Acute augmentation of brachial artery retrograde shear with external pneumatic compression is associated with changes in vascular compliance and altered peripheral wave reflections

Objectives: External pneumatic cuff compression over the forearm is widely used in vascular research to induce and augment retrograde shear in a graded manner in the brachial artery, but the mechanisms underlying this model have not been explored in detail. We hypothesised that augmentation of retrograde shear with application of external pressure over the forearm was secondary to increased peripheral wave reflections resulting from peripheral vasoconstriction and altered vascular compliance. Materials and Methods: We applied graded pneumatic pressure at 25, 50 and 75 mmHg over the forearm for 3 min in 22 healthy participants. Brachial-radial pulse wave velocity (Br-Ra PWV) was recorded using applanation tonometry as a surrogate for regional compliance, while alternating current (AC) and direct current (DC) components of photoplethysmography (PPG) signal from the middle finger were recorded as a surrogate for peripheral vasoconstriction. Results: Mean retrograde shear rate increased at 50 mmHg ( p < 0.05) and 75 mmHg ( p < 0.001) compression as compared to baseline. Br-Ra PWV at 75 mmHg was significantly lower than baseline ( p < 0.001), 25 mmHg ( p < 0.001) and 50 mmHg ( p < 0.001). DC component of PPG increased at 75 mmHg ( p < 0.01) and 50 mmHg ( p < 0.05) as compared to baseline. AC component decreased at 25 mmHg ( p < 0.05), 50 mmHg ( p < 0.001) and 75 mmHg ( p < 0.001) as compared to baseline. Conclusion: These results indicate that increased vascular compliance and altered peripheral wave reflections due to external pneumatic cuff application augment brachial artery retrograde shear in a dose-dependent manner.