EXERCISE ON-TRANSIENT GAS-EXCHANGE KINETICS ARE SLOWED AS A FUNCTION OF AGE

The purpose was to characterize gas exchange kinetics following the on -transient of exercise in men aged 30-80 yr. Forty-six men completed s quare wave exercise tests from loadless cycling to subventilatory thre shold (VET) work rates with gas exchange measured breath-by-breath. Si gnal averaged data were fit with a monoexponential equation to derive time constants (tau) for gas exchange and ventilation (tau VO2, tau VC O2, tau V-E) and heart rate (tau HR). There was a significant slowing of ventilation and gas exchange kinetics across age with linear regres sion yielding an increase of 0.67 s.yr(-1) for tau VO2, (39 s in young to 61 s in old), 0.57 s.yr(-1) for tau VO2, and 0.65 s.yr(-1) for tau V-E, whereas tau HR (44 to 41 s) was not changed significantly. The s lowed VO2 kinetics with age may reflect limitations in muscle blood fl ow or in control of the rate of oxidative metabolism. The less marked slowing of tau VO2 compared with tau VO2 across age may reflect reduce d CO2 storage capacity with loss of muscle tissue. The tau V-E change across age was similar to that for tau VCO2 (tau VE/tau VCO2 unchanged ). The present study demonstrated marked age-related slowing of gas ex change dynamics at exercise onset.