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 patients with DM, and 8 patients with DM + MC. With the patients under fasting conditions, contrast-enhanced ultrasound perfusion imaging of the forearm flexor muscles was performed to evaluate capillary blood flow and blood volume 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 approximate to 50% reduction in capillary recruitment and a approximate to 60% to 70% reduction in capillary blood flow during both low- and high-intensity exercise compared with 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 that correlated with plasma glucose (p = 0.001) and C-reactive protein (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. (J Am Coll Cardiol 2009;53:2175-83) (C) 2009 by the American College of Cardiology Foundation