THE RELATIONSHIP BETWEEN BLOOD VELOCITY AND DIAMETER IN THE BRACHIAL ARTERY

The vascular endothelium is integral to the development of the cardiovascular diseased state. Endothelial health can be predicted using brachial flow mediated dilatation (FMD), a measure of the capacity of the endothelium to vasoact in response to increased blood velocity shear stress. However, FMD is subject to a number of limitations and may lack sensitivity and reproducibility. PURPOSE 1) to investigate the relationship between blood velocity and diameter; 2) determine whether indirect local heating can be used in conjunction with FMD to improve the sensitivity and reliability of FMD; 3) determine the effects of cigarette smoking on the blood velocity-diameter relationship. METHOD: Six male and female non-smokers (23+3 years) and an additional six male and female (20+1 years) occasional cigarette smokers were recruited. Blood velocity through the brachial artery was controlled through the use of: 1) ischemia; 2) progressive intensity handgrip exercise; and 3) progressive local indirect heating. At the highest level of indirect heating (42°C) FMD was repeated to determine if heating influences the sensitivity of the vasoactive response. Reproducibility was determined by repeating the study conditions on one subsequent day. To determine the effects of cigarette smoking, the smokers were subjected to the above procedures before and after smoking one cigarette on subsequent days. RESULTS Time average maximum blood velocity and diameter were strongly related (R2=0.92, P > 0.05). Diameter measurements had coefficients of variation between 2.9 and 8.3%. 42°C FMD had a greater effect size compared to room temperature FMD (11.9+5.1 vs 18.4+10.4 %FMD P < 0.05). Smoking 1 cigarette impaired the room temperature FMD response (11.6+6.7 v 6.7+3.8 %FMD P < 0.05) but otherwise did not alter the velocity diameter relationship. CONCLUSIONS Handgrip exercise and indirect local-heating provide stable increases in brachial artery diameter that are insensitive to blocking NO. The diameter response to ischemia maybe sensitive to NO because of it's transient nature. The use of exercise and indirect heating may enhance the ability to monitor vascular health. Supported by R01 HL65179