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Brain & Heart

ORIGINAL RESEARCH ARTICLE
Respiratory sinus arrhythmia in humans:

Correlation analysis with breathing-specific
heart rate

Jacopo P. Mortola*

Department of Physiology, Faculty of Medicine, McGill University, Montreal, Quebec, Canada

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 (f resp), 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) (f h) allow
for quasi-continuous blood flow. Based on experimental findings in dogs, it has
been suggested that an elevated f h 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 f h (ΔHR’ = HR’ peak – HR’ trough) and the breathing-specific f h (f h/f resp). 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 (f h, f resp, HR’ peak, and HR’ trough). A strong statistically significant
*Corresponding author:
Jacopo P. Mortola (r > 0.9) correlation between f h/f resp and ΔHR’ was observed. These findings support
(jacopo.mortola@mcgill.ca) the hypothesis that RSA may be a mechanism for improving the match between the
quasi-continuous blood flow and the intermittent airflow.
Citation: Mortola JP. Respiratory
sinus arrhythmia in humans:
Correlation analysis with breathing-
specific heart rate. Brain & Heart. Keywords: Cardiac arrhythmia; Cardiorespiratory design; Parasympathetic control;
2024;2(4):3956. Pulmonary gas exchange; Ventilation-perfusion matching
doi: 10.36922/bh.3956
Received: June 17, 2024
Accepted: October 29, 2024
1. Introduction
Published Online: December 2,
2024 The acceleration of the heart during inspiration, known as respiratory sinus arrhythmia
(RSA), is perhaps the most recognized and most benign form of cardiac arrhythmia.
Copyright: © 2024 Author(s).
1
This is an Open-Access article Documented nearly two centuries ago, RSA can often be detected through simple
distributed under the terms of the auscultation or by palpating pulses at the wrist. The heart rate (HR) (f h) accelerates
Creative Commons Attribution synchronously with inspiration due to the temporary inhibition of the nucleus
License, permitting distribution,
and reproduction in any medium, ambiguus (the cardioinhibitory center), which results in the inhibition of the vagal
provided the original work is (parasympathetic) output to the sinoatrial node of the heart and a shortening of the
properly cited. inter-beat interval (IBI). The inspiratory inhibition of the nucleus ambiguus arises from
Publisher’s Note: AccScience peripheral inputs sensing changes in intrathoracic pressure or lung expansion, as well
Publishing remains neutral with as from central inputs, involving direct interaction between the respiratory pattern
regard to jurisdictional claims in
published maps and institutional generator in the nucleus of the tractus solitarius and the nucleus ambiguus. Since the
2,3
affiliations. early work in the 1930s, many experiments have investigated the relative contributions
Volume 2 Issue 4 (2024) 1 doi: 10.36922/bh.3956