Age, period, and cohort effects. Influences on differences between cross-sectional and longitudinal pulmonary function results

Period and cohort effects: consequences on spirometric lung function in Norway during the 20th century

Background and aim

Several factors can influence measured lung function over time. The aim of this study was to investigate period and cohort effects on spirometric measures in a large general population sample in Norway during the 20th century, using Global Lung Function Initiative (GLI-2012) equations as a reference.

Methods

36 466 subjects (born 1894-1969) from four cross-sectional surveys conducted between 1965 and 1999 were included, with harmonised data on smoking habits, respiratory symptoms, lung diseases, education and spirometry. Changes in forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) z-scores in healthy subjects across surveys were explored to investigate period effects. Linear mixed-effects models of FEV₁ and FVC z-scores on birth cohort, with survey as random effect, were used to investigate cohort effects, both in subjects of the total population and in healthy ones.

Results

Relatively higher FEV₁ and FVC z-scores in healthy subjects were found in the first survey (1965-1970) compared to the more recent ones (1988-1999), suggesting period effects. FEV₁ and FVC z-scores increased significantly with birth cohort from 1894 to 1935, after adjustment for covariates. A more stable trend of FEV₁ and FVC z-scores with birth cohort was evidenced for subjects born more recently (1945-1969).

Conclusions

An increase of lung function with year of birth was observed in Norwegian subjects during the first half of the 20th century. The impact of period effects on lung function decreased from 1965 to 1999.

Age-related longitudinal change in cardiac structure and function in adults at increased cardiovascular risk

AIM

Heart failure (HF) incidence increases markedly with age. We examined age-associated longitudinal change in cardiac structure and function, and their prediction by age and cardiovascular disease (CVD) risk factors, in a community-based cohort aged ≥60 years at increased CVD risk but without HF.

METHODS AND RESULTS

CVD risk factors were recorded in 3065 participants who underwent a baseline echocardiographic examination, of whom 2358 attended a follow-up examination 3.8 [median, inter-quartile range (IQR) 3.5, 4.2] years later. Median age was 71 (IQR 67, 76) years and 55% of participants were male. Age was associated with longitudinal increase in left ventricular (LV) mass index (LVMI); decrease in LV volumes; increase in LV ejection fraction; decrease in mitral annular systolic velocity; decrease in diastolic function (decreased mitral early diastolic annular velocity (e'); and increase in left atrial volume index, mitral peak early diastolic flow velocity (E)/e' ratio, and tricuspid regurgitant velocity (TR_Vmax ) in men and women, except for TR_Vmax in men). In multivariable analysis, longitudinal increase in LVMI was explained by CVD risk factors alone, whereas age, together with CVD risk factors, independently predicted longitudinal change in all other echocardiographic parameters. CVD risk factors were differentially associated with longitudinal change in different echocardiographic parameters.

CONCLUSIONS

Whereas the increase in LVMI with age was explained by CVD risk factors alone, age, together with risk factors, independently predicted longitudinal change in all other echocardiographic parameters, providing evidence for age-specific mechanisms of change in cardiac structure and function as people age. Age-associated change in LVMI, LV volumes, and diastolic function resembled what might be expected for the evolution of HF with preserved ejection fraction. Given the differential association of different CVD risk factors with longitudinal change in different echocardiographic parameters, therapies aimed at attenuation of age-associated change in cardiac structure and function, and HF evolution, will likely need to address multiple CVD risk factors.

Socioeconomic Status and Longitudinal Lung Function of Healthy Mexican Children

Introduction

Our aim was to estimate the longitudinal effect of Socioeconomic status (SES) on lung function growth of Mexican children and adolescents.

Materials and Methods

A cohort of Mexican children in third grade of primary school was followed with spirometry twice a year for 6 years through secondary school. Multilevel mixed-effects lineal models were fitted for the spirometric variables of 2,641 respiratory-healthy Mexican children. Monthly family income (in 2002 U.S. dollars [USD]) and parents’ years completed at school were used as proxies of SES.

