The effects of exposure to moderate altitude on cardiovascular autonomic function in normal subjects.

Cardiovascular responses to altitude have been studied on well-trained young subjects, generally at high altitudes (>4000 m). Less known are the effects of exposure to lower altitudes, easily reached by the general population. The aim of the study was to evaluate the effects of exposure to a moderate altitude (2950 m) on heart rate (HR), blood pressure (BP) profile, and cardiovascular autonomic function, and their correlation with hemoglobin oxygen saturation (HbO2S), in untrained subjects of a wide age range. Twenty-seven healthy normotensive subjects (age range 6-83; 8 children, 9 adults, and 10 elderly subjects) underwent a battery of noninvasive cardiovascular reflex tests and 24-h ambulatory BP monitoring. Corrected QT interval was also calculated. HbO2S was measured with a transcutaneous oxymeter. All measurements were performed at about 200 m (s.l.) and repeated at 2950 m. 24-h HR and systolic/diastolic BP mean values increased at 2950 m in children (% change respectively: 6.4 +/- 6.4, p<0.05; 6.5 +/- 4.0/13.5 +/- 6.9, p < 0.05), adults (4.9 +/- 8.1, NS; 6.0 +/- 5.1/8.1 +/- 5.8, p < 0.05), and elderly subjects (7.2 +/- 4.8, p < 0.05; 5.1 +/- 2.3/2.8 +/- 4.1, p < 0.05 for systolic BP only). Standard deviation of BP mean values increased during night-time in the adult group (p < 0.05). All subjects scored normal cardiovascular test results and no differences were observed after exposure to 2950m, at both 1 hour and 24 hours from arrival. After exposure to altitude, HbO2S decreased significantly in the three groups, both on arrival and after 24 hours. No correlation was found between changes in HbO2S and BP/HR responses, and cardiovascular test results. In conclusion, exposure to moderate altitudes, easily and often reached by the general population, causes a small but significant increase in BP and HR in healthy untrained subjects of a wide age range (6-83 years). Some physiological factors (eg, lower environmental temperature and lifestyle modification) together with hypoxia, possibly more than altered cardiovascular reactivity, seem responsible for this cardiovascular change. In terms of end-organ damage, the clinical relevance of this increase in BP and BP variability for repeated exposure is not known.