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Original Research: COPD |

An Isolated Reduction of the FEV3/FVC Ratio Is an Indicator of Mild Lung InjurySignificance of a Reduced FEV3/FVC Ratio FREE TO VIEW

Zachary Q. Morris, MD; Angel Coz, MD; Dominik Starosta, MD
Author and Funding Information

From the Division of Pulmonary and Critical Care Medicine (Drs Morris and Starosta), Henry Ford Health System, Detroit, MI; and the Division of Pulmonary, Critical Care, and Sleep Medicine (Dr Coz), University of Kentucky, Lexington, KY.

Correspondence to: Zachary Q. Morris, MD, Division of Pulmonary and Critical Care Medicine, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI 48202; e-mail: zmorris1@hfhs.org.


For editorial comment see page 1089

Part of this article was presented in poster form at the American College of Chest Physicians meeting, Atlanta, GA, October 24, 2012.

Funding/Support: The authors have reported to CHEST that no funding was received for this study.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2013;144(4):1117-1123. doi:10.1378/chest.12-2816
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Background:  The FEV3/FVC ratio is not discussed in the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines for lung function interpretation in spite of narrow confidence limits of normal and its association with smoking. We sought to determine whether a reduction in only the FEV3/FVC ratio was associated with physiologic changes compared with subjects with normal FEV1/FVC and FEV3/FVC ratios.

Methods:  Lung volumes and diffusion were studied in individuals with concomitant spirometry. Patients with restriction on total lung capacity (TLC) were excluded, as were repeat tests on the same patient. A total of 13,302 subjects were divided into three groups: (1) normal FEV1/FVC and FEV3/FVC (n = 7,937); (2) only a reduced FEV3/FVC (n = 840); and (3) reduced FEV1/FVC (n = 4,525).

Results:  Subjects with only a reduced FEV3/FVC compared with those with normal FEV1/FVC and FEV3/FVC ratios had higher mean % predicted TLC (99.1% vs 97.1%, P < .001), residual volume (RV) (109.4% vs 102.3%, P < .001), and RV/TLC ratio (110.1% vs 105.4%, P < .001). They had lower mean % predicted FEV1 (82.6% vs 90.2%, P < .001), inspiratory capacity (94.5% vs 98.2%, P < .001), and diffusing capacity of lung for carbon monoxide (Dlco) (78.3% vs 81.9%, P < .001). Their mean BMI was lower (30.8 vs 31.5, P < .005), they were older (61.2 vs 57.2, P < .001), and more likely male (52.0% vs 40.4%, P < .001), with no racial differences. Comparing this group to those with a reduced FEV1/FVC, similar but greater differences were noted in all of the previous measurements, though mean age and sex were not significantly different.

Conclusions:  The FEV3/FVC ratio should be routinely reported on spirometry. An isolated reduction may indicate an early injury pattern of hyperinflation, air trapping, and loss of Dlco.

Over the last half century, there has been a quest to find a sensitive measurement for mild or early airways disease. In 1955, Leuallen and Fowler1 coined the term mid-flow obstruction, describing flow rates between 25% and 75% of the FVC. Though flow rates of other percentages of the FVC have been described, the most enduring has been the forced expiratory flow between 25% and 75% of FVC (FEF25-75).

In 2006, Hansen et al,2 using the National Health and Nutrition Examination Survey III (NHANES III) database,3 created race-adjusted predicted regression equations for the FEV3/FVC ratio and compared its efficacy for identifying mild airways obstruction against the FEF25-75. They also described its relationship to a smoking history. They found almost 700 citations for the FEF25-75, but only 22 for the FEV3 and FEV3/FVC. Almost all of the FEF25-75 studies used observational % predicted values of about 75% to 80% to determine the lower limit of normal. This practice continued even after 1978 when Knudsen and Lebowitz4 published spirometry predicted data demonstrating the lower 95% limit of normal for the FEF25-75 was around the mid-50th percentile of predicted in individuals over 36 years of age. In 1984, the Intermountain Thoracic Society recommended using the FEV3/FVC and its 95% confidence limits of normal rather than the FEF25-75,5 using the regression equations of Crapo,6 eliminating the FEF25-75 from consideration1,7,8 because it did not add significantly to the FEV1/FVC and the FEV3/FVC.8,9 Using our institutional pulmonary function laboratory database of > 70,000 patients, we compared subjects with no airways obstruction on spirometry to those with an isolated reduction of the FEV3/FVC to determine whether there were other physiologic differences supporting that this is a finding of not only mild airways obstruction but also an indicator of early lung injury.

