Abstract
Individuals with type 2 diabetes have a reduced maximal oxygen consumption (VO2max) compared to non-diabetics. The mechanisms responsible for this are unknown & data regarding maximal arteriovenous oxygen difference (a-VO2max) & maximal cardiac output (Qmax) are sparse. Impairment of left ventricular diastolic function (LVDF) has been associated with limited exercise capacity in healthy individuals & diastolic function has also frequently been reported to be abnormal in type 2 diabetic subjects. PURPOSE To determine relationships between VO2max, LVDF, Qmax and a-VO2max in type 2 diabetic subjects compared to sedentary, age & body mass index matched non-diabetic subjects. METHODS VO2max was measured using cycle ergometry & respiratory gas analysis in type 2 diabetic (n=14) & non-diabetic (n=16) subjects. Resting LVDF was measured by Doppler echocardiography (early to late filling velocity [E/A] ratio) & Tissue Doppler Imaging (early filling velocity to early mitral annulus velocity [E/E'] ratio). Qmax was measured by the CO2 rebreathing technique & a-VO2max was calculated by dividing VO2max by Qmax. Group comparisons & relationships were made using unpaired t-tests & linear regressions. RESULTS VO2max was significantly lower in type 2 diabetic subjects compared to non-diabetics (18.5±3.8 vs. 24.5±5.6 ml/kg/min, p < 0.01). E/A ratio was similar in both groups (1.03±0.32 vs. 1.13±0.23, p>0.05). However, E' was lower (8.07±1.78 vs. 9.65±2.19 cm/s, p < 0.05) & E/E' ratio was higher in the type 2 diabetic compared to the non-diabetic group (8.4±1.6 vs. 7.1±1.4, p < 0.05). Qmax was not different between the groups (10.28±1.86 vs. 11.04±2.05 l/min, p>0.05) while a-VO2max was lower (14.3±3.7 vs. 17.6±3.4 ml O2/100 ml, p < 0.05) in the type 2 diabetic subjects. E/E' correlated inversely with VO2max (r = −0.44). CONCLUSION Although reductions in VO2max in type 2 diabetes are associated with impaired LVDF, a decreased peripheral utilisation of oxygen rather than reduced cardiac output in type 2 diabetes indicated a peripheral rather than central limitation to VO2max.
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