Cardiovascular changes were recorded in a 32-month prospective study of exposure to chronic intermittent hypoxia (ICH), with a focus on pulmonary pressure response, blood pressure and heart rate variability. We studied 29 miners, aged 25 +- 5 yr., who worked 7 days at high altitude (HA) (3,800 - 4,600 m) and rested for 7 days at sea level (SL). Subjects underwent a medical examination, ECG, echocardiography and Doppler in order to measure pulmonary pressure during normoxia and simulated hypoxia at SL, and 24-h monitoring of ECG and arterial pressure at SL and HA. Basal evaluations were performed at SL before the first exposure to hypoxia. Measurements were repeated after a mean period of 12, 19 and 31 months. Pulmonary arterial pressure always increased in hypoxia, but further registers did not show any pattern of pulmonary hypertension. Right ventricle showed a slight dilatation. Systemic arterial blood pressure showed a great variability, increasing in most subjects during acute hypoxia but with no signs of permanent hypertension. Mean blood pressure decreased at the end of the exposure to ICH period, at sea level and at high altitude. Heart rate variability showed a modulation of sympathetic and parasympathetic systems during each acute exposure to HA, with no changes after a period of intermittent chronic exposure at SL or HA. In conclusion, subjects did not show the cardiac status of HA residents and maintained their pulmonary and systemic vascular response after this period. There were no major cardiac events in this model of chronic intermittent hypoxia.
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