Mining activities in North Chile expose a great number of workers to chronic intermittent hypoxia (CIH). This model of exposure to CIH was studied in a prospective study in order to know whether this condition may progressively lead to a chronic pattern or to a specific condition. Twenty-nine miners, aged 25 +- 5 yr., working 7 days at high altitude (HA) (3800 - 4600 m) and resting 7 days at sea level (SL) were studied. Subjects underwent a physical examination, including EKG, hematological status, maximal exercise test, ventilatory and cardiac response to hypoxia (FiO2=0.114) at rest and exercise, pulmonary vascular response to hypoxia by echocardiography, 24-h monitoring of EKG and arterial pressure. HA measurements were: daily Acute Mountain Sickness (AMS) score, sleep status, 24-h monitoring of EKG and arterial pressure. All measurements were repeated after a mean period of 12, 19 and 31 months. Hematocrit increased but reached values lower than those observed in chronic permanent exposure. Systemic and pulmonary arterial pressure measured at SL did not change, but were higher in hypoxia. Right ventricle showed slight dilatation. Exercise performance decreased by 12.3% and maximal heart rate by 6.8% after 31 months of CIH. Ventilatory acclimatization developed after 12 months. Symptoms of AMS and sleep disturbances were still seen on the first 2 days at HA, whatever the time of exposure to CIH. In conclusion, CIH led to a status of acclimatization different from chronic hypoxia. However, subjects are still at risk of acute altitude-induced illnesses.
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