Menopausal hot flashes: their cycles and relation to air temperature.

The occurrence of hot flashes was investigated exhaustively in 1 woman. She recorded the clock time of each hot flash in a notebook for 100 days. Fluctuations were circadian and day to day with sawtoothed periodicity. The circadian peak was always between 18 and 21 hours. The circadian nadir and the mean daily rate varied directly with outdoor temperature. The occurrence of hot flashes was not related to internal body temperature, and hence not to environmental heating or cooling of the body. Therefore impulses from temperature receptors altered the rate of formation and release of a hypothetic central nervous system neurohumor that stimulated the hypothalamic heat loss center. This mechanism did not exhibit acclimatization to heat. Comparably thorough studies on more women are needed.