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Pulmonary function is a crucial parameter for the comprehensive evaluation of respiratory system functions such as airway ventilation capacity. Pulmonary function tests are mainly used to detect the patency of the airway and the lung capacity, including a variety of diagnostics that assess how well the lungs work; the most basic pulmonary function test is spirometry (1). The interpretation of spirometric test results, such as airflow obstruction (AFO) levels, can help identify abnormal patterns that may be related to the presence of disease (2).
The physiological definition of AFO is a reduction in the ratio of forced expiratory volume in the first second (FEV1) to forced vital capacity (FVC). Importantly, AFO has been found to be a critical element of certain diseases, such as chronic obstructive pulmonary disease (COPD) (2). Among individuals with AFO, 43%–74% are COPD patients (3-5), and COPD has become a major public health problem in China (6). The aim of this study was thus to estimate the level and characteristics of lung function and AFO in a sample population of adults living in Beijing in order to better serve populations such as those suffering from COPD.
The study was performed using baseline data (from September 2017 to May 2018) obtained from the Beijing Population Health Cohort Study. It is a large, prospective dynamic cohort study with a total of 24,990 subjects aged 18–74 years. The details of this study’s design are discussed in another publication (7). This study’s methodology excluded individuals who did not meet the age requirements and/or lacked important information, such as lung function indicator values, which left 21,426 participants in the analysis.
A standardized questionnaire was administered by trained staff. Smoking severity was determined by the smoking index (SI) [SI, calculated as (daily smoking count) × (years of smoking). Light: SI≤200; Moderate: 200<SI<400; Severe: SI≥400]. Weight and height were measured by trained staff, and body mass index (BMI) was subsequently calculated. Spirometry tests were conducted by trained technicians on participants in a sitting position with a nose clip using a spirometer. The spirometer was calibrated daily. Participants completed three tests of lung function. This study then used the GOLD lung function criteria (FEV1/FVC <70%) to define individuals with AFO. The participants provided written informed consent. The Ethics Review Committee of the Beijing Center for Disease Prevention and Control approved the study protocol [No. 2017D(6)].
This study estimated standardized prevalence using the 2010 census of the Chinese population. Categorical data are shown as numbers (percentages). The mean±standard deviation is used to represent the continuous variables. This investigation assessed the statistical significance of differences either by one-way ANOVA or the Kruskal-Wallis H test for continuous variables and used the chi-squared test to compare prevalence. P values for trends were calculated using the Cochran-Armitage trend test for proportions. All statistical tests were two-sided, and P<0.05 was considered statistically significant. All statistical analyses were performed using Stata 16.0 (StataCorp LLC, College Station, Texas, USA).
The basic characteristics of the study subjects are listed in Table 1 and Table 2. Of the 21,426 subjects, 9,876 were males and 11,550 were females. Overall, males had higher vital capacity (VC), FVC, and FEV1, but males had slightly lower FEV1/FVC than females. The results of lung function testing are shown in Table 3. In males, the mean values of VC and FVC were significantly different in the age, residence, education level, smoking status, smoking index level, and BMI groups. The mean value of FEV1 was not significantly different among the different BMI groups. In females, the mean value of VC was significantly different in the age, education level, and BMI groups. The mean values of FVC and FEV1 were not significantly different among the different smoking index levels.
