[Effect of aging on control of breathing]

In an attempt of elucidate the effect of aging on control of breathing, we measured hypercapnic ventilatory responses (HCVR) under three different conditions in 14 elderly volunteers (mean age: 69 yrs) and in young control subjects (29 yrs). There was no significant difference in the slope value (S) of HCVR between the two groups when the test was conducted under hyperoxic conditions. However, under hypoxic conditions, the "S" was significantly increased only in the young subjects, but not so in the elderly. When an resistive load (17 cmH2O/L-sec) was added to an inspiratory line, the "S" was not changed as a result of augmented P0.1 response in the young subjects, while the "S" was significantly decreased without any increase in P0.1 response in the elderly. The dyspnea score at the end-tidal PCO2 of 50 Torr, which was evaluated by visual analogue scale, was consistently higher in the elderly than in the young under any conditions. These results suggest that hypoxic-hypercapnic interaction on ventilation and load compensation reflex to inspiratory resistive loading are impired in the elderly subjects and that these are not associated with bluntness of respiratory sensation.