Passive Expiration From Total Lung Capacity Can Estimate Expiratory Function in Infants A Retrospective Study.

Background: Evaluating expiratory airway function in infants is challenging because the criterion standard, the raised-volume rapid thoracoabdominal compression technique, is technically difficult and has a high failure rate.

Research question: Are measurements obtained during passive expiration from total lung capacity correlated with forced expiration measurements obtained by the raised-volume technique in infants?

Study design and methods: This observational retrospective analysis included infants born ≥ 36 weeks' gestation who underwent pulmonary function testing using the raised-volume rapid thoracoabdominal compression technique at Hadassah Medical Centre between January 2011 and December 2019. Technically acceptable forced and passive flow-volume curve measurements were included in the analysis.

Results: Out of 296 eligible infants, 276 (93%) had technically acceptable passive flow-volume curves, whereas 226 (76%) had acceptable forced curves (P < .001). The success rate of producing an acceptable curve was 70% for the passive curves and 39% for forced curves (P < .001). The Spearman correlation coefficients of vital capacity, expiratory volume at 0.5 seconds, maximal expiratory flow, and expiratory flow at 50%, 75%, and 85% of vital capacity were 0.92, 0.72, 0.83, 0.66, 0.67, and 0.68, respectively (n = 226; P < .001 for all). The correlation remained high regardless of the level of expiratory airway obstruction, sex, or age. The mean intermaneuver coefficients of variation were fairly low for both methods (5.2% vs 5.4%, P = not significant).

Interpretation: The passive flow-volume curve offers reliable and reproducible data with high correlation to the forced flow-volume curve. Therefore, the passive flow-volume curve can serve as an alternative tool in evaluating expiratory airway function in infants.