Sympathetic activation and myocardial ischaemia: a role for cold adaptation?

Recently, a marked increase in the number of acute myocardial infarction cases during winter has been reported. Approximately 53% more cases were reported in winter than during summer [1]. The abrupt rupture of atherosclerotic plaques that occurs during cold exposure has been associated with an increase in sympathetic tone that causes increased blood pressure, heart rate and cardiac workload [2]. The aim of our study was to investigate the effects on blood pressure and heart rate of sudden exposure to cold water (14 °C for 20 min) after 90 days of short intermittent exposure to cold water in 259 men and women. The cold adaptation was obtained by a programme of immersion of the whole body up to the neck in a waterfilled bath, the temperature of which was decreased gradually from 22 °C to 14 °C. The time of exposure was increased from 5 to 20 min over a period of 90 days. The programme was designed in four stages : the first three gradually acclimatize the body to water temperature, and the last is the re-warming phase. The stages were as follows: (1) acclimatization of the feet to cold water and touch; (2) acclimatization of the lower half of the body to cold water ; (3) total body immersion (the duration of this stage varied from 5 to 20 min) ; (4) re-warming phase. Table 1 presents the results for arterial blood pressure, heart rate and the rate pressure product (systolic blood pressure¬heart rate) at baseline and immediately after the head-out water immersion for 20 min at 14 °C. The heart rate and the pressure rate product were significantly reduced in these cold-adapted men and women after