Respiratory sinus arrhythmia in humans: Correlation analysis with breathing-specific heart rate

Abstract

In adult humans at rest, pulmonary ventilation and cardiac output share similar values, both approximately 5 L/min. Airflow is intermittent, with tidal volumes exceeding dead space, low breathing frequency (fresp), and zero air velocity at both end-inspiration and end-expiration. In contrast, the cardiac pump is in series with the vasculature, such that the small stroke volume and high heart rate (HR) (fh) allow for quasi-continuous blood flow. Based on experimental findings in dogs, it has been suggested that an elevated fh during inspiration (known as respiratory sinus arrhythmia [RSA]) decreases the disparity between air and blood flow patterns. Thus, one might hypothesize a positive correlation between the peak-trough difference of instantaneous fh (ΔHR’ = HR’peak – HR’trough) and the breathing-specific fh (fh/fresp). To test this hypothesis, we combined breath-by-breath data for ΔHR’ from several previous studies, resulting in a database of over 600 subjects. This extensive dataset allowed us to construct statistically meaningful correlations between ΔHR’ and variables associated with RSA (fh, fresp, HR’peak, and HR’trough). A strong statistically significant (r > 0.9) correlation between fh/fresp and ΔHR’ was observed. These findings support the hypothesis that RSA may be a mechanism for improving the match between the quasi-continuous blood flow and the intermittent airflow.