CARDIOVASCULAR AND VENTILATORY RESPONSE TO ISOCAPNIC HYPOXIA AT SEA-LEVEL AND AT 5,050 M

To assess the effect of chronic hypoxic conditions on ventilatory, hea rt rate (KR), and blood pressure (BP) responses to acute progressive i socapnic hypoxia, we studied five healthy Caucasian subjects (3 men an d 2 women). Each subject performed one rebreathing test at sea level ( SL) and two tests at the Pyramid laboratory at Lobuche, Nepal, at the altitude of 5,050 m, 1 day after arrival (HA1) and after 24 days of so journ (HA2). The effects of progressive isocapnic hypoxia were tested by using a standard rebreathing technique. BP, electrocardiogram, arte rial oxygen saturation, airflow and end-tidal CO2 and O-2 were recorde d. For each subject, the relationships between arterial oxygen saturat ion and HR, systolic BP and minute ventilation (VE), respectively, wer e evaluated. At HA1, the majority of subjects showed a significant inc rease in iiE and BP response and a decrease in HR response to progress ive isocapnic hypoxia as compared to SL. At HA2, VE and BP responses f urther increased, whereas the HR response remained similar to that obs erved at HA1. A significant relationship between hypoxic ventilatory r esponses and both systolic and diastolic BP responses to progressive h ypoxia was found. No significant correlation was found between hypoxic ventilatory and HR responses.