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


  • Research support was provided by the Pittsburgh Mind-Body Center (National Institutes of Health Grant HL 076852/076858) and by National Institutes of Health Grant T32HL007560. We thank Charles Atwood, M.D., and the University of Pittsburgh Department of Pulmonary Medicine for their assistance and loan of the pneumotachograph.

Address correspondence to: Victoria Egizio, Western Psychiatric Institute and Clinic, 3811 O'Hara St., Room E1329, Pittsburgh, PA 15213, USA. E-mail:


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.