Article Figures & Data
Figures
- Fig. 1.
Example of the determination of flow decay: the slope of the exhaled volume versus ln(1/flow). The top row of panels shows the data derived from a healthy subject. The middle row (row 2) is from a subject with reactive airway disease. The bottom row is from a subject with COPD. The left column shows the flow-volume tracings measured during spirometry for each subject. The center column shows the volume versus the inverse of the flow during the mid-expiratory (25–75%) portion of forced exhalation. The right column shows the volume versus the natural logarithm of the inverse of flow and includes the r2 values that support the linearity of the relationships. For each subject, the slope of the line in the right column represents flow decay, which reflects the increase in dynamic airway resistance as the lung volume decreases (see text). The upper limit of the normal range for flow decay was estimated to be 0.802 L−1.
- Fig. 2.
Repeated measurement of flow decay among 7 healthy volunteers. The longer horizontal bars represent median flow decay among the repeated measures of each subject; shorter bars represent the corresponding 25th and 75th percentiles. The mean ± SD flow decay for the entire derivation group was 0.588 ± 0.107 L−1. The mean + 2 × SD (0.802 L−1) in this group defined the upper limit of normal for the next phase of the study.
- Fig. 3.
Flow decay means among healthy volunteers compared with the flow decay of subjects with reactive airway disease. Among the healthy subjects, 92% (23 of 25) of the flow decays were < 0.802 L−1, the upper limit of normal that had been estimated from the derivation group (see Fig. 2). Only 6% (2 of 31) of the flow decay values in the reactive airway group and 5% (3 of 62) of the values in the COPD group were below the upper limit of normal.
