Abnormal Skeletal Muscle Capillary Recruitment During Exercise in Patients With Type 2 Diabetes Mellitus and Microvascular Complications

Objectives We sought to determine whether skeletal muscle capillary recruitment is impaired in type 2 diabetes mellitus (DM) with and without microvascular complications (MC). Background Insulin and exercise each stimulate recruitment of skeletal muscle capillaries. Insulin-mediated recruitment is impaired in insulin-resistant humans and animals, but exercise-mediated recruitment has not been studied. Methods We studied 20 control subjects, 22 with DM, and 8 with DM+MC. Under fasting conditions, contrast-enhanced ultrasound perfusion imaging of the forearm flexor muscles was performed to evaluate capillary blood flow (CBF) and blood volume (CBV) at rest and during low-or high-intensity contractile exercise (25% and 80% maximal handgrip). Rheologic parameters of erythrocyte deformability and plasma viscosity were measured. Results Muscle capillary responses to exercise were similar between the control and DM groups, but were reduced (p<0.05) in those with DM+MC. The DM+MC group had a ≈50% reduction in capillary recruitment, and a ≈60–70% reduction in CBF during both low- and high-intensity exercise compared to the control group. These abnormalities were independent of disease duration. Patients with DM+MC were more insulin resistant than DM patients, and had an elevated whole blood viscosity which correlated with plasma glucose (p=0.001) and C-reactive protein (CRP) (p=0.003). Conclusions Capillary recruitment during low- and high-intensity exercise is normal in uncomplicated type 2 DM but is impaired in those with microvascular complications. Abnormalities in capillary recruitment may be related to abnormal hemorheology, although larger trials are needed to establish this relation.