Comparison of spirometric reference values

Lung-function reference values play a vital role in the management of respiratory disorders. There are many proposed reference equations for pediatric spirometry. Recently, spirometric reference equations were proposed, using data from people aged 8-80 years living in the US compiled by the third National Health and Nutrition Examination Survey. Our objective was to compare the predictive value of wider age-range reference equations to established pediatric reference equations for the pediatric population. Spirometry, height, and weight were obtained from 70 normal children aged 6-18 years. The difference between measured and predicted values as suggested by different reference equations was compared. Predicted values from general equations significantly differed from those generated from pediatric equations and from measured values in this population. The difference between measured and predicted values from the wider age-range equations varied between 7-16% for forced expired volume in 1 sec (FEV1) and forced vital capacity (FVC). The difference between measured and predicted values for the pediatric equations varied between 1-4%. Although wider age-range equations provide continuity through age ranges, their predictive accuracy may be low in the pediatric age group, especially for the youngest, smallest children. Extrapolating reference equations beyond the age range of subjects used to generate then is not recommended.     

Post-bronchodilator spirometry reference values in adults and implications for disease management

RATIONALE: International guidelines promote the use of post-bronchodilator spirometry values in the definition and severity classification of chronic obstructive pulmonary disease. However, post-bronchodilator reference values have not yet been developed. OBJECTIVES: To derive reference values for post-bronchodilator forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and FEV1/FVC, and to compare these reference values with locally derived and existing pre-bronchodilator reference values. METHODS: Based on a random sample of a general adult population, 2,235 subjects (70% of invited subjects) performed spirometry with reversibility testing. A reference population of healthy never-smokers constituted 23% of the study population (n=515). Reference values for median and lower-limit-of-normal pre- and post-bronchodilator lung function and bronchodilator response were modeled using quantile regression analyses. MAIN RESULTS: The reference population had equal proportions of men and women in the age range 26-82 yr. Both FEV1 and FVC decreased with age and increased with height. FEV1/FVC decreased with age, although this trend was not statistically significant for men after bronchodilatation. Linear models gave the best overall fit. Lower-limit-of-normal post-bronchodilator FEV1/FVC exceeded 0.7 for both sexes. Post-bronchodilator prediction equations gave higher predicted FEV1 and FEV1/FVC than both locally derived and existing pre-bronchodilator equations. The bronchodilator response decreased with age. CONCLUSIONS: The present study is the first to develop reference values for post-bronchodilator lung function. Post-bronchodilator prediction equations can facilitate better management of patients with chronic obstructive pulmonary disease by avoiding falsely high FEV1% predicted with a subsequent underestimation of disease severity.     

Reference values for spirometry,including vital capacity,in Japanese adults calculated with the LMS method and compared with previous values

BackgroundReference values for lung function tests should be periodically updated because of birth cohort effects and improved technology. This study updates the spirometric reference values, including vital capacity (VC), for Japanese adults and compares the new reference values with previous Japanese reference values.MethodsSpirometric data from healthy non-smokers (20,341 individuals aged 17–95 years, 67% females) were collected from 12 centers across Japan, and reference equations were derived using the LMS method. This method incorporates modeling skewness (lambda: L), mean (mu: M), and coefficient of variation (sigma: S), which are functions of sex, age, and height. In addition, the age-specific lower limits of normal (LLN) were calculated.ResultsSpirometric reference values for the 17–95-year age range and the age-dependent LLN for Japanese adults were derived. The new reference values for FEV₁ in males are smaller, while those for VC and FVC in middle age and elderly males and those for FEV₁, VC, and FVC in females are larger than the previous values. The LLN of the FEV₁/FVC for females is larger than previous values. The FVC is significantly smaller than the VC in the elderly.ConclusionsThe new reference values faithfully reflect spirometric indices and provide an age-specific LLN for the 17–95-year age range, enabling improved diagnostic accuracy. Compared with previous prediction equations, they more accurately reflect the transition in pulmonary function during young adulthood. In elderly subjects, the FVC reference values are not interchangeable with the VC values.     

