The Blunted Ventilatory Response to Hypoxia in Cyanotic Congenital Heart Disease

The ventilatory response to acute hypoxia (transient nitrogen inhalation) was compared in cyanotic congenital heart disease, noncyanotic heart disease and normal subjects; in two of six cyanotic subjects, the ventilatory response was reassessed after the cardiac defects were repaired. Ventilatory responses were quantitated by relating the maximum increase in ventilation to maximum decrease in arterial oxygen saturation for each period of nitrogen inhalation. The ventilatory responses of cyanotic subjects were significantly less than normal, and a direct relation was found between the degree of chronic hypoxemia and the reduction of ventilatory response to acute hypoxia. However, unlike the irreversible diminished ventilatory responses of natives born at high altitude, the blunting of the hypoxic response caused by cyanotic congenital heart disease was reversed when the hypoxemia was abolished.