<i>Respiratory Adaptations to Chronic High Altitude Hypoxia</i>

Respiration, arterial acid-base equilibrium and blood hemoglobin dissociation curves were studied in subjects residing continuously for many years (long-term residents) at 3990 and 4515 meters above sea level and in a group of lowlanders (newcomers) within 8 weeks of their arrival at these altitudes. At 3990 m, average values for resting pulmonary ventilation were, respectively, 5.4 ± 0.25 and 5.2 ± 0.24 l/min/m2 in two groups of newcomers and 4.5 ± 0.14 l/min/m2 in 11 long term residents. At 4515 m two newcomers averaged 5.6 l/min/m2 and 20 long term residents 4.9 ± 0.10 l/min/m2. In eight subjects residing and studied at sea level, average ventilation was 3.8 ± 0.13 l/min/m2. Changes in alveolar Pco2, alveolar ventilation and oxygen ventilatory equivalent were in accordance with those in total ventilation. Therefore hyperventilation was greater in the newcomers than in the long term residents at high altitude. Oxygen breathing at 3990 and 4515 m depressed average pulmonary ventilation more in the newcomers than in the long term residents but not to sea level values. Respiratory response to inhaled CO2 was greater in newcomers at 3990 m than that found in normal subjects at sea level while in the long term residents at 3990 and 4515 m the response was equal or somewhat less than in the subjects at sea level. Hemoglobin oxygen affinity and arterial phs of long term residents at high altitude were found to be within the normal sea-level ranges. Submitted on May 14, 1956