Results

Individuals with higher SES tended to have greater height for age, and smaller sitting height/standing height and crude lung function. For each 1-year increase of parents’ schooling, Forced expiratory volume in 1 sec (FEV₁) and Forced vital capacity (FVC) increased 8.5 (0.4%) and 10.6 mL (0.4%), respectively (p <0.05) when models were adjusted for gender. Impact of education on lung function was reduced drastically or abolished on adjusting by anthropometric variables and ozone.

Conclusions

Higher parental schooling and higher monthly family income were associated with higher lung function in healthy Mexican children, with the majority of the effect likely due to the increase in height-for-age.

Longitudinal lung function growth of Mexican children compared with international studies

Introduction

Our aim was to compare the longitudinal lung function growth of Mexican children and adolescents with the collated spirometric reference proposed for international use and with that of Mexican-Americans from the National Health State Examination Survey III (NHANES) III study.

Materials and Methods

A cohort of Mexican children in third year of primary school was followed with spirometry twice a year through secondary school. Multilevel mixed-effects lineal models separated by gender were fit for the spirometric variables of 2,641 respiratory-healthy Mexican children expressed as Z-scores of tested reference equations. Impact of adjustment by sitting height on differences with Mexican-American children was observed in a subsample of 1,987 children.

Results

At same gender, age, and height, Mexican children had increasingly higher forced expiratory volume in 1 s (FEV₁) and Forced vital capacity (FVC) than the children from the collated reference study (mean Z-score, 0.68 for FEV₁ and 0.51 for FVC) and than Mexican-American children (Z-score, 0.23 for FEV₁ and 0.21 for FVC) respectively. Differences with Mexican-Americans were not reduced by adjusting by sitting height.

Conclusions

For reasons that remain unclear, the gender-, age-, and height-adjusted lung function of children from Mexico City is higher than that reported by several international studies.

Accelerated spirometric decline in New York City firefighters with α₁-antitrypsin deficiency

BACKGROUND

On September 11, 2001, the World Trade Center (WTC) collapse caused massive air pollution, producing variable amounts of lung function reduction in the New York City Fire Department (FDNY) rescue workforce. α₁-Antitrypsin (AAT) deficiency is a risk factor for obstructive airway disease.

METHODS

This prospective, longitudinal cohort study of the first 4 years post-September 11, 2001, investigated the influence of AAT deficiency on adjusted longitudinal spirometric change (FEV₁) in 90 FDNY rescue workers with WTC exposure. Workers with protease inhibitor (Pi) Z heterozygosity were considered moderately AAT deficient. PiS homozygosity or PiS heterozygosity without concomitant PiZ heterozygosity was considered mild deficiency, and PiM homozygosity was considered normal. Alternately, workers had low AAT levels if serum AAT was ≤ 20 μmol/L.

RESULTS

In addition to normal aging-related decline (37 mL/y), significant FEV(1) decline accelerations developed with increasing AAT deficiency severity (110 mL/y for moderate and 32 mL/y for mild) or with low AAT serum levels (49 mL/y). Spirometric rates pre-September 11, 2001, did not show accelerations with AAT deficiency. Among workers with low AAT levels, cough persisted in a significant number of participants at 4 years post-September 11, 2001.

CONCLUSIONS

FDNY rescue workers with AAT deficiency had significant spirometric decline accelerations and persistent airway symptoms during the first 4 years after WTC exposure, representing a novel gene-by-environment interaction. Clinically meaningful decline acceleration occurred even with the mild serum AAT level reductions associated with PiS heterozygosity (without concomitant PiZ heterozygosity).

Development of pulmonary abnormalities in patients with common variable immunodeficiency: associations with clinical and immunologic factors

BACKGROUND

Patients with common variable immunodeficiency (CVID) have low serum IgG, IgA, and/or IgM levels and recurrent airway infections. Radiologic pulmonary abnormalities and impaired function are common complications. It is unclear to what extent IgG replacement treatment prevents further pulmonary damage and how factors beside infections may contribute to progression of disease.

OBJECTIVES

To study the development of pulmonary damage and determine how clinical and immunologic factors, such as serum IgG, may contribute to possible changes.

