Effect of Postural Changes on Cardiorespiratory Coordination in Humans

In this study we assessed the effect of body postural changes from the supine (Sup) to the upright (Up) position on the magnitude and phase of respiratory sinus arrhythmia (RSA) and the phase-locking between the heart rhythm and respiration. In eight healthy human subjects, electrocardiograms (ECG) and respiratory signals were recorded. The magnitude and phase of RSA were evaluated by selective averaging of R-R interval changes from multiple respiratory cycles over the respiratory phase. For the assessment of cardiorespiratory coordination, we analyzed the phase-locking between heart rate, computed from R-R intervals of ECG, and respiratory rate, computed from intervals of inspiratory onsets of respiration, using Hilbert transform. A significant decrease in the magnitude of RSA and percentage and duration of phase-locking between heart rate and respiratory rate was observed during Up as compared to Sup. Further, there was a significant increase in the phase of RSA during Up as compared to Sup. In conclusion, measures of RSA and interaction between cardiac and respiratory rhythms are affected by body posture in humans.