A total of 641 patients from 20 sites were enrolled in the clinical trial. Performance data from 620 of 641 patients (97%) with 3,782 time points and 13,615 spirometry maneuvers were available for analysis. The missing data included all performance data from 1 site (four patients), leaving 19 sites in the analysis. Spirometry was performed by 107 different investigators, two thirds of whom had no previous experience performing spirometry. The average patient age was 33 years, and almost half were obese (Table 1). The mean FEV1 on ED arrival was 38% of predicted, and the mean Borg dyspnea index was 6.7 (index scale, 0 to 10, with 10 indicating the most dyspnea). After 4 h of ED care, 14% of patients required extended care (further ED management, or admission to an observation unit or the hospital). On the tenth day of follow-up, 421 participants returned for a study visit, and 380 patients returned on day 28. The others were either hospitalized during the ED visit (and not required to follow up), relapsed before the scheduled follow-up visit, withdrawn from the study, or were unavailable for follow-up.
Descriptive statistics for the three maneuver quality checks (when applied to the maneuver with the highest FEV1) are given in Table 2. All patients were able to blow for at least 1 s in at least one effort for all time points. One hour after presentation, > 90% of the patients achieved a BEV < 5% of the FVC, a PEFT 2 s. As the distribution of values indicates, most patients met or came close to meeting good start and satisfactory exhalation criteria at the various time points (Table 3). Almost all patients were able to produce two or more efforts, even on ED arrival (Table 4). Most patients were able to give three or more efforts, especially after the first time period.
Overall, the study acceptability criteria (two largest FEV1 efforts having a FET > 2 s and either BEV < 5% of the FVC or 0.15 L, whichever was greater, or a PEFT < 120 ms) was met by 91 to 99% of patients (Table 5). Between 74% and 94% of patients were successfully coached to meet or exceed the reproducibility goals for test session quality (two largest acceptable FEV1 efforts within 10% of each other). The percentage of spirometry test sessions meeting study quality goals improved over time in the ED (Fig 1). The ability to meet reproducibility criteria appeared to plateau at approximately the 1-to 2-h (third to fourth) time point, while the FEV1 continued to rise even after ED discharge.
Predictors of Success
Univariate factors associated with meeting spirometry quality goals included the site, initial FEV1 percentage of predicted, and the time since initial ED assessment. Among the 19 sites, reproducibility success at ED arrival ranged from 50 to 100% (Table 6); a logistic regression model indicated intersite differences were significant (p = 0.001). Spirometry quality improved at 1 h at nearly every site (p < 0.001) [Table 6]. The severity of obstruction on ED arrival influenced the ability to obtain reproducibility. For an initial FEV1 50% of predicted, 77% met the goals (p = 0.02). At 1 h, there were no longer significant differences in meeting reproducibility goals for the three FEVj categories (86%, 90%, 92%; p = 0.42). Reproducibility was less likely to be achieved at time points 0 min and 30 min compared to subsequent time points (p < 0.001). The number of study patients enrolled at each site, the presence of accessory muscle use or the dyspnea score on arrival, age, body mass index (BMI), gender, and race were not predictors of success. In addition, whether investigators had training and experience in spirometry prior to this study did not influence their ability to achieve reproducibility. In multivariate models, the initial ED time point, site, and a baseline FEV1 < 25% of predicted remained as independent predictors of achieving reproducibility on ED arrival.
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Comparison With ATS/ERS Guidelines
We reanalyzed study performance using criteria from the 1994 ATS and 2005 ATS/ERS standardization of spirometry guidelines. Specifically, for start of study acceptability criteria, we no longer considered PEFT but only a BEV < 5% of the FVC or 0.15 L, whichever was greater. Reproducibility was achieved if the two largest FEV1 values were within 0.20 L (1994 criteria) or 0.15 L (2005 criteria). Since investigators were required to obtain a minimum of two acceptable maneuvers (but not three as recommended by ATS/ERS guidelines), we did not reanalyze performance for three acceptable spirograms.