Variable Total (n=21,426) Male (n=9,876) Female (n=11,550) Age (years), mean (±SD) 45.97 (14.28) 45.95 (14.52) 45.99 (14.08) Age group, n (%) 18–29 3,332 (15.55) 1,620 (16.40) 1,712 (14.82) 30–39 4,876 (22.76) 2,226 (22.54) 2,650 (22.94) 40–49 4,079 (19.04) 1,723 (17.45) 2,356 (20.40) 50–59 4,274 (19.95) 1,996 (20.21) 2,278 (19.72) 60–74 4,865 (22.71) 2,311 (23.40) 2,554 (22.11) BMI (kg/m2)，mean (±SD) 25.14 (3.84) 25.91 (3.67) 24.47 (3.86) BMI group, n (%) <18.5 496 (2.31) 117 (1.18) 379 (3.28) 18.5–23.9 8,783 (38.19) 2,871 (29.07) 5,312 (45.99) 24.0–27.9 8,277 (38.63) 4,362 (44.17) 3,915 (33.90) ≥28.0 4,470 (20.86) 2,526 (25.58) 1,944 (16.83) Residence, n (%) Urban 7,400 (34.54) 3,095 (31.34) 4,305 (37.27) Suburban 14,026 (65.46) 6,781 (68.66) 7,245 (62.73) Education level, n (%) Primary and below 1,765 (8.24) 657 (6.65) 1,108 (9.59) Middle and high school 8,793 (41.04) 4,434 (44.90) 4,359 (37.74) College and above 10,868 (50.72) 4,785 (48.45) 6,083 (52.67) Smoking status, n (%) Current smoker 5,090 (23.76) 4,839 (49.00) 251 (2.17) Former smoker 1,143 (5.33) 1,083 (10.97) 60 (0.52) Never smoker 15,193 (70.91) 3,954 (40.04) 11,239 (97.31) Smoking index level*, n (%) Light 1,418 (32.07) 1,334 (31.51) 84 (44.68) Moderate 1,008 (22.80) 962 (22.72) 46 (24.47) Severe 1,996 (45.14) 1,938 (45.77) 58 (30.85) VC (L), mean (±SD) 3.09 (0.90) 3.59 (0.87) 2.66 (0.68) FVC (L), mean (±SD) 2.66 (0.89) 3.12 (0.90) 2.27 (0.67) FEV1 (L), mean (±SD) 2.22 (0.83) 2.60 (0.87) 1.90 (0.63) FEV1/FVC (%), mean (±SD) 83.63 (15.04) 83.41 (15.31) 83.82 (14.81) Note: Data are the number (percentage) for categorical variables and the mean±standard deviation for continuous variables.
* For smoking index level, the total number was 4,422, including 4,234 males and 188 females.
Abbreviation: SD=standard deviation; BMI=body mass index; VC=vital capacity; FVC=forced vital capacity; FEV1=forced expiratory volume in the first second.Table 1. Basic characteristics of the sample population.
Variable Total
(n=21,426)18–29
(n=3,332)30–39
(n=4,876)40–49
(n=4,079)50–59
(n=4,274)60–74
(n=4,865)Residence, n (%) Urban 7,400 (34.54) 1,234 (37.03) 1,616 (33.14) 1,239 (30.38) 1,485 (34.74) 1,826 (37.53) Suburban 14,026 (65.46) 2,098 (62.97) 3,260 (66.86) 2,840 (69.62) 2,789 (65.26) 3,039 (62.47) Education level, n (%) Primary and below 1,765 (8.24) 18 (0.54) 30 (0.62) 82 (2.01) 315 (7.37) 1,320 (27.13) Middle and high school 8,793 (41.04) 751 (22.54) 826 (16.94) 1,312 (32.16) 2,778 (65.00) 3,126 (64.25) College and above 10,868 (50.72) 2,563 (76.92) 4,020 (82.44) 2,685 (65.82) 1,181 (27.63) 419 (8.61) Smoking status, n (%) Current smoker 5,090 (23.76) 783 (23.50) 1,116 (22.89) 899 (22.04) 1,169 (27.35) 1,123 (23.08) Former smoker 1,143 (5.33) 83 (2.49) 145 (2.97) 192 (4.71) 261 (6.11) 462 (9.50) Never smoker 15,193 (70.91) 2,466 (74.01) 3,615 (74.14) 2,988 (73.25) 2,844 (66.54) 3,280 (67.42) Smoking index level, n (%)* Light 1,418 (32.07) 545 (88.33) 501 (54.22) 152 (19.64) 110 (10.26) 110 (10.63) Moderate 1,008 (22.80) 67 (10.86) 337 (36.47) 240 (31.01) 237 (22.11) 127 (12.27) Severe 1,996 (45.14) 5 (0.81) 86 (9.31) 382 (49.35) 725 (67.63) 798 (77.10) BMI group, n (%) <18.5 496 (2.31) 254 (7.62) 147 (3.01) 36 (0.88) 15 (0.35) 44 (0.90) 18.5–23.9 8,183 (38.19) 1,726 (51.80) 2,159 (44.28) 1,539 (37.73) 1,267 (29.64) 1,492 (30.67) 24.0–27.9 8,277 (38.63) 818 (24.55) 1,639 (33.61) 1,641 (40.23) 1,994 (46.65) 2,185 (44.91) ≥28.0 4,470 (20.86) 534 (16.03) 931 (19.09) 863 (21.16) 998 (23.35) 1,144 (23.51) Note: Data are the number (percentage).
* For smoking index level, the total number was 4,422.
Abbreviation: BMI=body mass index.Table 2. Distribution of sample population by residence, educational level and smoking status by age group.
