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Cardiac chemoreflex control of cardiac stroke work and energy consumption

Apura, J.; Rosário, Luís Brás; Pinto, F.; Rocha, I.; Sequeira, Adélia

FASEB Journal, 30(1) (2016), S. 1286.5

The activation of cardiac chemosensitive receptors elicit the Bezold-Jarish reflex, which triggers parasympathetic activity and inhibits sympathetic activity, resulting in bradycardia and decreased arterial pressure. This is a cardioprotective reflex, strongly amplified by products of acute myocardial ischemia and its effect has been extensively evaluated on heart rate and arterial pressure. Cardiac stroke work and total energy consumption are tightly regulated and we hypothesized that the Bezold-Jarish reflex can participate in this regulation.

In anesthetized, paralyzed and artificially ventilated rabbits the Bezold-Jarish reflex was evoked by cardiac injection of ATP. An intraventricuar impedance catheter was used to measure simultaneously ventricular pressure and volume. All experiments were performed according to national laws and international guidelines.

We employed this pressure-volume framework to characterize left ventricular and arterial physiologic properties. We designed a custom software to compute single beat left ventricle end-systolic elastance (Ees), arterial elastance (Ea) and their ratio (Ees/Ea) to analyze ventriculo-arterial coupling. From this data we calculated left ventricular stroke work (SW), total energy expenditure (PVA), ratio of the SW to its theoretical maximum (Qload) and energetic efficiency (Eff=SW/PVA).

Statistical analysis with paired Student’s t-test of our results (Table 1) show a significant increase in Ees and a non significant decrease in Ea, without a major change in their coupling ratio (Ees/Ea). This resulted in a significant decrease in both SW and PVA with such a balance that Qload and Eff remained unchanged.

These results indicate that the Bezold-Jarish reflex participates in the regulation of the cardiac SW and PVA in a protective way that decreases oxygen demand. In fact previous work has shown that PVA is proporcional to total cardiac oxygen demand. This regulation of cardiac work and total energy consumption by the Bezold-Jarish reflex may protect the heart during ischemia. This protective decrease in SW and PVA by the Bezold Jarish is obtained without sacrifice of the energetic efficicency of the heart.