Changes in the FEV1/FVC ratio during childhood and adolescence: an intercontinental study.

In children, the ratio of forced expiratory volume in 1 s (FEV1) to forced vital capacity (FVC) is reportedly constant or falls linearly with age, whereas the ratio of residual volume (RV) to total lung capacity (TLC) remains constant. This seems counter-intuitive given the changes in airway properties, body proportions, thoracic shape and respiratory muscle function that occur during growth. The age dependence of lung volumes, FEV1/FVC and RV/TLC were studied in children worldwide. Spirometric data were available for 22,412 healthy youths (51.4% male) aged 4-20 yrs from 15 centres, and RV and TLC data for 2,253 youths (56.7% male) from four centres; three sets included sitting height (SH). Data were fitted as a function of age, height and SH. In childhood, FVC outgrows TLC and FEV1, leading to falls in FEV1/FVC and RV/TLC; these trends are reversed in adolescence. Taking into account SH materially reduces differences in pulmonary function within and between ethnic groups. The highest FEV1/FVC ratios occur in those shortest for their age. When interpreting lung function test results, the changing pattern in FEV1/FVC and RV/TLC should be considered. Prediction equations for children and adolescents should take into account sex, height, age, ethnic group, and, ideally, also SH.

Age- and size-related reference ranges: a case study of spirometry through childhood and adulthood.

Age-related reference ranges are useful for assessing growth in children. The LMS method is a popular technique for constructing growth charts that model the age-changing distribution of the measurement in terms of the median, coefficient of variation and skewness. Here the methodology is extended to references that depend on body size as well as age, by exploiting the flexibility of the generalised additive models for location, scale and shape (GAMLSS) technique. GAMLSS offers general linear predictors for each moment parameter and a choice of error distributions, which can handle kurtosis as well as skewness. A key question with such references is the nature of the age-size adjustment, additive or multiplicative, which is explored by comparing the identity link and log link for the median predictor.There are several measurements whose reference ranges depend on both body size and age. As an example, models are developed here for the first four moments of the lung function variables forced expiratory volume in 1 s (FEV(1)), forced vital capacity (FVC) and FEV(1)/FVC in terms of height and age, in a data set of 3598 children and adults aged 4 to 80 years. The results show a strong multiplicative association between spirometry, height and age, with a large and nonlinear age effect across the age range. Variability also depends nonlinearly on age and to a lesser extent on height. FEV(1) and FVC are close to normally distributed, while FEV(1)/FVC is appreciably skew to the left. GAMLSS is a powerful technique for the construction of such references, which should be useful in clinical medicine.

Using the lower limit of normal for the FEV1/FVC ratio reduces the misclassification of airway obstruction.

AIM: The prevalence of airway obstruction varies widely with the definition used. OBJECTIVES: To study differences in the prevalence of airway obstruction when applying four international guidelines to three population samples using four regression equations. METHODS: We collected predicted values for forced expiratory volume in 1 s/forced vital capacity (FEV(1)/FVC) and its lower limit of normal (LLN) from the literature. FEV(1)/FVC from 40 646 adults (including 13 136 asymptomatic never smokers) aged 17-90+years were available from American, English and Dutch population based surveys. The prevalence of airway obstruction was determined by the LLN for FEV(1)/FVC, and by using the Global Initiative for Chronic Obstructive Lung Disease (GOLD), American Thoracic Society/European Respiratory Society (ATS/ERS) or British Thoracic Society (BTS) guidelines, initially in the healthy subgroup and then in the entire population. RESULTS: The LLN for FEV(1)/FVC varied between prediction equations (57 available for men and 55 for women), and demonstrated marked negative age dependency. Median age at which the LLN fell below 0.70 in healthy subjects was 42 and 48 years in men and women, respectively. When applying the reference equations (Health Survey for England 1995-1996, National Health and Nutrition Examination Survey (NHANES) III, European Community for Coal and Steel (ECCS)/ERS and a Dutch population study) to the selected population samples, the prevalence of airway obstruction in healthy never smokers aged over 60 years varied for each guideline: 17-45% of men and 7-26% of women for GOLD; 0-18% of men and 0-16% of women for ATS/ERS; and 0-9% of men and 0-11% of women for BTS. GOLD guidelines caused false positive rates of up to 60% when applied to entire populations. CONCLUSIONS: Airway obstruction should be defined by FEV(1)/FVC and FEV(1) being below the LLN using appropriate reference equations.

