The response of ventilation and of heart rate to hypoxia and hypercapnia was determined in eight young normal men age 22-30 yr and eight elderly men age 64-73. The elderly men were selected and carefully screened to eliminate the possibility of cardiopulmonary disease. All the subjects were born at low altitude and had no significant prior exposure to hypoxia. The ventilatory response to hypoxia was measured as the exponential slope constant. k, of regression lines relating the logarithm of incremental ventilation to PAo2 during isocapnic progressive hypoxia. The heart rate response to hypoxia was measured as the percentage change in heart rate between PAo2 = 100 and PAo2 = 40 mm Hg. The ventilatory response to hypercapnia was measured as the slope of regression lines relating ventilation to PAco2 during rebreathing with PAo2 > 200 mm Hg. The heart rate response to hypercapnia was measured as the percentage change in heart rate between control values at the start of the rebreathing test and PACO2 = 55 mm Hg.
Richard S. Kronenberg, Charles W. Drage