Is Oxygen Consumption and Oxygen Delivery During Leg Exercise Compromised in Type II Diabetes?

Abstract

Evidence is emerging that muscle oxygen delivery and possibly also muscle oxygen consumption responses may be blunted in type II diabetes (T2D). PURPOSE: To determine whether dynamic and steady state adjustments in VO2 to exercise are impaired in T2D and whether this is accompanied by slower and/or reduced muscle blood flow responses. METHODS: Four males with T2D (54.8 ± 4.1 yrs) and six healthy, activity matched male controls (CON) (44.3 ± 2.7 yrs) performed 3 protocols of supine, two-leg knee extension/flexion exercise i) incremental exercise to exhaustion, ii) rest to low intensity step (LO7.5kg; 7.5 kg resistance), iii) rest to moderate intensity step (VT90%; 90% of ventilatory threshold) on separate days. Femoral artery blood flow (FABF; Doppler and Echo ultrasound), and VO2 (Metabolic Cart) were measured continuously at rest and throughout exercise. RESULTS: Means are ±SE. Fasting plasma glucose and HbA1c% were elevated in T2D vs. CON (8.2 ± 1.1 vs. 5.6 ± 0.3 mmol/L, P=0.035; 7.4 ± 0.9 vs. 5.3 ± 0.1 %, P=0.023). Neither peak VO2 nor peak work rate were different in T2D vs. CON (1711.1 ± 170.8 vs. 1852.0 ± 162.0 ml/min, P= 0.579; 16.4 ± 1.0 vs. 18.7 ± 1.4 kg) indicating matched fitness. For rest to exercise steps: the change from baseline (D) for VO2 was not different between groups at any time point for LO7.5kg (P=0.351), but DFABF in the rapid initial phase I response was blunted in T2D (FABF for two legs; 2120.4 ± 218.4 ml/min vs. 3435.6 ± 275.0, P= 0.018). Mean response time (MRT; time required to achieve 63% of the total response magnitude) tended to be slower (LO7.5kg; 23.1 ± 4.2s vs. 14.3 ± 1.7s; VT90%: 40.0 ± 7.5s vs.26.2 ± 3.5s; P=0.095). For incremental exercise: DVO2 was not different between groups at 7.5, 10 and 13 kg (P=0.264). DFABF in T2D was not statistically significantly reduced (P=0.098), whereas absolute FABF was lower at rest 617.0 ± 22.1 vs.959.8 ± 111.3 ml/min, P=0.04) and 10 and 13 kg workloads (P=0.035 and 0.007 respectively). Movement artifact prevented FABF measures above these work rates. CONCLUSIONS: T2D is characterized by impaired vasodilatory mechanisms involved in the rapid initial response to exercise, and may impair blood flow adjustments to incremental exercise. However, these effects do not impair increases in VO2, indicating increased oxygen extraction compensates in this exercise model.