Does ethnicity influence lung function in preschool children?

Effective management of respiratory diseases in young children requires objective outcome measures that do not rely simply on parental reports of symptoms, which are known to be unreliable [1,2]. Assessment of lung function forms an integral part of the diagnosis and management of lung disease in both older children and adults and continuous, objective assessments of lung function from birth have recently become possible [3,4]. However, reliable use of such measures is only possible if appropriate normative values are available to distinguish the effects of disease and treatment from those of growth and development.

Until recently, the preschool years (between the child’s second and sixth birthday) had been commonly referred to as the ‘dark ages’ of pediatric lung function testing. Over the last 15 years, an increasing number of publications have described how successful measurements can be obtained in children of this age, and international standards for data collection and interpretation have now been published. Reference data from healthy children are available for a variety of measurements in preschool children, but up until now almost all of these have been in white children.

What is known about the influence of ethnicity on lung function?

During infancy, airway and nasal resistance are significantly lower in black than white infants [5,6] owing to differences in nasal anatomy [7]. Tidal breathing indices, Hering–Breuer reflex activity and total respiratory compliance appear to be similar in the immediate newborn period [8]. Preliminary findings from our laboratory suggest that forced flows and volumes obtained using the raised volume rapid thoracic compression technique in infants of non-white mothers were significantly lower compared with their white counterparts [9]. However, larger numbers of individuals will need to be studied to confirm these findings.

Ethnic differences in lung function have been frequently reported in older children and adults. A recent review of the National Health and Nutrition Examination Survey III data confirmed that African–American subjects had considerably lower forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC), but similar flows and FEV₁/FVC compared with non-Hispanic white subjects [10], suggesting that ethnic differences in lung function are limited to dynamic lung volumes rather than airway or dynamic characteristics. Initially, differences in lung volume were attributed to smaller ratios of trunk-to-standing height among black compared with white subjects [11]. However, sitting height was not found to explain the variability observed in Asian subjects [12] and may not be appropriate for all ethnic groups.

Although there has been an increasing number of publications reporting lung function in preschool children, data from non-white children are sparse. When comparing lung function between black Caribbean and black African, Bangladeshi and white British children aged 2–10 years, McKenzie and colleagues showed that ethnicity was not associated with interrupter resistance [13], while Sylvester and colleagues demonstrated how inappropriate it was to use published prediction equations to interpret lung volume data from Afro–Caribbean children [14]. Given that forced expiratory volumes are significantly lower in older black children and adults compared with their white counterparts, and that similar preliminary findings have been observed in infants, it is highly likely that ethnicity also influences such outcomes during the preschool years. Indeed, preliminary findings from our laboratory have shown that FEV₁ and FVC were significantly lower in Asians compared with white preschool children [15].

Why is this important?

During recent years, there has been increasing awareness both of the social and ethnic inequalities within some lung diseases and the need to reduce such disadvantage [16].

While failure to access services and under-treatment might partly explain this differential [17], the Millennium Cohort [18] and ‘Determinants of Adolescent Social Well-being and Health’ (‘DASH’) [19] studies show that asthma is more prevalent in black Caribbean than white adolescent boys in the UK. The UK government has recently redoubled its efforts to tackle these health inequalities by proposing to tailor resources where health inequalities are concentrated, including stronger incentives for primary care workers to help diagnose problems earlier [20].

Despite progress with adapting methodology, clinical applications of preschool lung function tests were hindered by a lack of appropriate reference data for young children [21]. A recent international collaboration funded by Asthma UK enabled the development of the ‘all-age’ lung function growth charts from 3–80 years (see [101]) [10,22], but these are limited to white subjects as few data were collected from other ethnic groups. In the past, even when attempts to correct for such ethnic differences have been made, these have tended to apply the same fixed adjustment factor across all ages, all ethnic groups, both sexes and all spirometric outcome measures, an approach now shown to be over-simplistic [10,12]. This could potentially lead to misdiagnosis and over- or under-treatment for those of black African and South Asian origin.

The success of the Asthma UK study has contributed to the establishment of the Global Lungs Initiative, a European Respiratory Society Task Force (TF-2009-03) to establish improved all-age multi-ethnic lung function reference values (see [102]). Over 130,000 spirometry data sets from subjects aged 2.5–95 years around the world have now been collated. Findings from an interim report (January 2010) suggest that ethnic differences in lung function can only be resolved if based on comparisons of large numbers of subjects sampled from ethnically homogeneous populations, using similar equipment and techniques.

How do we classify ethnicity?

A word of caution here is necessary. Ethnic-specific equations are not necessarily the best solution to this problem, especially as most of those currently available are based on small samples that may be neither representative nor generalizable. In addition, ethnicity is extremely difficult to define. Terminology with respect to race, ethnicity and culture is likely to be a source of continuing debate and will change according to fashion and political correctness. Not only may self-assigned ethnicity differ from observer-assigned ethnicity, but in certain countries it is against the law to record ethnic origin for any purpose.

The future is ‘brown’

Furthermore, as we move towards a global skin color from marriages across the racial divide [23,24], classifying ethnicity may become an increasingly impossible task! An alternative approach would be for future research in this field to focus on finding appropriate proxy measure(s), which would account for the variability in lung function due to ethnicity.

Could body composition, shape & size be used as a proxy for ethnicity?

Over the past four decades, numerous studies have attempted to quantify the impact of body proportions and ethnic differences on lung function. A recent study confirms the negative effect of body fat on lung function of children and adolescents [25]. Although many studies have improved the extent to which the variance in lung function between certain ethnic groups can be explained, some ethnic and sex-specific differences in lung function remained. It is possible that the most appropriate chest dimensions were not selected or that the methodology for assessment of body composition such as BMI or skinfold thicknesses, which had been routinely used for decades, were inappropriate, as information on fat or lean mass from these methodologies were derived rather than measured [26]. Accurate, noninvasive measurements of body composition can now be readily obtained in the field using stable isotope technology [27]. In addition, a new technology for digital anthropometric measurements using whole-body 3D photonic scanning that could provide detailed data on regional body shape and surface topography has been pioneered [28]. The extent to which these new techniques will be able to identify key body dimensions with which to explain ethnic differences in lung function is, however, yet to be determined.

Conclusion

Although evidence regarding ethnic differences in lung function in preschool children remains sparse, it is likely that such differences do exist. Further data are necessary to explore this, ideally by studying multi-ethnic populations with identical equipment and protocols. Ultimately, correcting for ethnic differences requires a more sophisticated approach to characterizing body shape, size and composition so that global equations, applicable across a wide range of ethnic groups, can be produced, rather than simple use of ethnic population-specific equations. This is essential if we are to improve the accuracy with which we can identify and treat lung disease during early childhood, irrespective of background.

Financial & competing interests disclosure

Sooky Lum is funded by the Medical Research Council, UK and the Wellcome Trust Value in People award. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.