Voluntary body water and salt deficits as a cause of differences between men in their tolerance to heat

Summary Forty-nine unacclimatised Bantu mine workers divided into two groups were subjected to a standard heat exercise stress. One group had sweat losses replaced by drinking water and the other had no water at all. Salt and water deficits were measured by an indirect method based on the volume of urine and salt excreted over the four-hour period of the test. These excretions were correlated with the fourth-hour temperature response and showed good correlations. The difference in heat tolerance was found to be due to a difference in salt and water deficit. Osmolal clearance and free water clearance were additional measurements which showed agreement in the findings of the relative salt and water deficits.Blood chemistry and sweat physiology and chemistry could not discriminate between the heat intolerant and heat tolerant subjects.Certain features of blood and urine chemistry of water replacements and water deprivation were shown.

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Abbreviations RT₂ Rectal temperature at the end of the second hour - RT₄ Rectal temperature at the end of the fourth hour - HR₂ Heart rate at the end of the second hour - HR₄ Heart rate at the end of the fourth hour - SK₂ Skin temperature at the end of the second hour - SK₄ Skin temperature at the end of the fourth hour - Nac Sodium concentration - Nae Sodium excretion - Clc Chloride concentration - Cle Chloride excretion - Kc Potassium concentration - Ke Potassium excretion - U vol Urine volume - C_osm Osmolal clearance - F.W.C. Free water clearance - r Correlation coefficient - OSM Osmolality - Mosm Milliosmols - A.M. Before the test - P.M. After the test - S. Significant at the 5% level - N.S. Not significant at the 5% level