Thermoregulatory responses to cold transients: effects of menstrual cycle in resting women

Biophysics and Biomedical Modeling Division, US Army Research Institute of Environmental Medicine, Natick, Massachusetts 01760-5007 Effects of the menstrual cycle on heat loss and heat production ( M ) and core and skin temperature responses to cold were studied in six unacclimatized female nonsmokers (18-29 yr of age). Each woman, resting supine, was exposed to a cold transient (ambient temperature = mean radiant temperature = 20 to 5°C at 0.32°C/min, relative humidity = 50 ± 2%, wind speed = 1 m/s) in the follicular (F) phase ( days 2-6 ) and midluteal (L) phase ( days 19-23 ) of her menstrual cycle. Clothed in each of two ensembles with different thermal resistances, women performed multiple experiments in the F and L phases. Thermal resistance was 0.2 and 0.4 m 2 · K · W 1 for ensembles A and B , respectively. Esophageal temperature (T es ), mean weighted skin temperature ( sk ), finger temperature (T fing ), and area-weighted heat flux were recorded continuously. Rate of heat debt ( S ) and integrated mean body temperature ( b,i ) were calculated by partitional calorimetry throughout the cold ramp. Extensive peripheral vasoconstriction in the F phase during early periods of the ramp elevated T es above thermoneutral levels. Shivering thermogenesis ( M = M M basal , W /m 2 ) was highly correlated with declines in sk and T fing ( P