Closing volume detection by single-breath gas washout and forced oscillation technique

Abstract

Closing volume (CV) is commonly measured by single-breath nitrogen washout (CVSBW). A method based on the forced oscillation technique was recently introduced to detect a surrogate CV (CVFOT). As the two approaches are based on different physiological mechanisms, we aim to investigate CVFOT and CVSBW relationship at different degrees and patterns of airway obstruction. A mathematical model was developed to evaluate the CVSBW and CVFOT sensitivity to different patterns of airway obstruction, either located in a specific lung region or equally distributed throughout the lung. The two CVs were also assessed during slow vital capacity (VC) maneuvers in triplicate in 13 healthy subjects and pre and post-methacholine challenge (Mch) in 12 mild-moderate asthmatics. Model simulations suggest that CVSBW is more sensitive than CVFOT to the presence of few flow-limited or closed airways that modify the contribution of tracer-poor and tracer-rich lung regions to the overall exhaled gas. Conversely, CVFOT occurs only when at least ~65% of lung units are flow-limited or closed, regardless of their regional distribution. CVSBW did not differ between healthy subjects and asthmatics (17±9%VC vs 22±10%VC) while CVFOT did (16±5%VC vs 23±6%VC, p<0.01). In asthmatics, both CVSBW and CVFOT increased post-Mch (33±7%VC p<0.001 and 43±12%VC p<0.001, respectively). CVSBW weakly correlated with CVFOT (r=0.45, p<0.01). The closing capacities (CV+residual volume) were correlated (r=0.74, p<0.001) but the changes with Mch in both CVs and closing capacities did not correlate. CVFOT is easy to measure and provides a reproducible parameter useful for describing airway impairment in obstructive respiratory diseases.

Diagnostic Potential of Oscillometry: A Population-based Approach

“…These may suggest that inspiratory parameters better reflect intrinsic airway disease, in accordance with previous observations ( 49 ). The further increased presence of abnormal expiratory parameters and EFL T in COPD reflects dynamic airway narrowing that is due to a loss of elastic recoil becoming more evident at lower volumes ( 25 , 50 ). EFL T is associated with the highest risk of presenting respiratory diagnoses.…”

Oscillometry for personalizing continuous distending pressure maneuvers: an observational study in extremely preterm infants

“…Xrs may still be decreasing after 3 min at the lowest CDPs as slow lung derecruitment may occur [ 29 ]. Second, Xrs may not identify increasing inhomogeneity due to a small volume loss until significant lung derecruitment occurs [ 30 ].…”

Within-breath oscillometry for identifying exercise-induced bronchoconstriction in pediatric patients reporting symptoms with exercise

“…These may be the results of different mechanisms. The development of flow limitation in some airways ( 13 ), the lower elastic recoil, and higher collapsibility of the small airways at lower volumes ( 37 ) leads to higher ΔXrs both directly and indirectly by increasing heterogeneity during expiration. Our data showed that increased ΔXrs was not the result of a further Xrs exp decrease but of a faster Xrs insp recovery from the early postchallenge step fall.…”

“…There is increasing evidence that spirometry and oscillometry are not always in accordance as they describe lung mechanics under different conditions ( 6 , 12 , 37 ). Spirometry requires a high lung volume maneuver and FEV 1 reflects mainly airflow resistance of proximal airways ( 39 ).…”