Respiratory sinus arrhythmia is associated with efficiency of pulmonary gas exchange in healthy humans

Abstract

. Respiratory sinus arrhythmia is associated with efficiency of pulmonary gas exchange in healthy humans. Am J Physiol Heart Circ Physiol 284: H1585-H1591, 2003. First published January 23, 2003 10.1152/ajpheart.00893.2002.-Respiratory sinus arrhythmia (RSA) may be associated with improved efficiency of pulmonary gas exchange by matching ventilation to perfusion within each respiratory cycle. Respiration rate, tidal volume, minute ventilation (V E), exhaled carbon dioxide (V CO2), oxygen consumption (V O2), and heart rate were measured in 10 healthy human volunteers during paced breathing to test the hypothesis that RSA contributes to pulmonary gas exchange efficiency. Cross-spectral analysis of heart rate and respiration was computed to calculate RSA and the coherence and phase between these variables. Pulmonary gas exchange efficiency was measured as the average ventilatory equivalent of CO2 (V E/V CO2) and O2 (V E/V O2). Across subjects and paced breathing periods, RSA was significantly associated with CO2 (partial r ϭ Ϫ0.53, P ϭ 0.002) and O2 (partial r ϭ Ϫ0.49, P ϭ 0.005) exchange efficiency after controlling for the effects of age, respiration rate, tidal volume, and average heart rate. Phase between heart rate and respiration was significantly associated with CO 2 exchange efficiency (partial r ϭ 0.40, P ϭ 0.03). These results are consistent with previous studies and further support the theory that RSA may improve the efficiency of pulmonary gas exchange.heart rate variability; phase; ventilatory equivalent RESPIRATORY SINUS ARRHYTHMIA (RSA), the increase and decrease in heart rate within each respiratory cycle, occurs mainly as a result of fluctuations of parasympathetic output to the heart, although sympathetic outflow also may influence variability (26). During inspiration, impulses originating in stretch receptors in the lungs travel via the vagi to inhibit the cardioinhibitory area in the medulla. The tonic vagal discharge that keeps the heart rate slow decreases, and the heart rate rises. The degree to which this modulation occurs is a function of the level of tonic vagal discharge and blood pressure (9, 21). Thus measures of RSA are frequently used as an index of vagal tone (e.g., 2,12,19,20).Certain features of respiratory mechanics also affect the amplitude of RSA independent of changes in vagal tone. For example, changes in respiration rate and, to a lesser extent, tidal volume (V T ) can affect the magnitude of RSA in the absence of any change in tonic vagal activity (8,11,15,23). This slowing of respiration rate and increase in V T are believed to allow more time for the action of acetylcholine on muscarinic receptors at the sinoatrial node during exhalation (7, 25a). Other influences on the genesis and magnitude of RSA include feedback from arterial baroreceptors, a central rhythm generator in the brain stem, and intracardiac reflexes (3).Although a great deal of research has been published concerning the physiological mechanisms mediating RSA, the question of what function, if any, RSA serv...

Indirect measures of human vagal withdrawal during head-up tilt with and without a respiratory acidosis

“…Data shown are from a male (28 years) and the mean heart rate was 53 beats min -1 with HF and LF components of 56.8 NU and 39.1 NU respectively, when supine. During HUT, the mean heart rate was 86 beats min -1 with HF and LF components of 28.6 NU and 63.4 NU respectively J Physiol Sci (2009) 59: 31-36 33 ventilation, as shown by others [23][24][25][26][27]. Also, in the current study, a decrease in HF cardiac variability was shown with HUT, again similar to the findings of others [14,[18][19][20]33].…”

“…Others [5] reported that during HUT, tidal volume was slightly lower when ventilation was controlled with a metronome (0.33 Hz), and this resulted in no accompanying changes in transcutaneous P CO 2 . An improvement in alveolar gas exchange efficiency may have contributed to the lowering of PET CO 2 with HUT in the study by Cooke et al [14], but this would suggest an increase in respiratory sinus arrhythmia [26,36] and a concomitant increase in the HF component of HRV. However, Cooke et al [14] reported a decrease in HRV at respiratory frequency with head-up tilt, consistent with the findings of the present study.…”

“…However, directional changes in the LF component of HRV with tilting appear equivocal, with no change [14,18,21] or an increase [19,20,22] being reported for healthy subjects. Hypercapnia has consistently been shown to increase HF cardiac variability [7,[23][24][25], suggestive of an increase in respiratory sinus arrhythmia [24,[26][27][28] but shown to have variable effects on LF variability [29].…”

Vagal nerve activity contributes to improve the efficiency of pulmonary gas exchange in hypoxic humans

“…We could demonstrate an increase in alveolar dead space accompanied by a decrease in RSA magnitude. Giardino et al (2003) magnitude was positively associated with pulmonary gas exchange efficiency, measured as the average ventilatory equivalent of CO 2 and O 2 , in humans, and concluded that RSA might improve the efficiency of pulmonary gas exchange.…”

Respiratory sinus arrhythmia and pulmonary gas exchange efficiency: time for a reappraisal

“…This 'theory' has important clinical applications, and may partly account for the association between low RSA and a variety of cardiovascular/cardiopulmonary risk factors and disease processes (see references in the article by Sin et al 2010). Nevertheless, while the pioneering demonstrations in dogs (Hayano et al 1996) and humans (Giardino et al 2003) were appealing, recent findings by Tzeng, Galletly, Larsen and co-workers came, with time, to question Hayano's views (e.g. Tzeng et al 2007Tzeng et al , 2009).…”