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1 Division of Cardiology, Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033; and 2 Lebanon Veterans Affairs Medical Center, Lebanon, Pennsylvania 17042
The effects of changes in transmural
pressure on brachial artery mean blood velocity (MBV) were examined in
humans. Transmural pressure was altered by using a specially designed
pressure tank that raised or lowered forearm pressure by 50 mmHg within
0.2 s. Brachial MBV was measured with Doppler directly above the
site of forearm pressure change. Pressure changes were evoked during resting conditions and after a 5-s handgrip contraction at 25% maximal
voluntary contraction. The handgrip protocol selected was sufficiently
vigorous to limit flow and sufficiently brief to prevent autonomic
engagement. Changes in transmural pressure evoked directionally similar
changes in MBV within 2 s. This was followed by large and rapid
adjustments [
2.14 ± 0.24 cm/s (vasoconstriction) during
negative pressure and +2.14 ± 0.45 cm/s (vasodilatation) during
positive pressure]. These adjustments served to return MBV to resting
levels. This regulatory influence remained operative after 5-s static
handgrip contractions. Of note, changes in transmural pressure were
capable of altering the timing of the peak MBV response (5 ± 0, 2 ± 0, 6 ± 1 s ambient, negative, and positive
pressure, respectively) as well as the speed of MBV adjustment
(
2.03 ± 0.18,
2.48 ± 0.15,
0.84 ± 0.19 cm · s
1 · s
1
ambient, negative, and positive pressure, respectively) after handgrip
contractions. Vascular responses, seen with changes in transmural
pressure, provide evidence that the myogenic response is normally
operative in the limb circulation of humans.
myogenic response; regional blood flow; exercise; Doppler velocity
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