Assessing the calculation of conductive and acinar ventilatory heterogeneity indices S cond and S acin from multiple-breath washout data

• Published in: Journal of applied physiology (1985) 2023-04, Vol.134 (4), p.879-886
• Main Authors: Prisk, G Kim, Rutting, Sandra, Bozier, Jack, Thamrin, Cindy, Robinson, Paul D, Thompson, Bruce R
• Format: Article
• Language: English
• Subjects: Adult; Breath Tests - methods; Functional Residual Capacity; Humans; Lung; Respiration; Respiratory Function Tests - methods
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00423.2022

Sensor errors resulting in elevated values of N concentration [N ] in commercial multiple-breath washout (MBW) devices have been shown to prolong the washout and result in erroneously high functional residual capacity (FRC) and lung clearance index (LCI) values. The errors also affect the indices of conductive and acinar ventilatory heterogeneity ( and ) although the mechanism by which this change in values occurs remains unclear. Exploring these effects also provides a timely opportunity to examine the appropriateness of the algorithm used to calculate these indices. Using a two-compartment model with differing specific ventilation (SV) such that the lower SV unit empties late, noise-free MBW were simulated both corrected and uncorrected for the recent sensor error. was calculated using regression of normalized phase III slope (Sn ) against lung turnover (TO) from a TO range starting at 1.5 and ending at an upper turnover (TO ) between 4 and 8 (default 6) over a range of simulated values. The principal effect of the sensor error was that as the MBW proceeded the phase III slope of successive breaths was normalized by an increasingly overestimated [N ], resulting in Sn values that fell precipitously at high TO, greatly reducing . Reanalysis of previously published data and of simulated data showed a large proportional bias in , whereas was only minimally affected. In adult subject data, reducing TO below 5.5 was associated with a large drop of up to ∼60% in calculated from data corrected for sensor error. Raising the upper TO limit elevated by ∼20% but with a large concomitant increase in variability. In contrast to , was relatively unaffected by changes in TO with changes of