Specific airway resistance is overestimated during tidal breathing vs panting in healthy children

Rationale: Modern plethysmographic equipments allow the measurement of specific airway resistance (sRaw) during tidal breathing (tb), a potentially useful technique in children unable to perform the panting maneuver (p), a reference technique to minimize the thermal artifact. Equipment softwares are implemented with algorithms to correct for this artifact when computing sRawtb. It is not known how well this correction performs with reference to sRawp in children. The hypothesis tested here is that both techniques provide similar estimates of sRaw. Objective: To compare sRawtb and sRawp in children. Methods: sRawtb and sRawp were measured in 6 healthy children aged 7-10 years, using a commercially available pressure plethysmograph. Results: sRawtb (mean ± sd = 10.4±2.0 hPa·sec; breathing rate = 0.5±0.1 Hz) was significantly larger (p=0.006) than sRawp (5.8±2.2 hPa·sec, breathing rate = 3.1±0.5 Hz). The finding hold true for Raw computed from the associated measurement of thoracic gas volume (Rawtb = 6.3±1.2 hPa·sec/L; Rawp = 2.9±1.0 hPa·sec/L, p=0.005). Conclusion: sRaw is significantly overestimated by tb as compared with p. This is possibly explained by non instantaneous changes of gas temperature and humidity in the airways, a fact that may not be taken into account in the correction algorithm. The impact of overestimating sRawtb's - and hence Rawtb - on routine airway function testing in patients has to be identified.