Prediction equations for pulmonary function values in healthy young Iranians aged 8-18 years

OBJECTIVE: Pulmonary function test (PFT) variables are dependent on height, age and gender. In addition, there is evidence of PFT variation in different ethnic groups. Prediction equations for PFT from a healthy, non-smoking, urban young population in the city of Mashhad (north-east Iran) have been derived. METHODOLOGY: Prediction equations for normal pulmonary function were derived from 336 healthy, non-smoking subjects, including 187 males (height 103-188.5 cm) and 149 females (height 104-183 cm) aged 8-18 years. The subjects underwent measurement of spirometric flow and volume. The following variables were measured: FVC, FEV1, maximal mid-expiratory flow (MMEF), PEF, maximal expiratory flow at 75, 50 and 25% of the FVC (MEF75, MEF50, and MEF25, respectively), tidal volume (VT), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), inspiratory capacity (IC), and vital capacity (VC). Regression analysis using height and age as independent variables was applied to provide predicted values for both genders. RESULTS: There were positive correlations for each pulmonary function variable with height and age. The largest positive correlations were found for FEV1 with height and age, in both genders. Comparison of PFT variables derived from the equations obtained in the present study showed significant differences to those calculated from several previously published equations (P < 0.001 for most variables). For example, the values of FVC and FEV1 derived from the equations obtained in the present study were 2.83 +/- 0.99 and 2.50 +/- 0.89 for males, and 2.41 +/- 0.54 and 2.19 +/- 0.53 for females, while the values derived from the equations of the European Community for Steel and Coal study were 3.12 +/- 1.06 and 2.62 +/- 0.89 for males and 2.79 +/- 0.67 and 3.35 +/- 0.57 for females, respectively. CONCLUSIONS: A set of PFT reference values and prediction equations for both genders has been derived using a relatively large, healthy, non-smoking Iranian young population, and has generated results that differ from several other prediction equations.     

Canadian prediction equations of spirometric lung function for Caucasian adults 20 to 90 years of age: results from the Canadian Obstructive Lung Disease (COLD) study and the Lung Health Canadian Environment (LHCE) study

BACKGROUND:

Currently, no reference or normative values for spirometry based on a randomly selected Canadian population exist.

OBJECTIVE:

The aim of the present analysis was to construct spirometric reference values for Canadian adults 20 to 90 years of age by combining data collected from healthy lifelong nonsmokers in two population-based studies.

METHOD:

Both studies similarly used random population sampling, conducted using validated epidemiological protocols in the Canadian Obstructive Lung Disease study, and the Lung Health Canadian Environment study. Spirometric lung function data were available from 3042 subjects in the COLD study, which was completed in 2009, and from 2571 subjects in the LHCE study completed in 1995. A total of 844 subjects 40 to 90 years of age, and 812 subjects 20 to 44 years of age, were identified as healthy, asymptomatic, lifelong nonsmokers, and provided normative reference values for spirometry. Multiple regression models were constructed separately for Caucasian men and women for the following spirometric parameters: forced expiratory volume in 1 s (FEV₁), forced vital capacity (FVC) and FEV₁/FVC ratio, with covariates of height, sex and age. Comparison with published regression equations showed that the best agreement was obtained from data derived from random populations.

RESULTS:

The best-fitting regression models for healthy, never-smoking, asymptomatic European-Canadian men and women 20 to 90 years of age were constructed. When age- and height-corrected FEV₁, FVC and FEV₁/FVC ratio were compared with other spirometry reference studies, mean values were similar, with the closest being derived from population-based studies.

CONCLUSION:

These spirometry reference equations, derived from randomly selected population-based cohorts with stringently monitored lung function measurements, provide data currently lacking in Canada.     

Lung function values in healthy non-smoking urban adults in iran

BACKGROUND: The values of lung function tests (LFTs) are dependent on height, age, and sex. In addition, there is evidence of LFT variation in different ethnic groups. OBJECTIVE: We have therefore derived prediction equations for LFTs from a healthy, non-smoking, urban adult population in the city of Mashhad (northeast Iran). METHODS: Predicted equations for normal lung function have been derived from 572 healthy, non-smoking subjects including 326 men (height 154-195 cm) and 246 women (height 144-174 cm) aged 18-65 years. The subjects underwent measurement of spirometric flow and volume. The following variables were measured: forced vital capacity (FVC), forced expiratory volume in 1 s (FEV(1)), maximal mid-expiratory flow (MMEF), peak expiratory flow (PEF) and maximal expiratory flow at 75, 50 and 25% of the FVC (MEF(75), MEF(50), and MEF(25), respectively). Regression analysis using height and age as independent variables was applied to provide predicted values for both sexes. RESULTS: There was a negative correlation between each lung function and age. The largest negative correlations were found for FEV(1) and FVC in men and women, respectively. All parameters correlated positively with height; the largest positive correlation was observed for FVC in both sexes. Comparison of LFTs derived from the equations of the present study showed significant differences with those of several previous studies. CONCLUSION: In this study, a set of LFT reference values and prediction equations for both sexes have been derived using a relatively large, healthy, non-smoking Iranian, adult population which was different from several other prediction equations.     

