Cardiovascular response to whole-body cold exposure in humans with different initial autonomic tone

Abstract

Relevance. Cold exposure increases sympathetic activity and blood pressure. It can also promote intensification of hypertension symptoms and its progress in winter. However, the mechanisms of this phenomenon are poorly understood.Intention: To determine the dynamics of cardiovascular parameters in young people with different initial autonomic regulation of heart rate during experimental general cold exposure.Methodology. 30 healthy male volunteers aged 18–20 years were examined. In accordance with the initial type of autonomic regulation of the heart rate, all subjects were divided into 3 groups as follows: predominance of vagotonia (Group I, n = 9), optimal autonomic regulation – normotonia (Group II, n = 14), predominance of sympathicotonia (Group III, n = 7). The experiment included three stages: rest at a temperature (+20 0C); exposure to cold (–20 0C) for 10 minutes; warming the body (+20 0C). The heart rate variability (HRV) was recorded during each stage of the study using a portable complex “Varicard 2.8” (Russia). At the same time, blood pressure and temperature in the ear canal were recorded.Results and Discussion. Moderate short-term general air cooling causes generally the same type of temporary reactions of central hemodynamics (increase in blood pressure) and indicators of the total HRV power with an increase in parasympathetic activity. Baseline and dynamic values of heart rate and stress index in Group III were significantly higher than in Groups I and II. During body cooling, the stress index in individuals from Group III was 4 times lower, and in individuals from Group I was 1.5 times lower than before cooling. In Group I, baroreflex was less pronounced (slightly decreased heart rate and HRV) along with a significant increase in blood pressure, thus suggesting a high risk of cold-associated vessel injuries. In Groups II and III, a baroreflex was maintained (significant decrease in heart rate and SI) in response to an increase in blood pressure.Conclusion. Apparently, an increase in blood pressure during moderate exposure to cold does not disturb the protective mechanisms of the cardiovascular system in healthy residents of the North with normotonia and predomination of sympathicotonia. At the same time, a week baroreflex in Northerners with vagotonia can be considered at risk for developing cold arterial hypertension.