The purpose was to characterize gas exchange kinetics following the on-transient of exercise in men aged 30-80 yr. Forty-six men completed square wave exercise tests from loadless cycling to subventilatory threshold (VET) work rates with gas exchange measured breath-by-breath. Signal averaged data were fit with a monoexponential equation to derive time constants (T) for gas exchange and ventilation (V2, [tau]VCO2, [tau]VE) and heart rate ([tau]HR). There was a significant slowing of ventilation and gas exchange kinetics across age with linear regression yielding an increase of 0.67 s[middle dot]yr-1 for [tau]VO, (39 s in young to 61 s in old), 0.57 s-yr-1 for [tau]VCO2, and 0.65 s-yr-1 for [tau]V2, whereas [tau]HR (44 to 41 s) was not-changed significantly. The-slowed VO2 kinetics with age may reflect limitations in muscle blood flow or in control of the rate of oxidative metabolism. The less marked slowing of [tau]VCO2 compared with [tau]VO2 across age may reflect reduced CO2 storage capacity with loss of muscle tissue. The [tau]VE, 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 exchange dynamics at exercise onset.
(C)1994The American College of Sports Medicine