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ORIGINAL PAPERS: Epidemiology

Longitudinal study of the influence of lung function on vascular health from adolescence to early adulthood in a British multiethnic cohort

Lu, Yaoa,b; Sooky, Lumc; Silva, Maria Joãoa; Molaodi, Oarabile R.d; Karamanos, Alexise; Cruickshank, J. Kennedya; Harding, Seeromaniea

Author Information
doi: 10.1097/HJH.0000000000001455

Abstract

INTRODUCTION

In adulthood, impaired lung function is inversely related to the incidence of stroke [1], myocardial infarction, and cardiovascular mortality [2], independently of (after adjustment for) traditional cardiovascular risk factors in middle-age populations. Given lung function's significance for adult vascular health, surprisingly few studies have examined the interrelationships of their developmental trajectories from childhood. Lung development starts in utero and continues through adolescence and early adulthood [3,4], which raises the question whether suboptimal lung growth and development could affect later vascular function and blood pressure (BP).

Whether associations between low lung function and incidence of vascular events could be related to or mediated by its link with BP and vessel dysfunction remain unclear. The inverse association between lung function and BP has been reported in several adult studies [5–7]. In middle aged (45–59 years) and elderly (>60 years) population, lung function parameters measured at age 40 were stronger predictors of arterial stiffness [aortic pulse wave velocity (PWV) and pressure or flow wave reflection measured as augmentation index (AIx)] than lung function at age 60 [8–10]. Furthermore, lung function and vascular function may track each other through convergent inflammatory or metabolic pathways throughout life, or genetic susceptibility. Such low-grade systemic inflammation is indicated by higher levels of C-reactive protein, fibrinogen, and other systemic inflammatory markers [11].

There is increasing evidence of ethnic differences in the development of both lung function and BP. Lung function is lower among South Asians and Black African origin children compared with White European peers even after adjustment for age, sex, and height, findings which led to the recent development of ethnic specific equations [12].

A faster rise of BP has been observed among African origin children in the United States [13] and among all ethnic minority groups in the United Kingdom [14,15] than their White counterparts. These studies signal that ethnic differences in growth velocities in early life and postnatally are important determinants of cardiorespiratory development.

To date, information is lacking on the determinants of cardiorespiratory development from an ethnically diverse population in early adulthood, a time when physical health is at its peak and when early signs of disease begin to appear. Studies that tracked growth from childhood and collected biomarkers and vascular measures are mainly of White Europeans with few in Europe varying in ethnic make-up [16,17]. The Determinants of Adolescent Social Well-Being and Health (DASH) study, established in 2002, has followed health and social exposures of over 6000 young Londoners (United Kingdom), including 80% ethnic minorities, over the last 12 years. A pilot follow-up study of the cohort, now in their early 1920s, was recently completed. We used the DASH study to examine potential associations between lung function and BP, PWV, and AIx from early adolescence to early 1920s, and whether any observed association is influenced by sex, health behaviours, and socioeconomic circumstances (SEC).

METHOD

Details of the Determinants of Adolescent Social Well-Being and Health study can be found elsewhere

In 2002–2003, a total of 6643 students, aged 11–13 years, from 51 secondary schools in 10 London boroughs, were recruited [18]. In 2005–2006, 4785 (88% of children in 49 schools, 72% of the initial cohort), participated in the first follow-up aged 14–16 year. A 10% subsample (N = 665, 97% of those contacted) participated in the pilot follow-up, completed in March 2014. The subsample consisted of 107 White UK, 102 Black Caribbean, 132 Black African, 99 Indian, 111 Bangladeshi or Pakistani, and 115 other (mainly mixed) ethnicities. We first located the sample and 81% (5414 of 6643) of the cohort was traced through friendship networks, social media, and community campaigns. We then randomly selected 100 (50 per sex) per ethnic group, and pragmatically attempted, by repeated random selection, to ensure representation across the London boroughs, schools, and SEC at 11–13 years.

The study was approved by the Multicentre Research Ethics Committee and additionally at age 21–23 years from National Health Service Local Research Ethics Committees. Written informed consent was obtained from all participants. Ethnicity was self-reported, checked against reported parental ethnicity, and grandparents’ country of birth. Bangladeshis and Pakistanis were combined because of small sample sizes.

Spirometry data management and exclusion criteria

Spirometric assessments were undertaken using a portable Micro-plus spirometer (Micro Medical Ltd., Kent, UK) at 11–13 years and 21–23 years in accordance with published guidelines [19]. Details of data quality and acceptability from 11–13 years survey have been published [20]. Data collected at 21–23 years were overread by a senior respiratory physiologist (University College London Great Ormond Street Institute of Child Health) to ensure appropriate quality control.

