What is the clinical evidence from this study?

Population: Muscle metaboreflex activation during exercise (n=9). Intervention: Alpha1-adrenergic blockade (prazosin) vs. Control (no blockade). Primary outcome: Coronary vascular conductance during metaboreflex activation (ml·min⁻¹·mmHg⁻¹) (p=<0.05).

April 23, 2010Journal of Applied PhysiologyOpen Access

Muscle metaboreflex-induced coronary vasoconstriction functionally limits increases in ventricular contractility

Q: What are the key findings of this study?

Systemic alpha1-adrenergic blockade with prazosin during muscle metaboreflex activation resulted in significantly greater increases in coronary vascular conductance, circumflex blood flow, and ventricular contractility compared to control.

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Key result

Systemic alpha1-adrenergic blockade with prazosin during muscle metaboreflex activation resulted in significantly greater increases in coronary vascular conductance, circumflex blood flow, and ventricular contractility compared to control.

Why the study?

Does systemic alpha-1 adrenergic blockade improve coronary vasodilation and left ventricular contractility during muscle metaboreflex activation in exercising dogs?

Structured PICO

Does systemic alpha-1 adrenergic blockade improve coronary vasodilation and left ventricular contractility during muscle metaboreflex activation in exercising dogs?

Population

9 female mongrel dogs chronically instrumented to measure cardiovascular hemodynamics during mild exercise and muscle metaboreflex activation.

Intervention

Systemic alpha(1)-adrenergic blockade with prazosin (~50 microg/kg IV) during mild exercise (2 mph) with muscle metaboreflex activation (via partial inflation of terminal aorta occluder).

Comparator

Control experiments (mild exercise with muscle metaboreflex activation without prazosin) in the same dogs.

Outcome

Changes in coronary vascular conductance, circumflex blood flow, cardiac output, maximal derivative of ventricular pressure (dP/dtmax), and preload recruitable stroke work (PRSW).surrogate

Main Result

Absolute Event Rate: 0.64% vs 0.46%

p-value: p=<0.05

Sympathetic restraint of coronary vasodilation via alpha-1 adrenergic receptors functionally limits reflex increases in left ventricular contractility during exercise.

Limitations

Cardiac power is a relatively novel measure of cardiac function used as an index of myocardial oxygen consumption.
Left ventricular volume values calculated from sonomicrometry crystals underestimated stroke volume.
Systemic vasodilation occurred after alpha1-receptor blockade, which may reflect skeletal muscle vasodilation via epinephrine release.

Discussion

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Implication

May enhance coronary flow and contractility during metaboreflex; hypothesis-generating for human exercise physiology.

Cite This Study

Coutsos et al. (2010) studied Muscle metaboreflex activation during exercise (n=9). Alpha1-adrenergic blockade (prazosin) vs. Control (no blockade) was evaluated on Coronary vascular conductance during metaboreflex activation (ml·min⁻¹·mmHg⁻¹) (p=<0.05). Systemic alpha1-adrenergic blockade with prazosin during muscle metaboreflex activation resulted in significantly greater increases in coronary vascular conductance, circumflex blood flow, and ventricular contractility compared to control.

synapsesocial.com/papers/6a74e6a533d16877c7f5547a https://doi.org/10.1152/japplphysiol.01243.2009

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Muscle metaboreflex-induced coronary vasoconstriction functionally limits increases in ventricular contractility

Structured PICO

Main Result

Limitations

Discussion

Implication

Cite This Study

Muscle metaboreflex-induced coronary vasoconstriction functionally limits increases in ventricular contractility

Structured PICO

Main Result

Limitations

Discussion

Implication

Cite This Study

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