Beyond the peak flow meter: newer technologies for determining and documenting changes in lung function in the workplace.

There are many potential problems with the use of serial peak expiratory flow (PEF) measurement to investigate potential occupational asthma. Among these are inaccurate and incomplete recording of results. However, PEF meters will continue to be used because of their relatively low cost and the availability of improved graphing methods and computer-assisted interpretation (OASYS-2). New technologies that automatically record PEF values and the time at which the maneuver was performed have improved the reliability of serial PEF measurements. Further, new hand-held spirometers not only record the test time but also the FEV&inf1; and FEV&inf6;, in addition to PEF. Automated assessment of maneuver quality with immediate feedback to the worker may improve test quality. The storage of raw volume-time or flow-volume curves, not yet widely available, can be used by reviewers to evaluate the quality of the maneuver on which PEF and FEV&inf1; values are based-further improving the reliability of serial measurements. Mechanical stimulators and testing waveforms are available to thoroughly test these new devices and insure that they meet the minimum ATS requirements for monitoring devices.

Spirometric reference values from a sample of the general U.S. population.

Spirometric reference values for Caucasians, African-Americans, and Mexican-Americans 8 to 80 yr of age were developed from 7,429 asymptomatic, lifelong nonsmoking participants in the third National Health and Nutrition Examination Survey (NHANES III). Spirometry examinations followed the 1987 American Thoracic Society recommendations, and the quality of the data was continuously monitored and maintained. Caucasian subjects had higher mean FVC and FEV1 values than did Mexican-American and African-American subjects across the entire age range. However, Caucasian and Mexican-American subjects had similar FVC and FEV1 values with respect to height, and African-American subjects had lower values. These differences may be partially due to differences in body build: observed Mexican-Americans were shorter than Caucasian subjects of the same age, and African-Americans on average have a smaller trunk:leg ratio than do Caucasians. Reference values and lower limits of normal were derived using a piecewise polynomial model with age and height as predictors. These reference values encompass a wide age range for three race/ethnic groups and should prove useful for diagnostic and research purposes.

Reproducibility of lung volume measurements.

Test reproducibility is an important consideration when interpreting results and should be set as a goal during data collection. Reproducibility criteria may need to be different for different subject groups and are instrument and procedure-dependent. Ideally, the within-subject variability for each lung volume and measurement technique used should be established for each laboratory. These values also need to be established for each different subject group (age and disease). At a minimum, test reproducibility should be monitored and controlled and each laboratory should define their between-day reproducibility of measurements on at least one "reference" subject from ongoing periodic (e.g., weekly or monthly) measurements as part of their laboratory's quality control programme. For plethysmographic measurements functional residual capacity (FRC)pleth multiple determinations and a corresponding test reproducibility criteria is probably justified.

Weight gain and longitudinal changes in lung function in steel workers.

Associations among dust exposure, smoking habits, and demographic factors and longitudinal changes of lung function were assessed among male steel workers. Cohort descriptive data analysis was conducted in 541 steel workers who had performed spirometry at least twice between 1982 and 1991 (mean follow-up, 6.1 years). The annual change (slope) in FVC, FEV1, FEV1/FVC%, and in body weight was determined by simple linear regression. The Pearson correlation coefficient between weight change and spirometry changes was calculated. Comparisons were also done in 75 pairs of steel workers matched by age, height, initial FEV1, and smoking status, but whose FEV1 declines differed by > or = 60 mL/yr. The FEV1 and FVC declined an average of 44 and 50 mL/yr, respectively, for the cohort as a whole. The FEV1 and FVC declined 52 and 54 mL/yr for current smokers, 43 and 53 mL/yr for ex-smokers, and 36 and 43 mL/yr for nonsmokers, respectively. Increasing weight was highly correlated with accelerated decline in lung function (p<0.0001). In the matched pairs, mean slopes for FVC, FEV1, and FEV1/FVC ratio were -96 mL/yr, -95 mL/yr, and -0.40%/yr for the rapid decliners; and +5 mL/yr, +10 mL/yr, and +0.10%/yr for their partners (p<0.0001). Matched pair comparisons showed that the rapid decliners averaged a 4.313 kg weight gain, while their partners gained 1.044 kg during the follow-up period. The slope of weight gain was 0.708 kg/yr for rapid decliners and 0.191 kg/yr for comparison workers (p<0.0036). Weight gain, in addition to aging and cigarette smoking, was found to be associated with the longitudinal rate of decline in FVC, FEV1, and FEV1/FVC ratio.

