(Chest. 2005;128:1297-1303.)
© 2005
American College of Chest Physicians
Discordance Between Lung Function of Chinese University Students and 20-Year-Old Established Norms*
Alice Yee-Men Jones, PhD;
Elizabeth Dean, PhD;
Peggo Kwok-Wai Lam, MPhil and
Sing-Kai Lo, PhD
* From the Department of Rehabilitation Sciences (Dr. Jones and Mr. Lam), The Hong Kong Polytechnic University, Hong Kong; the School of Rehabilitation Sciences (Dr. Dean), University of British Columbia, Vancouver, BC, Canada; and the Institute for International Health (Dr. Lo), The University of Sydney, Sydney, NSW, Australia.
Correspondence to: Elizabeth Dean, PhD, Department of Rehabilitation Sciences, University of British Columbia, T325–2211 Wesbrook Mall, Vancouver, BC, Canada V6T 2B5; e-mail: elizdean{at}interchange.ubc.ca
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Abstract
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Objective: We examined the validity of the 20-year-old established Asian norms for pulmonary function in a contemporary cohort of Hong Kong Chinese university students.
Design and participants: Pulmonary function testing was conducted in university students (n = 805).
Setting: A university campus in Hong Kong.
Measurements and results: Parameters recorded included gender, age, height, weight, standard lung function variables (ie, FEV1, FVC, and peak expiratory flow rate [PEFR]), and exhaled carbon monoxide (CO) level. Subjects completed a questionnaire on pulmonary health, smoking history, and their dietary and exercise habits within 3 months of the study. Data were compared with the established norms for lung function for Chinese persons from Hong Kong. On average, subjects were taller than those reported in the original cohort, on whom the established norms are based; however, FEV1, FVC, and PEFR were lower. As predicted, the exhaled CO level was higher in smokers. Those who exercised regularly had a higher FEV1 and FVC, and reported fewer respiratory complaints.
Conclusions: Our findings support the idea that lung function norms not only differ across ethnic groups, but that they may be susceptible to change over a single generation within an ethnic group living in the same geographic region. Assuming the equivalence of our testing methods and those on which established norms are based, our findings shed further insight into the dynamic nature of lung function, and have implications regarding the definition of normal pulmonary function and its variance over the short term.
Key Words: Asian lung function norms • lifestyle factors • physical activity • university students
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Introduction
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Although ethnicity is an established determinant of lung function, predictive values for non-Western individuals in non-Asian countries are largely based on a proportion of established Western standards.12 An Asian nomogram3 based on 3,000 Hong Kong Chinese subjects who were 20 years of age, however, continues to be the reference standard used in Hong Kong. Since the time of that study, modifying factors of lung function have been reported or their effects have been better appreciated clinically. These effects include dietary factors,456 obesity,78 air pollution,9 and physical activity.10 With rapid economic growth and development over the last 20 years, the current generation of young adults in Hong Kong, has grown up with improved nutrition yet higher pollution.11 The objective of this study was to validate the lung function norms that were established 20 years ago in a cohort of Hong Kong Chinese students who were born at the time that these norms were derived.
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Materials and Methods
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Ethics approval was obtained from the ethics review committee of the Hong Kong Polytechnic University. Approval was also obtained from the student union of the university. Written informed consent was obtained from each subject prior to the data collection.
