Arterial Chemoreflex influence in Cardiac Energetics
Authors: Apura Joao , Rocha Isabel , Pinto Fausto J , Sequeira Adelia , Bras‐Rosario Luis 
Published: November 2023

The arterial chemoreflex is a negative feedback mechanism that regulates the ventilatory responses to changes in arterial oxygen and carbon dioxide concentrations, sensed by carotid chemoreceptors. Whenever the arterial pressure of oxygen increases above a critical level, parasympathetic nervous activity increases, contributing a decrease in heart rate and arterial blood pressure. As the chemoreflex influences cardiac output to compensate for changes in oxygen arterial pressure, we hypothesized that it must influence the mechanical interaction between the left ventricle and the arterial tree, as well as cardiac energy consumption and efficiency.

The ventriculo‐arterial coupling was evaluated on a beat‐per‐beat basis, upon the application of lobeline in the left‐carotid sinus of anesthetized, paralyzed and artificially ventilated rabbits. An intraventricular impedance catheter was used to measure simultaneously ventricular pressure and volume. All experiments were performed according to national laws and international guidelines.

We designed a custom software to characterize single‐beat left‐ventricular and arterial physiologic properties. From this data, left‐ventricle end‐systolic elastance (Ees), arterial elastance (Ea) and the coupling ratio (Ea/Ees) were computed to analyze ventriculo‐arterial coupling. We also calculated left‐ventricular stroke work (SW), total energy expenditure (PVA), ratio of the SW to its theoretical maximum (Qload) and cardiac work efficiency (CWE=SW/PVA).

Upon the application of the carotid chemoreflex, Ees and Ea both increased, though without any noticeable change in their coupling ratio (Ees/Ea). Stroke work and total energy consumption (oxygen demand) both decreased, without sacrifice of the mechanical and energetic efficiency of the heart. Ventriculo‐arterial coupling was maintained in the interval of optimal cardiac efficiency. For statistical analysis with paired Student's t‐test, please refer to Table 1.

In conclusion, the arterial chemoreflex is a control mechanism of the cardiovascular system that exerts a feedback modulation on ventilatory responses through an increase in both cardiac contractility and arterial input impedance, in such a balance that ventriculo‐arterial coupling, mechanical and energetic efficiency are maintained between optimal values. This approach can now be applied to test acute interventions on the circulatory system, including diseases such as myocardial infarction, drug and device therapy.

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PHYSIOMAT ‐ Modelação Matemática e Computacional da Fisiologia Humana (2013) Fundação para a Ciência e Tecnologia EXCL/MAT‐NAN/0114/2012

Mean and standard deviation of cardiac parameters before and after lobeline injection, and p‐values from paired Student's t‐test.

baseline (20 beats)
after injection (20 beats)
p‐value (paired t‐test)

Arterial pressure
mmHg
92 ± 3.258
102 ± 6.283
<0.001

Instantaneous Heart Rate
bpm
243 ± 0.923
235 ± 4.528
<0.001

Arterial elastance (Ea)
mmHg/mL
71.143 ± 3.085
79.450 ± 6.195
<0.001

End‐systolic elastance (Ees)
mmHg/mL
59.736 ± 1.990
71.001 ± 6.423
<0.001

Ventriculo‐arterial coupling (Ea/Ees)
‐
1.188 ± 0.062
1.142 ± 0.097
0.23

Ejection fraction (EF)
%
45 ± 1.289
47 ± 1.262
0.22

Stroke volume (SV)
mL
1.456 ± 0.034
1.221 ± 0.135
<0.001

Stroke work (SW)
mmHg*mL
148.621 ± 4.717
136.506 ± 10.595
<0.001

Total energy expenditure (PVA)
mmHg*mL
234.629 ± 9.483
219.733 ± 16.439
0.001

Stroke work to its maximum (Qload)
‐
0.992 ± 0.005
0.994 ± 0.004
0.20

Cardiac work efficiency (CWE)
%
63 ± 0.012
62 ± 0.033
0.15