Reliability of respiratory inductive plethysmography for measuring tidal volume during exercise

This study was designed to determine the reliability of measurements of respiratory volumes obtained with a respiratory inductive plethysmograph (RIP) during exercise. Tidal volumes (VT) from the RIP were compared with simultaneous flowmeter volumes in 8 healthy subjects at 5 incremental work rates of 60, 90, 120, 150, and 180 W during cycling and treadmill exercise. During cycling, average RIP and flowmeter values did not differ significantly at work rates below 180 W for 63% of the subjects. Average RIP and flowmeter VT were similar at work rates below 180 W for 50% of the subjects, and for 83% of the subjects at intensities below 150 W. The variability in these results may be attributed to several factors including RIP calibration errors and slippage of the RIP elastic bands containing the inductive coils. Correlations of breath-by-breath flowmeter and RIP VT were significant for subjects during cycling (R = 0.73, P < 0.05) and treadmill exercise (R = 0.78, P < 0.05). These findings suggest that the RIP should be considered a semi-quantitative method for measurements of tidal volume during exercise with and without respirator wear.