Method to produce American Thoracic Society flow-time waveforms using a mechanical pump.

The American Thoracic Society (ATS) recently adopted a new set of 26 standard flow-time waveforms for use in testing both diagnostic and monitoring devices. Some of these waveforms have a higher frequency content than present in the ATS-24 standard volume-time waveforms, which, when produced by a mechanical pump, may result in a pump flow output that is less than the desired flow due to gas compression losses within the pump. To investigate the effects of gas compression, a mechanical pump was used to generate the necessary flows to test mini-Wright and Assess peak expiratory flow (PEF) meters. Flow output from the pump was measured by two different independent methods, a pneumotachometer and a method based on piston displacement and pressure measured within the pump. Measuring output flow based on piston displacement and pressure has been validated using a pneumotachometer and mini-Wright PEF meter, and found to accurately measure pump output. This method introduces less resistance (lower back-pressure) and dead space volume than using a pneumotachometer in series with the meter under test. Pump output flow was found to be lower than the desired flow both with the mini-Wright and Assess meters (for waveform No. 26, PEFs 7.1 and 10.9% lower, respectively). To compensate for losses due to gas compression, we have developed a method of deriving new input waveforms, which, when used to drive a commercially available mechanical pump, accurately and reliably produces the 26 ATS flow-time waveforms, even those with the fastest rise-times.

Longitudinal and cross-sectional analyses of lung function in steelworkers.

We evaluated associations between dust exposure, demographic factors, and lung function by longitudinal and cross-sectional analyses in 475 steelworkers who participated in at least three spirometry tests over 5 yr between 1982 and 1991. Baseline and follow-up spirometry and changes between baseline and final follow-up assessment attributable to age, height, weight, weight gain, smoking status, pack-years, and years worked in dusty areas were examined using stepwise multiple linear regression techniques. Smoking, aging, being overweight, excessive weight gain, and dust exposure were related to a lower level and a steeper slope of decline of pulmonary function. Cigarette smoking was also an important risk factor. Dust exposure was related to the level of lung function, with a stronger effect at baseline than at follow-up. Estimated loss at baseline of FEV1, FVC, and FEV1/FVC% was 9.3, 6.4 ml, and 0.1 % per year of employment in a dusty area, respectively, whereas the association between dust exposure and longitudinal decline of lung function was weak. However, a strong relationship between weight gain and longitudinal decline of FEV1 and FVC was found. Estimated decreases in FEV1 and FVC attributable to weight gain were 4.7 and 6.3 ml per lb/yr, respectively. This work suggests that weight gain is an important determinant for longitudinal lung function decline. This large impact of weight gain in the decline of lung function in a middle-age and relatively overweight working population has not been previously reported. Additional work needs to be undertaken to show the strength of this relationship in other populations.

Comparison of spirometric reference values for Caucasian and African American blue-collar workers.

Interpretation of lung-function test results, specifically the forced vital capacity and forced expiratory volume in one second, generally involves the comparison of these parameters with reference values based on an individual's age, height, sex, and race. Such comparisons are often used to make important decisions concerning an individual, such as job placement or disability rating. Several studies have shown that predicted values for African Americans are approximately 15% less than those for Caucasians, most likely because of the use of standing height to estimate the size of the thorax. When an adjustment for race is applied to reference values based on a Caucasian population, a single value (15%) is usually applied to all individuals. When using a group of blue-collar workers (766 Caucasian and 633 African-American subjects) without any race adjustment, 10.2% of the Caucasians and 37.4% of the African-American subjects were below the lower limit of normal. When a single adjustment factor was used, 11.5% of the African-American subjects were below the lower limit of normal. Between-subject variability within an ethnic group was far greater than variability between groups. Our results suggest that although a difference between Caucasian and African-American test results for forced vital capacity and forced expiratory volume in one second exists, an application of a single adjustment factor universally applied to all individuals, regardless of their age, sex, and height, is not optimal, and alternative approaches are needed.

