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Association of Airway Responsiveness With Asthma and Persistent Wheeze in a Chinese Population^*

^* From the Program of Population Genetics (Drs. Xu, Niu, Chen, and Wang), Harvard School of Public Health, Boston, MA; Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital (Dr. Weiss), Harvard Medical School, Boston, MA; Anhui Meizhong Institute for Biomedical Science and Environmental Health (Dr. Yang), Anqing, Anhui, China; and Anhui Medical University Center for Ecogenetics and Disease Control (Dr. Jin), Hefei, Anhui, China.

Correspondence to: Xiping Xu, MD, Associate Professor, Program for Population Genetics FXB-101, 665 Huntington Ave, Boston, MA 02115; e-mail: xxu{at}ppg.harvard.edu

Study objectives: Data from a cross-sectional study were analyzed to examine the association of increased airway responsiveness with physician-diagnosed asthma and persistent wheeze.

Design: Two methods for calculating the provocative dose that decreases the airflow rate by 20% (PD₂₀) were used as indexes for increased airway responsiveness: (1) a 20% drop in FEV₁ calculated from baseline FEV₁ (PD₂₀b), and (2) a 20% drop in FEV₁ from FEV₁ measurements after inhalation of saline solution (PD₂₀s). Both PD₂₀b and PD₂₀s were measured through induction by varying doses of methacholine.

Setting: Anqing, Anhui Province, China.

Participants: Study subjects were 8 to 74 years of age and were classified into four groups: children (< 15 years old), young adults (15 to 29 years old), adults (30 to 44 years old), and older adults ( 45 years old).

Interventions: The differences in estimated odds ratios of airway hyperresponsiveness with asthma and wheeze, sensitivity and specificity, and coefficients of variation were compared between PD₂₀b and PD₂₀s. The sample for analysis consisted of 10,284 subjects from 2,663 nuclear families with complete data on wheeze, asthma, and major potential confounding factors.

Measurements and results: The prevalence of asthma in this sample was lowest in subjects with no demonstrable PD₂₀ and had a reverse dose-response relationship with PD₂₀ across all age groups. Using the receiver operating characteristic, the sensitivity and specificity of the PD₂₀s or PD₂₀b were found to be almost identical. A similar trend was found for persistent wheeze, although the estimated odds ratios for persistent wheeze appeared slightly smaller than those for physician-diagnosed asthma.

Conclusions: This study demonstrates a dose-response relationship between increased airway responsiveness and asthma and wheeze in this Chinese population. PD₂₀s or PD₂₀b yielded virtually indistinguishable results, which indicated that either of the two tests could serve as an index of airway hyperresponsiveness.

Key Words: airway responsiveness • asthma • wheeze

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