Physiological changes in urinary and salivary electrolytes due to physical activity in warm environments
Changes in heart rate; oral temperature; mean skin temperature; urinary pH, volume, sodium, potassium, chloride, urea and creatinine; salivary pH, sodium, potassium and urea; expired air and oxygen consumption have been monitored in young men doing ( 1) exercise on an ergometer for 4 min at 10C, 20C, 30C and 40C dry bulb 50% rh at 120-320 W; (2) 20 min at 30C dry bulb at 50% rh, 60% rh, and 85% rh at 120W, 145W and 170W; and (3) 60 min at 20C, 30C and 40C dry bulb and 50% rh at 170w. Changes in work rate, environmental temperature, relative humidity and exposure time were found to correlate well with the urinary and salivary changes and in most cases changes in both work rate and ambient temperature produced simple summation effects. The increase in salivary components correlated well with the decrease in urinary components. Salivary sodium, potassium and Na+/K+ ratio increased significantly when work intensity, exposure time and environmental temperature were increased. Salivary urea correlates significantly with increased exposure time. The elevated values for salivary components may be explained on the basis of volatilization caused by forced ventilation during exercise; increased penetration of plasma components into saliva; increased water reabsorption, decreased sodium reabsorption, and increased potassium secretion in the ductile system of the salivary glands due to increased sympathetic activity. The results show that changes in saliva give a valid indication of the body's response to work and environmental stress and suggest that saliva could be used to study the combined effects of work and heat in places where it is impracticable to obtain samples of blood or urine.