Cardiorespiratory coupling improves cardiac pumping efficiency in heart failure

Recent trials of a neuronal pacemaker have shown
that cardiac pumping efficiency increases when respiratory sinus
arrhythmia (RSA) is artificially restored in animal models of
heart failure. This novel device sheds new light on the functional
role of RSA, which has long been debated, by allowing the
strength of cardiorespiratory coupling to be artificially varied.
Here we show that RSA minimizes the cardiac power dissipated
within the cardiovascular network. The cardiorespiratory system
is found to exhibit mode-locked synchronized regions within
which viscoelastic dissipation is reduced relative to the scenario
where cardiorespiratory coupling is absent. We determine the
gain in cardiac output as the magnitude of RSA increases. We
find that cardiac pumping efficiency improves up and until the
cardiac frequency, within each breadth intake, is approximately
1.5 times greater than the cardiac frequency in the expiratory
phase, at which point it reaches a plateau. RSA was found to be
most effective at low cardiac frequencies, in good agreement with
clinical evidence. Simulation of the cardiac power saved under
RSA is in good agreement with the 17-20% increase in cardiac
output observed in RSA-paced animal models.