EFFECTS OF AGING ON RESPIRATORY LOAD COMPENSATION AND DYSPNEA SENSATION

To clarify effects of aging on the load compensation and the sensation of dyspnea, we examined 28 healthy male volunteers for ventilatory and P-0.1 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 PET(CO2) nor Delta P-0.1/Delta PET(CO2) was different between the two groups without loading. In the control group, the Delta P-0.1/Delta PET(CO2) increased with loading (p < 0.01) without a change in the Delta VE/Delta PET(CO2). In the older group, the Delta(0.1)/Delta PET(CO2) did not change with loading so that the Delta VE/Delta PET(CO2) decreased with loading (p < 0.01). In the 28 subjects as a whole, the percent change in Delta P0.1/Delta PET(CO2) with loading was inversely correlated with age (r = -0.53, p < 0.01). At PET(CO2) 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 P-0.1 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 PET(CO2).