Measurement of the specific airway resistance by plethysmography in young children accompanied by an adult

The purpose of this study was to evaluate a procedure for measurement of specific airway resistance (sRaw) by whole body plethysmography in young awake children accompanied by an adult. sRaw was measured by a single-step procedure, omitting the measurement of the thoracic gas volume. The frequency dependency of sRaw was investigated and the accuracy of simulating body temperature, atmospheric pressure and saturation with water vapour (BTPS) conditions by electronic compensation was assessed. One hundred and thirty one children with asthma were studied. In 57 children (mean (SD) age 5.6 (1.8) yrs) who performed measurements with and without an accompanying adult, the mean value of sRaw was 1.45 (0.36) and 1.44 (0.38) kPa x s, respectively, with a mean difference of 0.008 (0.152) kPa x s, and mean within-subject coefficients of variations (CV) of 8% and 10%, respectively. In 52 children (mean age 3.3 (0.8) yrs), for whom measurements made only in the presence of an accompanying adult, the CV was 8.5%. No measurements could be obtained in 22 children (17%) (mean age 2.8 (0.5) yrs). Measurements exhibited a significant frequency dependency, and electronic BTPS compensation substantially overestimated SRaw. In conclusion, the use of electronic compensation for simulating body temperature, atmospheric pressure and saturation with water vapour introduces a bias that affects the accuracy of the estimate of specific airway resistance. Nevertheless, plethysmographic measurements with and without an accompanying adult yielded comparable and equally repeatable estimates of specific airway resistance. The single-step plethysmographic procedure with an accompanying adult is a clinically useful method for evaluating airway function in children too young to perform plethysmographic measurements alone.