Prediction equations for lung function in healthy, life time never-smoking Malaysian population

Several equations have been used to predict lung function standard results for different populations. It is important lung function evaluations use appropriate standards for the study population. The objective of this study was to develop a prediction equation for lung function test results for the Malaysian population. Spirometry was performed among 5,708 subjects and 1,483 healthy, lifetime never smoked subjects (386 males and 1,097 females). Prediction equations were derived for both men and women for FVC and FEV1 results. The equations were validated on new subjects (n = 532, 222 males and 310 females) who met the same inclusion and exclusion criteria as the main cohort. There was a positive correlation between the measured values and the values derived from the new prediction equations (0.62 for FEV1 and between 0.66 and 0.67 for FVC; both p < 0.05) for both men and women with a smaller bias and limit of agreement compared to the published reference equations of ECCS, Knudson, Crapo and NHANES III. The reference equations derived from local spirometry data were more appropriate than generally used equations based on data from previous studies in different population.     

Reference equations for the single-breath diffusing capacity. A cross-sectional analysis and effect of body size and age

A longitudinal study was implemented in an unpolluted rural area of northern Italy (near Venice), before the start of the operation of a large oil-burning thermoelectric power plant, in order to investigate the effects of the future exposure to air pollution and to elucidate the natural history of obstructive airways diseases. During the first cross-sectional survey, a sample of the general population (n=3,300, 8 to 64 yr of age) performed several lung function tests, and information on risk factors and on the presence of respiratory symptoms were obtained by a standardized questionnaire. There were 712 subjects who were classified as normal on the basis of rigid criteria and who were able to perform satisfactorily a single-breath CO diffusing capacity (DLCOsb) test. The DLCOsb values showed an increase with height and age early in life and a later decrease with age. Two age groups were selected to determine an age at which DLCOsb stopped increasing and began to decline. Reference equations were computed (using age and height) in these 2 different age groups in each of the sexes. Similar equations were calculated for the total lung capacity derived from single-breath helium dilution measurements. The DLCOsb values in this study were higher than reported by other investigators. The method of selection of the study population, the strict criteria for normal, as well as technical, differences probably explain this finding. Reference equations for diffusing capacity corrected to lung volume (DL/VA) were computed only for adults (much greater than 20) in both sexes, because age and height coefficients in young subjects were insignificant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Updated spirometric reference values for adult Chinese in Hong Kong and implications on clinical utilization

STUDY OBJECTIVES: The accuracy of reference values of lung function is important for assessment of severity and functional impairment of respiratory diseases. The aim of the study was to establish updated prediction formulae of spirometric parameters for Hong Kong Chinese and to compare the reference values with those derived from other studies in white and Chinese subjects. DESIGN: Cross-sectional multicenter study. SETTING: Lung function laboratories of eight regional hospitals in Hong Kong. PARTICIPANTS: Subjects were recruited by random-digit dialing. One thousand one hundred seventy-six subjects who fulfilled recruitment criteria underwent spirometry. MEASUREMENTS: Spirometry was performed according to American Thoracic Society recommendations, and the technique was standardized among the eight participating lung function laboratories. RESULTS: Evaluable data of 1,089 (494 men and 595 women) healthy nonsmokers aged 18 to 80 years were analyzed. Age and height were found to be the major determinants of FEV1 and FVC, with a linear decline of height-adjusted values with age in both sexes. Spirometric values of this population have increased compared to Chinese populations of similar sex, age, and height two decades ago. Reference values derived from white populations were higher than our values by 5 to 19%, and the degree of overestimation varied with age, sex, and lung function parameter. We also demonstrated that the blanket application of correction factors for Asian populations may not be appropriate. In this study cohort, the distribution-free estimation of age-related centiles was more appropriate for the determination of lower limits of normal. CONCLUSIONS: Our findings underscore the need to use reference values based on updated data derived from local populations or those matched for ethnicity and other sociodemographic characteristics.     

Spirometry values in a Greek population: Is there an appropriate reference equation?