Subjects
An invitation to participate in a lung function assessment session was sent to all students at one of the universities in Hong Kong by mass electronic mailing. The assessment sessions were conducted at the university podium over a 2-week period. To limit interindividual differences due to age and time of year, the data collection was limited to young university students over a restricted time frame. To maximize the number of subjects recruited into the study, we compared pulmonary function testing performed in the field to that performed in the laboratory. This was also consistent with the procedures used by Lam and colleagues.3
Procedures
The study was explained and written consent was obtained from all subjects. Height and weight were then measured, and body mass index (BMI) calculated. Pulmonary function tests were conducted using two spirometers (Microlab 3300; Micro Medical Ltd; Kent, UK) and exhaled carbon monoxide (CO) level measured with a CO meter (Micro CO Meter; Micro Medical Ltd). Oxygen saturation was determined by a finger pulse oximeter (Onyx 9500; Nonin Medical, Inc; Plymouth, MN). Prior to the study, the CO meter was calibrated with a standard concentration of CO gas. The volume of each of 100 strokes of air from a 2-L super syringe to the two spirometers was recorded daily. The coefficients of variation of the volume measured by the two spirometers were 
1%. The proper technique for performing lung function measurements was demonstrated to each subject, and the best result of three measurement trials was recorded.212 The subjects completed a questionnaire that asked about smoking history, respiratory complaints and symptoms (eg, wheezing, shortness of breath on minimal exertion, cough, and sputum), nutritional status, and whether the subject participated in regular exercise over the past 3 months.
Statistical Analysis
A two-sample t test was used to compare the lung function parameters (ie, FEV1, FVC, and peak expiratory flow rate [PEFR]) and height, measured in this study, with the mean values of the same parameters reported by Lam and colleagues.3 For this comparison, the age of the subjects was stratified as reported in the study by Lam et al3 (ie, 19 to 20, 21 to 22, and 23 to 24 years of age). Regression analysis was used to develop prediction equations for FEV1, FVC, and PEFR from the data, and thereby to compare these pulmonary indexes derived from our data and those of Lam and colleagues.3 The difference in lung function parameters between smokers and nonsmokers was tested by fitting two-way analysis of variance models, including the main effects of smoking and gender, and their interaction. If the interaction was not significant, then a simple main-effects analysis was adopted to determine the differences between smokers and nonsmokers. Subject characteristics, prevalence of respiratory symptoms, dietary habits, exercise habits, and differences between male and female subjects were compared with 
2 tests, two-sample t tests, or Mann-Whitney tests, where appropriate. The association between respiratory symptoms and exercise habits was tested with 2 analysis. Lung function parameters were also compared among subjects with different exercise frequency, separately for each gender, with two-way analysis of variance models. The interaction between gender and exercise frequency was also examined. While the overall significance level was set at 0.05, the sharpened Bonferroni method13 was used to adjust for individual 
levels when multiple testing was performed.
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Results
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A total of 805 subjects participated in this study, of whom 518 were men and 287 were women. The smoking status of one male subject was unknown, thus he was excluded from the analysis. Only 5.7% of the subjects were smokers, and 2.2% were ex-smokers. Over one third of the subjects were living with family members who smoked. Subjects who smoked had a higher level of exhaled CO than nonsmokers (p < 0.005) [Table 1
].
The BMIs of subjects were not reported in the study by Lam et al.3 Our subjects, both men and women, were taller than those reported by Lam and colleagues.3 There were, however, some distinctions between the genders. When we compared the men’s data with those of Lam et al,3 FEV1, FVC, and PEFR were all lower in our cohort for subjects in each age category, specifically those who were 19 to 20, 21 to 22, and 23 to 24 years of age (Table 2 ). One exception was FVC for men who were 23 to 24 years old in cases in which there was no change. For the women, FEV1, FVC, and PEFR were lower in our cohort, with the exception of FEV1 for those in the group of subjects 23 to 24 years of age, and FVC for those in the groups of subjects 21 to 22 and 23 to 24 years of age (Table 2).
Obesity was uncommon in our student cohort, with the mean BMI being < 22 kg/m2 for both men and women. There was no indication that dietary habits reported in the literature (ie, supplemental vitamin C, and fresh fruit, vegetable, and fish consumption)456 contributed to the lung function of our cohort. Seventy-six percent of the male students and 53% of the female students reported that they had participated in "regular" exercise over the past 3 months, but 50% of the men and 67% of the women who did so exercised only once a week or less. A detailed descriptive analysis is shown in Table 3
. The FEV1 and FVC values of male students who exercised three times a week were higher than those who exercised less than once a week (Table 4
).
