The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

A PROPOSED SPIROMETRIC INDEX FOR EVALUATING PATIENTS WITH DECREASED FEV1.



Chang-Jiang Zheng, MD, PhD, Alexander B. Adams, MPH, RRT, FAARC, Michael P. McGrail, MD, MPH, John Marini, MD, Ian A. Greaves,MD. Pulmonary/Occupational Medicine, Regions Hospital/Healthpartners, Univ. of MN., St. Paul, MN.



Background:
"Curvi-linearity" observed in the descending segment of the forced expiratory flow-volume curve is a hallmark for airflow obstruction. Currently, there is no available spirometric index that directly quantifies the degree of curvature. We propose a "curvature" index , , and we examined a sample of spirometric data to explore the relationship between and FEV1.

The Model:
A simple quadratic function ( ) is fit to the descending phase of a flow-volume curve:  = flow rate,  = volume and  are unknown coefficients to be estimated from a goodness of fit analysis of the patient's flow-volume data. The degree of curvature is measured by   ;  if . A mechanistic interpretation of this relationship (Barnea et al., Comput Biol Med 26:123-31;1996) associates a curvature component ( ) with the rate of airway-resistance increase as exhaled volume increases.

Design/ Methods:
Spirometric records from 67 sequential patients undergoing PF testing were analyzed using the statistical program SYSTAT .

RESULTS:
The overall mean estimate of  was 0.25. The relationship between  and FEV1 ยป .
We observed that when FEV1 < 2.0 L, the index  shows a wide range of variation.
Conclusions:
relates, exponentially, to FEV1. This curvature index may be more sensitive to the severity of disease and, therefore, potentially useful in diagnosis and longitudinal monitoring. We plan further investigations of associations between and air-trapping, late expiratory flow indices and/or symptoms of airflow obstruction.

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