For early diagnosis of atherosclerosis, functional assessments of endothelial cells (ECs) and smooth muscle cells (SMCs) are important. EC function has been evaluated with flow mediated dilation (FMD) test. Evaluation of SMC function has not been established. To evaluate SMC contractility, we developed a pressure mediated contraction (PMC) method in which myogenic contraction of the human brachial artery is induced by applying 50 mmHg of negative pressure to an airtight chamber attached to the arm for 120 s. One of the problems of this method was found to be displacement of brachial artery following negative pressure application. To overcome this problem, we developed a method to evaluate SMC function by measuring myogenic response of the artery by applying chopped positive (20-30 mmHg) or negative pressure (-50 mmHg) synchronized with electrocardiogram. By measuring arterial diameter during unloading phase, the displacement of artery caused by the pressure loading could be reduced markedly from 2.98±1.17 mm (mean ± SD, n = 8) for conventional PMC to 0.20±0.09 mm (n = 8). We also observed that the rate of arterial relaxation under chopped positive pressure was 5.3 ± 1.2 % (n = 6), while that of arterial contraction under chopped negative pressure was 10.2±3.1 % (n = 6). This may indicate that artery has more room for contraction than for relaxation, which is beneficial against sudden decrease in blood pressure.