METHODS

In a retrospective, longitudinal study of 54 patients with CVID already treated with immunoglobulins, we examined changes of lung function and findings on high-resolution computed tomography (HRCT), obtained at 2 time points (the date of the last pulmonary function measurement before April 2005 [T1] and the date of the measurement performed closest to 5 years earlier [T0]) 2 to 7 years apart and explored possible relations to clinical and immunologic factors such as levels of IgG, tumor necrosis alpha (TNF-alpha), and mannose-binding lectin (MBL) in serum.

RESULTS

Despite a mean (SD) serum IgG level of 7.6 (2.3) g/L for all the patients during the entire study period, lung function decreased from T0 to T1. The combination of a low serum IgA level and serum MBL was associated with the presence of bronchiectasis and lower lung function and with worsening of several HRCT abnormalities from T0 to T1. Increased serum levels of TNF-alpha were related to deterioration of gas diffusion. A mean serum IgG level less than 5 g/L between T0 and T1 was associated with worsening of linear and/or irregular opacities seen on HRCT.

CONCLUSION

For a period of 4 years, lung function and HRCT deteriorated in CVID patients treated with immunoglobulins.

Lung function in rescue workers at the World Trade Center after 7 years

BACKGROUND

The terrorist attacks on the World Trade Center on September 11, 2001, exposed thousands of Fire Department of New York City (FDNY) rescue workers to dust, leading to substantial declines in lung function in the first year. We sought to determine the longer-term effects of exposure.

METHODS

Using linear mixed models, we analyzed the forced expiratory volume in 1 second (FEV(1)) of both active and retired FDNY rescue workers on the basis of spirometry routinely performed at intervals of 12 to 18 months from March 12, 2000, to September 11, 2008.

RESULTS

Of the 13,954 FDNY workers who were present at the World Trade Center between September 11, 2001, and September 24, 2001, a total of 12,781 (91.6%) participated in this study, contributing 61,746 quality-screened spirometric measurements. The median follow-up was 6.1 years for firefighters and 6.4 years for emergency-medical-services (EMS) workers. In the first year, the mean FEV(1) decreased significantly for all workers, more for firefighters who had never smoked (a reduction of 439 ml; 95% confidence interval [CI], 408 to 471) than for EMS workers who had never smoked (a reduction of 267 ml; 95% CI, 263 to 271) (P<0.001 for both comparisons). There was little or no recovery in FEV(1) during the subsequent 6 years, with a mean annualized reduction in FEV(1) of 25 ml per year for firefighters and 40 ml per year for EMS workers. The proportion of workers who had never smoked and who had an FEV(1) below the lower limit of the normal range increased during the first year, from 3% to 18% for firefighters and from 12% to 22% for EMS workers, stabilizing at about 13% for firefighters and 22% for EMS workers during the subsequent 6 years.

CONCLUSIONS

Exposure to World Trade Center dust led to large declines in FEV(1) for FDNY rescue workers during the first year. Overall, these declines were persistent, without recovery over the next 6 years, leaving a substantial proportion of workers with abnormal lung function.

Interpreting longitudinal spirometry: weight gain and other factors affecting the recognition of excessive FEV1 decline

BACKGROUND

Excessive FEV(1) loss in an individual or a group can reflect hazardous exposures and development of lung disease. However, multiple factors may affect FEV(1) measurements.

METHODS

Using medical screening data collected in 1884 chemical plant workers between 1973 and 2003, the influence of multiple factors on repeated measurements of FEV(1) was examined.

RESULTS

The FEV(1) level was associated with age, height, race, sex, cigarette smoking, changes in body weight, and spirometer model. After controlling for these factors, longitudinal FEV(1) decline averaged 23.8 ml/year for white males; an additional loss of 8.3 ml was associated with one pack-year smoking and 5.4 ml with a one pound weight gain. Depending on the spirometer model, FEV(1) differed by up to 95 ml.

CONCLUSIONS

The study results provide quantitative estimates of the effect of specific factors on FEV(1), and should be useful to health professionals in the evaluation of accelerated lung function declines.

Changes in body mass index by birth cohort in Japanese adults: results from the National Nutrition Survey of Japan 1956-2005

Background The National Nutrition Survey, Japan (NNS-J) provides annual anthropometric information for a whole nation over 50 years. Based on this survey, the mean body mass index (BMI) of Japanese men and elderly women has increased in recent decades, but that of young women has decreased. We examined the effect of birth cohort on this phenomenon.

