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Correspondence to: Paul Enright, MD, University of Arizona, HSC 2342, 1501 N Campbell Ave, Tucson, AZ 85724; e-mail: lungguy{at}aol.com
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Abstract |
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Design: Observational.
Participants: More than 4,000 public school students, ages 9 to 18 years.
Measurements: Spirometry was performed annually for 3 years, with the recording of maneuver quality measures of forced expiratory time, end-of-test volume, back-extrapolated volume, and time to peak expiratory flow (PEFT), and the recording of differences between best and second-best FVC, FEV1, and peak expiratory flow (PEF) values.
Results: Regression analyses showed significant influences of participant age, gender, ethnicity, size, clinical status, and previous testing experience, as well as differences among individual test technicians. In general, these influences were small and explained little of the variance in performance. On average, children with a history of asthma or wheeze performed better quality spirometry than did others. Only PEFT improved significantly from year to year. Overall, only 15% of girls’ tests and 32% of boys’ tests met the PEFT criterion derived from adults in the Lung Health Study.
Conclusion: Most of the children met adult-based ATS goals for spirometry test performance. Age group-specific criteria are needed to ensure adequately fast PEFT and reproducible PEF values.
Key Words: children • peak flow • quality control • spirometry
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionSummaryReferences |
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The 1994 American Thoracic Society (ATS) criteria for satisfactory spirometry performance1 are based almost exclusively on studies of adults. To determine whether these criteria (goals) are suitable for younger populations, we reviewed the spirometry data from 3 successive years of testing in the Children’s Health Study,2 3 a 10-year longitudinal investigation of air pollution and other environmental risk factors, which involves several thousand subjects aged 9 to 18 years.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionSummaryReferences |
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12. As many as six technicians performed spirometric
tests concurrently in the same room, each using a dry rolling seal
spirometer with a personal computer-based data acquisition system
(Spiroflow model 132; PK Morgan Ltd; Gillingham, UK). Coaching, data
acquisition, and data management techniques were similar to those in
the Six Cities Study.4
Frequent checks against a 3.00-L
calibration syringe (Flow Volume Calibrator; Jones Medical Instrument;
Oak Brook, IL) ensured that data were consistent between different
spirometers and across time.5
In year 6 only, about 4% of
tests were performed at the homes of subjects who had moved away from
the study school districts. In each annual test session, the subject was vigorously coached by the technician to perform forced expirations until three acceptable maneuvers (or a maximum of seven) were recorded. The initial criteria for an acceptable maneuver were the following: (1) FVC and FEV1 values that were at least 95% of the largest values; (2) back-extrapolation volume (BEV) < 5% of FVC; (3) end-of-test volume (EOTV) of < 50 mL in the final 2 s; and (4) forced expiratory time (FET) of at least 6 s. A color video graphics array monitor displayed a real-time tracing of exhaled volume vs time, which was viewed by the subject and the technician. Numeric results relevant to criteria 2 to 4 were displayed after each maneuver, and results were relevant to criterion 1 after all but the first maneuver. Data from all maneuvers were stored on the hard disk (and copied to a floppy disk) for subsequent analysis.
A QA officer (W.S.L.) made unannounced visits to observe field testing and reviewed the collected data to look for consistent differences between technicians in the incidence of unsatisfactory test performances. In years 1 to 3, evaluations were performed ad hoc, based on the numeric data generated by the data acquisition program. Beginning in year 4, the central QA review and the reporting software developed for the Lung Health Study (LHS)6 were implemented, in parallel to the usual data acquisition. Thereafter, the QA officer used the review software to inspect all flow-volume tracings from subjects with questionable performance, overriding the selection of the spirometer software algorithm of the "best" maneuver on rare occasions. The software then stored performance data for each subject, calculated the average flow and volume quality grades for all subjects tested by an individual technician, and generated monthly written reports for technicians and investigators.
