Comparison of two methods of determining lung de-recruitment, using the forced oscillation technique

Airway closure has proved to be important in a number of respiratory diseases and may be the primary functional defect in asthma. A surrogate measure of closing volume can be identified using the forced oscillation technique (FOT), by performing a deflation maneuver and examining the resultant reactance (Xrs) lung volume relationship. This study aims to determine if a slow vital capacity maneuver can be used instead of this deflation maneuver and compare it to existing more complex techniques. Three subject groups were included in the study; healthy (n = 29), asthmatic (n = 18), and COPD (n = 10) for a total of 57 subjects. Reactance lung volume curves were generated via FOT recordings during two different breathing manoeuvres (both pre and post bronchodilator). The correlation and agreement between surrogate closing volume (Vol_crit) and reactance (Xrs_crit) at this volume was analysed. The changes in Vol_crit and Xrs_crit pre and post bronchodilator were also analysed. Across all three subject groups, the two different measures of Vol_crit were shown to be statistically equivalent (p > 0.05) and demonstrated a strong fit to the data (R² = 0.49, 0.78, 0.59, for asthmatic, COPD and healthy subject groups, respectively). A bias was evident between the two measurements of Xrs_crit with statistically different means (p < 0.05). However, the two measurements of Xrs_crit displayed the same trends. In conclusion, we have developed an alternative technique for measuring airway closure from FOT recordings. The technique delivers equivalent and possibly more sensitive results to previous methods while being simple and easily performed by the patient.