Methods We analysed data from the NNS-J for subjects aged 20–69 years. BMI during 1956–2005 and the prevalence of overweight and obesity (BMI ≥ 25 kg/m²) during 1976–2005 were estimated.

Results The BMI increased with age in every birth cohort, with similar increments, and did not peak until 60–69 years of age. However, with cross-sectional age, the BMI usually peaked before 60–69 years of age. The differences among cohorts already existed at 20–29 years of age, and slightly increased in men between 20–29 and 30–39 years of age. The BMI in all male age groups increased from the 1891–1900 through 1971–80 cohorts. However, in women, the figure increased until the 1931–40 cohorts, but later decreased. Changes in prevalence were generally consistent with changes in BMI. The recent increase (decrease in young women) in the mean BMI is attributable to birth cohort, indicating that thinner (fatter) and less recent birth cohorts have been replaced by fatter (thinner) ones.

Conclusions A cohort effect was quantitatively demonstrated based on a repeated annual survey. In Japan, the differences in BMI among cohorts were already established by young adulthood.

The association between hospitalisation for pneumonia and the diagnosis of lung cancer

Pneumonia may mask or be the first sign of lung cancer. The literature is, however, sparse. We compared the incidence of lung cancer among patients hospitalised for pneumonia with a general population. The patients (index group, N=7044) were hospitalised for pneumonia from 1988 to 2002 at Akershus University Hospital. The reference group was recruited from a general population survey (N=81,373) performed during 1984-1986 and 1995-1997. We had detailed information on smoking habits in both groups. Data on lung cancer incidence, emigration, and death were obtained from the Cancer Registry of Norway. Data were analyzed using multivariate Poisson regression. There were 177 cases of lung cancer in the index group and 608 cases in the reference group. Current smoking modified the association between pneumonia and lung cancer. Among current smokers and non-smokers the incidence density ratio (IDR) was 6.0 (95% confidence interval) (4.6-7.8) and 12.0 (8.6-16.9) in the index group compared with the references, respectively. The crude IDR decreased from 78.4 (43.8-146) 0-3 months after the inclusion to 2.4 (1.4-3.7) 6 years after inclusion. In the index group the IDR was only slightly higher for smokers than non-smokers. Patients hospitalised for pneumonia had an increased incidence of lung cancer compared with the general population. This risk persisted for 6 years after the onset of the lung infection.

Pulmonary function after exposure to the World Trade Center collapse in the New York City Fire Department

RATIONALE

On September 11, 2001, the World Trade Center collapse created an enormous urban disaster site with high levels of airborne pollutants. First responders, rescue and recovery workers, and residents have since reported respiratory symptoms and developed pulmonary function abnormalities.

OBJECTIVES

To quantify respiratory health effects of World Trade Center exposure in the New York City Fire Department.

MEASUREMENTS

Longitudinal study of pulmonary function in 12,079 New York City Fire Department rescue workers employed on or before 09/11/2001. Between 01/01/1997 and 09/11/2002, 31,994 spirometries were obtained and the FEV(1) and FVC were analyzed for differences according to estimated World Trade Center exposure intensity. Adjusted average FEV(1) during the first year after 09/11/2001 was compared with the 5 yr before 09/11/2001. Median time between 09/11/2001 and a worker's first spirometry afterwards was 3 mo; 90% were assessed within 5 mo.

MAIN RESULTS

World Trade Center-exposed workers experienced a substantial reduction in adjusted average FEV(1) during the year after 09/11/2001 (372 ml; 95% confidence interval, 364-381 ml; p < 0.001) This exposure-related FEV(1) decrement equaled 12 yr of aging-related FEV(1) decline. Moreover, exposure intensity assessed by initial arrival time at the World Trade Center site correlated linearly with FEV(1) reduction in an exposure intensity-response gradient (p = 0.048). Respiratory symptoms also predicted a further FEV(1) decrease (p < 0.001). Similar findings were observed for adjusted average FVC.