Standard flow-time waveforms for testing of PEF meters.

The American Thoracic Society (ATS) has recommended the use of 24 volume-time waveforms for the testing of spirometers. Although these waveforms include values of peak expiratory flow (PEF), they were not originally intended to test PEF meters, but, rather, volume parameters for spirometers. In addition, the practice of using ATS volume-time Waveform 24 with varying multiplying factors does not provide the range of flow-time waveform shapes (rise times) needed to evaluate PEF meters. Accordingly, we have developed a set of 26 flow-time waveforms specifically selected to evaluate PEF meters. PEF and other flow parameters (rise time and time to PEF) can be directly measured from these flow-time waveforms. When PEF determined directly from the flow-time curve was compared with PEF determined indirectly from a volume-time curve (ATS-recommended algorithm with an 80 ms time segment), as much as a 10.7% difference between the two methods was observed using a waveform with a fast rise time. In contrast, there was very little difference between the various methods of deriving PEF for waveforms with slower rise times. These 26 flow-time waveforms provide a means of defining PEF for the testing of software algorithms and the testing of PEF meters with computer-driven mechanical pumps.

Frequency response of portable PEF meters.

Peak expiratory flow (PEF) is a dynamic parameter and therefore requires a measuring device with a high-frequency response. This study evaluated the frequency-response characteristics of eight commercially available PEF meters, using simulated forced-expiratory maneuvers with a computer-controlled mechanical pump. Three different PEF levels were used (200, 400, and 600 L/min) at six levels of harmonic-frequency content similar to those observed in human subjects. For waveforms with higher frequency content (at the high end or above the physiologic range), the Assess, Vitalograph, Pocket Peak, and Spir-O-Flow PEF meters all overread PEF (greater than 15% difference from target values) at all three PEF levels. These results suggest that the frequency response of PEF meters is an important consideration in the selection of such meters and should be included in device requirements. The current practice of using various levels of American Thoracic Society (ATS) waveform 24 with its low-frequency content may not adequately evaluate the frequency characteristics of PEF meters. An upper range (5% of the fundamental frequency) of 12 Hz, within the range observed in normal subjects, appears to be more practical than an upper limit of 20 Hz.

Comparing MiniWright and spirometer measurements of peak expiratory flow.

The accuracy and instrument variability of the MiniWright (Clement Clarke) peak expiratory flow (PEF) meter was determined with 6 of the 24 American Thoracic Society's (ATS) standard waveforms using a mechanical pump. Both room air and air heated to 37 degrees C and saturated with water vapor were used. In addition, MiniWright-determined PEF measurements were compared with those obtained using a dry rolling-seal spirometer (Ohio No. 822; Ohio Medical Products; Madison, Wis) from 75 subjects on 2 different days. The MiniWright average coefficient of variation within a waveform was found to be 2.8%. Results using heated and humidified air (body temperature, ambient pressure, and saturated with water: body conditions) were 2.5% lower than those obtained using room air. Comparisons with mechanically simulated PEF and with spirometry-determined peak flow in 75 human subjects showed that MiniWright meters over-estimated flows at lower flow rates and slightly under-estimated flows at higher flow rates. These results suggest that the new "mechanical PEF" MiniWright scale should be used instead of the "traditional" MiniWright scale.

BTPS correction for ceramic flow sensor.

Several commercially available spirometers use unheated ceramic elements as flow sensors to determine flow and calculate volume of air. The usual method of correcting the resulting flow and volume values to body temperature pressure saturated (BTPS) is to apply a constant factor approximately equal to 30 percent of the full BTPS correction factor. To evaluate the usual BTPS correction factor technique, we tested several sensors with a mechanical pump using both room air and air heated to 37 degrees C and saturated with water vapor. The volume signals used to test the sensors were volume ramps (constant flow) and the first four American Thoracic Society (ATS) standard waveforms. The percent difference in FEV1 obtained using room vs heated-humidified air (proportional to the magnitude of the BTPS correction factor needed) ranged from 0.3 percent to 6.2 percent and varied with the number of maneuvers previously performed, the time interval between maneuvers, the volume of the current and previous maneuvers, and the starting temperature of the sensor. The temperature of the air leaving the sensor (exit temperature) showed a steady rise with each successive maneuver using heated air. When six subjects performed repeated tests over several days (each test consisting of at least three maneuvers), a maneuver order effect was observed similar to the results using the mechanical pump. These results suggest that a dynamic, rather than static, BTPS correction factor is needed for accurate estimations of forced expiratory volumes and to reduce erroneous variability between successive maneuvers. Use of exit air temperature provides a means of estimating a dynamic BTPS correction factor, and this technique may be sufficient to provide an FEV1 accuracy of less than +/- 3 percent for exit air temperatures from 5 degrees to 28 degrees C.

