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Respiratory system reactance reflects communicating lung volume in chronic obstructive pulmonary disease
Stephen Milne1,2,3, Kanika Jetmalani1, David G Chapman1,4
1The Woolcock Emphysema Centre and Airway Physiology and Imaging Group, Woolcock Institute of Medical Research and Sydney Medical School, University of Sydney, Glebe, New South Wales , Australia.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|February 15, 2019
Summary
Respiratory system reactance (Xrs) measured by the forced oscillation technique (FOT) in chronic obstructive pulmonary disease (COPD) relates to communicating lung volume, not absolute lung volume. This finding clarifies FOT interpretation in COPD.
Area of Science:
- Pulmonary Physiology
- Respiratory Mechanics
- Diagnostic Techniques
Background:
- Respiratory system reactance (Xrs), measured by the forced oscillation technique (FOT), is theoretically linked to lung volume.
- In chronic obstructive pulmonary disease (COPD), a portion of lung volume may be non-communicating, potentially affecting the Xrs-volume relationship.
- Previous studies suggest Xrs reflects lung characteristics, but its precise relationship with lung volume in COPD requires further elucidation.
Purpose of the Study:
- To investigate the determinants of respiratory system reactance (Xrs) in chronic obstructive pulmonary disease (COPD).
- To examine the relationship between Xrs and different measures of lung volume in COPD patients and healthy individuals.
- To determine if Xrs relates to absolute lung volume or communicating lung volume in COPD.
Main Methods:
- Collected forced oscillation technique (FOT) and lung function data from 51 individuals with COPD and 40 healthy volunteers.
- Measured respiratory system reactance at 5 Hz (X5) and functional residual capacity via body plethysmography (FRCpleth).
- Assessed expiratory reserve volume (ERV) and single-breath alveolar volume (VaSB) as estimates of communicating lung volume.
Main Results:
- Healthy volunteers exhibited an inverse relationship between X5 and FRCpleth, as expected.
- COPD subjects showed no significant relationship between X5 and FRCpleth.
- In COPD, X5 demonstrated an inverse relationship with both ERV and VaSB, indicating a correlation with communicating lung volume.
Conclusions:
- The theoretical Xrs-volume relationship is preserved in COPD but is dependent on communicating lung volume, not absolute lung volume.
- Reduced communicating lung volume is a key determinant of Xrs in COPD.
- These findings enhance the understanding and interpretation of FOT measurements in COPD and potentially other pulmonary diseases.
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