The prevalence of respiratory symptoms in our subjects was not related to lung function values. However, of the subjects who complained of occasional or frequent cough and sputum production, a higher percentage had not participated in exercise in the previous 3 months (Table 5
).
As the focus of this study was on university students of a limited age group, it was not deemed appropriate to produce lung function prediction equations for direct comparison with those from the study by Lam et al.3 For our restricted age group, the regression equations were as follows: FEV1 (1) = –3.80 + 0.59 * sex + 4.07 * height (R2 = 67.5%) FVC (1) = –5.18 + 0.61 * sex + 5.09 * height (R2 = 62.1%) PEFR (L/s) = –3.74 + 2.36 * sex + 5.53 * height (R2 = 48.7%)
where 1 is male gender and 0 is female gender.
These predicted values illustrate a decrease of at least 10 to 14% when compared with the norms developed by Lam et al3 20 years prior. Age was excluded in all equations, and the R2 values were comparable with those reported in the study by Lam et al.3 Separate analyses by gender were not conducted because the age-by-gender interaction was not significant.
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Discussion
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The objective of this study was to validate the established lung function norms that are commonly used in Asia, in particular in Hong Kong, for contemporary use. We compared the lung function indexes in a contemporary cohort of Hong Kong university students with established norms that were derived 20 years ago. These students were born at the time that the norms established by Lam et al3 were published. Discordance of our findings with those of Lam et al3 supports changes in the Hong Kong population over one generation. Any comparative interpretation must be guarded, however, given that several factors, including technological, environmental, and lifestyle factors, could explain the discrepancy in lung function.
Instrumentation and standardization of testing and measurement procedures are well known for influencing the reliability and validity of lung function measures.212 However, even though the spirometers used in the present study and in those of the study by Lam et al3 were produced by different manufacturers, both systems were calibrated prior to use. Further, the difference in time frame in measures between the two studies was one generation, roughly 20 years, during which time one might expect the effect of instrumentation differences in pulmonary function measurement to be minimal.
With improvement in socioeconomic status as well as the continuing government effort to promote better public health,11 it is to be expected that the health status of the Hong Kong population should improve. This study showed that the BMI of our student cohort fell within the normal range of values and that obesity remains a relatively uncommon finding in our subject population. We anticipated that the subject’s height and possibly BMI would increase with the improved socioeconomic and nutritional status of the people of Hong Kong over the past 20 years. Further, as FEV1 and FVC are proportional to the square of the subject’s height,13 and PEFR is directly proportional to height,3 we expected an increase in lung function parameters. On the contrary, this study supported the idea that the pulmonary indexes for our contemporary cohort of university students were lower than those reported in the study by Lam et al.3
The effect of air pollution on lung function has been well-established,9 and, as southern China becomes more industrialized, air pollution in Hong Kong is worsening. In 1987, the Hong Kong Government established air quality objectives14 for different pollutants using international standards for air quality management. In 2000, the reported annual average of "respirable suspended particulates" in one particularly populated area in Hong Kong was 101 µg/m3, which is twice the amount recommended by the annual air quality objectives. Particulate matter data for 1982 are not available, preventing scientific comparison of air quality between now and 20 years ago; however, data over the past 13 years have shown a marked and progressive decline in the air quality of Hong Kong. The worsening of air quality in Hong Kong over the 20-year lifespan of our subjects may have had a cumulative deleterious effect on their lung function.
The effect of factors such as physical activity and nutrition has been a focus in population health and is emerging as an interest in lung health. There is some evidence10 to support the idea that the reduced physical activity of our cohort may have contributed to the low pulmonary indexes. The only indicator of relative population fitness is the exercise data that are based on self-reports. To achieve the beneficial effects of exercise, an individual should engage in "30 min or more of moderate-intensity physical activity on most, preferably all, days of the week."15 However, only 10% of our male subjects and 6.5% of our female subjects exercised three times a week.
