What question did this study set out to answer?

To determine whether rapid vasodilation proportional to contraction intensity drives immediate exercise hyperemia during the first cardiac cycle following a single isometric contraction.

January 31, 2004Journal of Applied Physiology150 citations

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Immediate exercise hyperemia in humans is contraction intensity dependent: evidence for rapid vasodilation

Q: What is the clinical evidence from this study?

Study design: Other. Population: Healthy (n=10). Intervention: Single 1-s isometric forearm contractions at varying intensities (5-70% MVC) and arm positions vs. Arm above heart (AH) vs arm below heart (BH) positions. Primary outcome: Immediate increases in forearm blood flow (FBF) (slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH, p=<0.05).

MTMichael E. TschakovskyPreventive Cardiology ARAnna RogersEarlham Institute KPKyra E. PykeUniversity of Alberta

Key Result

Single 1-s isometric forearm contractions produced immediate increases in forearm blood flow proportional to intensity, which were greater in below-heart vs above-heart positions (P<0.05).

Key Points

To determine whether rapid vasodilation proportional to contraction intensity drives immediate exercise hyperemia during the first cardiac cycle following a single isometric contraction.
Ten healthy subjects (N=10) performed single 1-s isometric forearm contractions across varying intensities (5%, 10%, 15%, 20%, 30%, 50%, and 70% of maximal voluntary contraction [MVC]) with the arm positioned above heart (AH) and below heart (BH) levels.
Forearm blood flow (FBF) was measured beat by beat using Doppler ultrasound alongside continuous arterial tonometry for blood pressure and strain-gauge plethysmography for venous emptying.
Forearm venous emptying was fully maximized at 5% MVC, indicating that greater contraction intensities did not further augment venous drainage.
Immediate FBF increased linearly with contraction intensity in the AH position (slope = 4.4 ± 0.5%ΔFBF/%MVC) and curvilinearly in BH, with BH showing significantly greater immediate and peak FBF increases compared to AH across 15–50% MVC (P < 0.05).

Structured PICO

Does contraction intensity determine immediate exercise hyperemia in healthy subjects?

Population

10 healthy subjects performing single 1-s isometric forearm contractions at varying intensities and arm positions.

Intervention

Single 1-s isometric forearm contractions at 5, 10, 15, 20, 30, 50, and 70% maximal voluntary contraction intensity (MVC) in arm above heart (AH) and below heart (BH) positions

Comparator

Different contraction intensities (5-70% MVC) and arm positions (AH vs BH)

Outcome

Forearm blood flow (FBF) measured beat by beatsurrogate

Immediate exercise hyperemia is proportional to contraction intensity, supporting the existence of rapid-acting vasodilatory mechanisms at the onset of human forearm exercise.

Main Result

Effect estimate: slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH

p-value: p=<0.05

Abstract

We tested the hypothesis that rapid vasodilation proportional to contraction intensity contributes to the immediate (first cardiac cycle after initial contraction) exercise hyperemia. Ten healthy subjects performed single 1-s isometric forearm contractions at 5, 10, 15, 20, 30, 50, and 70% maximal voluntary contraction intensity (MVC) in arm above heart (AH) and below heart (BH) positions. Forearm blood flow (FBF; brachial artery mean blood velocity, Doppler ultrasound), mean arterial pressure (arterial tonometry), and heart rate (electrocardiogram) were measured beat by beat. Venous emptying (measured with a forearm strain gauge) was already maximized at 5% MVC, indicating that increases in contraction intensity did not further empty the forearm veins. Immediate increases in FBF were linearly proportional to contraction intensity from 5 to 70% MVC in AH (slope = 4.4 +/- 0.5%DeltaFBF/%MVC). In BH, the immediate increase in FBF demonstrated a curvilinear relationship with increasing contraction intensity and was greater than AH at 15, 20, 30, and 50% MVC (P < 0.05). Peak changes in FBF were greater in BH vs. AH from 10 to 50% MVC, even when venous refilling was complete (P < 0.05). These data support the existence of a rapid-acting vasodilatory mechanism(s) at the onset of human forearm exercise.

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Cite This Study

Tschakovsky et al. (Sat,) conducted a other in Healthy (n=10). Single 1-s isometric forearm contractions at varying intensities (5-70% MVC) and arm positions vs. Arm above heart (AH) vs arm below heart (BH) positions was evaluated on Immediate increases in forearm blood flow (FBF) (slope = 4.4 +/- 0.5%DeltaFBF/%MVC in AH, p=<0.05). Single 1-s isometric forearm contractions produced immediate increases in forearm blood flow proportional to intensity, which were greater in below-heart vs above-heart positions (P<0.05).

synapsesocial.com/papers/6a6d0a73439bab0cabc28c85 https://doi.org/https://doi.org/10.1152/japplphysiol.00769.2003

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