Breath-by-breath quantification of progressive airflow limitation during exercise in COPD: A new method

Ma, Shuyi; Hecht, Ariel; Varga, Janos; Rambod, Mehdi; Morford, Sarah; Goto, Shinichi; Casaburi, Richard; Porszasz, Janos

doi:10.1016/j.rmed.2009.10.014

« Previous Next »Respiratory Medicine
Volume 104, Issue 3 , Pages 389-396, March 2010

Breath-by-breath quantification of progressive airflow limitation during exercise in COPD: A new method

Shuyi Ma
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA
Ariel Hecht
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA
Janos Varga
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA
Mehdi Rambod
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA
Sarah Morford
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA
Shinichi Goto
- Tokyo Women's Medical University School of Medicine, Tokyo, Japan
Richard Casaburi
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA
- Corresponding author. Tel.: +1 310 222 8200; fax: +1 310 222 8249.
Janos Porszasz
- Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson Street, Torrance, CA 90502, USA

Received 13 August 2009; accepted 19 October 2009. published online 23 November 2009.

Summary

During heavy exercise in chronic obstructive pulmonary disease (COPD), dynamic airways compression leads to a progressive fall in intrabreath flow. This is manifested by concavity in the spontaneous expiratory flow–volume (SEFV) curve. We developed a method to quantify the SEFV curve configuration breath-by-breath during incremental exercise utilizing a computerized analysis. The flow signal was digitized at 100Hz. For each breath's SEFV curve, points of highest flow () and end-expiration () were identified to define a rectangle's diagonal. Fractional area within the rectangle below the SEFV curve was defined as the “rectangular area ratio” (RAR); RAR <0.5 signifies concavity of the SEFV. To illustrate the utility of this method, time courses of RAR during incremental exercise in 12 healthy and 17 COPD individuals (FEV₁ %Pred.=39±12) were compared. SEFV in healthy individuals manifested progressively more convex SEFV curves throughout exercise (RAR=0.56±0.08 at rest and 0.61±0.05 at peak exercise), but became progressively more concave in COPD patients (RAR=0.52±0.08 at rest and 0.46±0.06 at peak exercise). In conclusion, breath-by-breath quantification of SEFV curve concavity describes progressive shape changes denoting expiratory flow limitation during incremental exercise in COPD patients. Further studies are warranted to establish whether this novel method can be a reliable indicator of expiratory flow limitation during exercise and to examine the relationship of RAR time course to the development of dynamic hyperinflation.