Dysfunctional Muscle Blood Flow Regulation During Exercise in Type 2 Diabetes
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There is some evidence to suggest that oxygen consumption (VO2) and oxygen delivery to muscle are reduced at exercise onset and steady state in individuals with type 2 diabetes (T2D), although no studies have combined measurements of both muscle blood flow and VO2 during exercise in this population. OBJECTIVES: 1) To determine whether a reduction in VO2 during exercise would be accompanied by reduced leg blood flow (LBF). 2) To examine the dynamic response characteristics of LBF to determine whether feedforward and/or feedback control systems of blood flow regulation are impaired. METHODS: Four men with T2D and six healthy, activity matched controls (CON) performed supine, two-leg knee extension/flexion exercise tests involving progressive increase in exercise intensity to exhaustion and step increases to a low intensity equivalent to lifting 7.5 kg (LO7.5kg), and a moderate intensity equivalent to 90% of ventilatory threshold (VT90%). MEASUREMENTS: LBF, VO2, mean arterial pressure, heart rate, and stroke volume were measured continuously. RESULTS: Means ± SE, CON vs. T2D. 1) ∆VO2 was not different between groups during the incremental test (P= 0.264), ∆LBF in T2D tended to be lower (P = 0.098). 2) ∆VO2 was not different between groups at any time during LO7.5kg (P = 0.351). Individuals with T2D demonstrated a lower ∆LBF at time = 15 s (3435.6 ± 275.0 vs. 2120.4 ± 218.4 ml/min, P = 0.018). 3) Gains for baseline (G0) and phase I (G1) LBF adaptation to LO7.5kg were lower in T2D compared to CON (G0: 959.8 ± 111.3 vs. 617.0 ± 22.1 ml/min, P = 0.044; G1: 3662.1 ± 229.0 vs. 2128.1 ± 161.6 ml/min, P = 0.002). 4) The time required to achieve 63% of the total response magnitude tended to be slower in T2D (LO7.5kg: 14.3 ± 1.7 vs. 23.1 ± 4.2 s; VT90%: 26.2 ± 3.5 vs. 40.0 ± 7.5 s; P = 0.095). CONCLUSIONS: 1) The initiatory rise in LBF is significantly lower in individuals with T2D, likely due to impairments in feedforward control mechanisms of blood flow regulation, 2) Individuals with T2D do not demonstrate lower VO2 responses to exercise despite an impaired LBF response.