Rationale: Analysis of maximal expiratory flow-volume curves (MEFVCs) allows for determination of airway obstruction, but quantitative methods to describe these curves are not commonly used.Objectives: We sought to determine the variability in MEFVC concavity assessment by pulmonary physicians, whether objective indices of concavity can be substituted for subjective expert impression, and whether MEFVC concavity correlates with clinical outcomes.Methods: A survey of 37 MEFVCs (plus 3 duplicates) was sent to pulmonologists for quantitative assessment of MEFVC concavity. Objective indices (b-angle, ratio forced expiratory flow at 50% of total lung volume to peak expiratory flow rate [FEF 50 /PEFR], ratio of maximum mid-expiratory flow to FVC [MMEF/FVC], k max , and averaged flow-volume second derivatives) were calculated for each MEFVC and were correlated with the mean expert score. Both the mean expert scores and the best-performing index were then correlated with hospitalizations.Measurements and Main Results: Ninety-two respondents provided usable data. There was substantial variability in concavity scores between subjects, but strong intrasubject reliability. Mean expert score did not differ by physician years of experience. Several indices (b-angle, FEF 50 /PEFR, FEV 1 /FVC, MMEF/FVC, FEF 50 , and forced expiratory flow between 25 and 75% of total lung volume) correlated strongly with mean expert scores. A new variable (b-MMEF) was constructed using coefficients from stepwise linear regression and accurately predicted the mean expert score (R 2 = 0.96). Mean expert score and b-MMEF showed similar odds ratios for hospitalization (2.13 and 2.32, respectively) with identical positive (z71%) and negative (87%) predictive values. The b-MMEF was also associated with hospitalizations in two independent cohorts of children with asthma and cystic fibrosis. Conclusions:The b-MMEF is an objective measure of maximal expiratory flow-volume curve concavity and highly correlates with expert impression. Both the mean expert score for expiratory curve concavity and the b-MMEF were associated with increased risk of subsequent hospitalization. The b-MMEF may be a useful biomarker for disease severity in asthma and cystic fibrosis.

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Introduction High‐frequency chest compression (HFCC) is used for airway clearance, but may have other effects. We sought to determine if HFCC provides augmented ventilation. Methods During treatment, capnometry was measured with the HFCC vest set to 6‐20 Hz. End‐tidal CO2 (etCO2) was compared using generalized estimating equations. Results Twenty‐four measurements were obtained from 15 subjects with mean age 15.2 ± 2.5 years and forced expiratory volume in one second (FEV1) % predicted 70 ± 23. EtCO2 decreased with HFCC at 6 Hz when compared with baseline (P < .001), with small changes with increasing oscillation frequency. Change in etCO2 was not predicted by FEV1, body mass index, age, or sex. Conclusions While HFCC has been shown to be a suitable method of airway clearance, investigators have failed to demonstrate differences between techniques. Assessment of these methodologies will become important as new airway clearance devices are proposed. Other outcome measures (besides FEV1) may be needed to assess effects of airway clearance, and we propose that physiologic measures might be one such measure which deserves further exploration.

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