Abstract
BACKGROUND:
Though forced expiratory volume in the first second (FEV1) is the primary indicator of airway obstruction, curvilinearity in the expiratory flow-volume curve is used to support the quantitative assessment of obstruction via FEV1. Currently there is no available index to quantify a pathological contour of curvilinearity.
STUDY PURPOSE:
We propose a “curvature” index (k max) and compare FEV1 values to the index with a sequential sample of spirometry data.
METHODS:
The hyperbolic function b
0
Q̇ + b
1
Q̇V + b
2
V = 1 (in which Q̇ = flow rate, V = volume, and b
0, b
1, and b
2 are estimated from the patient's flow-volume data) is fit to a fixed segment of the descending phase of the expiratory flow-volume curve. A previously developed biomechanical interpretation of this relationship associates the coefficient b
1 with the rate of airway-resistanceincrease as exhaled volume increases. A global curvature index k
max = b
1/
RESULTS:
Individual k max estimates appeared to correspond well with the degree of curvilinearity observed and were related in an exponential manner to FEV1.
CONCLUSIONS:
We defined a curvature index to quantify the curvilinearity phenomenon observed in the expiratory limb of flow-volume loops from patients with obstructive lung disease. This index uses data from a major segment of the flow-volume curve, and our preliminary data indicate an exponential relationship with FEV1. This new index allows the putative association between curvilinearity and obstructive lung disease to be examined quantitatively in clinical practice and future studies.
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