This study was performed with the permission of the institutional review board for Henry Ford Hospital (Detroit, Michigan; IRB 7341). None of the authors had a conflict of interest to report. Data were collected from a database of pulmonary function tests performed over 10 years by a core group of technicians. A staff pulmonologist read and reviewed all tests daily, as well as testing being monitored by the laboratory supervisor for the purpose of quality control and adhering to the American Thoracic Society (ATS) standards (as delineated later in this section). Patients younger than the age of 20 years were excluded. Race was self-selected from an institutional approved list.

Only Vmax equipment and software were used for testing, though updated software versions were added as the laboratory expanded over the years (Legacy and Spectra versions; CareFusion Corporation). The first test was selected in which a patient had combined spirometry, plethysmography volumes, and diffusion. Testing protocols and calibration adhered to guidelines recommended by the ATS in 199110 and later updated by the ATS/European Respiratory Society (ERS) in 2005.1114

For spirometry, only tests that achieved a minimum expiratory time of 6 s were used for this study, taking the effort with the best FEV1 + FVC. Only predilator spirometry was studied, noting that often postdilator studies were not ordered or not performed because the patient was routinely taking these medications. It is recognized on subsequent testing, patients may have improved with training or after receiving bronchodilators.15

Plethysmography was performed using variable pressure technique, calibrating daily according to the manufacturer’s guidelines and monthly using biologic controls. The order of expiratory reserve volume and vital capacity maneuvers was adjusted based on the severity of lung disease and degree of dyspnea. Although nitrogen volumes and plethysmography are usually simultaneously performed in our laboratories, for the purpose of this study, we only included patients who had plethysmography performed. If the slow vital capacity (SVC) (obtained during the performance of lung volume measurements) was lower than the FVC, the larger of the values was used for calculating the total lung capacity (TLC).

Diffusion calibration was performed internally prior to each patient test according to the manufacturer, along with using frequent biologic controls. Using a single-breath technique, a minimum of two acceptable efforts was collected with averaging of results. The diffusing capacity of lung for carbon monoxide (Dlco) was corrected for hemoglobin or carboxyhemoglobin whenever recent values were available. Both hemoglobin corrected and uncorrected values are reported with similar results.

Patients were categorized into three groups using NHANES III spirometry 95% lower confidence limits of normal: group 1, normal FEV1/FVC and FEV3/FVC; group 2, only FEV3/FVC reduced; or group 3, FEV1/FVC reduced.2,16 Crapo-predicted volumes and their 95% confidence limits of normal (TLC, residual volume [RV], RV/TLC, inspiratory capacity [IC]) were used for whites, and corrected for blacks according to ATS/ERS guidelines (TLC × 0.88, RV × 0.93, and RV/TLC × 1.05).15,17 Miller nonsmoking predicted equations were used for diffusion and corrected downward 0.93 for blacks.15,18 The 4% belonging to other races were adjusted according to ATS/ERS guidelines. To adjust for demographic differences in race, sex, age, and height, the % predicted values were compared, although absolute values were also compared with similar results.

The study variables of interest were compared between the three paired groups. For the dichotomized categorical comparison variables (smoker, sex, race), comparisons were made using the χ2 test for binomial data. Numeric and normally distributed variables were compared using two-sample t tests (BMI, weight in kilograms, age, and % predicted FVC, FEV1, TLC, RV/TLC, IC, and Dlco). Numeric and non-normally distributed variables were compared using the Wilcoxon rank sum test (% predicted RV). The Bonferroni multiple comparison adjusted was used to reduce each test’s rejection level for significance from P = .05 to P = .017. SAS software (version 9.2; SAS Institute Inc) was used to run the statistical analysis.

This discussion will focus on the comparison of the patients without restriction on TLC (based on 95% lower limits of normal). Comparisons will first be made between those who have no evidence of obstruction on spirometry (group 1: FEV1/FVC and FEV3/FVC ratios normal), to those with only a reduced FEV3/FVC ratio (group 2) (Tables 1, 2). Comparisons will then be made between those with only a reduced FEV3/FVC (group 2), to those that had a reduced FEV1/FVC (group 3). In Tables 1 and 2, we did not compare the group with normal ratios (FEV1/FVC and FEV3/FVC) to those with a reduced FEV1/FVC (group 1 vs group 3) because the results are what one would expect to find and add nothing to the discussion.

Table Graphic Jump Location
Table 1 —Comparison Results for Demographic Data Excluding Subjects With Restriction on TLC

Categorical data are given as fraction (%) of group. (C) = χ2 test; TLC = total lung capacity.

a 

Statistically significant, P < .017.

Table Graphic Jump Location
Table 2 —Comparison Results for Degree of Obstruction Excluding the Patients With Low TLC

Numeric data are given as mean ± SD. DL = diffusing capacity; ExpT = expiratory time; Hb Adj = hemoglobin adjusted; IC = inspiratory capacity; RV = residual volume; sGaw = specific conductance; SVC = slow vital capacity; (T) = two-sample t test; (W) = Wilcoxon rank sum test; Wt = weight. See Table 1 legend for expansion of other abbreviation.

a 

Statistically significant, P < .017.

