Validation of the thoracic impedance derived respiratory signal using multilevel analysis

J.H. Houtveen¹, P.F.C. Groot² and E.J.C. de Geus³

¹Department of Health Psychology, Utrecht University, The Netherlands
²Department of Instrumentation (ITM), Vrije Universiteit, Amsterdam, The Netherlands
³Department of Biological Psychology, Vrije Universiteit, Amsterdam, The Netherlands

The purpose of the current study was to validate the change in thoracic impedance (dZ) derived respiratory signal obtained from four spot electrodes against incidental spirometry. A similar validation was performed for a dual respiratory belts signal to compare the relative merit of both methods. Participants were 38 healthy adult subjects (half male, half female). Cross-method comparisons were performed at three (paced) respiration frequencies in sitting, supine, and standing postures. Multilevel regression was used to examine the within and between-subjects structure of the relationship between spirometric volume and the respiratory amplitude signals obtained from either dZ or respiratory belts. Both dZ derived respiratory rate and dual-belts derived respiratory rate accurately reflected the pacing frequencies. For both methods, fixed factors indicated acceptable but posture-specific regression on spirometric volume. However, random factors indicated large individual differences, which was supported by variability of gain analyses. It was concluded that both the dZ and dual-belts methods can be used for measurement of respiratory rate and within-subjects, posture-specific, changes in respiratory volume. The need for frequent subject-specific and posture-specific calibration combined with relatively large measurement errors may strongly limit the usefulness of both methods to assess absolute tidal volume and minute ventilation in ambulatory designs. Additionally, the results of an exploratory multilevel path analysis on this data set will be presented. This analysis was used to examine the extent to which changes in posture and respiration can confound the Pre Ejection Period (PEP) and Respiratory Sinus Arrhythmia (RSA) as indices of cardiac sympathetic and vagal activity.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.

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