Establishment and application of reference equations for FEF50 and FEF75 in the Chinese population

Abstract

Background Reference equations for forced expiratory flow at 50% and 75% of forced vital capacity (FVC) (FEF 50 and FEF 75 ) in the Chinese population are lacking. It is of great importance to establish equations covering most age groups and to study their applicability in clinical practice. Methods Using the lambda-mu-sigma (LMS) method, reference equations for FEF 50 and FEF 75 were constructed based on pulmonary function data from healthy subjects collected from January 2007 to June 2010 at 24 centers throughout China. Differences between the established equations and extraneous equations were compared using standardized means (Z values) and percentage errors (PE). The proportion of small airway dysfunction (SAD) defined by the present equations was calculated. The Fisher precision probability test and the Mann-Whitney test were used to analyze the magnitude of changes in small and large airway indices after bronchodilator inhalation in patients with suspected asthma and chronic obstructive pulmonary disease (COPD). Results Reference equations for FEF 50 and FEF 75 were established based on data from 7,115 healthy individuals (aged 4 to 80 years, 50.9% female, height between 95 and 190 cm). The present equations (all Z values were −0.0 and PE ranged from 2.0% to 4.2%) showed advantages over the European Community for Steel and Coal (ECSC) equations in 1993 (with Z values ranging from −0.7 to −0.2 and PE ranged from −23.4% to −4.5%). A total of 4,356 patients with suspected asthma (51.1% female; a mean age of 45.4 years) and 6,558 patients with suspected COPD (10.1% female; a mean age of 65.0 years) were included. The present equations defined 95.7% and 99.9% of SAD in these patients. After bronchodilator inhalation, greater mean improvement rates in small airway indices were observed both in patients with suspected asthma [mean ± standard deviation (SD) =48%±47%] and in patients with suspected COPD (mean ± SD =20%±30%) (P<0.05). Conclusions The reference equations for FEF 50 and FEF 75 established in this study should be considered for use in China. Further studies are needed to validate their value in the diagnosis of some chronic respiratory diseases.

Combining small airway parameters with conventional parameters obtained during spirometry to diagnose airflow obstruction: A cross‐sectional study

“…It has been reported that the current reference values provide a better interpretation of spirometry in Chinese people compared with the Global Lung Function Initiative reference values. 15,16 However, our study also has some limitations. Firstly, there was a lack of information on other variables, such as environmental pollution, antenatal tobacco smoke exposure, smoking history, premature birth, childhood lung infection and other clinical characteristics.…”

“…To satisfy application of standard spirometry reference values for Chinese, only cases with known sex, age between 4 and 80 years, and height between 95 and 190 cm were included. 15,16 Cases with missing values that could not be classified into a spirometric pattern were excluded. Cases that met the contraindications for spirometry and BDR were also excluded.…”

“…The lower limit of normal (LLN) and Z-scores for each spirometric parameter, as estimated using the reference equations developed by Jian et al in 2017 and Wang et al in 2024, were considered the gold standard for interpreting these parameters. 15,16 Abnormal results were defined as the measured values <LLN, corresponding to a Z-score <À1.645. 15,16 In spirometry, a normal pattern is when both the large and small airway parameters are greater than the LLN.…”

“…15,16 Abnormal results were defined as the measured values <LLN, corresponding to a Z-score <À1.645. 15,16 In spirometry, a normal pattern is when both the large and small airway parameters are greater than the LLN. A restrictive pattern is classified when FVC < LLN and FEV 1 / FVC ≥ LLN, while an obstructive pattern is classified when FVC ≥ LLN and FEV 1 /FVC < LLN.…”

The challenge of interpreting diminished mid‐expiratory flow in the presence of normal FEV1 and FVC

“…The paper has several notable strengths, including the large sample size and population-specific limits of normal for MEF parameters. 7 Importantly, these reference data account for normal ageing-associated MEF decline to prevent the over-diagnosis of age-related small airway disease.…”