Impedance pneumography for assessment of a tidal breathing parameter in patients with airway obstruction

Introduction: Short-term tidal breathing analysis (TBA) parameters, like tptef:te, have indicated change in airway obstruction level in pediatric subjects, to whom conventional PFTs are inapplicable. Nocturnal TBA could provide new means for differential diagnosis and phenotyping of pediatric asthma. Recently, ambulatory impedance pneumography (IP) was reported to accurately estimate tptef:te in healthy subjects (Seppa, V.-P. et al. Chest 2010; 138(4S):816A). Objectives: Assess the agreement between a direct pneumotachograph (PNT) measurement and the indirect IP measurement in estimating the tptef:te parameter in patients with suspected airway obstruction. Methods: A simultaneous 3-minute tidal breathing recording of PNT and IP was conducted on 35 patients referred for spirometry in Tampere University Hospital. Reliable IP measurements were obtained from 27 subjects (age 18-65) having FEV1pred% mean 75% (range 26-103%) and BMI 24.8 (16.7-31.0). Agreement between methods was evaluated using the Bland-Altman analysis. Results: The agreement between the methods was found very good with mean difference 0.00 and 95% CI -0.10, +0.10. The agreement remained high throughout the encountered range of tptef:te values and it did not degrade in patients with more severe airway obstruction (n=6, FEV1pred% ≤60%). Conclusion: IP was found suitable for assessing a tidal breathing parameter regardless of presence of an airway obstruction.