Accuracy of ventilatory measurement employing ambulatory inductive plethysmography during tasks of everyday life

Ambulatory inductive plethysmography (AIP) has recently been introduced to permit monitoring of ventilation outside the clinic and laboratory. It provides a method for nonintrusive assessment of both timing (e.g. respiration rate; RR) and volumetric parameters (e.g. tidal volume and minute ventilation volume; V(T) and V'(E), respectively). Although inductive plethysmography has been validated in laboratory investigations, quantitative validation during ambulatory, naturalistic conditions has not yet been assessed. Should AIP yield accurate estimation of ventilatory parameters, real-life monitoring of breathing pattern may provide new insights into respiratory functioning in health and disease. We examined the accuracy of AIP for assessing RR, V(T) and V'(E) during a 90-min protocol simulating activities of everyday life. A mobile backpack metabolic cart with integrated flowmeter was employed as the reference standard. Within- and between-participant minute-by-minute comparisons were made for each ventilatory measure among 9 healthy adults. Average within-participant minute-by-minute correlations between reference method and AIP were 0.96, 0.91 and 0.92 for V'(E), V(T) and RR, respectively. Average correlations across participants yielded r's of 0.98, 0.98 and 1.0. Analysis of mean task levels across participants revealed, in all cases, very close correspondences between both methods of measurement, with only a significant but minor deviance during a period of supine posture. Additionally, results indicated that within-individual variations in oxygen consumption were highly correlated with AIP-estimated V'(E), suggesting that ambulatory assessment of V'(E) may provide a reliable index of metabolic activity during everyday life.