Measurement of flow-mediated dilatation using near-infrared transmission images of finger blood vessels (Comparison with brachial-ankle pulse wave velocity)

Abstract

Arterial endothelial function is known as a factor that correlates with progression of arteriosclerosis. This is measured by flowmediated dilatation (FMD) testing. This test is performed by measuring the brachial artery diameter with an ultrasound system or by measuring digital pulse volumes. Technical and cost-related problems have been pointed out for both methods. We came up with an idea to apply the near-infrared light-based vascular visualization to the measurement of changes in vessel diameter. So, at first, we investigated whether the FMD reaction can be detected with near-infrared transmission images. Next, we derived the estimated values that is considered to correspond to the FMD reaction from the vascular image change. We aimed to determine if these estimated values correlate with brachial-ankle pulse wave velocity (baPWV), which is related to arteriosclerosis. In 50 adult males varying in age, the right upper arm was compressed with a cuff at 200 mmHg for 5 min to cause the FMD reaction after the cuff release. In a 11-min period including time points before and after the cuff compression, near-infrared (wavelength: 850 nm) transmission images near the bilateral finger joints were taken with a CCD camera. The mean brightness was calculated from the images. While no major temporal changes in mean brightness were observed before cuff release, the mean brightness of the hyperemic finger sharply decreased after cuff release. This result suggested that the FMD reaction can be detected with near-infrared transmission images. When the brightness decrease ratio (BDR1) before and after cuff release were compared among age groups, BDR1 at age 50 over years group was significantly smaller than that at age 20-29 years group (p<0.05). BDR1 showed a significant negative correlation with baPWV (R=0.34). This measurement method is considered to have a possibility of estimating FMD reaction and arterial endothelial function.