Variable Total (n=21,426) Male (n=9,876) Female (n=11,550) n VC (L) (mean) FVC (L) (mean) FEV1 (L) (mean) n VC (L) (mean) FVC (L) (mean) FEV1 (L) (mean) n VC (L) (mean) FVC (L) (mean) FEV1 (L) (mean) Age group (years) 18–29 3,332 3.45
(0.94)2.97
(1.01)2.54
(0.91)1,620 4.02
(0.83)3.50
(0.99)2.98
(0.90)1,712 2.92
(0.70)2.47
(0.73)2.11
(0.68)30–39 4,876 3.36
(0.90)2.93
(0.92)2.50
(0.84)2,226 3.95
(0.81)3.46
(0.90)2.96
(0.83)2,650 2.87
(0.64)2.49
(0.68)2.12
(0.63)40–49 4,079 3.12
(0.84)2.71
(0.82)2.30
(0.75)1,723 3.68
(0.79)3.23
(0.81)2.75
(0.76)2,356 2.70
(0.59)2.34
(0.59)1.98
(0.55)50–59 4,274 2.91
(0.82)2.51
(0.77)2.06
(0.72)1,996 3.37
(0.76)2.91
(0.76)2.40
(0.73)2,278 2.51
(0.64)2.15
(0.58)1.76
(0.56)60–74 4,865 2.69
(0.80)2.28
(0.74)1.80
(0.67)2,311 3.07
(0.75)2.62
(0.71)2.04
(0.70)2,554 2.34
(0.67)1.96
(0.61)1.57
(0.56)P value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Residence Urban 7,400 3.03
(0.90)2.47
(0.87)2.04
(0.79)3,095 3.53
(0.88)2.90
(0.91)2.40
(0.85)4,305 2.66
(0.72)2.15
(0.69)1.79
(0.63)Suburban 14,026 3.12
(0.90)2.77
(0.88)2.31
(0.83)6,781 3.62
(0.86)3.22
(0.87)2.69
(0.86)7,245 2.65
(0.66)2.34
(0.65)1.96
(0.63)P value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.422 <0.001 <0.001 Education level Primary and below 1,765 2.61
(0.83)2.16
(0.73)1.68
(0.68)657 3.05
(0.79)2.57
(0.78)1.96
(0.78)1,108 2.35
(0.73)1.92
(0.58)1.52
(0.55)Middle and high school 8,793 2.92
(0.86)2.49
(0.83)2.04
(0.77)4,434 3.35
(0.81)2.89
(0.82)2.37
(0.80)4,359 2.48
(0.66)2.09
(0.62)1.71
(0.57)College and above 10,868 3.30
(0.89)2.88
(0.90)2.45
(0.82)4,785 3.89
(0.82)3.41
(0.89)2.90
(0.83)6,083 2.84
(0.64)2.46
(0.66)2.10
(0.62)P value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 Smoking status Current smoker 5,090 3.52
(0.87)3.07
(0.90)2.56
(0.86)4,839 3.57
(0.85)3.12
(0.89)2.60
(0.85)251 2.60
(0.75)2.14
(0.64)1.73
(0.60)Former smoker 1,143 3.41
(0.88)2.94
(0.88)2.38
(0.86)1,083 3.45
(0.87)2.99
(0.87)2.41
(0.86)60 2.61
(0.68)2.17
(0.69)1.83
(0.63)Never smoker 15,193 2.92
(0.86)2.50
(0.83)2.09
(0.78)3,954 3.66
(0.88)3.15
(0.91)2.64
(0.88)11,239 2.66
(0.68)2.27
(0.67)1.90
(0.63)P value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.425 0.003 <0.001 Smoking index level Mild 1,418 3.80
(0.89)3.35
(0.94)2.84
(0.88)1,334 3.87
(0.84)3.42
(0.91)2.91
(0.85)84 2.67
(0.80)2.20
(0.65)1.81
(0.58)Moderate 1,008 3.62
(0.88)3.14
(0.91)2.64
(0.86)962 3.67
(0.85)3.19
(0.88)2.68
(0.84)46 2.58
(0.82)2.04
(0.68)1.69
(0.66)Severe 1,996 3.25
(0.77)2.83
(0.78)2.30
(0.77)1,938 3.27
(0.76)2.86
(0.77)2.32
(0.76)58 2.44
(0.66)2.09
(0.63)1.59
(0.57)P value <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.210 0.368 0.105 BMI group <18.5 496 2.92
(0.84)2.49
(0.82)2.13
(0.78)117 3.39
(0.90)2.95
(0.96)2.47
(0.92)379 2.77
(0.76)2.34
(0.72)2.02
(0.69)18.5–23.9 8,183 3.00
(0.86)2.59
(0.86)2.17
(0.80)2,871 3.56
(0.89)3.09
(0.93)2.58
(0.89)5,312 2.70
(0.67)2.32
(0.68)1.95
(0.65)24.0–27.9 8,277 3.14
(0.91)2.72
(0.90)2.25
(0.83)4,362 3.61
(0.84)3.14
(0.88)2.61
(0.85)3,915 2.61
(0.67)2.24
(0.65)1.86
(0.61)≥28.0 4,470 3.17
(0.96)2.72
(0.92)2.27
(0.86)2,526 3.61
(0.89)3.12
(0.90)2.61
(0.86)1,944 2.61
(0.73)2.20
(0.64)1.81
(0.60)P value <0.001 <0.001 <0.001 0.004 0.021 0.151 <0.001 <0.001 <0.001 Abbreviation: BMI=body mass index; VC=vital capacity; FVC=forced vital capacity; FEV1=forced expiratory volume in the first second. Table 3. Levels of pulmonary function indicators in the sample population aged 18–74 years old.
