Positional differences in reactive hyperemia provide insight into initial phase of exercise hyperemia

Abstract

Jasperse JL, Shoemaker JK, Gray EJ, Clifford PS. Positional differences in reactive hyperemia provide insight into initial phase of exercise hyperemia. J Appl Physiol 119: 569 -575, 2015. First published July 2, 2015; doi:10.1152/japplphysiol.01253.2013.-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 Ϯ 11, 178 Ϯ 24, 291 Ϯ 25, and 398 Ϯ 33 ml/min above the heart and 96 Ϯ 19, 279 Ϯ 62, 550 Ϯ 60, and 711 Ϯ 69 ml/min below the heart (P Ͻ 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 ϭ 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 Ϯ 7.9, 37.5 Ϯ 5.9, 55.1 Ϯ 9.9, and 68.9 Ϯ 8.6% dilation) than from 48 mmHg (mimicking pressure in the arm above the heart; 20.8 Ϯ 4.8, 22.6 Ϯ 4.4, 31.2 Ϯ 5.8, and 49.2 Ϯ 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. muscle blood flow; muscle contraction; skeletal muscle pump; functional hyperemia AT THE ONSET OF DYNAMIC EXERCISE, there is a rapid increase in blood flow [30,31,41, and see Fig. 2 in Clifford and Hellsten (5)]. In fact, even a single muscle contraction produces a prompt increase in blood flow (1,7,14,26,36,39). There has been a debate over the last few decades about whether this rapid hyperemia is due to the muscle pump mechanism or to rapid vasodilation (5, 35).The muscle pump, as described by Laughlin (20), depends on an increased pressure gradient across the skeletal muscle vascular bed. Muscle contraction compresses the veins within the contracting muscle, expelling blood from the veins. ...

Studies into the determinants of skeletal muscle oxygen consumption: novel insight from near‐infrared diffuse correlation spectroscopy

“…; Jasperse et al . ), showing remarkably similar responses in Doppler‐derived brachial artery blood flow to those found in this investigation. Contrary to our hypothesis, however, steady‐state DCS‐derived microvascular BFI did not differ between arm positions, suggesting that in healthy young adults, muscle perfusion is closely matched to metabolic demand, regardless of conduit blood flow or perfusion pressure.…”

“…; Jasperse et al . ). The order of the arm position (above versus below) was randomized between subjects, and each condition was separated by a minimum of 20 min.…”

“…; Jasperse et al . ). Given that skeletal muscle blood flow tracks changes in perfusion pressure, we hypothesized that skeletal muscle oxygen utilization (Fick‐derived and NIRS–DCS‐derived) would change in opposition to delivery in order to maintain oxygen consumption.…”

Age‐associated impairments in contraction‐induced rapid‐onset vasodilatation within the forearm are independent of mechanical factors

“…For contraction and extravascular compression trials (via pneumatic cuff inflation), subjects lay in the supine positioned with the experimental (left) arm in three different randomized positions: above (45 deg), at (∼0 deg) and below (45 deg) heart level (Figure ). These positions (above and below) were used to manipulate forearm perfusion pressure (Jasperse et al., ; Tschakovsky et al., ) with the at heart level position (∼0 deg) used as a reference condition. Therefore, comparisons were made relative to the control condition (at heart level) to interrogate the influence of hydrostatic forces by using the following arm positions: (i) above heart level to decrease perfusion pressure and facilitate venous emptying; and (ii) below heart level to enhance perfusion pressure (Jasperse et al., ; Tschakovsky et al., ).…”

“…These positions (above and below) were used to manipulate forearm perfusion pressure (Jasperse et al., ; Tschakovsky et al., ) with the at heart level position (∼0 deg) used as a reference condition. Therefore, comparisons were made relative to the control condition (at heart level) to interrogate the influence of hydrostatic forces by using the following arm positions: (i) above heart level to decrease perfusion pressure and facilitate venous emptying; and (ii) below heart level to enhance perfusion pressure (Jasperse et al., ; Tschakovsky et al., ). Before each contraction/compression trial, the experimental arm was positioned to the given position, and 5 min of rest was allowed for stabilization of haemodynamics.…”