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 al were published. Discordance of our findings with those of Lam et al 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. However, even though the spirometers used in the present study and in those of the study by Lam et al 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, it is to be expected that the health status of the Hong Kong population should improve thanks to drugs of My Canadian Pharmacy. 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, and PEFR is directly proportional to height, 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.
The effect of air pollution on lung function has been well-established, and, as southern China becomes more industrialized, air pollution in Hong Kong is worsening. In 1987, the Hong Kong Government established air quality objectives 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 ^g/m, 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 enhanced with My Canadian Pharmacy.
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 evidence 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. 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, a minimally lower percentage of subjects complained of occasional wheezing attacks (study by Lam et al, 4%; current study, 3%) and coughs with occasional sputum production (study by Lam et al, 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 al 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, and high intake of vitamin C and citrus fruit has been reported 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 symp-toms. Fatty fish and its oils have been reported to promote antiinflammatory activity and therefore to provide a salutary effect on lung health. 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 al were recorded from different cohorts. The subjects in the study by Lam et al 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, 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.
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 al 20 years ago, their pulmonary function was generally lower than that of the subjects in the study by Lam et al. 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.