Background and objective: Most published reference values for lung function test (LFT) parameters introduce systematic bias. The aim of this study was to compare measured values of FEV₁ and FVC with the corresponding normal predicted values in a Greek population, and to produce reference equations for LFT parameters in this population. Methods: In a cross‐sectional study conducted in Macedonia, Greece, 1080 adult healthy, non‐smokers (432 men, 648 women, aged 18–80 years), underwent spirometry. Measured values of FVC and FEV₁ were compared with predicted values determined using three existing sets of reference equations: one recently derived from a European population and two others widely used in Europe (European Coal and Steel Community; ECSC) and the USA (National Health and Nutrition Examination Survey; NHANES III). Height and age were entered into the multivariate regression analysis to produce reference equations for LFT parameters. Results: All three published sets of equations underpredicted FEV₁ in men. FVC was accurately predicted by all equations except NHANES III. The discrepancy was even greater among women; the ECSC equation underpredicted both FEV₁ and FVC, the NHANES III equation overpredicted both FEV₁ and FVC, while the third set of equations accurately predicted FEV₁ but overpredicted FVC. The derived reference equation for FEV₁ in men was ?0.28 × age + 0.057 × height ? 4.91, and in women ?0.021 × age + 0.039 × height ? 2.58. The derived reference equation for FVC in men was ?0.28 × age + 0.071 × height ? 6.763, and in women ?0.019 × age + 0.056 × height ? 5.018. Conclusions: Measured FEV₁ and FVC values in a Greek population differed significantly from those predicted using previously published reference equations. The new locally derived spirometry reference equations may be more suitable for evaluation of lung function in everyday practice.     

Reference values and repeatability of inspiratory capacity for men and women aged 65-85

The inspiratory capacity (IC) has recently gained importance because it may signal the occurrence of dynamic hyperinflation at rest or during exercise by reflecting changes in the end expiratory lung volume (EELV). However, reliable predicted values for IC are not currently available. The aim of the study was to generate predictive equations for reference values of IC in adults aged 65-85 living in Italy and to determine its limits of the within test-session repeatability. From the control group (n=429) of the SARA study data base, 241 (161 females) never smoked, non-obese (BMI<30 kg/m2) healthy subjects aged 65-85 who were able to correctly perform at least two manoeuvres of IC were selected. A model that incorporated age, height and body mass index as significant predictors in either sexes produced predicting equations for IC with a coefficient of determination of r2=.36 and .34 for females and males, respectively. Ninety per cent of all the subjects were able to keep the second highest IC within 200 ml (<9%) from the best IC. No significant gender difference was found for IC repeatability. We provided the equations for deriving reliable IC reference values that can be applied in the elderly people living in southern Europe. In this population IC showed limits of the within-session repeatability similar to those accepted for other spirometric indices such as FEV1 and FVC.     

Population values of lung volumes and flows in children: effect of sex, body mass and respiratory conditions.

The functional relationship of gender, anthropometric measures and respiratory condition in predicting respiratory function in children was explored, using data collected in a random sample survey in Central Italy (2,176 subjects). Regression equations for the logarithmic transformation of the functional data were obtained, using sex, ln(height), ln(body mass index) (BMI) and ln(age) as predicting variables. The fit of the model was better for forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and peak expiratory flow (PEF) (R2 = 0.655, 0.603 and 0.312, respectively) than for maximal expiratory flows. Variables indicating the presence of respiratory conditions (recent respiratory infections, asthma, cough and/or phlegm) were forced in the models; only a marginal change in the predictions was observed. Data analysis while controlling for FVC, as a proxy for total lung capacity, revealed no substantial sex difference in airways; furthermore, airways size relative to lung size falls with increasing FVC in both sexes. In overweight subjects (BMI greater than 90th percentile) the relationship between height and lung volume was modified by sex, the coefficient for ln(height) being higher in girls and lower in boys. A comparison between equations from the present study and available reference data revealed that our population differs from standards derived from laboratory data and is more similar to those derived from population studies.     

Normal spirometric reference values for Omani children and adolescents

OBJECTIVES: Normal lung function has been shown to be population specific. The aim of this study was to derive normal reference spirometric values for Omani children and adolescents. METHODOLOGY: Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV(1)), peak expiratory flow and forced mid-expiratory flow were measured in 837 healthy Omani school children aged 6-19 years. Multiple linear regression analysis was performed for each spirometric parameter against age, height and weight for boys and girls separately. RESULTS: All measured spirometric parameters increased with age and height and were significantly higher in boys than girls. Height explained the maximum variance for all parameters. After accounting for height in the prediction equations, the contribution of age and weight was minimal. The expiratory ratio (FEV(1)%FVC) was independent of age and height and its mean values (+/- standard deviation) were slightly higher in girls (91.1 +/- 6.1%) than boys (86.5 +/- 7.1%; P < 0.001). The predicted normal values of the subjects using the derived equations were between 5 and 10% lower than the respective values for subjects in Caucasian sample groups. CONCLUSION: The developed prediction equations can be used in clinical practice in Oman and can be considered for use in neighbouring Arab countries.     