Medical screening using periodic spirometry for detection of chronic lung disease.

Approximately half of a worker population may benefit from the addition of a longitudinal comparison of their spirometry results, over only using annual comparisons with a cross-sectional LLN. The ATS recommendation of 15% for year-to-year changes appears to be essentially equivalent to a longitudinal LLN method based on the SEE. Therefore, a practical method for longitudinal interpretations is to establish a baseline value for a worker's FEV1 through several initial spirometric examinations. The FEV1 longitudinal LLN is calculated by taking 85% of this baseline value minus the expected decline over the time period based on the individual's age (e.g., for individuals older than 35 years at their initial examination, one approach is to use 30 mL/year times the number of years of follow-up). However, before any final classification is rendered, the data should be reviewed for stability. This analysis demonstrates that longitudinal spirometry adds sensitivity to spirometry screening efforts. The spirometry examinations should probably be performed annually in order to detect survey biases and determine the stability of the FEV1 measurements. If spirometry results indicate that someone has crossed either the longitudinal or the cross-sectional LLN, intervention activities should be initiated for that individual. As new data and studies become available, these suggested procedures will need to be revised-particularly estimates for the expected annual decline in FEV1.

Instrumentation for spirometry.

In addition to improvements in spirometry instrumentation, the availability and quality of mechanical pump-testing equipment have also improved. These devices have largely relied on the ATS 24 standard waveforms and appear to simulate human FVC maneuvers reasonably well, at least with respect to testing using room air. Testing using mechanical pumps filled with heated and humidified air to better simulate the human FVC maneuver is still evolving. With the availability of these testing devices, many problems in both spirometric hardware and software can be identified and corrected. Perhaps the two most significant emerging advancements in spirometry instrumentation are the automated test acceptability and reproducibility assessments with immediate feedback to the technician and the development of small portable spirometers. At least two major studies (LHS8 and NHANES12) have described a second generation of comprehensive on-line assessment of test quality with immediate feedback to the spirometry technician. The use of quality assessment software appears to significantly improve the quality of the spirometry data through feedback to technicians. Spirometry hardware is also advancing as several hand-held devices are being developed to measure not only peak flow but also FEV1, FVC, and other parameters. These battery-powered portable spirometers will continue to decrease in size and cost and may eventually displace the hand-held peak flow meters in current use.

Changes in forced expiratory volume in one second and peak expiratory flow rate across a work shift among unexposed blue collar workers.

Pre- and postshift spirometry was obtained on 1,113 blue collar workers employed at 35 work sites judged to have no hazardous occupational respiratory exposures on the basis of inspection visits and environmental sampling. In addition to spirometry, a standardized questionnaire was administered by trained personnel. A study population of 944 remained after exclusion of workers for incomplete demographic data and/or spirometry with poor within-session reproducibility, i.e., greater than or equal to 10% variability in the two largest values of either FVC and/or FEV1. Overall mean values of changes across the work shift in FEV1 and peak expiratory flow rate (PEFR) were -0.8% (-0.04 L) and +2.1% (+0.13 L/s), respectively. Standard deviations for these across-shift changes were 5.8% (0.19 L) and 13.2% (1.19 L/s) for FEV1 and PEFR, respectively. In univariate analyses, mean values of across-shift changes were not statistically related to age, race, sex, smoking status, work shift, or FEV1/FVC ratio. However, variability (i.e., standard deviation) of across-shift changes were significantly related to some of these factors. These observations provide a basis for interpreting results of occupational respiratory morbidity surveys involving measurement of changes in FEV1 and/or PEFR across a work shift.