As the cohort is a healthy community sample of young people, the forced expired volume in 1 s (FEV1) provides the optimal survey measure of airway caliber, with lower values or rapid decline in FEV1 being associated with higher morbidity or unfavourable prognosis [21]. Missing data, implausible values or extreme outliers (−3< or >3 Z-scores) for height and FEV1, (e.g.: when FEV1 between 11–13 years and 21–23 years differed by <100 ml), or those with current asthma were excluded (n = 177; Figure S1, https://links.lww.com/HJH/A804).

After adjusting for sex, age, and standing height, FEV1 was expressed as Z-scores using the Global Lung Function Initiative (GLI-2012) ethnic-specific equations [12]. As reliable spirometric equations for South Asians are lacking, the GLI-Black equation, which provided a better approximation for interpreting South Asian data was used instead [22]. Within a healthy population, the mean (SD) FEV1 Z-scores would approximate 0(1). A Z-score difference in FEV1 is equivalent to 12% of predicted FEV1 at these ages.

Anthropometry, blood pressure, arterial stiffness, and wave reflection measurements

Field staff was trained for 1 week prior to the start of fieldwork, and were recertified at 6-month intervals. Equipments were calibrated regularly by the field supervisors. During adolescence, assessments were conducted in schools and at 21–23 years, in community locations (e.g. local general practitioner's surgeries, local community pharmacies, survey clinic rooms at Kings College London).

Height was measured using portable stadiometers (Leicester, UK), to the nearest 0.1 cm and weight using Salter electronic scales, to the nearest 0.1 kg. Waist circumference (cm) was measured midway between the 10th rib and the top of the iliac crest, and 0.5 cm subtracted to correct for measurement over T-shirt or vest. The mean of two duplicate measures was derived for the waist to height ratio (WHtR). SBP, and DBP were measured at both time points using validated OMRON M5-I semiautomatic devices (Kyoto, Japan), and appropriately sized cuffs, after participant had sat quietly for a timed 5 min, with more than 1 min between three readings. The mean of second and third readings was analysed, as previously reported [14]. At 21–23 years, central SBP (cSBP), pulse, PWV, central AIx (AIxao), and brachial BP were also measured using the Arteriograph 24-h device (TensioMed, Budapest, Hungary), previously calibrated and standardized [23].

Social exposures

A self-administered questionnaire measured smoking, alcohol consumption, racism, and SEC at 11–13 years and 21–23 years. Reported racism was assessed using validated questions on unfair treatment on grounds of race, skin colour, country of birth, or religion in various locations (school, neighbourhoods, and work) [24]. In adolescence, SEC was assessed using parental employment and the Family Affluence Scale [25] based on number of cars, computers, and holidays. In adulthood, SEC was measured using own education and employment.

Statistical analyses

Continuous variables (SBP, DBP, WHtR, FEV) did not require transformation as the Shapiro–Wilk test indicated normal distributions. For BP, we first examined the cross-sectional associations between FEV1 Z-score and BP at 11–13 years and at 21–23 years, using linear regression models. We then used linear mixed models to examine the association between the change in FEV1 and the change in BP, between 11–13 years and 21–23 years. In these latter analyses zFEV1, sex, and ethnicity at 11–13 years were added as fixed covariates, and change in zFEV1 and remaining social exposures were added as time varying covariates. All variables were added stepwise and two models (model with age, sex, ethnicity, WHtR, and the model with further adjustment for all social exposures) were presented. For outcomes that were measured only at 21–23 years (cSBP, PWV, Aix, and FEV1), linear regression models were used to examine associations between these outcomes and forced expiratory volume Z-scores in 1 s (zFEV1) at 11–13 years and at 21–23 years. Two sets of models were run. The first set was with zFEV1 at 11–13 years to examine, whether at this critical period of adolescence, there was an association with these outcomes at 21–23 years. The second repeated the analyses with zFEV1 at 21–23. All the analyses were performed STATA 13 (Stat Corp., College Station, Texas, USA). P < 0.05 were considered to be statistically significant.

RESULTS

Study population

After exclusions, 488 subjects (53.1% males) were included in the analyses. At age 11–13 years, the longitudinal sample's profile for most anthropometric parameters, BP and FEV1 did not vary significantly by gender (Table 1). At 21–23 years, men were taller and had higher BP, brachial SBP, cSBP, and PWV but a lower heart rate and AIxao. Mean zFEV1 for all ethnic groups and at both ages were within ± 0.5 Z-scores; Table S1, https://links.lww.com/HJH/A804). The 10-year increase in height, SBP, and DBP was greater for Whites than for other ethnic minority groups (Table S2, https://links.lww.com/HJH/A804). At 21–23 years, Whites also had a higher PWV and lower AIxao (Table S1, https://links.lww.com/HJH/A804).

