RESPIRATORY SHORT-TERM POTENTIATION (AFTER-DISCHARGE) IN ELDERLY HUMANS

During a ventilatory stimulus, respiratory short-term potentiation (ST P, after-discharge) develops, so that ventilation after the stimulus i s greater than that before the stimulus. When the stimulus is withdraw n STP gradually decays, tending to prevent hypoventilation and therefo re stabilizing breathing pattern. STP has been demonstrated in young h umans after brief hypoxic stimuli. Since respiratory arrhythmias incre ase with age, we examined the decay of STP in normal elderly humans (m ean age 62), comparing them with young normals (mean age 27). Resting subjects were exposed to 35-50 sec hypoxia (end-tidal P(O2) = 55 Torr) followed by hyperoxia and breathing analyzed during the hyperoxic per iod, when the subjects were also hypocapnic. With hypoxia, ventilation increased to 152% of control in both the older and younger subjects w hile end-tidal CO2 fell to 92.0% of control in the older subjects and 94.7% of control in the younger. In both groups the hypoxic increase i n ventilation was almost entirely due to an increase of tidal volume. During hyperoxia, ventilation and tidal volume declined over 20-25 sec to control, pre-hypoxic levels, without an apparent undershoot, and t here were no consistent differences between the older and younger subj ects. Prolonging the hypoxic exposure to 90 sec had no influence on ST P in the older subjects. We conclude that neither age nor prolonging t he hypoxic stimulus from 50 to 90 sec influenced STP.