Validation of lung function prediction equations from patient survival data

Diagnosing and managing pulmonary disease usually requires judging lung function against predicted values. We explored patient survival data to help identify the best equations for our population. The earliest spirometry, lung volumes and gas transfer data for all Caucasian patients were extracted from our database. Survival status was available for 8,139 patients. Lung function as standardised residuals (SR) from various prediction equations was used in Cox regression to predict the hazard ratio (HR) for death. The best lung function predictor of all-cause mortality was diffusing capacity of the lung for carbon monoxide (D(L,CO)), followed by forced vital capacity (FVC). These were best with the equations of Miller, derived from a US population, with Chi-squared values of 1,468 and 1,043 for D(L,CO) and FVC, respectively, having taken age, sex, smoking status and body mass index into account. The HR (95% CI) for SR < -3 were 8.5 (6.0-12.1) and 2.9 (2.3-3.5), respectively. Spirometric equation prediction models varied less than those for D(L,CO), with the Miller equations being slightly better than Lambda-Mu-Sigma (LMS) equations. Some D(L,CO) equations introduced sex bias (male sex HR of 3.0 versus 1.5 for other equations). We conclude that LMS or Miller spirometry equations and Miller's D(L,CO) equations were best for our patient population. Using patient survival data is a new approach to help select which lung function prediction equations to use.     

Effect of choice of reference equation on analysis of pulmonary function in cystic fibrosis patients

Pulmonary function is an important measure of disease severity and prognosis in cystic fibrosis (CF). It is generally expressed as a percentage of a predicted value, calculated using regression equations derived from a reference population. A number of reference equations are in widespread use. The purposes of this study were to determine: 1) the extent to which, for a given absolute FEV(1) value, percent of predicted (PPFEV(1)) values vary when derived by different reference equations; and 2) whether these differences affect conclusions of longitudinal and cross-sectional analyses. Subjects were all Caucasians 6-18 years old in the 1990 Cystic Fibrosis Foundation Registry. We found clinically important discrepancies in PPFEV(1) when calculated by the methods of Dockery et al. [Am Rev Respir Dis 1983;128:405-412] and Wang et al. [Pediatr Pulmonol 1993;15:75-78] as compared to Knudson et al. [Am Rev Respir Dis 1983;127:725-734] or Polgar and Promadhat [Pulmonary Function Testing in Children 1971; Philadelphia: W.B. Saunders]. In longitudinal analyses, the choice of reference equation resulted in varying apparent rates of decline in FEV(1). For example, among subjects ages 12-14 years in 1990, the decline in PPFEV(1) from 1990-1995 varied between 2-11%, depending on the choice of reference equation. In cross-sectional analyses, the choice of reference equation affected the distribution of subjects classified as having mild, moderate, or severe lung disease. CF physicians should be aware of the impact of choice of reference equation in both clinical care and research.     

Age and gender specific lung function predictive equations provide similar predictions for both a twin population and a general population from age 6 through adolescence

BACKGROUND: There have been numerous studies of asthma in twins, but no study has evaluated whether lung function predictive models yield similar results between twin and general populations. We sought to evaluate this in late childhood and adolescent subjects. METHODS: We generated cross-sectional, sex- and age-specific regression models of FEV(1), and FVC, in a community-based cohort of 3140 healthy, non-smoking Chinese twins using generalized estimating equations to adjust for correlations within twin pairs. We applied the model to a healthy non-smoking general population cohort of 2187 subjects from the same region, and compared %predicted FEV(1) and FVC values between the two populations. RESULTS: Stratified by age and sex, the associations of height with FEV(1) or FVC varied by age group. During the adolescent growth spurt (age 13 for girls and ages 14-16 for boys), the associations of height with FEV(1) or FVC were nonlinear and greater than that seen at other ages. During adolescence, FEV(1) and FVC for a given height increased with age. The percent predicted values of FEV(1) and FVC in the twin population were similar to that of the general population. CONCLUSIONS: Twin and general populations have similar patterns of lung function change over middle childhood and adolescence. Similar equations may be used to estimate percent predicted values. Finally, a single prediction equation cannot completely describe patterns of lung function from childhood through adolescence due to puberty related changes.     

