Pulmonary gas exchange in Andean nativos with excessive polycythemia - efecct of hemodilution

Abstract

Pulmonary gas exchange in andean natives (n =8) with excessive high-altitude (3,600-4,200 m) polycythemia (hematocrit 65.1 +- 6.6%) and hipoxemia (arterial PO2 45.6+-5.6 Torr) in the absence of pulmonary or cardiovascular disease was investigated both before and after isovolemic hemodilution by use of the inert gas elimination technique. The investigations were carried out in La Paz, Bolivia (3,650 m, 500 mmHg barometric poressure). Before hemodilution, a low ventilation-perfusion (VA/Q) mode (VA/Q <0.1 without true shunt accounted for 11.6+-5.5% of the total blood flow and was mainly responsible for the hypoxemia. The hypoventilation with a low mixed venous PO2 value may have contributed to the observed hypoxemia in the absence of an impairment in alveolar capillary diffusion. After hemodilution, cardiac output and ventilation increased from 5.5 +- 1.2 to 6.9 +-1.2 1/min and from 8.5 +- 1.4 to 9.6 +- 1.3 1/min, respectively, although arterial and venous PO2 remained constant. VA/Q mismatching fell slightly but significantly. The hypoxemia observed in subjects suffering from high-altitude excessive polycythemia was attributed to an increased in blood flow perfusing poorly ventilated areas, but without true intraor extrapulmonary shunt. Hypoventilation as well as a low mixed venous PO2 value may also have contributed to the observed hypoxemia.