Respiration of dehydrating men undergoing heat stress.

Senay, L. C.; Christensen, Margaret L.

doi:10.1152/jappl.1967.22.2.282

Cited by 14 publications

(11 citation statements)

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“…This is somewhat divergent from high intensity exercise in which a fall in blood pH is considerably greater in adults than in children (38). The overall decrease in blood pH in the present study may be due to increased ventilation (as shown by the PCO 2 decrease) and increased skin blood flow (perfusion), both promoted by increased body temperature (39).…”

Section: F Meyer Et Alcontrasting

confidence: 68%

Effect of age and gender on sweat lactate and ammonia concentrations during exercise in the heat

Meyer

Laitano

Bar‐Or

et al. 2007

Braz J Med Biol Res

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The dependence of sweat composition and acidity on sweating rate (SR) suggests that the lower SR in children compared to adults may be accompanied by a higher level of sweat lactate (Lac -) and ammonia (NH 3 ) and a lower sweat pH. Four groups (15 girls, 18 boys, 8 women, 8 men) cycled in the heat (42ºC, 20% relative humidity) at 50% VO 2max for two 20-min bouts with a 10-min rest before bout 1 and between bouts. Sweat was collected into plastic bags attached to the subject's lower back. During bout 1, sweat from girls and boys had higher Lac -concentrations (23.6 ± 1.2 and 21.2 ± 1.7 mM; P < 0.05) than sweat from women and men (18.2 ± 1.9 and 14.8 ± 1.6 mM, respectively), but Lac -was weakly associated with SR (P > 0.05; r = -0.27). Sweat Lac -concentration dropped during exercise bout 2, reaching similar levels among all groups (overall mean = 13.7 ± 0.4 mM). Children had a higher sweat NH 3 than adults during bout 1 (girls = 4.2 ± 0.4, boys = 4.6 ± 0.6, women = 2.7 ± 0.2, and men = 3.0 ± 0.2 mM; P < 0.05). This difference persisted through bout 2 only in females. On average, children's sweat pH was lower than that of adults (mean ± SEM, girls = 5.4 ± 0.2, boys = 5.0 ± 0.1, women = 6.2 ± 0.5, and men = 6.2 ± 0.4 for bout 1, and girls = 5.4 ± 0.2, boys = 6.5 ± 0.5, women = 5.2 ± 0.2, and men = 6.9 ± 0.4 for bout 2). This may have favored NH 3 transport from plasma to sweat as accounted for by a significant correlation between sweat NH 3 and H + (r = 0.56). Blood pH increased from rest (mean ± SEM; 7.3 ± 0.02) to the end of exercise (7.4 ± 0.01) without differences among groups. These results, however, are representative of sweat induced by moderate exercise in the absence of acidosis.

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Section: F Meyer Et Alcontrasting

confidence: 68%

Effect of age and gender on sweat lactate and ammonia concentrations during exercise in the heat

Meyer

Laitano

Bar‐Or

et al. 2007

Braz J Med Biol Res

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“…The high-frequency component of blood pressure variability is believed to result from mechanical changes in intrathoracic pressure associated with respiration (Dornhorst et al 1952;Elghozi et al 1991). Heat stress increases the ventilatory rate (Gaudio and Abramson 1968;Senay and Christensen 1967). We did not measure tidal volume in this study, but the possible increase of tidal volume during heating may act to increase the high-frequency variability of arterial pressure in the tilt period.…”

Section: Discussionmentioning

confidence: 96%

Thermal stress modulates arterial pressure variability and arterial baroreflex response of heart rate during head-up tilt in humans

Yamazaki

Sone

2001

Eur J Appl Physiol

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To examine the effects of thermal stress on the blood pressure variability and the arterial baroreceptor-cardiac reflex during orthostatic stress, 11 male volunteers underwent whole body thermal stress using a cool or hot water-perfused suit during 5 min of 70 degrees head-up tilt (HUT). The spontaneous variability in arterial pressure was quantified by power spectrum analysis. The sensitivity of the arterial baroreceptor-cardiac reflex was calculated from the spontaneous changes in beat-to-beat arterial pressure and heart rate (fc). During supine rest the variability of arterial pressure decreased during cooling, while it remained unchanged during heating. The variability increased with HUT; it was greater (P < 0.05) with heating than with cooling. In the supine condition, the arterial baroreflex sensitivity of fc increased during cooling, while it did not change during heating. The sensitivities decreased (P < 0.05) with HUT during both thermal stresses; the decreased rate of sensitivity from the pre-tilt value was greater during heating [mean 63 (SEM 4)%] and smaller during cooling [mean 11 (SEM 24)%] than during normothermia [mean 47 (SEM 4)%] (both, P < 0.05). There were significant negative correlations between the sensitivities and the amplitude of the arterial pressure variability during normothermia and heating (P < 0.0001). The results suggest that the spontaneous baroreflex response of fc is a modulatory factor for the changes of arterial pressure variability brought about by thermal stress during orthostatic stress.

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“…Hyperventilation has been reported to occur in hyperthermic humans (Gaudio and Abramson 1968;Natalino et al 1977;Rowell et al 1969;Senay and Christensen 1967). Hyperventilation during hyperthermia has also been shown to increase arterial PO 2 and pH and to decrease arterial PCO 2 (Rowell 1969).…”

Section: Discussionmentioning

confidence: 99%

Effects of acute hyperthermia on the carotid baroreflex control of heart rate in humans

Yamazaki

Sagawa

Torii

et al. 1997

International Journal of Biometeorology

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The purpose of this study was to examine the effect of hyperthermia on the carotid baroreceptor-cardiac reflexes in humans. Nine healthy males underwent acute hyperthermia (esophageal temperature -38.0 degrees C) produced by hot water-perfused suits. Beat-to-beat heart rate (HR) responses were determined during positive and negative R-were-triggered neck pressure steps from +40 to -65 mm Hg during normothermia and hyperthermia. The carotid baroreceptor-cardiac reflex sensitivity was evaluated from the maximum slope of the HR response to changes in carotid distending pressure. Buffering capacity of the HR response to carotid distending pressure was evaluated in % from a reference point calculated as (HR at 0 mm Hg neck pressure-minimum HR)/HR range x 100. An upward shift of the curve was evident in hyperthermia because HR increased from 57.7 +/- 2.4 beats/min in normothermia to 88.7 +/- 4.1 beats/min in hyperthermia (P < 0.05) without changes in mean arterial pressure. The maximum slope of the curve in hyperthermia was similar to that in normothermia. The reference point was increased (P < 0.05) during hyperthermia. These results suggest that the sensitivity of the carotid baroreflex of HR remains unchanged in hyperthermia. However, the capacity for tachycardia response to rapid onset of hypotension is reduced and the capacity for bradycardia response to sudden hypertension is increased during acute hyperthermia.

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Respiration of dehydrating men undergoing heat stress.

Cited by 14 publications

References 0 publications

Effect of age and gender on sweat lactate and ammonia concentrations during exercise in the heat

Effect of age and gender on sweat lactate and ammonia concentrations during exercise in the heat

Thermal stress modulates arterial pressure variability and arterial baroreflex response of heart rate during head-up tilt in humans

Effects of acute hyperthermia on the carotid baroreflex control of heart rate in humans

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