| Keywords |
Hypoxia ; Heat and exercise stress ; Human ; Thermoregulation |
| Abstract |
Eight non-smoking healthy men (21±3 yrs, 176±5 cm, 73±10 kg, 12±4% body fat, 57±9 ml·g?1·in?1 VO2peak) participated in four experimental sessions. In each session, they rested for 15 min and walked on a treadmill for 30 min at 45% of maximal aerobic capacity followed by 15 min of recovery. For the sessions, each subject was randomly assigned to one of four conditions; air breathing in 26oC (Air-N), carbon monoxide (CO) breathing (150 ppm) in 26oC (CO-N), air breathing in 36oC (Air-H), and CO breathing in 36oC (CO-H). During the tests, their rectal (Tre) and mean skin temperature (Tsk), and heart rate (HR) were measured. Blood samples were drawn during resting, 15th and 30th min of exercise, and 15th min of recovery for the analyses of carboxy-hemoglobin (COHb), lactate dehydrogenase (LDH), creatine phosphokinase (CPK), epinephrine (E), norepinephrine (NE), hemoglobin, hematocrit, lactate, glucose, and free fatty acids. COHb was higher in CO-N and CO-H (6%) than in Air-N and Air-H (1%). Tre increased during exercise in all conditions but not different among groups in any time periods. Tsk was higher at 36oC (34-35oC) than 26oC but not different between Air-N and CO-N, or Air-H and CO-H. HR was maintained elevated during exercise (117-124 beat·in?1) but not different during exercise among conditions. Sweat rate was higher in H than N conditions (P<0.05). No changes were noticed during testing in LDH. However, CPK in CO-H was higher than other conditions throughout the testing (P<0.05). While E was not different among conditions, NE was higher in H than N conditions at 30 min of exercise (P<0.05). Other blood variables were not significantly different among conditions. Based on the results, inhalation of 150 ppm of CO during exercise in 36oC did not induce any additional changes in thermoregulatory and general metabolic responses over breathing normal ambient air. However, there was a tendency of metabolic adjustment to CO breathing in hot environment such as less reliance on aerobic metabolism. |