In the present study, we established the reference values for PEF using data from 11,717 healthy middle-aged and elderly Chinese adults according to age and sex. The mean values of PEF were 354.10 ± 132.40 and 254.10 ± 94.98 L/min for men and women, respectively. The PEF was higher in men than in women for all age subgroups. The PEF value was decreased with age in both men and women. Our data also suggested that, in both men and women, age, height, weight, waist circumference, handgrip strength, residence in urban, smoking status were significantly associated with PEF. Besides, education level, clean heating energy use were associated with PEF only in men, and number of comorbidities and clean energy use were associated with PEF only in women significantly. The cut-off values of low PEF (mean – 2 SD) were 89.38 L/min and 64.12 L/min for men and women, respectively. And the prevalence of low PEF in men and women were 1.62%, 2.16% separately.
As a physiologic measure and an important index, PEF, has been proposed to estimate airflow obstruction, which could be used to help the management of asthma  and screening COPD . Compared with formal spirometry, which is usually unavailable in primary care settings, especially in developing countries , PEF test is much cheaper and easier, although it is a crude measure. In addition, considering its rapid and easy-to-get results, it is also feasible for use in large-scale surveys . In recent years, some researchers found that PEF was not only related to respiratory disease, but also demonstrated strong relationships with some poor outcomes [19, 25, 26], especially in older adults. Thus, the measurement of PEF has an important effect in clinical practice and is of practical significance in public health. And it is essential and urgent to establish a unique reference for Chinese.
Global Lung Function Initiative has recommended multi-ethnic spirometry reference values for Northeast Asians, which were established based on largely urban Caucasian data in 2012 . However, the reference value did not include PEF. Previous to our study, PEF reference values for Chinese were estimated. However, several disadvantages limited the national wide usage, for example, based on children and adolescence, or small local regions, or small samples [15, 16, 28-31]. Jian estimated the reference value for 7,115 healthy Han nationality people aged 4~80 years old. Parameters and equations for low limit of normal for PEF in separate age segment were shown in their study. However, that is not convenient for clinical practice in screening the people who are abnormal in lung function. Moreover, potential factors associated lung function were not taken into account. Household air pollution, for example, has been found with respiratory disease, cardiovascular disease, and lung functions. And the association between PEF and household air pollution has not been explored in elderly. Therefore, our study based on the CHARLS, which involves 17,708 middle-aged and elderly participants from 450 counties of 28 provinces in China. And cut-off points for men and women were estimated respectively. Those would make the clinical screening for patients who are abnormal very simple and practical.
There are some differences between our study and the previous study . First, our study focuses on the middle-aged and elderly, including 11,717 Chinese people aged over 40 years. In the previous study, there was a wide range of age of 4–80 years for 7,115 subjects but the middle-aged and older accounted for only a small proportion. PEF is very important for screening and treatment for asthma and COPD, especially for adults and elderly those who declined in lung function with age. Second, one of the key inclusion criteria in the previous study was life-long non-smokers; however, smokers were not excluded from our study. On one hand, we believe that smokers also represented a considerable part of the “healthy” population; on the other hand, logically, we want to consider the effect of smoking on the value of PEF. Third, limitations in the previous article did not include the factors influencing pulmonary function, such as economic conditions, residential environment, and nutrition. However, in the present study, we explored the relationship between PEF and BMI, weight, waist circumference, handgrip strength, education level, smoking status, place of residence and number of comorbidities, in addition to sex and age.
Our data suggested that height, weight, handgrip strength, residence in urban, and clean heating energy use were positively associated with PEF, and age, waist circumference, smoking were negatively associated with PEF significantly in both men and women. Besides, education level was associated with PEF only in men, and number of comorbidities was associated with PEF only in women significantly. In addition, cut-off point was defined as 2 SD below mean value from subjects under 65 years. a diagnose criteria from fixed value are very practical in clinical practice.
There are several limitations should be considered. First, the study population only comprised the middle-aged and elderly in China, which limits the generalizability of the results to other populations. Second, we did not consider the influence of some risk factors, such as nationality, environmental pollution, and physical activity, because such information was unavailable. Third, the impact of risk factors on PEF in the present study was based on a cross-sectional study, which limits the inferences of causality.