Medical College of Wisconsin
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Positional differences in reactive hyperemia provide insight into initial phase of exercise hyperemia. J Appl Physiol (1985) 2015 Sep 01;119(5):569-75

Date

07/04/2015

Pubmed ID

26139221

Pubmed Central ID

PMC4556838

DOI

10.1152/japplphysiol.01253.2013

Scopus ID

2-s2.0-84942312903 (requires institutional sign-in at Scopus site)   26 Citations

Abstract

Studies have reported a greater blood flow response to muscle contractions when the limb is below the heart compared with above the heart, and these results have been interpreted as evidence for a skeletal muscle pump contribution to exercise hyperemia. If limb position affects the blood flow response to other vascular challenges such as reactive hyperemia, this interpretation may not be correct. We hypothesized that the magnitude of reactive hyperemia would be greater with the limb below the heart. Brachial artery blood flow (Doppler ultrasound) and blood pressure (finger-cuff plethysmography) were measured in 10 healthy volunteers. Subjects lay supine with one arm supported in two different positions: above or below the heart. Reactive hyperemia was produced by occlusion of arterial inflow for varying durations: 0.5 min, 1 min, 2 min, or 5 min in randomized order. Peak increases in blood flow were 77 ± 11, 178 ± 24, 291 ± 25, and 398 ± 33 ml/min above the heart and 96 ± 19, 279 ± 62, 550 ± 60, and 711 ± 69 ml/min below the heart (P < 0.05). Thus a standard stimulus (vascular occlusion) elicited different responses depending on limb position. To determine whether these differences were due to mechanisms intrinsic to the arterial wall, a second set of experiments was performed in which acute intraluminal pressure reduction for 0.5 min, 1 min, 2 min, or 5 min was performed in isolated rat soleus feed arteries (n = 12). The magnitude of dilation upon pressure restoration was greater when acute pressure reduction occurred from 85 mmHg (mimicking pressure in the arm below the heart; 28.3 ± 7.9, 37.5 ± 5.9, 55.1 ± 9.9, and 68.9 ± 8.6% dilation) than from 48 mmHg (mimicking pressure in the arm above the heart; 20.8 ± 4.8, 22.6 ± 4.4, 31.2 ± 5.8, and 49.2 ± 7.1% dilation). These data support the hypothesis that arm position differences in reactive hyperemia are at least partially mediated by mechanisms intrinsic to the arterial wall. Overall, these results suggest the need to reevaluate studies employing positional changes to examine muscle pump influences on exercise hyperemia.

Author List

Jasperse JL, Shoemaker JK, Gray EJ, Clifford PS



MESH terms used to index this publication - Major topics in bold

Adult
Animals
Blood Pressure
Blood Pressure Determination
Brachial Artery
Exercise
Female
Humans
Hyperemia
Male
Muscle Contraction
Muscle, Skeletal
Physical Conditioning, Animal
Plethysmography
Rats
Rats, Sprague-Dawley
Regional Blood Flow
Vasodilation