Baker et al (1) have recently investigated cardiovascular changes that occur with nocturnal hot flushes during sleep. They investigated changes in heart rate, blood pressure, and pre-ejection period in 86 women aged between 43-60 years who had at least one objectively-recorded nocturnal hot flush during an overnight laboratory PSG recording. Fifty-one percent of the nocturnal hot flushes were associated with arousals/awakenings and these were accompanied by an increase in systolic (~6 mmHg) and diastolic (~5mmHg) blood pressure and heart rate (~20% increase), sustained for several minutes. In contrast, nocturnal hot flushes not resulting in arousal/awakening, which occurred in 28.6% cases, were accompanied by a drop in systolic blood pressure and a marginal increase in heart rate, likely components of the heat dissipation response. All nocturnal hot flushes were accompanied by decreased pre-ejection period, suggesting an increased cardiac sympathetic activity, with a prolonged increase for nocturnal hot flushes associated with arousals/awakenings. Older age predicted greater likelihood of nocturnal hot flush arousals/awakening.
The findings of this study suggest that nocturnal hot flushes associated with arousals/awakenings, which are in the majority and more likely in older women, lead to increases in heart rate and blood pressure, which could have a long-term impact on nocturnal cardiovascular restoration in women with multiple nocturnal hot flushes. Sleep is not a passive event, but rather an active process involving characteristic physiological changes that occur throughout the body(2). There are a variety of physiological and behavioral changes during normal wakefulness, NREM and REM sleep which are most commonly noted in the somatic and autonomic nervous system and affect the respiratory, cardiovascular, gastrointestinal, endocrine, renal, sexual and thermoregulatory systems. Heart rate, blood pressure, cardiac output, and peripheral vascular resistance decrease during NREM sleep and decrease further in REM sleep. Cerebral blood flow decreases during NREM sleep but increases in REM sleep. All these profound hemodynamic changes, which cause maximal oxygen desaturation, periodic breathing and intermittent increase of sympathetic activity during REM sleep, may initiate platelet aggregation, plaque rupture and coronary arterial spasm leading to myocardial infarction, ventricular arrhythmias and even sudden death, especially in the early hours of the morning. (2,3) Nocturnal hot flushes are very common during the menopausal transition and they frequently, but not universally, awake women from their sleep. Not every nocturnal flush is associated with an awakening and not every awakening is associated with a vasomotor event. In one study, a significant association between the occurrence of hot flushes and awakenings during the night in postmenopausal women in that 45 of 47 hot flushes were associated with an awakening, but of note 31 awakenings were not related to a vasomotor episode. Of particular note was the fact that on average, the awakening preceded the vasomotor instability by about 36 seconds (4). Other studies have reported that nocturnal hot flushes occur before an awakening only in the first half of the night, or that the majority of nocturnal hot flushes coincide with awakenings, with no differences in the first and second part of the night. (5,6) Baker et al have analyzed an area in sleep which still lacks specific knowledge but which may well impact significantly in quality and quantity of life in the long term.
Professor Emeritus Department of Obstetrics and Gynaecology
University of Witwatersrand
Baker FC, Forouzanfar M, Goldstone AM, Claudatos SA, Javitz H, Trinder J, de Zambotti M. Changes in heart rate and blood pressure across nocturnal hot flashes associated with or without arousal from sleep. Sleep. 2019 Aug 13.
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de Zambotti M, Colrain IM, Javitz HS, Baker FC. Magnitude of the impact of hot flashes on sleep in perimenopausal women. Fertil Steril 2014;102:1708-15 e1.