelectrical impedance analysis to estimate body fluid compartments after acute variations of the body hydration level

Physiological measurements including body mass, plasma osmolality, natremia, plasma volume measured by Evans Blue dilution, and total body water (TBW) and extracellular water (ECW) volumes estimated by bioelectrical impedance analysis (BIA) were recorded in eight healthy young Caucasian subjects before and after acute variations of their body hydration state on four separate occasions: 1) euhydration or control trial (C); 2) heat-induced dehydration of 2.8% body mass (D); 3) exercise-induced dehydration of 2.8% body mass (E); and 4) glycerol-hyperhydration (H). Heart rate, rectal and mean skin temperatures were also recorded throughout the experiment. The main result of the study is that BIA only half predicted the body water loss after exercise, although conditions were standardized (electrode placement, side of the body, limb position, posture, and ambient temperature). Differences in body temperatures cannot explain such an unexpected result, nor did the study of plasma osmolality and sodium concentration. If BIA appears to adequately predict changes in TBW after heat-induced dehydration and glycerol hyperhydration, further studies including measures of TBW and ECW by dilution tracer methods would be necessary to establish the validity of using the BIA method to measure such changes and to interpret ECW variations.

Comparison of passive heat or exercise-induced dehydration on renal water and electrolyte excretion: the hormonal involvement.

Abstract. The effects of hydromineral hormones and catecholamines on renal water and electrolyte excretion were examined during and after dehydration induced by either passive heat or exercise. Eight healthy young Caucasian subjects participated in three separate trials, each including three consecutive phases. Phases 1 and 3 involved a 90-min period at rest in a thermoneutral environment, while phase 2 involved a 120-min period designed to provide: (1) euhydration (control trial), (2) passive heat-induced dehydration of 2.8% body mass, or (3) exercise-induced dehydration of 2.8% body mass. During the two dehydration procedures, the decreases in urine flow and sodium excretion were more marked during exercise (P<0.05). An increase in plasma catecholamines occurred only during exercise, together with a reduction in creatinine clearance and more marked increases in plasma renin and aldosterone than during passive heat exposure (P<0.05). Although plasma vasopressin was elevated during the two dehydration procedures, urine osmolality did not change and, moreover, free water clearance increased during exercise (P<0.05). Plasma levels of atrial natriuretic peptide increased markedly only during exercise compared to the other trials (P<0.05). After the dehydration procedures, urine flow decreased again and urine osmolality increased markedly (P<0.05), while plasma vasopressin remained elevated. These results suggest that sympatho-adrenal activation during exercise plays a major role in the more marked reduction in diuresis and natriuresis than during passive heat exposure. Despite high plasma vasopressin concentrations during the two dehydrating events, the observed antidiuresis was not due to an increased renal concentrating ability, and the vasopressin was more effective after the dehydration procedures.

Effect of ingestion pattern on rehydration and exercise performance subsequent to passive dehydration.

Six male volunteers performed three tests, each comprising a passive heating session to obtain dehydration (loss of 2.6% body mass), followed by exercise on a treadmill until exhaustion (50% of maximal oxygen consumption) in a warm environment (dry bulb temperature 35° C, relative humidity 20%–30%). In one test, the subjects exercised without rehydration (Dh). In the two other tests, 50% of the fluid lost in the dehydration session was replaced by drinking mineral water given either in one amount [913 (SEM 23) ml] before the exercise (Rh1) or divided into four equal portions [228 (SEM 5) ml] before the exercise and on three occasions at 15-min intervals during exercise (Rh4). Rehydration increased exercise duration in Rh1 compared to Dh [112 (SEM 7) min and 82 (SEM 3) min, respectively;P < 0.05]. The difference was not significant with Rh4 [103 (SEM 9) min]. A restoration of the time course of changes in plasma volume, plasma osmolality, heart rate and rectal temperature occurred immediately in Rh1 and was delayed in Rh4 until after 60 min of exercise. Our results demonstrated that the swift replacement of the fluid loss in the dehydrated subjects was beneficial to exercise performance by rapidly correcting the disturbances in body fluid balance.

Substrate utilization during prolonged exercise with ingestion of 13C-glucose in acute hypobaric hypoxia (4,300 m)

AbstractEnergy substrate oxidation was measured using indirect respiratory calorimetry combined with tracer technique in five healthy young male subjects, during a 80-min exercise period on ergocycle with ingestion of 140xa0g of 13C-labelled glucose, in normoxia and acute hypobaric hypoxia (445xa0mmHg or 4,300xa0m), at the same relative nn

Effects of acute hypobaric hypoxia on the appearance of ingested deuterium from a deuterium oxide-labelled carbohydrate beverage in body fluids of humans during prolonged cycling exercise

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Hyperhydration induced by glycerol ingestion: hormonal and renal responses

and absolute workload (161±8xa0W, corresponding to 77 and 54% nn