Aging effects on the interaction of hypercapnia and hypoxia as ventilatory stimuli

We measured ventilatory responses to progressive hypercapnia at two steady-state levels of oxygenation and to progressive hypoxia at two steady-state levels of CO2 in 10 elderly and 10 young individuals. Under hyperoxic conditions, the ventilatory response to progressive hypercapnia was not significantly different between age groups but, under hypoxic conditions, the response to hypercapnia was lower in the elderly group. The interaction of hypercapnic and hypoxic stimuli was greater among young persons as indicated by a higher ratio of the hypercapnic response slopes (hypoxic/hyperoxic); 1.48 +/- 0.19 versus 0.98 +/- 0.11, p less than .05. The ventilatory response to hypoxia at the lower CO2 level was significantly greater among elderly than among young adults but not significantly different between age groups at the higher CO2 level. The ratio of hypoxic response slopes (high PCO2/lower PCO2) was 1.56 +/- 0.17 among elderly participants and 3.14 +/- 0.63 among young participants (p less than .05). These results suggest that aging diminishes the multiplicative effect of hypercapnia and hypoxia as ventilatory stimuli.