The effect of occult diabetic status and oral glucose intake on brachial artery vasoactivity in patients with peripheral vascular disease

Abstract

Brachial artery vasoactivity is a well known non-invasive method of assessing arterial endothelial function in vivo. Brachial artery vasoactivity has been found to be impaired in overt diabetes and in patients with coronary artery disease. Impaired brachial artery vasoactivity is felt to be an early indicator of atherosclerosis. The authors identified a group of patients with lower extremity peripheral vascular disease, who had normal fasting glucose level and were not known to be diabetics. An oral glucose tolerance test was performed in this group of patients. Brachial artery vasoactivity was assessed at each step of the oral glucose tolerance test to examine their occult diabetic status and correlate brachial artery vasoactivity to that status. The authors studied 23 randomly selected patients from the vascular surgery clinic between the ages of 50 and 79 years. Serum glucose level was assessed after a 10-h fast and at 30, 60 and 120 min after a 75-g oral glucose challenge. Any patient with two serum glucose values >140 mg/dl was considered to have a positive oral glucose tolerance test. Using duplex ultrasound, the brachial artery diameter (cm) and blood volume (ml/min) were assessed before and after tourniquet occlusion at each step of the oral glucose tolerance test. Paired and unpaired t-tests were used to evaluate the results, P<0.05 was considered significant. Nine patients had abnormal oral glucose tolerance test for a prevalence of 39%. There was no significant difference in fasting glucose levels between positive and negative oral glucose tolerance test patients (97.4±16.7 versus 88.5±5.8, P=0.23). Patients with a positive oral glucose tolerance test had impaired vasoactivity at fasting and at each step of the test with no significant changes in brachial artery diameter or blood flow in response to brachial artery occlusion. Patients with a negative oral glucose tolerance test exhibited increased brachial artery diameter at fasting in response to brachial artery occlusion (0.43±0.02 versus 0.46±0.02, P=0.03), but not after oral glucose challenge. In patients with a negative oral glucose tolerance test, brachial artery flow volume increased significantly in response to hyperemia at fasting (240±61 versus 578±262, P=0.001) and at 30 min after glucose intake (260±53 versus 358±72, P=0.01). At 60 and 120 min after glucose intake, brachial artery flow volume did not significantly increase in response to brachial artery occlusion. These results indicate that individuals with PVD and normal fasting glucose levels have a high prevalence of positive oral glucose tolerance test (39%). Patients with normal fasting glucose levels and abnormal oral glucose tolerance test have impaired brachial artery vasoactivity at fasting and after oral glucose challenge. This is in contrast to patients with normal oral glucose tolerance test who have normal fasting hyperemic response to brachial artery occlusion. However, this normal brachial artery vasoactivity is lost in the negative oral glucose tolerance test group in response to oral glucose load. These results suggest that endothelial function in diabetics is impaired in the early stages of the disease even before overt hyperglycemia occurs. Tight control of blood glucose level in glucose-intolerant patients prior to occurrence of overt fasting hyperglycemia may prove protective.