Polycythemia and Right Ventricular Hypertrophy.

• The chronic hypoxia of high altitude produces an elevated pulmonary arterial pressure" resulting in right ventricular hypertrophy.' Cournand has proposed that the pulmonary hypertension and subsequent right ventricular hypertrophy found in patients with chronic pulmonary disease are associated with polycythemia, hypervolemia, and increased cardiac output secondary to the hypoxemia present in these individuals. Rotta et al. have suggested similarly that high altitude-induced pulmonary hypertension might be due at least in part to polycythemia with an elevation of the circulating blood volume. More recently Naeye has reported that in response to chronic hypoxia there is a marked thickening of the smooth muscle layer of pulmonary arterioles and an extension of the smooth muscle to some small precapillary vessels that ordinarily do not have a smooth muscle coat. Accordingly Fishman has concluded that the elevated pulmonary arterial pressure associated with the chronic hypoxia of high altitude appears to arise predominantly from the circulation of polycythemic blood through small pulmonary arteries whose walls are thickened by hypertrophic smooth muscle. It seemed important therefore to examine, separately from the hypoxia of high altitude, the role that polycythemia plays in producing pulmonary arterial hypertension. To this end, mice and rats housed at a barometric pressure equivalent to "sea level" were made polycythemic by the administration of CoCl2 or by the intraperitoneal