The forced vital capacity (FVC) maneuver used in pulmonary function testing (PFT) allows the subject to inhale to total lung capacity (TLC) with a breath hold and then exhale forcibly. The maneuver of lung volume history done in Impulse Oscillometry (IOS) entails quiet deep inhalation to TLC followed by quiet exhalation. It is known that FVC maneuver results in decreased maximal expiratory flow especially in patients with COPD and hyper-reactive airways. The following questions were evoked; does the decrease in expiratory flow associated with FVC maneuver occur with lung volume history maneuver in IOS as well? Is that decrease in expiratory flow associated with a comparable increase in airway resistance measured in IOS? And if so, how do different pulmonary diseases influence its magnitude? The aim of this study is to determine if there is a significant difference in the indices of airway resistance measured in IOS during both normal and deep (lung volume history) breathing in normal individuals and in patients with abnormal PFT.
163 patients were included in the study. All patients had a conventional PFT and IOS performed on the same day. Based on TLC, FEV1/FVC ratio, FEF25-75%, post-bronchodilator response; patients were categorized as; restrictive, obstructive, mixed, small airway disease, and normal. Indices of airway resistance in IOS (central and peripheral resistance, resonance frequency, Resistance at 5Hz and 20 Hz) were compared between act-1(normal breathing) and act-2(post- volume history) using wilcoxon signed ranks test.
There was no statistically significant difference in resistance indices in the IOS between act-1 and act-2 neither in the total population nor in any of the categories (P >0.05).
Lung volume history maneuver neither increases central or peripheral airway resistance in normal individuals or in patients with pulmonary function abnormalities.
IOS provides a technique for assessment of airway resistance without the technique significantly influencing the results. Lung volume history does not produce significant alteration in airway resistance and thus can be utilized in different pulmonary assessments.
H.F. Ghali Hana, None.