For this review, we analyzed data obtained via the QA software in years 4, 5, and 6, which covered 4,143 subjects, including the grade 4 cohort recruited in year 4 (typical age in year 4, 9 years [with no prior lung function testing experience]), the original grade 4 cohort (typical age in year 4, 12 years [with 3 years of prior experience]), and the original grade 7 cohort (typical age in year 4, 15 years [with 3 years of prior experience]). Thus, the review included both naive subjects near age 9 years and older, experienced subjects up to age 18 years.
Of all subjects, 49% were boys, 34% belonged to ethnic minorities (mostly Mexican Americans, African Americans, and Asian Americans), 14% had a history of physician-diagnosed asthma, and an additional 19% had a history of wheeze without a diagnosis of asthma. These subjects performed a total of 9,528 test sessions. Because of personnel turnover, this analysis included 11 different technicians, both new and experienced, with a wide range of educational and occupational backgrounds. An additional three short-term substitute technicians, who together performed < 1.8% of all tests, had spirometry quality similar to the regular technicians. However, their results were excluded from the analysis to limit the number of regression variables required (see below). An additional 1.7% of all tests were included in descriptive statistics but not in regression analyses, because data were missing for one or more predictor variables.
To assess the overall quality of performance by our subjects and technicians, descriptive statistics were calculated for the maneuver acceptability variables BEV, time to peak expiratory flow (PEFT), EOTV, and FET for the single best maneuver from each test session, as determined by the QA software, and for differences between the best and second-best FVC (dFVC), FEV1 (dFEV1), and PEF (dPEF) values within a spirometry test session. These reproducibility variables, which were not stored by the QA software, were extracted from a separate Children’s Health Study database that covered years 1 to 5, and the best maneuvers were selected separately for each spirometry variable. Thus, differences were analyzed over 2 years (years 4 and 5), rather than over 3 years, and were not necessarily based on a single composite best maneuver, as was the case for the maneuver-acceptability variables.
To identify significant influences on performance, multiple regression analyses were performed on each performance-quality variable. The initial regressions included continuous independent variables for year, age, height, and body mass index (kilograms/meters squared; BMI), as well as dichotomous independent variables (false, 0; true, 1) for male gender, ethnic minority status, naive subject (first testing experience), and home testing. (In preliminary analyses, the effect of new vs experienced technicians was tested and found to be unimportant, so that variable was excluded.) Additional dichotomous independent variables represented each individual technician, using one technician with near-average performance as a reference. From the initial result, independent variables with near-significant (p < 0.15) or significant (p < 0.05) effects were identified and entered into a second regression, which yielded the final model.
Because data distributions of QA variables tended to be skewed, with longer tails on the side of poorer performance, alternative regression analyses were performed after log transformations to obtain more nearly normal distributions, or with the most "outlying" poor performers excluded (described below). For the variables derived from the best single blow (ie, maneuver-acceptability checks), conclusions from the original and alternative regression analyses were not substantially different; accordingly, the original untransformed variables are reported. However, for the reproducibility variables, the original and the alternative analyses differed, indicating that original analyses were heavily influenced by a few outliers. Accordingly, for the difference variables, we report the results from analyses that exclude the poorest performances, which were defined as > 10% dFVC or dFEV1, or > 20% dPEF. Analyses were performed using statistical software (BMDP-DYNAMIC; SPSS Inc; Chicago, IL; or SAS, version 6; SAS Institute; Cary, NC).
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionSummaryReferences |
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It was more difficult for the children to meet the PEFT criteria (used by the LHS) than the BEV criteria (recommended by the ATS). The girls’ PEFTs were > 120 ms in 15% of tests, while the boys’ PEFTs were > 90 ms in 32% of tests. Of those subjects with an "unacceptably" high PEFT, 17% met the BEV criteria.
