Differential effects of age and type 2 diabetes on dynamic vs. peak response of pulmonary oxygen uptake during exercise

We investigated if the magnitude of the type 2 diabetes (T2D)-induced impairments in peak oxygen uptake (VO₂) and VO₂ kinetics was affected by age. Thirty-three males with T2D (15 30 middle-aged, 18 older), and 21 non-diabetic (ND) males (11 middle-aged, 10 older) matched by age were recruited. Participants completed four 6-minute bouts of constant-load cycling at 80% VT for the determination of VO₂ kinetics. Cardiac output (CO) (inert gas rebreathing) was recorded at rest, 30 and 240 s during two additional bouts. Peak VO₂(determined from a separate graded test) was significantly (P<0.05) reduced in middle-aged and older men with T2D compared with their respective non-diabetic counterparts (middle-aged, 3.2±0.5 vs. 2.5±0.5 l.min¯¹; older, 2.7±0.4 vs. 2.4±0.4 l.min¯¹) and the magnitude of these impairments was not affected by age. However, the time constant of phase II of the VO₂ response was only slowed (P<0.05) in middle-aged men with T2D compared with healthy counterparts while it was similar among older men with and without T2D (middle-aged, 26.8±9.3 vs. 41.6±12.1 s; older, 40.5±7.8 40 vs. 41.1±8.5 s). Similarly, the “gains” in systemic vascular conductance (SVC) (estimated from the slope between CO and mean arterial pressure responses) were lower (P<0.05) in middle-aged men with T2D than ND controls but similar between the older groups. The results suggest that the mechanisms by which T2D induces significant reductions in peak exercise performance are linked to a slower dynamic response of VO₂ and reduced SVC responses in middle-aged men whereas this is not the case in older men.