Pressure sensor plethysmography: a method for assessment of respiratory motion in children

Noncalibrated respiratory inductance plethysmography has been used to measure respiratory function by calculation of the phase angle and, more recently, by determination of the ratio of each time to reach peak tidal expiratory flow to total expiratory time (TPEF/TE). Since TPEF/TE is known to be decreased in airway obstruction when derived from flow signals obtained by a pneumotachograph, we wanted to develop an alternative method to measure rib cage and abdominal respiratory movements. For this purpose, we used two pressure sensors attached to the skin above the umbilicus and in the right medioclavicular line at the fourth intercostal space: "pressure sensor plethysmography". We tested the ability of this method to assess thoracoabdominal asynchrony and TPEF/TE by comparison with respiratory inductance plethysmographic and pneumotachographic measurements in 30 children, aged 1-12 yrs, with airway obstruction. The mean difference (95% confidence interval (95% CI)) between phase angles obtained by respiratory inductance plethysmography and pressure sensor plethysmography was only -5.8 degrees (range -18.0 to +6.4 degrees). Similarly, all methods used to measure TPEF/TE agreed well: mean differences (95% CI) between pneumotachographic and respiratory inductance plethysmographic, pneumotachographic and pressure sensor plethysmographic, and respiratory inductance plethysmographic and pressure sensor plethysmographic measurements of TPEF/TE were +0.01 (range -0.05 to +0.06), -0.03 (-0.09 to +0.03) and -0.03 (-0.10 to +0.04), respectively. We conclude that pressure sensor plethysmography is a simple and noninvasive method, and suitable to measure thoracoabdominal asynchrony and TPEF/TE ratios as well as respiratory inductance plethysmography and pneumotachography.