Journal of Applied Physiology, Vol 65, Issue 6 2714-2719, Copyright © 1988 by American Physiological Society
Respiratory enthalpy changes in mine rescue workers exercising under heat stress
J. Leigh, R. K. Griffits and C. G. Ellis
National Institute of Occupational Health and Safety, Joint Coal Board Medical Division, New South Wales, Australia.
Respiratory enthalpy change, rectal temperature, and heart rate of mine
rescue workers exercising at a metabolic energy production rate of 4 met (1
met-58.15 W.m-2) in a 40 degrees C saturated environment, wearing
closed-circuit breathing apparatus, were continuously measured in 10
volunteer subjects. The effects of using liquid O2 and compressed O2
apparatus were compared in each subject. Evaporative heat exchange was much
greater with the liquid O2 type of apparatus, causing a significantly lower
rate of rise of rectal temperature and heart rate. Convective heat exchange
was negligible. Mean values for evaporative heat loss (maximum) were 61 +/-
16 (SD) W with liquid O2 and 20 +/- 18 W with compressed O2 (P less than
0.0001, 2-sided t test). Mean values for rectal temperature (rate of
increase) were 0.022 +/- 0.009 (SD) degrees C.min-1 for liquid O2 and 0.036
+/- 0.015 degrees C.min-1 for compressed O2 (P less than 0.005, 2-sided
paired t test). Mean values for heart rate (rate of increase) were 2.64 +/-
0.74 (SD) min-2 for liquid O2 and 3.27 +/- 0.89 min-2 for compressed O2 (P
less than 0.02, 2-sided paired t test). This study quantifies, for the
first time, the respiratory enthalpy change in exercising heat-stressed
mine rescue workers and shows, from a physiological point of view, that the
liquid O2 apparatus is clearly superior to the compressed O2 apparatus.