Spirometric reference values in Senegalese black adults

Spirometric volumes and expiratory flows were measured among 448 Senegalese males and females of 25-80 yrs of age. The values obtained are similar to those reported for black Africans and black Americans in the literature. Volumes are 15-25% lower in males and 23% lower in females than in Caucasians. Forced expiratory flow between 25-75% of vital capacity (VC), (FEF25-75) is 5-18% lower in males and 19% lower in females. FEF25-75/VC ratio is higher in blacks than in Whites, but the forced expiratory volume in one second FEV1/VC ratio is similar in black and white subjects. However, we cannot use proportional factors to determine spirometric black standards from white reference values, so, equations of regression and nomograms with age and height are proposed for black Africans.     

Static lung volumes: reference values from a Latin population of Spanish descent.

BACKGROUND AND OBJECTIVES: The aim of this study was to develop a set of prediction equations and 90% confidence intervals for static lung volumes using the multibreath helium equilibration method from a sample of asymptomatic Caucasian subjects of Spanish descent. Moreover, these equations were compared with those of previous studies. METHODS: Measurements of static lung volumes using techniques recommended by the American Thoracic Society and the European Community for Steel and Coal were carried out on a selected sample of 591 healthy nonsmoking volunteers (305 men and 286 women) aged 18-88 years, living in the metropolitan area of Valencia, on the east coast of Spain. Multiple regression analysis using height, age and weight as independent variables were used to provide predicted values for both sexes. These reference values were compared with other sets of prediction equations reported in the literature using an independent sample of 69 subjects (32 men and 37 women). RESULTS: Simple linear regression equations using age, height and body weight predicted all the subdivisions of lung volumes (vital capacity, expiratory reserve volume (ERV), inspiratory capacity, functional residual capacity (FRC), residual volume (RV), total lung capacity (TLC), FRC/TLC and RV/TLC) as well as more complex equational models. The distribution of residuals fulfilled the assumptions of multiple regression analysis (independence, homoscedasticity and Gaussian distribution of residuals), except for ERV, using simple linear models. The derived equations did not differ significantly from most of the previously reported equations and were usually superior in their ability to predict the lung volumes. CONCLUSIONS: The use of the present prediction equations is recommended in the Latin population of Spanish descent and in populations with similar Caucasian characteristics.     

Diffusing capacity in healthy elderly Chinese

Diffusing capacity (DLCO) was measured in 260 healthy subjects aged 60-86 years who were leading an active life in the community. DLCO correlated with body surface area and spirometric indices, and declined with age. It was lower in women, in smokers and in those with chronic bronchitis. Multiple regression equations based on age and body surface area were derived for elderly Chinese men and women. Compared with predicted values based on studies of Caucasians of all ages, those for elderly Chinese men were higher, while those for elderly women were similar. Predicted values for an elderly Chinese population should be derived from equations established from this survey rather than those extrapolated from Caucasians of all ages. DLCO/VA correlated with weight and body surface area but not with height, and declined with age. There was no difference between men and women, and between those with or without symptoms of chronic bronchitis. Predicted values from this study of elderly Chinese were comparable to those derived from Caucasians of all ages. Differences in DLCO values for elderly Chinese compared to Caucasians may be explained by differences in lung volumes rather than ethnic variations in the diffusing characteristics of the alveolar capillary membrane, and by the small numbers of elderly subjects in some of the studies of Caucasian subjects.     

Annual lung function changes in young patients with chronic lung disease.

Reference equations for ventilatory function that use different statistical models may introduce artifacts that affect the estimated change of lung function during growth in young subjects. The effect of differently modelled reference equations on the estimated annual change of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) in young patients with chronic lung disease was assessed. Four frequently used reference equations were used to describe the longitudinal changes of FEV1 and FVC in 52 patients (23 females) with cystic fibrosis (CF) during a mean follow-up of 3.9 yrs. Choice of reference equations directly affected value and, most importantly, estimated annual change of FVC and FEV1. Mean+/-SD annual change of FEV1 varied from 2.2+/-6.2 to -2.2+/-3.6% of predicted. For two reference equations the estimated individual changes of FEV1 and FVC in CF were positively correlated with mean individual age. This probably reflects underestimation of deteriorating lung function. Variability of annual change was independent of age only when reference equations that were designed to accurately predict lung function during the pubertal growth spurt were used. These findings have implications for patient care and clinical research.