Author(s): NAITO, Y., KAJI, M., KUNIMATSU, N., OGOH, S., ITO, K., SHIBASAKI, M., Institution: NARA WOMEN'S UNIVERSITY, Country: JAPAN, Abstract-ID: 1829

INTRODUCTION:
Blood flow in the brachial artery is typically characterized by an antegrade component during [1systole, followed in some individuals by a retrograde component during early diastole [1]. The presence and magnitude of this retrograde flow are believed to reflect downstream peripheral vascular resistance [2]. However, direct experimental evidence demonstrating how acute and graded changes in peripheral resistance alters brachial artery blood flow waveform characteristics remains limited. Therefore, the purpose of this study was to examine the effects of experimentally induced alterations in peripheral vascular resistance on brachial artery blood flow waveforms in humans.
METHODS:
Seventeen healthy adults participated in this study. Brachial artery diameter was measured using B-mode ultrasonography, and blood flow velocity waveforms were obtained using pulsed-wave Doppler ultrasound. Peripheral vascular resistance was manipulated by applying a pneumatic cuff to the distal forearm. Cuff pressure was increased stepwise from 10 to 90 mmHg in 20-mmHg increments every 2 min. Brachial blood pressure was measured before and after the cuff inflation protocol. In addition to the mechanical manipulation, flow-mediated dilation (FMD) of the brachial artery was assessed as an index of endothelial function. FMD was induced by 5 min of forearm cuff occlusion, with brachial artery diameter and blood flow velocity measured baseline and after cuff release. A cold pressor test (CPT) was performed to induce sympathetic activation. The CPT was applied to the same (left) arm in which brachial artery blood flow was measured, by immersing the hand in cold water (≈4°C) for 3 min. Doppler velocity waveforms were obtained during baseline and CPT. At each stage, Doppler velocity waveforms were ensemble-averaged over a stable 20-s period and used for analysis. Antegrade and retrograde components were quantified as the time-integrated positive and negative portions of the velocity waveform, and retrograde fraction was calculated as retrograde / (antegrade + retrograde).
RESULTS:
With increasing cuff pressure, the retrograde fraction of the brachial artery blood flow waveform increased in most participants. When cuff pressure exceeded diastolic blood pressure, retrograde flow was consistently observed throughout diastole, indicating a marked alteration in waveform morphology. During the CPT, the retrograde fraction increased compared with baseline, consistent with enhanced sympathetic vasoconstrictor activity.
CONCLUSION:
These findings demonstrate that peripheral vascular resistance is a key determinant of brachial artery blood flow waveform morphology, particularly with presence and magnitude of retrograde flow.
REFERENCES:
1. Jamison, J. P., Campbell, A., Devlin, C., Johnson, C. D., Adv Physiol Educ, 2022; 46(3), 498–506.
2. Thijssen, D. H. J., Dawson, E. A., Tinken, T. M., Cable, N. T., Green, D. J. Hypertension, 2009; 53(6), 986–992.