P253 Association between a computed cardiopulmonography (CCP) ventilation-inhomogeneity index and conventional markers of small-airway function

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Introduction Small airway dysfunction has gained increasing attention for its critical role in pathophysiological changes associated with chronic airway disease. Computed cardiopulmonography (CCP) is novel physiological technique: A bespoke molecular flow sensor measures accurate, highly-time-resolved respired gas composition and flow-rate data during a multiple breath washout test.2 These data enable the determination of patient-specific parameters describing respiratory physiology using a computational lung model. One such parameters, σlnCL, is a sensitive index of ventilation inhomogeneity that reflects the variability in lung inflation/deflation (alveolar compliance) across the lung. We hypothesise that σlnCL is a sensitive parameter indicating small-airway dysfunction. Aim To assess the association between σlnCL and conventional markers of small-airway dysfunction obtained using impulse oscillometry (Tremoflo) and spirometry. Method Forty asthmatic patients participated in this cross-sectional study. The average age was 56 ±15 years (mean ± S.D.) and 22(55%) were male. Patients had varying disease severity: 13(33%) patients were at GINA steps I-III, 18(45%) were at GINA IV-V (not on biologics) and 9 (22%) at GINA V on biologics. Patients were assessed using spirometry, oscillometry and CCP. Forced expiratory flow (FEF) 25–75 % predicted and R5–20 Z score were considered conventional assessments of small airway function. Spearman correlation was used to evaluate associations between each of these parameters and σlnCL. Results Figure 1 demonstrates our results. σlnCL is significantly correlated with both FEF25–75 % predicted (r = -0.52, p=0.0006) and R5–20 Z score (r = 0.63, p<0.0001). Conclusion The significant correlation between σlnCL and parameters of small airway dysfunction reveals its potential as a sensitive measure of physiological changes in the smaller airways in asthma. References DOI: 10.1152/japplphysiol.00745.2017. DOI: 10.1126/sciadv.1600560.

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