Intraindividual variability of infant whole-body plethysmographic measurements: Effects of age and disease

The intraindividual variability of whole-body plethysmographic measurements was studied in a large series of consecutive infants (N = 144), divided in to two groups: a group of infants born very prematurely (PM, N = 63), with (N = 28) or without (N = 35) a history of bronchopulmonary dysplasia (BPD), and a group of infants with persistent respiratory symptoms (PRS, N = 81), i.e., wheezing (N = 53) or cough (N = 28). The intraindividual variability was determined within each test and between tests, separated by a 10-min i nterval. In both study groups, the between-test variability was significantly larger than that within tests. Expressed as the median coefficient of variation ( CV), the between-test repeatabilities in the PRS group were 8.0% for thorac ic gas volume (TGV), 17.5% for airway resistance (Raw), and 18.4% for speci fic airway conductance (sGaw), and in the PM group, 8.9% for TGV, 20.4% for Raw, and 20.7% for sGaw. However, the individual range of CVs was large, r anging from 3 to 19% for TGV and from 5 to 55% for sGaw. With respect to TG V, the difference between the groups was statistically significant (P = 0.0 3). In infants with a history of BPD, there was also a significant negative age dependency in CVs of sGaw (r = -0.50, P = 0.009), showing larger varia tion among younger individuals. The presenting symptom (wheezing or cough) in the PRS group did not influence the measurement variability significantl y, and neither did the degree of bronchial obstruction. We conclude that on a group basis, the repeatability of infant body plethys mographic measurements may be satisfactory for scientific studies demonstra ting pharmacodynamic effects; however, the intraindividual measurement vari ability should be reported for each test conditions and for infant groups i n each study. Due to the large range in individual variation and the influe nce of age and disease processes on the variation, for an individual child there is only questionable benefit from a given measurement, unless the int rasubject, between-test variability is assessed individually before interve ntions, such as a bronchodilation test. Pediatr Pulmonol. 1999; 28:356-362. (C) 1999 Wiley-Liss, Inc.