Our study further supported the idea that subjects who exercised regularly reported a lower prevalence of all respiratory symptoms. When compared to the findings of the study by Lam et al,3 a minimally lower percentage of subjects complained of occasional wheezing attacks (study by Lam et al,3 4%; current study, 3%) and coughs with occasional sputum production (study by Lam et al,3 14%; current study, 11.6%). However, 4.2% of our university students complained of shortness of breath on minimal exertion compared to < 1% of the subjects in the study by Lam et al3 with similar complaint; thus this may suggest that while the prevalence of respiratory symptoms does not appear to have changed over the last 20 years, the cardiopulmonary fitness of our young adults may have deteriorated. Longitudinal studies are needed to monitor precisely the fitness changes occurring across generations and their relationship to lung function.
A potential effect of improved nutrition in our cohort of Hong Kong young adults was of interest, given that this group has had the benefit of improved economic conditions, and potentially improved nutrition and diets, compared with their parents, for example. Both FEV1 and FVC have been related to the mean daily intake of vitamin C,5 and high intake of vitamin C and citrus fruit has been reported16 to be associated with good lung function, as indicated by high maximum FEV1. High dietary intake and serum concentrations of vitamin C have been proposed as being protective against respiratory symptoms.17 Fatty fish and its oils have been reported to promote antiinflammatory activity and therefore to provide a salutary effect on lung health.6 Our data, however, did not support the ideas that lung function in our cohort was associated with vitamin C consumption or that respiratory complaints were associated with lower fish consumption. Although compelling, a relationship between nutrition and lung health is a relatively new area of research. This area warrants greater study, given the dietary differences among cultures and individuals, and the changing dietary patterns within the Western culture.
Lung function norms need to be revisited for Asians living in Asia, and, further, such norms may not necessarily be relevant for Asians living in Western countries. Rapid economic growth and development in Asia and elsewhere, and the impact of lifestyle factors may impact on normative values even within a single generation within an ethnic group living in the same geographic region. These findings have implications regarding the definition of normal pulmonary function and its variance over the short term, and shed new light on the dynamic nature of lung function and the meaning of the term norm.
Limitations of the Study
The data for our study and those for the study by Lam et al3 were recorded from different cohorts. The subjects in the study by Lam et al3 were volunteers from among students, residents of homes for the aged, and government service employees, rather than university students. Although both groups had indexes measured in the field rather than in the laboratory, PEFR measurements may be affected by the spirometer that was used. In the study by Lam et al,3 PEFR was measured using a Wright peak flowmeter, and forced expiratory volumes were recorded using a wedge bellows dry spirometer (Vitalograph; Lenexa, KS). The spirometer used in the current study (Microlab 3300; Micro Medical Ltd) employed a digital volume transducer to directly measure expired air at body temperature and ambient pressure saturated with water vapor. Advances in technology make it impractical to standardize these two spirometers, but the decreasing trend in FEV1 and PEFR lends some credence to our comparison.
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Conclusion
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Despite the involvement of our subjects who were Chinese university students, were taller, smoked less, and were not obese, when compared with the data reported by Lam et al3 20 years ago, their pulmonary function was generally lower than that of the subjects in the study by Lam et al.3 Lung function norms not only need to be revisited for Asians living in Asia, but rapid economic growth and development, and the impact of environmental and lifestyle factors may impact on normative values even within a single generation within an ethnic group living in the same geographic region. Our findings shed further insight into the dynamic nature of lung function and have implications regarding the definition of normal pulmonary function and its variance over the short term.
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Acknowledgements
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The investigators are indebted to Christal Kam and Horace Wong for their untiring assistance in the process of data collection.
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Footnotes
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Abbreviations: BMI = body mass index; CO = carbon monoxide; PEFR = peak expiratory flow rate
This project was sponsored by the Celki Medical Company.
Received for publication September 1, 2004.
Accepted for publication January 4, 2005.
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References
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Abstract
Introduction
