Effects of aging on respiratory load compensation and dyspnea sensation

To clarify effects of aging on the load compensation response and the sensation of dyspnea, we examined 28 healthy male volunteers for ventilatory and P0.1 responses to hyperoxic progressive hypercapnia with and without inspiratory flow-resistive loading (17 cm H2O/L/s) while the intensity of dyspnea was simultaneously assessed by visual analogue scaling every 15 s. Of the 28 subjects, 14 were 61 to 79 yr of age and were classified as the older group; the others, 19 to 48 yr of age, were classified as the control group. Neither delta VE/delta PETCO2 nor delta P0.1/delta PETCO2 was different between the two groups without loading. In the control group, the delta P0.1/delta PETCO2 increased with loading (p < 0.01) without a change in the delta VE/delta PETCO2. In the older group, the delta P0.1/delta PETCO2 did not change with loading so that the delta VE/delta PETCO2 decreased with loading (p < 0.01). In the 28 subjects as a whole, the percent change in delta P0.1/delta PETCO2 with loading was inversely correlated with age (r = -0.53, p < 0.01). At PETCO2 levels of 45, 50, and 55 mm Hg, irrespective of loading, the dyspnea intensity was greater in the older group than in the control group, whereas the P0.1 expressed as its ratio to the predicted maximal inspiratory mouth pressure was not different between the two groups. We conclude that aging attenuates the compensatory response to inspiratory flow-resistive loading and it increases the intensity of dyspnea for a given level of PETCO2.