Cardiopulmonary effects of brief, intense thermal exposures

Abstract

To evaluate the cardiovascular and respiratory effects of brief, intense heat stress, 6 clothed human subjects were exposed to 2 10-min. thermal pulses (reaching 150 and 205[degree] C) with indwelling arterial and venous catheters and an expired-air collection system; wall temperatures rose 28[degree] C/min. The 205[degree] C exposures approached tolerance limits; average skin temperatures reached 5[degree] C, rectal temperatures rose 0,5[degree] C, sweat rate exceeded I ]/hr,, and weakness and presyncopal symptoms were common. Heart rate and cardiac output rose to peak levels quickly, followed by progressive increases in systolic blood pressure, systolic ejection rate, and central venous pressure values, as circulation time, diastolic blood pressure, and systemic vascular resistance fell gradually. Estimated plasma volume fell approximately 8%. Respiratory rate remained unchanged, while tidal volume rose along with arterial O2 content and pH as CO2 content fell; O2 consumption rose slightly. Two subjects bled into subcutaneous tissues at catheterization sites 4-6 hr. after the exposures.