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1 Mayo Clinic
2 Mayo Clinic & Foundation
* To whom correspondence should be addressed. E-mail: Casey.Darren{at}mayo.edu.
We evaluated the contribution of changes in systemic arterial pressure and local vasodilation to blood flow restoration in contracting human muscles during acute hypoperfusion. Healthy subjects (n=10) performed rhythmic forearm exercise (10% and 20% of maximum) while a balloon in the brachial artery located above the elbow was inflated. Each trial included three minutes of; rest, exercise, exercise with balloon inflation, and exercise after balloon deflation. Forearm blood flow (FBF) was measured using Doppler-ultrasound. Blood pressure on both the sides of the balloon was measured using a brachial artery catheter (distal pressure), and Finometer for proximal (systemic) arterial pressure. Balloon inflation during exercise reduced distal arterial pressure and FBF fell 37-41%. There was also a surprising acute increase in forearm vascular resistance (distal pressure/FBF). This was followed by recovery of distal arterial pressure and forearm vasodilation that caused a marked (~75%) restoration of flow that was not associated with significant changes in systemic arterial pressure. During validation trials (n=6) at rest and with exercise both balloon and brachial artery diameters were stable when the balloon was inflated. Our findings indicate that at these exercise intensities: a) the restoration of FBF during exercise with hypoperfusion relied primarily on local dilator responses in conjunction with restoration of distal perfusion pressure likely as a result of increased collateral flow around the elbow, and b) a loss of pulsatile flow and elastic recoil in the forearm may have contributed to the acute increase in vascular resistance seen at the onset of hypoperfusion.
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