TABLE 1
TABLE 1:
Sample characteristics by sex

Forced expiratory volume Z-scores in 1 s and blood pressure

Analyses of the cross-sectional data at 11–13 years showed that zFEV1 was positively and independently associated with SBP at 11–13 year (Table 2). Unadjusted, an increase in 1 zFEV1 score was associated with +2.1 [95% confidence interval (CI) 1.3–2.9] mmHg rise in SBP. Adjusting for age, sex, ethnicity, and WHtR reduced this effect a little [+1.90 (1.11–2.68) mmHg]. There was no significant change on further adjustment of racism, parental employment, current smoking, and alcohol use. zFEV1 was not associated with DBP at 11–13 years. At 21–23 years, zFEV1 was positively but not significantly associated with SBP (Table 2). Figure 1 shows the predicted means by ethnicity, derived from the core model, adjusted for age, sex, and WHtR. A similar pattern was observed across the ethnic groups, with a stronger association between zFEV1 and SBP at 11–13 years than 21–23 years. zFEV1 was not associated with DBP (Table S3, https://links.lww.com/HJH/A804).

TABLE 2
TABLE 2:
Cross-sectional and longitudinal associations between forced expiratory volume in 1 s and SBP from early childhood to young adults
FIGURE 1
FIGURE 1:
Predicted mean systolic blood pressure by zFEV1 (superscript for footnote) at 11–13 years and at 21–23 years, derived from linear regression models adjusted for age, sex, ethnicity, and waist to height ratio. DASH, The Determinants of Adolescent Social Well-being and Health; zFEV1, forced expiratory volume Z-scores in 1 s.

In analysis of the longitudinal data, changes in zFEV1 between 11–13 years and 21–23 years were associated with SBP between 11–13 years and 21–23 years (Table 2). Adjusting for age, gender, ethnicity, changes in WHtR were positively associated with SBP, the pooled average being +1.38 (0.3–1.6) mmHg, unaltered by lifestyle and social exposures. Changes in zFEV1 were not associated with DBP between 11–13 years and 21–23 years (Table S4, https://links.lww.com/HJH/A804).

The associations between forced expiratory volume Z-scores in 1 s and central SBP, pulse wave velocity, and central augmentation index

zFEV1 at 11–13 years or 21–23 years was not significantly associated with cSBP, PWV, or AIx at 21–23 years (Table 3). PWV was significantly associated with sex (women lower), age, WHtR, and heart rate, the latter two also reducing AIx, which was unaffected by age or social exposures.

TABLE 3
TABLE 3:
The influence of forced expiratory volume in 1 s from early childhood to young adults on central blood pressure, pulse wave velocity, and augmentation index at 21–23 year

DISCUSSION

To the best of our knowledge, this is the first longitudinal study with a diverse ethnic composition, as yet from a pilot follow-up, to report an association between lung function and SBP between adolescence and early adulthood. The longitudinal changes in lung function are positively associated with SBP during this part of the life course when considerable growth occurs. The mechanisms underlying these associations are not well understood but could illustrate how greater lung growth marginally, but likely reversibly, impairs venous return to the heart over this growth period, with a reflex rise in SBP.

Normal developmental trajectory for lung function shows that it increases in childhood, peaks in young adulthood and then gradually decreases with age [12,26,27]. A US-based longitudinal study (N = 508) showed that a decline in lung function from average peak age (29.4 years) to 35 years significantly predicted incidence of hypertension between mean ages 35–45 years. In correspondence with DASH findings, the cross-sectional Wheezing Illnesses Study Leidsche Rijn (WHISTLER) study of 5-year-olds (N = 382) in the Netherlands showed a positive relationship between FEV1 and SBP (+4.8 mmHg/l, 95% CI: −0.3 to 10.0). WHISTLER also showed a positive relationship with DBP (+4.6 mmHg/l, 95% CI: −0.2 to 9.4) adjusted for age, sex, weight, and height [28]. The results of WHISTLER and DASH, though discrepant in relation to DBP, suggest that the positive relationship between BP and lung function is normal physiological development in childhood and in early adolescence. As the WHISTLER result suggests a litre change in FEV1 was associated with ∼5 mmHg in SBP change in a 5-year-old child, when mean (SD) FEV1 would be only 1.3(0.2) l, a change of 200 ml (1 SD) in FEV1 would be associated with a 1 mmHg increase in SBP. Similar results were observed here in DASH.