Ethnic minority subjects took longer to reach peak flow and had larger BEVs than non-Hispanic white (ie, ethnic majority) subjects, but their EOTV and FET values were essentially the same. Later analyses of specific ethnic categories (not tabulated) explored the BEV differences in more detail. Ethnic majority subjects showed significantly lower BEVs if tested by ethnic majority technicians than if tested by ethnic minority technicians. Subjects who classified themselves as Hispanic or of mixed ethnicity (ie, mostly of Mexican or Central American ancestry, including some native Spanish speakers) showed significantly lower BEV values if tested by bilingual Hispanic technicians than if tested by other technicians. Too few data were available to test for similar effects in other ethnic minority groups.
Table 3 summarizes regression results for the reproducibility measures (ie, dPEF, dFEV1, and dFVC), based on 5,457 test sessions in the earlier 2 years with complete predictor data (excluding outliers). The initial models included all predictors listed in Table 2 ; only those that were significant for at least one reproducibility measure are listed in Table 3 . Ethnic majority subjects showed better reproducibility than minority subjects for all three function measures. Taller subjects showed more reproducible FVC and PEF values, while more obese subjects (ie, those with a higher BMIs) showed less reproducible PEF values. Few significant differences were seen in the ability of individual technicians to obtain reproducible PEF, FEV1, and FVC values.
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionSummaryReferences |
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9 years also can meet each of the ATS criteria about 95% of
the time. Automated maneuver quality checks with messages displayed immediately after each maneuver enable the technician (or patient) to perform additional maneuvers, increasing their ability to meet the test session quality goals.
The spirometry maneuver may be divided into the following three steps (or phases), each of which requires a different type of effort: (1) "take a deep breath" (maximal inhalation); (2) "blast out your air" (maximal exhalation effort); and (3) "keep blowing until all your air is gone" (prolonged exhalation). Poor effort may occur during any (or all) of these steps and is usually due to suboptimal interaction between the technician and the subject. A submaximal inhalation falsely reduces the PEF, FEV1, and FVC values. A submaximal blast falsely reduces the PEF values, variably affects the FEV1 values, and may increase the FVC values. A premature termination of the exhalation falsely reduces only the FVC values, provided that termination occurs after the first second. Objective QA measurements are designed to detect all these faults and, thereby, to identify any poorly performed maneuver or test session that could result in false-positive or false-negative diagnoses in the clinical setting or in increased measurement noise/bias in epidemiologic and intervention studies.
Poor inhalation effort is common but is not objectively evident in any single spirometric record, being detectable only by invasive physiologic measurements or possibly by subjective visual observation of the subject’s performance. Thus, for practical purposes, poor inhalation effort can be detected only in terms of poorly reproducible FVC and FEV1 values across multiple maneuvers. Submaximal blast and premature termination can, however, be identified objectively from the recording of any single blow. The following sections summarize findings in this and earlier studies, and our recommendations based on these findings, concerning each type of fault.
Criteria to Detect Poor Reproducibility
We found that a history of asthma or wheeze predisposed our
subjects to better performance, in contrast to several adult studies
that indicate that poor performance is more common in individuals with
clinical evidence of impaired respiratory health.7
10
13
Ng’ang’a and coworkers12
noted that young men with
bronchial hyperresponsiveness and young women who were cigarette
smokers were more likely than others to fail to meet the
dFEV1 criterion of < 0.1 L. About 12% of their
subjects failed to meet that reproducibility criterion. In a large
1-antitrypsin disease registry at 37 sites,
Stoller and coworkers13
noted that only 2% of the
participants failed to meet the dFEV1
criterion. Spirometry of subjects who failed to meet the
criterion was more likely to occur at those sites using older
water-sealed spirometers without personal computer displays of
flow-volume curves, but the failure to meet the criterion was not
associated with asthma, gender, or age. Their patients with severe
airways obstruction were much less likely to fail to meet the
dFEV1 criterion than those with relatively normal
lung function.
Most of our study subjects with a history of wheezing or asthma had only mild, if any, manifestations of disease at the times of testing. We do not know how many also performed spirometry or peak flow maneuvers during visits to their private physicians (which would potentially improve their test quality). Whether similarly high levels of performance can be obtained in the clinical testing of children seen for respiratory diseases is less certain. In clinical populations, illness and higher anxiety levels may impair performance more frequently. On the other hand, fewer distractions and the ability to take more time might offset these factors.