CONCLUSIONS

World Trade Center exposure produced a substantial reduction in pulmonary function in New York City Fire Department rescue workers during the first year after 09/11/2001.

Repeated measures of FEV1 over six to twelve months: what change is abnormal?

Monitoring change in FEV1 (deltaFEV1) is useful for assessing adverse respiratory effects in an individual, but high variability impedes reliable recognition of accelerated decline. The American Thoracic Society (ATS) recommends a > or =15% year-to-year FEV1 decline for clinical significance. To evaluate the applicability of this criterion in health monitoring programs, we examined the mean, lower 5th percentile, and lower 5% cutoff value of deltaFEV1 determined from 2 tests at 6- and 12-month intervals using data obtained with ATS-recommended equipment and procedures in 389 white male workers, each with 3 to 11 spirometry tests over 5 years. Results indicate that when healthy working males perform spirometry according to ATS standards, a yearly decline in FEV1 greater than 8% or 330 mL should not be considered normal, whereas the 15% ATS criterion could be appropriate in clinical settings.

Depressive symptoms and mortality in a prospective study of 2,558 older adults

OBJECTIVE

The authors report results from a 7-year prospective study of depression and mortality in 2,558 Medicare recipients age 65 and older.

METHODS

This report is based on a secondary data analysis of a randomized controlled trial that evaluated the cost-effectiveness of preventive services for older enrollees in an HMO.

RESULTS

Subjects with mild-to-moderate depression at baseline did not have an increased risk of mortality compared with those without significant depression. The 3% of older adults with the most severe depressive syndromes, however, had significant increases in mortality, even after adjusting for demographics, health risk behaviors, and chronic medical disorders.

CONCLUSION

The increase in mortality in this group of older adults was comparable to that in participants with chronic medical disorders such as emphysema or heart disease.

Familial correlation in the decline of forced expiratory volume in one second

Studies have shown evidence of significant parent-offspring and sibling correlation in FEV1, but familial aggregation of decline of FEV1 over time has not been reported. Our study population comprised 392 families enrolled in the Tucson Epidemiological Study of Airway Obstructive Diseases. Subjects were older than 18 yr of age and performed at least 3 pulmonary function tests over 5 to 20 yr. The slope of FEV1 was calculated for each subject using simple linear regression. Multiple regression models were used to compute standardized residual slope values adjusted for possible confounders. Familial correlation analysis on residual slope values demonstrated no evidence of spousal or parent-offspring correlation. However, sibling pairs were highly correlated (r = 0.256, p < 0.001, n = 166), especially smoking-concordant pairs (r = 0.483, p < 0.01 for ever-smokers, and r = 0.280, p < 0.05 for never-smokers). The residual slopes of smoking-discordant siblings were not significantly correlated (r = 0.031, p < 0.77). Genetic susceptibility to an accelerated rate of decline associated with smoking may be evidenced in the increased correlation among smoking sibling pairs, and in the lack of correlation among smoking-discordant sibling pairs. High sibling correlation in the absence of parent-offspring correlation is compatible with a recessive model of inheritance.

Changes in carbon monoxide transfer over 22 years in middle-aged men

We measured single breath CO transfer (T(LCO)), single breath alveolar volume (VA), CO transfer coefficient (K(CO)) and forced expiratory volume in 1 sec (FEV1) in 84 men, mean age 40.5 years at recruitment, in 1975 and in 1997. At recruitment, 42 men were cigarette smokers and 42 were not smoking. Mean annual decline in FEV1 was similar in never- (34.2 ml yr(-1)) and ex- (33.1 ml yr(-1)) smokers and faster (51.0 ml yr(-1)) in continuing smokers. In contrast to predictions from cross-sectional reference values, there was no fall in T(LCO) or K(CO) in men who did not smoke over the period of follow-up. In the 16 men who smoked throughout follow-up there was a 10% fall in T(LCO) (P = 0.043) but most of this was due to a significant fall in VA (P = 0.017), presumably reflecting uneven gas mixing. These results indicate the need for population-based longitudinal studies of T(LCO) and K(CO). If single breath estimates of VA are used in subjects with even mild airflow obstruction, K(CO) rather than T(LCO) should be used to assess alveolar function.