Modelling the lung function of Caucasians during adolescence as a basis for reference values.

BACKGROUND: In childhood the relationship between lung size and stature changes during the adolescent growth spurt. This is not allowed for in models of lung function based on stature alone. For spirometric indices inclusion of an age x stature interaction (A x St) can overcome the difficulty. AIM: The study tested the hypothesis that this simple, interactive model might also be effective for total lung capacity and its subdivisions and the single breath transfer factor for carbon monoxide. SUBJECTS AND METHODS: Data were available for 695 asymptomatic non-smokers (Caucasians) aged 7-20 years (440 boys, 255 girls). Each lung function index was described using the above model and the fit was compared with that from a linear, power or polynomial model based on stature alone. RESULTS: After allowing for stature, the A x St interaction term was significant for almost all indices. The improved fit was most apparent for the lung function of older adolescent boys. Reference values using the model are reported. CONCLUSIONS: A simple model based on stature and an interaction between stature and age can account for the changing relationship between body habitus during the growth spurt and lung size and transfer factor in a single equation encompassing children and adolescents. Its use is recommended for deriving reference values when the explanatory variables are limited to stature and age.

Body mass, fat percentage, and fat free mass as reference variables for lung function: effects on terms for age and sex.

BACKGROUND: Sex specific cross sectional reference values for lung function indices usually employ a linear model with terms for age and stature. The effects of also matching for body mass index (BMI = mass/stature(2)) or its components, fat percentage of body mass (fat%) and fat free mass index (FFMI = fat free mass/stature(2)) were studied. METHODS: The subjects were 458 asymptomatic male and female non-smokers (383 men) and 22 female ex-smokers. Measurements were made of ventilatory capacity, lung volumes, transfer factor (diffusing capacity, single breath CO method), and body composition (skinfold method). Linear and proportional regression models were used. RESULTS: Terms for fat% and FFMI significantly improved the accuracy of reference values for all the primary lung function indices. The improvements in subjects with atypical physiques (fat% and FFMI at the ends of the distributions for the subjects) were in the range 0.3-2.3 SD compared with conventional regression equations. The new partial regression coefficients on age were independent of age related changes in body fat. The coefficient for total lung capacity (TLC) on age in men was now positive. Most differences between the sexes were eliminated. A term for BMI improved the descriptions of subdivisions of TLC but lacked the other advantages. CONCLUSION: Allowance for fat% and FFMI increases the accuracy of reference equations for lung function, particularly for subjects with a lot of fat and little muscle or vice versa. Allowance for BMI is less informative.

The Medical Research Council Pneumoconiosis Research Unit, 1945-1985: a short history and tribute.

The Pneumoconiosis Research Unit (PRU) was set up to obtain the information needed to eliminate pneumoconiosis of coal workers. To this end, instruments and procedures were developed for dust sampling, delivering dust to animals, testing lung function, reading chest radiographs, conducting respiratory surveys and extracting the relevant information. A provisional estimate of safe working conditions was made using data from four pits. The National Coal Board extended the research to an additional 20 pits, refined the estimate and applied it nationally. Meanwhile at PRU aspects of treatment were explored, immunological techniques were added to the repertoire of skills, other occupational disorders were highlighted and new information obtained on biological variation in lung function and blood pressure. The work laid the foundations for medical epidemiology and evidence-based medicine. Starting in 1959, the Unit took the lead in a world campaign to control lung diseases due to asbestos. This account indicates how these successes were achieved, what were the failures, some tensions which developed and what might have been if some events had been handled differently. If there is a message, it is that for success in research the problem under consideration should be the prime focus of attention and resources.

Longitudinal effects of change in body mass on measurements of ventilatory capacity.