Results of the additional analyses are found in Table 7. At all time points, spirometry performance met ATS reproducibility guidelines in most patients, even though these standards were retrospectively applied. The exclusion of PEFT as an acceptability criteria was in part responsible for the slight drop in performance when comparing study guidelines to ATS/ERS guidelines. Performance was also generally better using the less rigid 1994 reproducibility ATS standards compared to 2005 ATS/ERS standards.
There was one reported adverse event related to spirometry testing. A 66-year-old man had a brief syncopal episode during spirometry testing at the 10-day follow-up visit. He subsequently reported similar episodes while micturating, coughing, or performing peak flow measurements. Because of the syncope, he was hospitalized briefly, and on discharge the etiology of the syncope was believed to be vasovagal.
Figure 1. Top series: Change over time in the percentage of spirometry test sessions meeting study-specific acceptability and reproducibility criteria (boxes). Bottom series: Change in the maximum FEV1 percentage of predicted over time (diamonds).
Table 1—Patient Demographic and Clinical Characteristics
|Years of asthma||18.5||12.2||0-65|
|Dyspnea duration, h||38.5||62.3||0-672|
|Dyspnea index at baseline*||6.7||2.2||0-10/td>|
|Dyspnea index at 30 min||5.0||2.3||0-10|
|Dyspnea index at 4 h||1.9||2.0||0-10|
|FEV1 % predicted||38.4||13.5||9-71|
|ED visits in last yr, No.||3.1||4.9||0-50|
|Hospitalizations in last 3 yr, No.||1.5||3.7||0-36|
|Female gender||343 (57)|
|Prior intubation||71 (11.9)|
|Prior hospitalization||241 (39.5)|
|Accessory muscle usage||165 (26.8)|
|Need for extended care||85 (14.0)|
Table 2—Maneuver Quality Checks
|Time Points||FET, s||PEFT, ms||BEV, % of FVCt||BEV, L|
|1-1.99||2.0-3.99||4.0-5.99||> 6.0||< 85||85-119||> 120||< 5 5||9-||I> 7.5||I< 0.1||0.1-14.9||> 0.15|
Table 3—Maneuver Quality Check Distributions
|Time Points||FET, s||PEFT, ms||BEV, % of FVCt|
|Median||Lower 10%||ILower 5%||Median||Upper 90%||Upper 95%||IMedian||Upper 90%||Upper 95%|
Table 4—The Frequency of Efforts Given at Each Time Period
|Time Points||One Effort||Two Efforts||Three Efforts||Four Efforts||Five Efforts||Six or More Efforts|
Table 5—Ability to Meet Overall Test Session Quality Goals
|Time Points||Mean FEV1 % of Predicted||Mean No. of Efforts||Two or More Efforts Acceptable,%*||Reproducibility Within 10%/ %f|
Table 6—Ability To Meet Spirometry Reproducibility Criteria by Site
|Site||Number of Patients at the Site*||% Reproducible Upon ED Arrival||% Reproducible at 1 h|
Table 7—Spirometry Characteristics of Patients Meeting Additional Criteria for Reproducibility
|Time Points||FEV1, L (SD; Range)||Reproducibility Within 0.2 L, % of Patients||Reproducibility Within 0.15 L, % of Patients|
|ED arrival||1.27 (0.50; 0.32-2.92)||74.9||71.1|
|30 min||1.58 (0.57; 0.41-3.61)||83.4||79.7|
|1h||1.74 (0.65; 0.40-4.13)||86.8||83.2|
|2h||1.89 (0.71; 0.42-4.61)||88.7||85.1|
|4h||2.10 (0.75; 0.50-4.88)||88.2||82.8|
|Day 10||2.37 (0.83; 0.71-5.72)||86.1||78.9|
|Day 28||2.30 (0.91; 0.42-7.47)||87.4||80.7|