EXPLORING THE ROLE OF SKELETAL MUSCLE MICROVASCULAR BLOOD FLOW IN EXERCISE CAPACITY AMONG INDIVIDUALS WITH CONTROLLED TYPE 2 DIABETES

Abstract

INTRODUCTION & AIMS The cardiac and macrovascular system is vital for human exercise capacity, yet the microvascular network is primarily responsible for delivering nutrients and oxygen to metabolically active tissues like skeletal muscle. Due to methodological limitations, few studies have investigated the role of muscle microvascular blood flow in determining exercise capacity or intolerance in individuals with chronic conditions such as type 2 diabetes. Our aim was to use modern contrast-enhanced ultrasound to directly measure microvascular blood flow in skeletal muscle at rest and after a maximal treadmill exercise test in individuals with controlled type 2 diabetes. METHODS Fifteen adults with controlled type 2 diabetes (age: 62.5 ± 8.0 years [M ± SD]; BMI: 31.6 ± 6.9 kg/m2; HbA1c: 6.7 ± 0.9%; 13 females and 2 male) attended the laboratory after a 2-hour fast and completed a Modified Bruce treadmill exercise test until exhaustion. Microvascular blood velocity, volume, and flow in the vastus lateralis muscle was assessed at rest, immediately post-exercise, and 30 minutes post-exercise via contrast-enhanced ultrasound during a constant-rate intravenous contrast agent infusion (DEFINITY®). Participants also completed a whole-body dual x-ray absorptiometry scan and a six-minute walk test (6MWT). RESULTS Microvascular blood velocity, volume, and flow increased immediately after exercise (∼230%, ∼79%, and ∼529%, respectively; all p<0.001), and remained elevated above baseline levels 30 minutes post-exercise (∼79%, ∼25%, and ∼139%, respectively; all p≤0.003). Resting and post-exercise skeletal muscle microvascular blood flow measures were not associated with VO2peak (ml/min/kg), time to exhaustion, or six-minute walk distance (all p>0.05). CONCLUSION Muscle microvascular blood flow remains elevated for up to 30 minutes following maximal aerobic exercise in individuals with controlled type 2 diabetes. The lack of association between muscle microvascular blood flow and exercise capacity is not clear but may indicate considerable blood flow redundancy or reserve within the vascular network.