As with lung function, the association between PWV and lung function has not been studied before in healthy children. A cross-sectional study of asthmatic children (aged 6.1–15.3 years) in Switzerland showed that carotid-femoral PWV was inversely associated (r2=0.20, P = 0.004) with FEV1[29]. It is noteworthy that the effect size of about +2 mmHg increase in SBP these studies with 1 Z-score of FEV1 is comparable across these studies of 5-year-old and of 11–13 years in DASH. Perhaps in contrast to the DASH findings, a cross-sectional community-based study of 249 8-year-old children in Australia showed FEV1 was inversely associated with carotid (not brachial, as here) AIx75 (coefficient = −0.17, P = 0.03) and forced vital capacity (coefficient = −0.29, P < 0.001) [30].

Our results showed that lung function is associated with SBP at 11–13 years, and the change in lung function from 11 to 23 years is associated with the change in SBP. At 21–23 years lung function was not associated with SBP or PWV. There are very few studies that have examined cardiorespiratory health in healthy young adults. Garcia-Larsen et al.[31] showed no association between lung function and hypertension in 25-year-olds. We are not aware of any studies that have examined the association of lung function and PWV in young adults. One possible explanation for the lack of association between lung function and PWV is that PWV was measured only at 21–23 years (not at 11–13 years). At 11–23 years, lung and vascular function are expected to be within a normal range. Thus, these findings cannot be extrapolated to older age when other risk factors can affect both parameters. In addition, pollutants can deeply influence BP [32] as well as lung function [33], even in adolescence. The impact of pollution is the focus of separate analyses.

Strengths and weaknesses of study

Social exposures, for example, deprivation, influence growth [34], which in turn influences cardiorespiratory development. The studies cited above did not examine potential moderating influences from social exposures. DASH contains information on socioeconomic disadvantage and behaviours, which enabled an examination of their association on the zFEV1-cardiovascular disease measure. DASH contains a diverse sample, has high retention rates and low item-nonresponse, mainly because of enormous community support. Lung function was not measured at the second follow-up of the cohort at 14–16 years, which could have provided valuable insight into the pattern of changing associations with BP in adolescence. The lack of data before age 11 years and the relatively small sample sizes for the ethnic groups in the pilot follow-up are limitations. Prior to DASH a large-scale study with an explicit focus on ethnicity had not been attempted. The use of the GLI-2012 ethnic-specific equations rather than absolute FEV also strengthened the analysis. These robust equations have been shown to be appropriate for London school children [35] and the small offset (≤0.5 Z-scores) in mean FEV1 in all ethnic groups observed in this study suggest a sample size issue. Quanjer et al. suggested that a dataset of at least 300 (150 men and 150 women) would be required to validate reference values to avoid spurious differences because of sampling error [36]. Despite relatively small numbers, these findings in a tight age range provide strong justification for future studies on the degree and how childhood and adolescent lung function influence vascular development to improve understanding of the developmental interaction of cardio-respiratory systems.

ACKNOWLEDGEMENTS

We acknowledge the invaluable support of participants and their parents, the Participant Advisory Group, schools, civic leaders, local GP surgeries and community pharmacies, the Clinical Research Centre at Queen Mary University of London, the Clinical Research Facility at University College Hospital, the survey assistants and nurses involved with data collection, Rachel Bonner, senior respiratory physiologist (UCL GOS ICH) for spirometry training and over-reading of data for quality control, the Primary Care Research Network, and Professor Sanders and J.K.C at the Diabetes and Nutritional Sciences Division at Kings College London for hosting the feasibility study. H.S. is the Principal Investigator of DASH. All authors contributed to study design, analyses, and writing of the article. The study was funded by the MRC (MC_U130015185/MC_ UU_12017/13), Chief Scientist Office (SPHSU13), North Central London Research Consortium, and the Primary Care Research Network.

Conflicts of interest

There are no conflicts of interest.

Reviewers’ Summary Evaluations

Reviewer 2

The present longitudinal study aims to demonstrate a relationship between vascular and lung function considering that the alterations of both systems can predict cardiovascular events. The most interesting and intriguing finding is that forced expiratory volume modifications are associated with systolic blood pressure values from adolescence (11-13 years) to young adulthood (10 years after). Obviously, the study is descriptive and it is not possible to establish a clear cause-effect relationship, also considering that lung function is not related to aortic pulse way velocity, one of the main determinants of systolic blood pressure. However, the study demonstrates an important relationship between pulmonary and vascular function, which might be of great relevance in the pathogenesis of cardiovascular disease.

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Keywords:

augmentation index; blood pressure; forced expiratory volume; longitudinal studies; pulse wave velocity

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