A total of 3,415 (15.94%) participants had a FEV1∶FVC ratio less than 70% and were therefore diagnosed with AFO. The standardized prevalence of AFO in Beijing adults aged 18–74 years was estimated to be 14.68%. The prevalence of AFO did not differ significantly (P=0.062) between men (16.44%) and women (15.51%). The prevalence was significantly different by age group, residence, education level, and smoking status (Table 4). People with poor lung function and high prevalence of AFO were mainly those who were older, lived in an urban environment, were current or former smokers, and/or had a low education level, high smoking index, and an abnormal BMI.
Variable Total (n=21,426) Male (n=9,876) Female (n=11,550) Cases/N Prevalence of AFO (%)
(95% CI)Cases/N Prevalence of AFO (%)
(95% CI)Cases/N Prevalence of AFO (%)
(95% CI)Age group (years) 18–29 423/3,332 12.70 (11.60–13.86) 205/1,620 12.65 (11.10–14.34) 218/1,712 12.73 (11.22–14.38) 30–39 562/4,876 11.53 (10.65–12.44) 242/2,226 10.87 (9.63–12.22) 320/2,650 12.08 (10.88–13.36) 40–49 509/4,079 12.48 (11.49–13.52) 202/1,723 11.72 (10.27–13.31) 307/2,356 13.03 (11.72–14.44) 50–59 758/4,274 17.74 (16.61–18.90) 360/1,996 18.04 (16.40–19.77) 398/2,278 17.47 (15.95–19.07) 60–74 1,163/4,865 23.91 (22.72–25.12) 615/2,311 26.61 (24.84–28.44) 548/2,554 21.46 (19.90–23.08) P value* <0.001 <0.001 <0.001 Residence Urban 1,300/7,400 17.57 (16.71–18.45) 563/3,095 18.19 (16.86–19.58) 737/4,305 17.12 (16.02–18.27) Suburban 2,115/14,026 15.08 (14.49–15.68) 1,061/6,781 15.65 (14.80–16.53) 1,054/7,245 14.55 (13.75–15.37) P value <0.001 0.002 <0.001 Education level Primary and below 478/1,765 27.08 (25.05–29.19) 211/657 32.12 (28.63–35.76) 267/1,108 24.10 (21.65–26.68) Middle and high school 1,688/8,793 18.97 (18.16–19.80) 857/4,434 19.33 (18.19–20.51) 811/4,359 18.61 (17.47–19.78) College and above 1,269/10,868 11.68 (11.08–12.29) 556/4,785 11.62 (10.73–12.55) 713/6,083 11.72 (10.93–12.55) P value* <0.001 <0.001 <0.001 Smoking status Current smoker 832/5,090 16.35 (15.35–17.38) 780/4,839 16.12 (15.10–17.18) 52/251 20.72 (16.06–26.05) Former smoker 226/1,143 19.77 (17.54–22.16) 220/1,083 20.31 (18.00–22.79) 6/60 10.00 (4.28–19.45) Never smoker 2,357/15,193 15.51 (14.94–16.10) 624/3,954 15.78 (14.67–16.94) 1,733/11,239 15.42 (14.76–16.10) P value <0.001 0.001 0.036 Smoking index level Mild 188/1,418 13.26 (11.57–15.10) 169/1,334 12.67 (10.97–14.53) 19/84 22.62 (14.69–32.39) Moderate 138/1,008 13.69 (11.67–15.92) 132/962 13.72 (11.66–16.00) 6/46 13.04 (5.63–24.92) Severe 419/1,996 20.99 (19.25–22.82) 403/1,938 20.79 (19.03–22.64) 16/58 27.59 (17.37–39.97) P value* <0.001 <0.001 0.583 BMI group <18.5 69/496 13.91 (11.08–17.16) 21/117 17.95 (11.82–25.64) 48/379 12.66 (9.60–16.29) 18.5–23.9 1,267/8,183 15.48 (14.71–16.28) 485/2,871 16.89 (15.56–18.30) 782/5,312 14.72 (13.79–15.69) 24.0–27.9 1,373/8,277 16.59 (15.80–17.40) 740/4,362 16.96 (15.87–18.10) 633/3,915 16.17 (15.04–17.35) ≥28.0 706/4,470 15.79 (14.75–16.89) 378/2,526 14.96 (13.61–16.40) 328/1,944 16.87 (15.26–18.59) P value* 0.233 0.057 0.003 Abbreviation: AFO=airflow obstruction; BMI=body mass index; CI=confidence interval.
