Evaluating the physiological significance of respiratory sinus arrhythmia: looking beyond ventilation–perfusion efficiency

Key points  •  Respiratory sinus arrhythmia (RSA) is the variation of heart rate with breathing: heart rate increases during inspiration and decreases during expiration. •  RSA is seen in many species including humans where it is strongest in the young and fit. The loss of RSA has been linked with cardiac mortality; however, the function of RSA is presently unknown. •  One hypothesis proposed previously is that RSA allows for more efficient gas exchange between the lungs and the blood. •  Our theoretical study does not support this hypothesis. Instead, a new hypothesis is proposed and tested using computational tools – that RSA helps the heart do less work while maintaining healthy levels of blood gases. •  Of course, this new hypothesis needs to be further tested both experimentally and by using more sophisticated mathematical models, but if correct, it could explain why inducing RSA artificially in patients with cardiovascular disease improves their health.