Direct effect of PaCO2 on respiratory sinus arrhythmia in conscious humans

Author:

Sasano Nobuko1,Vesely Alex E.1,Hayano Junichiro2,Sasano Hiroshi1,Somogyi Ron1,Preiss David1,Miyasaka Kiyoyuki1,Katsuya Hirotada3,Iscoe Steve4,Fisher Joseph A.1

Affiliation:

1. Department of Anesthesia, University Health Network, University of Toronto, Toronto, Ontario, Canada M5G 2C4;

2. Third Department of Internal Medicine;

3. Department of Anesthesiology and Resuscitology, Nagoya City University Medical School, Nagoya, Japan 467-8601; and

4. Department of Physiology, Queen's University, Kingston, Ontario, Canada K7L 3N6

Abstract

Respiratory sinus arrhythmia (RSA) may improve the efficiency of pulmonary gas exchange by matching the pulmonary blood flow to lung volume during each respiratory cycle. If so, an increased demand for pulmonary gas exchange may enhance RSA magnitude. We therefore tested the hypothesis that CO2directly affects RSA in conscious humans even when changes in tidal volume (VT) and breathing frequency ( F B), which indirectly affect RSA, are prevented. In seven healthy subjects, we adjusted end-tidal Pco 2 (Pet CO2 ) to 30, 40, or 50 mmHg in random order at constant VT and F B. The mean amplitude of the high-frequency component of R-R interval variation was used as a quantitative assessment of RSA magnitude. RSA magnitude increased progressively with Pet CO2 ( P < 0.001). Mean R-R interval did not differ at Pet CO2 of 40 and 50 mmHg but was less at 30 mmHg ( P < 0.05). Because VT and F B were constant, these results support our hypothesis that increased CO2directly increases RSA magnitude, probably via a direct effect on medullary mechanisms generating RSA.

Publisher

American Physiological Society

Subject

Physiology (medical),Cardiology and Cardiovascular Medicine,Physiology

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