Efficient and cost-effective estimation of the influence of respiratory variables on respiratory sinus arrhythmia

Abstract

Researchers are interested in respiratory sinus arrhythmia (RSA) as an index of cardiac vagal activity. Yet, debate exists about how to account for respiratory influences on quantitative indices of RSA. T. Ritz, M. Thons, and B. Dahme (2001) developed a within-individual correction procedure by which the effects of respiration on RSA may be estimated using regression models. We replicated their procedure substituting a spectral high-frequency measure of RSA for a time-domain statistic and a respiratory belt's relative measure of tidal volume for the direct assessment provided by a pneumotachograph. The standardized slopes from the respiratory belt and pneumotachography-derived regression equations (estimated across a 6-min paced breathing protocol) were positively correlated (r=0.93, p<.001); correlations were similar across 2- and 4-min time courses parsed from the 6-min protocol. Our results offer methodological alternatives to the research community.

Figure 1

Diagrammatic view of likely sources of vagal influence on the heart, omitting central influences and emphasizing areas related to respiratory function.

Figure 2

Correlation between the slopes from the regressions of HF-HRV/V_T Pneumo and HF-HRV/V_T Belt upon T_TOT. Note. r = 0.93, p < 0.01.