Based on our 95th percentile results (Table 1) , we recommend that the 1994 ATS reproducibility criterion of striving for a < 0.20-L difference between the highest and second-highest values (dFEV1 and dFVC) apply when testing children (Table 4 ). About 95% of our subjects also met the more stringent 1987 ATS criteria of a < 5% difference. We also recommend that when PEF is being measured using a spirometer, the reproducibility criteria of dPEF of < 1.0 L/s and < 15% should be applied when testing children and adolescents.
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The criteria for an acceptably short PEFT developed by the LHS from smoking adults (women, < 90 ms; men, < 120 ms) appear too strict when applied to the young people in our study. Miller and coworkers14 measured the PEF 10 to 90% rise time in adult patients using a pneumotach (flow sensor)-based spirometer and found that the values from 95% of the patients were < 140 ms. Their patients with airway obstruction had considerably shorter rise times when compared to those with relatively normal lung function. For a given maneuver, the measured PEFT will be slightly larger than the 10 to 90% rise time. For children, we recommend using a PEFT threshold of > 160 ms to detect a "slow start," since 95% of our subjects produced a PEFT less than this value. More so than the other QA criteria, the measured PEFT may vary from system to system. When tested in Salt Lake City using a waveform generator, our spirometers overestimated PEF values at higher PEF values, suggesting that the systems were underdamped. Therefore, it is likely that the relatively longer PEFTs obtained in our study were due to less phase II "blast" effort than to an underdamped measuring system. The ATS did not mention PEFT acceptability criteria for diagnostic spirometry in 1994, but the PEFT, dPEF, and dFEV1 were all independent predictors of month-to-month variability in FEV1 in the LHS.2
The ATS recommendations stated that: "Although there may be some benefit from using PEF reproducibility to improve subject effort, no specific [PEF] reproducibility criterion is recommended at this time."1 Coates and coworkers8 found that in children with asthma or cystic fibrosis who were tested by hospital-based pulmonary function laboratory technicians, that variation in FEV1 (ie, dFEV1) was much more closely associated with the variation in the FVC due to variation in the depth of inhalation preceding the FVC maneuver than with the variation in peak flow (ie, dPEF). Banks and coworkers15 used experienced technicians to study adult employees with two different spirometry systems and found that the newer system, which had automated maneuver quality checks and messages (ie, dPEF, EOTV, BEV, and an index similar to PEFT), resulted in higher FVC values (mean increase, 0.27 L) but no significant change in FEV1 values.
The 1994 ATS recommendations stated: "Computer-based systems that provide feedback to the technician when the above conditions [acceptability and reproducibility criteria] are not met are desirable." As hand-held electronic spirometers increase in popularity for ambulatory lung function measurements for clinical trials of asthma therapy that use PEF and FEV1 values as primary outcome measures of asthma control,16 automated acceptability and reproducibility maneuver quality checks such as PEFT, dPEF, and BEV, which detect poor-quality PEF and FEV1 results, will become important. In the ambulatory setting, the study subjects test themselves without a technician or a display of flow-volume curves to recognize unacceptable maneuvers.
