THERMOREGULATORY RESPONSES TO COLD TRANSIENTS - EFFECTS OF MENSTRUAL-CYCLE IN RESTING WOMEN

Effects of the menstrual cycle on heat loss and heat production (M) an d core and skin temperature responses to cold were studied in six unac climatized female nonsmokers (18-29 yr of age). Each woman, resting su pine, was exposed to a cold transient (ambient temperature = mean radi ant temperature = 20 to -5 degrees C at -0.32 degrees 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 r esistance was 0.2 and 0.4 m(2).K.W-1 for ensembles A and B, respective ly. Esophageal temperature (T-es), mean weighted skin temperature (<(T )over bar (sk)>), finger temperature (T-fing), and area-weighted heat flux were recorded continuously. Rate of heat debt (-S) and integrated mean body temperature (<(T)over bar (b,i)>) were calculated by partit ional calorimetry throughout the cold ramp. Extensive peripheral vasoc onstriction in the F phase during early periods of the ramp elevated T ,, above thermoneutral levels. Shivering thermogenesis (Delta M = M - M-basal, W/m(2)) was highly correlated with declines in <(T)over bar ( sk)> and T-fing (P < 0.0001). There was a reduced slope in M as a func tion of <(T)over bar (b,i)> in the L phase with ensembles A (P < 0.02) and B (P < 0.01). Heat flux was higher and -S was less in the L phase s with ensemble A (P < 0.05). An analytic model revealed that <(T)over bar (sk)> and T-es contribute as additive inputs and T-fing has a mul tiplicative effect on the total control of Delta M during cold transie nts (R-2 = 0.9). Endogenous hormonal levels at each menstrual cycle ph ase, core temperature and <(T)over bar (sk)> inputs, vascular response s, and variations in body heat balance must be considered in quantifyi ng thermoregulatory responses in women during cold stress.