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Measuring Airway Resistance and Characterizing the Flow‐Volume Envelope with External Expiratory Loading in Healthy Adults
Author(s) -
Erram Jyotika,
Bari Monica,
Can Daniel
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.09394
Subject(s) - medicine , airway resistance , spirometry , copd , plethysmograph , bronchoconstriction , airway , lung volumes , airway obstruction , cardiology , anesthesia , pulmonary function testing , asthma , lung
Expiratory flow limitation is a key characteristic in chronic obstructive pulmonary disease (COPD). Increased airway resistance occurs due to bronchoconstriction, destruction of elastic tissue in the airways, and mucus hypersecretion from goblet cells caused by irritation of the epithelium. Obstruction can lead to dynamic hyperinflation, dyspnea, and exercise intolerance. However, increased airway resistance is just one of many abnormalities in COPD and asthma ‐ COPD in particular is an exceedingly heterogeneous disease. Therefore, isolating the effects of expiratory airflow limitation is challenging. PURPOSE In order to study abnormal lung mechanics in isolation, we measured pulmonary function with and without expiratory loading in healthy adults. METHODS Forty‐eight volunteers (26±5 yr, 171.8±10.2 cm, 72.2±13.3 kg) completed spirometry and body plethysmography according to the ATS/ERS standards under three randomized conditions: control, expiratory loading of 7 and 11 cmH 2 O. The expiratory load was added by installing a threshold inspiratory muscle trainer in reverse. We analyzed the shape of the flow‐volume (F‐V) loops with rectangular area ratio (RAR) using custom MATLab software. RESULTS Airway resistance was increased (F[1.5, 27.5]= 446.0, p<0.05) with 7 and 11 cmH 2 O vs control (9.20±1.02 and 11.76±1.68 cmH 2 O vs. 2.53± 0.80 cmH 2 O). RAR (F[1.9, 77.9]= 3.71, p>0.05) was reduced with 7 and 11 cmH 2 O vs control (0.45±0.07 and 0.47±0.09L vs. 0.48±0.08L). FEV1 was reduced (F[1.6, 60.38.6]= 67.54, p<0.05) with 7 and 11 cmH 2 O vs control (3.26±0.82 and 3.23±0.79L vs. 4.03±1.04L). FVC was also reduced (F[1.5, 55.31] = 77.71, p<0.05) with 7 and 11 cmH 2 O vs control (4.15±1.01 and 4.17±1.02L L vs. 5.05±1.33L L). PEF was reduced (F[1.5, 55.99] = 72.69, p<0.05) with 7 and 11 cmH 2 O vs control (6.02±1.65 and 5.95±1.85L vs. 8.39±2.85L L). FEV1/FVC (F[1.9, 69.17] = 5.5, p> 0.05) and FRC (F[1.863, 33.53]= 0.93, p<0.05) were not different between resistance conditions or compared to the control. CONCLUSIONS Expiratory loading reduced FEV1, FVC, PEF and provided a doseresponse in airway resistance and RAR. There were no differences in FEV1/FVC. While RAR was reduced with expiratory loading, the magnitude was of little clinical importance. Therefore, a concave expiratory F‐V relationship was consistently absent – a key limitation for model comparison with pulmonary function in COPD. This is most likely due to the imposed resistance being applied outside of the airways, leading to higher airway pressures. The higher airway pressures are likely to resist dynamic airway compression and either maintain the equal pressure point position or possibly move it proximally.