* P value from Cochran-Armitage trend test for prevalence.Table 4. Prevalence of airflow obstruction in the sample population aged 18–74 years old.
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To date, this is the first large-scale, community-based study working to estimate the level of lung function and the prevalence of AFO among adults in Beijing. Based on results, this research concluded that the prevalence of AFO among adults aged 18–74 years in Beijing was 15.94%, and that the standardized prevalence of AFO was 14.68%. Compared to the 2010 census data, the proportion of people aged 18–29 and 40–49 in this study is higher, and the proportion of people aged 50–59 and 60–74 is lower. With increased age, lung function decreases and the prevalence of AFO increases. Therefore, the crude prevalence in this study will decrease after standardization. Compared to the China Pulmonary Health (CPH) Study, which was a survey of 10 provincial-level administrative divisions (PLADs) in China (Beijing Municipality, Shanghai Municipality, Liaoning, Shanxi, Shaanxi, Sichuan, Guizhou, Hubei, Zhejiang and Guangdong Provinces) from June 2012 to May 2015, this study revealed a higher prevalence of AFO than the prevalence of COPD in adults aged 20 years or older (8.6%) (8). In the study mentioned above, bronchodilators were used to identify patients with COPD. The use of bronchodilators could lead to the exclusion of some patients with bronchial asthma. Therefore, the prevalence of AFO is higher than that of COPD, which is a finding that is consistent with other studies (3,5).
Males always have higher index values of lung function. The results of this study were consistent with this phenomenon. With increasing age, various organs of the human body gradually age, and because people are exposed to risk factors such as smoking starting when they are young, the cumulative effect of these factors increases with age, causing lung function to decline with age. According to a previous study, the prevalence of COPD was higher in rural areas (6). This may be due to the lower economic status in rural areas, which leads to people being exposed to many risk factors that affect lung function. Beijing, the capital of China, is a modern international city with generally favorable economic conditions and lower exposure to life-threatening factors than rural areas. People in urban areas, however, may be exposed to more car exhaust than people in suburban areas due to traffic congestion. Urban populations had worse lung function and a higher prevalence of AFO in this study. People with lower education levels had lower levels of lung function and a higher prevalence of AFO, possibly because they are less aware of lung function protection and are more likely to be exposed to risk factors. People with low BMI are generally more likely to develop COPD, whereas being overweight or obese is often a protective factor for COPD (9), which is not entirely consistent with this study’s findings. In this study, females had worse lung function and a higher prevalence of AFO with increasing BMI. This result is however consistent with the findings of a study in the United States demonstrating that overweightness and obesity are risk factors for COPD (10). A BMI that is too high or too low can have an impact on lung function, so maintaining a normal weight is vital for health. Women who were current smokers and men who were former smokers had the worse lung function and the highest prevalence of AFO. The findings in males are consistent with another Chinese study (11). It may be that former smokers who are male have too much damage to lung function due to prior smoking habits and that their lung function has not fully recovered with smoking cessation. Nonsmokers have the best lung function, so it is essential to avoid cigarettes for health.
This study had several limitations. First, this study used the GOLD criteria (FEV1/FVC<70%). The ERS and the ATS promote the use of the lower limit of normal (LLN). However, using the LLN as a threshold can potentially exclude subjects with mild AFO. Therefore, this study decided to use the GOLD criteria. Second, this study did not use bronchodilators. In fact, bronchodilators have many side effects, such as dizziness. For safety reasons, bronchodilators were not used. Thirdly, when considering the prevalence of AFO in different age groups, it is necessary to analyze prevalence across different risk factors by age group. In this study, however, there were some overlapping risk factors exhibited by the same study participants.
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No conflicts of interest.
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