Criteria to Detect a Short Effort
End-of-test maneuver acceptability criteria are designed to detect
maneuvers that "quit too soon" resulting in an underestimation of
the true FVC. The 1987 ATS recommendations17
required FET
> 6 s, and an "obvious plateau" in the volume-time curve, defined
as a < 40-mL volume change during the final 2 s of the maneuver
(ie, EOTV). The European Respiratory Society decided not to
recommend EOTV criteria,18
apparently since
patients with moderate-to-severe airways obstruction can forcefully
exhale for > 20 s and still not reach a plateau, while healthy
children often reach a plateau in < 3 s. Desmond and
coworkers19
found that > 80% of the children in their
study (age range, 5 to 18 years) failed to meet the 1987 ATS EOTV
criteria (based on adults), while only 9% failed the ATS
dFEV1 or dFVC criteria. They proposed a revised
EOTV criterion using exponential curve fitting of the
volume-time data from each maneuver. School-aged children failed to
meet the new criterion only 4% of the time, but preschool children
(age, < 7 years) failed to meet it about 37% of the time. About 60%
of the adult COPD patients in one large study failed to meet the 1987
ATS EOTV criteria.13
About 95% of our subjects exhaled
< 56 mL during the last 2 s of the maneuver. Children performing
spirometry for the first time in our study had a mean EOTV that was 38
mL higher than those who had performed spirometry before. Three of the
technicians (technicians A, D, and H) were less likely to obtain
plateaus than the other technicians, but, surprisingly, the mean
expiratory times they obtained from the children they tested were not
significantly shorter.
It is easier to attain a low EOTV when using volume spirometers such as the dry-rolling seal that we used (when compared to flow-sensing spirometers), since the warm, exhaled air contracts when it cools quickly inside the spirometer, making it appear that the subject has reached a plateau even though very slow exhalation continues toward the end of the maneuver. Note that the EOTV was negative for half of our subjects (Table 1) , indicating contraction of the exhaled air (not slow inhalation or a leak).
The ATS reduced the importance of the EOTV criteria in 1994, stating that "a plateau should be observed, as defined by no change in volume for at least one second OR a reasonable expiratory time... usually 6 seconds." About 35% of our subjects had an exhalation time of < 6 s during their best maneuver, but only 5% had an FET of < 4 s. We propose that, when testing population samples of children, the message "premature termination of effort" be displayed when the FET is < 4 s or when the EOTV is > 60 mL, but that the EOTV criterion should not be applied when testing children known to have asthma or airways obstruction. Luckily, underestimation of the FVC is not clinically important when following patients or study subjects with asthma. The forced exhalation may stop after only 1 s when only the measurement of the PEF or FEV1 is sought.
Our results also suggest that ethnic and linguistic matching between subject and technician increases the probability of satisfactory performance but that gender matching has little influence. By some criteria, boys performed significantly better than girls, and non-Hispanic whites performed better than ethnic minority subjects. However, the differences were small, and almost all of the children from each group provided satisfactory data. Hankinson and Bang9 also noted that ethnicity was an independent factor associated with dFEV1 in the third National Health and Nutrition Survey population-based study.
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Summary |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionSummaryReferences |
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9 years can perform
forced expiratory spirometric maneuvers well enough to meet currently
established adult-based maneuver acceptability criteria for BEV, EOTV,
and FET, as well as within-test session maneuver reproducibility for
FEV1, FVC, and PEF. Factors related to age, size,
gender, ethnicity, and subject-technician affinity can influence
performance, but their overall effect is small with well-trained
technicians who have experience. Our findings suggest the need for
criteria to be added to those currently recommended by the ATS to
ensure adequately fast starts and reproducible PEF values
that are applicable to adults as well as to children. For 9- to
18-year-old children, we recommend the spirometry test session goals
(criteria) listed in Table 4
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Acknowledgements |
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Footnotes |
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{altfoot}*From the University of Arizona (Dr. Enright), Tucson, AZ; Department of Preventive Medicine (Messrs. Linn and Avol, and Drs. Gong and Peters), University of Southern California, Los Angeles; and California Air Resources Board (Ms. Margolis), Sacramento, CA.
Supported by the California Air Resources Board (contract No. A033–186), the National Institute of Environmental Health Sciences (grant No. 5P30ES07048–02), the US Environmental Protection Agency (contract No. CR824034–01-3), and the Hastings Foundation.
The statements and conclusions in this report are those of the authors and not necessarily those of the California Air Resources Board (or other sponsors). The mention of commercial products and their source or use in connection with the material reported herein is not to be construed as actual or implied endorsement of such products.
Received for publication September 28, 1999. Accepted for publication April 19, 2000.
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