Thermoregulatory responses to cold transients: effects of menstrual cycle in resting women |
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Authors: | Gonzalez, Richard R. Blanchard, Laurie A. |
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Abstract: | Effects of themenstrual cycle on heat loss and heat production(M) and core and skin temperatureresponses to cold were studied in six unacclimatized female nonsmokers(18-29 yr of age). Each woman, resting supine, was exposed to acold transient (ambient temperature = mean radiant temperature = 20 to5°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 andL phases. Thermal resistance was 0.2 and 0.4 m2 · K · W1for ensembles A andB, respectively. Esophagealtemperature (Tes), mean weightedskin temperature(sk),finger temperature (Tfing), andarea-weighted heat flux were recorded continuously. Rate of heat debt(S) and integrated mean bodytemperature(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 Tesabove thermoneutral levels. Shivering thermogenesis(M = M Mbasal,W /m2) was highly correlated withdeclines insk andTfing(P <0.0001). There was a reducedslope in M as a function ofb,i inthe L phase with ensembles A(P < 0.02) andB (P < 0.01). Heat flux was higher andS was less in the L phases withensemble A(P < 0.05). An analytic modelrevealed thatsk andTes contribute as additive inputsand Tfing has a multiplicativeeffect on the total control of Mduring cold transients(R2 = 0.9).Endogenous hormonal levels at each menstrual cycle phase, coretemperature andskinputs, vascular responses, and variations in body heat balance must beconsidered in quantifying thermoregulatory responses in women duringcold stress. |
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