Chest
Volume 124, Issue 1, July 2003, Pages 63-69
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Clinical Investigations
Asthma
Ratio Between Forced Expiratory Flow Between 25% and 75% of Vital Capacity and FVC Is a Determinant of Airway Reactivity and Sensitivity to Methacholine

https://doi.org/10.1378/chest.124.1.63Get rights and content

Study objective

The ratio between forced expiratory flow between 25% and 75% of vital capacity (FEF25–75) and FVC is thought to reflect dysanapsis between airway size and lung size. A low FEF25–75/FVC ratio is associated with airway responsiveness to methacholine in middle-aged and older men. The current study was designed to assess this relationship in both male and female subjects over a broader range of ages.

Study design

Data analysis of consecutive subjects who had a ≥ 20% reduction in FEV1 after ≤ 189 cumulative units of methacholine over a 7-year period.

Setting

Pulmonary function laboratory in a university-affiliated hospital.

Patients

A total of 764 consecutive subjects aged 4 to 91 years (mean ± SD age, 40.8 ± 19.6 years). There were 223 male (29.3%) and 540 female (70.7%) subjects.

Measurements and results

Airway reactivity was assessed as the dose-response slope of the reduction in FEV1 from baseline vs the cumulative dose of inhaled methacholine. The cumulative dose of methacholine causing 20% reduction in FEV1 (PD20) was used as the indicator of airway sensitivity. In a linear regression model that included age, height, and percentage of predicted FEV1, the FEF25–75/FVC ratio accounted for 7.6% of variability in airway reactivity (p < 0.0001, r2 = 0.076). Subjects with higher airway sensitivity, indicated by lower PD20, also had a lower FEF25–75/FVC ratio.

Conclusions

A low FEF25–75/FVC ratio, indicating small airway size relative to lung size, is associated with higher airway sensitivity and reactivity to methacholine in susceptible subjects.

Section snippets

Study Design

Consecutive subjects who had a ≥ 20% reduction in FEV1 after ≤ 189 cumulative units (cu) of methacholine between January 1993 and September 2000 were included in the study. Only subjects with known interstitial lung diseases, neuromuscular diseases, and diaphragm paralysis were excluded. All studies were performed in the Pulmonary Function Laboratory of Memorial Hospital of Rhode Island.

Pulmonary Function Testing

Spirometry was performed using standard techniques on the spirometer (Transfer Test Model C Apparatus; Morgan

Results

A total of 764 subjects were included in this analysis. Sixty-one of the subjects performed only spirometry, and the remaining 703 subjects had both spirometry and lung volume data. The ages of the subjects ranged from 4 to 91 years (mean ± SD, 40.8 ± 19.6 years). There were 224 male (29%) and 540 female (71%) patients. Baseline PFT results of the group were all within normal limits (Table 1).

There was a significant association between FEF25–75/FVC ratio and airway reactivity as assessed by a

Discussion

Analysis of this group of 764 subjects showed significant association between FEF25–75/FVC ratio and airway reactivity and sensitivity. Subjects with lower FEF25–75/FVC ratios had higher airway reactivity and sensitivity to methacholine as assessed by the DRS and PD20. This association existed for both male and female subjects, subjects of various age groups and remained significant after excluding subjects with evidence of overt airway obstruction.

Airway hyperresponsiveness is considered one

ACKNOWLEDGMENT

The authors thank Gail Dusseault and Laureen Sheehan for technical support.

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