Maximal expiratory flow at FRC (V'maxFRC): Methods of selection and differences in reported values

Area of Science:

• Pediatric Pulmonology
• Respiratory Physiology
• Infant Lung Function Testing

Background:

• Maximal expiratory flow at functional residual capacity (V'maxFRC) is a key measure of lung function in infants.
• Standardized reporting methods are crucial for accurate interpretation of V'maxFRC in pediatric respiratory assessments.

Purpose of the Study:

• To compare three distinct methods for reporting V'maxFRC derived from partial expiratory flow-volume curves (PEFVCs) in asymptomatic infants.
• To assess the agreement and interchangeability of different V'maxFRC reporting methods.

Main Methods:

• PEFVCs were obtained using the rapid thoracoabdominal compression technique (RTC) in 281 infants.
• Three V'maxFRC reporting methods were analyzed: highest measured flow (maxV'FRC), mean of three highest flows (mean3V'FRC), and composite curve flow (compV'FRC).
• Bland-Altman analysis and regression against height were used to evaluate agreement and differences between the indices.

Main Results:

• maxV'FRC was numerically higher than mean3V'FRC (7.4%) and compV'FRC (11.9%).
• mean3V'FRC was higher than compV'FRC (5%).
• Bland-Altman analysis revealed mean differences and wide 95% limits of agreement between all three methods, indicating poor interchangeability.

Conclusions:

• Despite high correlation, maxV'FRC and mean3V'FRC are not interchangeable for reporting infant V'maxFRC.
• Composite curve analysis (compV'FRC) did not improve reproducibility and is not recommended for routine use in its current form.
• Accurate reporting of V'maxFRC requires careful consideration of the chosen measurement and analysis method in pediatric lung function studies.