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.