BACKGROUND: In several longitudinal studies changes in body mass and in forced expiratory volume in one second (FEV1) have been found to be negatively correlated. This paper tests the hypothesis that failure to allow for the association can lead to error in the interpretation of longitudinal measurements of ventilatory capacity. METHODS: Male shipyard workers (n = 1005) were assessed on two occasions with an average interval between measurements of 6.9 years. A respiratory symptoms questionnaire, detailed anthropometric measurements, and dynamic spirometric tests were undertaken. Multiple regression analysis was used to identify variables which contributed to the changes in lung function. RESULTS: After allowing for age and growth in stature, a change in body mass of 1 kg was, on average, associated with a mean (SE) converse change in FEV1 of 17.6 (2.0) ml, and in forced vital capacity (FVC) of 21.1 (2.5) ml. Neglect of changes in body mass (which in this context reflected changes in body fat) led to underestimation of the longitudinal decline in FEV1 with age and failure to detect significant improvements in FEV1, both in smokers following discontinuation of smoking and in shipyard welders and caulker/burners as a consequence of leaving their employment. The estimated peak ages and associated peak levels of the indices were found to differ, depending on whether or not they were expressed at constant body mass. CONCLUSIONS: Neglect of changes in body mass can lead to erroneous conclusions being drawn from longitudinal measurements of FEV1.

Transfer factor (diffusing capacity) standardized for alveolar volume: validation, reference values and applications of a new linear model to replace KCO (TL/VA)

Transfer factor (TL) varies with alveolar volume (VA), but not in the manner implied by the carbon monoxide transfer coefficient (KCO (TL/VA)). This paper considers two other simple models (one linear and one exponential) which might standardize TL for VA, and asks the questions: 1) Is either model valid? 2) What are appropriate reference values? and 3) Will the model be useful? The relationship of TL to VA within subjects at different depths of inspiration, and between subjects having lungs of different sizes, were measured and compared. The subjects were asymptomatic, nonsmoking, Caucasian adults, including 31 males assessed in the laboratory and 503 male and female participants in population studies. The linear partial regression coefficients of TL on VA (L corrected for body temperature, atmospheric pressure and water saturation (BTPS)) standardized for height (H) in metres, were similar within- and between-subjects; the coefficients applied over a wide range of values for VA. This was not the case for the exponential model. The resulting reference equations in SI units for males and females were: TL = 11.52 H + 2.72 VA.H-2 - 0.051 Age -12.35. RSD 1.17; and TL = 4.87 H + 2.29 VA.H-2 - 0.019 Age -3.03. RSD 0.92, respectively. The residual standard deviations (RSD) about the new relationships were less than in other series. The new linear model could account for much of the variation between different published reference values for TL; it could be useful clinically, in circumstances when VA deviates from the norm. The model does not explain differences in TL associated with gender. Inclusion of VA.H-2 as a covariate in the reference equation for transfer factor, in addition to age and height, improves the accuracy of prediction of normal transfer factor compared with current reference values; its use suggests that some of the differences between published values is due to the volume term. The equations can be used clinically, and eliminate the need for carbon monoxide transfer coefficient.

Spirometric reference values for white European children and adolescents: Polgar revisited.

We analyzed six spirometric data sets collected in the Netherlands, Austria, the United Kingdom, Spain, and Italy. The objectives were to establish whether (1) it was possible to describe spirometric indices from childhood to adulthood, taking into account the adolescent growth spurt, and (2) there are systematic differences in ventilatory function between children and adolescents in different parts of Western Europe. The study comprised 2,269 girls and 3,592 boys, aged 6-21 years. The range in standing height was 110-185 in girls, 110-205 in boys. The model applicable to all data sets was ln FVC or ln FEV1 = a + (b + c x A) x H, where H = standing height and A = age; this model prevents the phase shift between the adolescent growth spurt in length and lung volume from leading to an age-dependent bias in predicted values. There was surprising agreement between most of the data sets; systematic differences are probably due to technical factors arising from ATPS-BTPS corrections and from defining the end of breath with pneumotachometer systems. Taking those into account, prediction equations for FVC, FEV1, and FEV1%FVC were developed with "lower limits of normal" which should be applicable to children and adolescents of European descent. It is proposed that the approach of analyzing available data sets should also be applied to other ventilatory indices, data collected in adults and elderly subjects, or in other ethnic groups, and that an international data base be set up to that end.