The data are shown in their entirety in Tables 3 and 4. Table 3 is the data set including patients with restriction based on TLC, and Table 4 is after removal of all patients with TLC below the lower limit of normal. The results are similar in both patient populations.

Table Graphic Jump Location
Table 3 —Comparison Results for Degree of Obstruction Using All of the Patients (Including Reduced TLCs)

Categorical data are given as fraction (%) of group; numeric data are given as mean ± SD. See Table 1 and 2 legends for expansion of abbreviations.

a 

Statistically significant, P < .017.

Table Graphic Jump Location
Table 4 —Comparison Results for Degree of Obstruction Without Restriction Based on TLC

Categorical data are given as fraction (%) of group, numeric data are given as mean ± SD. See Table 1 and 2 legends for expansion of abbreviations.

a 

Statistically significant, P < .017.

After eliminating patients with restriction on TLC, we had 7,937 patients in our group with no obstruction on spirometry, 840 subjects that only had a reduced FEV3/FVC, and 4,525 subjects with obstructive spirometry based on the reduced FEV1/FVC ratio (Table 1).

Table 1 shows the distribution of sex across the study groups. Women were more likely to have no obstruction than men (59.6% vs 40.4%) while the groups with only a reduced FEV3/FVC compared with those with a reduced FEV1/FVC were equally distributed between the sexes (P < .001). The higher proportion of women represented in the group with no evidence of obstruction on spirometry may in part be explained by there being a greater percentage of women being nonsmokers than men (76.9% vs 23.1%). Because we studied only the first patient test in which there was simultaneous spirometry, volumes, and diffusion, this may not have been the first time testing was performed. It was later discovered that the patient’s smoking history obtained during the initial evaluation did not automatically repopulate the demographics field. Though the smoking incidence is underrepresented, the findings of an increased incidence and severity of obstruction in those with a greater smoking history is not unexpected. Table 1 shows that subjects with normal ratios (no obstruction) had a lower incidence of a smoking history than those with only a reduced FEV3/FVC ratio (23.1% vs 28.3%, P < .001). And those with only a reduced FEV3/FVC ratio had less of a smoking history than when the FEV1/FVC was below the 95% lower limit of normal (28.3% vs 33.5%, P < .001).

There did not appear to be racial differences (Table 1) when comparing the group with normal ratios to those with only a reduced FEV3/FVC (P = .664), nor when the group with only a reduced FEV3/FVC was compared with those with a reduced FEV1/FVC (P = .051). When looking at all of the patients in Table 3, there is a racial difference comparing the group with normal ratios to those with a reduced FEV1/FVC (P < .001), with the white population tending to show a greater percentage with obstruction based on a reduced FEV1/FVC ratio.

The mean BMI progressively declined as obstruction worsened (Table 2). The group with normal ratios compared with the group with only a reduced FEV3/FVC was 31.5 vs 30.8 (P = .005), with an even greater difference between the two obstructed groups (groups 2 and 3, 30.8 vs 28.6, P < .001). This suggests a greater burden of systemic disease in those with more advanced airways obstruction.

The mean age of the group with no obstruction on spirometry was significantly lower than the two obstructed groups (57.2 years, P < .001). But, there was no difference in the mean age between the two obstructed groups (61.2 years vs 61.4 years, P = .617).

The mean % predicted FVC was not significantly different between the group with no obstruction compared with those with only a reduced FEV3/FVC (90.9% vs 91.0%, P = .835), but was significantly lower in the reduced FEV1/FVC group (83.4%, P < .001). On the other hand, the mean % predicted IC was progressively and significantly lower comparing the three groups (98.2% vs 94.5% vs 82.8%, P < .001). This suggests progressively worsening air trapping between the groups. When including the patients with restriction on TLC (Table 3), the FVC was significantly lower in the normal ratios group compared with when only the FEV3/FVC was reduced, but there was no difference in the IC. By including subjects with restrictive diseases, the lower FVC was expected as well as less air trapping reflected by the IC. Comparing the mean FEV1 % predicted in the group with no obstruction to those with only a reduced FEV3/FVC, and then the latter group to those with a reduced FEV1/FVC, the FEV1 progressively declined from 90.2% to 82.6% to 60.7%, with P values < .001.

Evidence of progressively increasing hyperinflation was noted in the TLC and RV, with increasing air trapping based on the RV/TLC ratio. Examining the progression in those with no obstruction on spirometry to those with only a reduced FEV3/FVC, and then comparing this group to those with a reduced FEV1/FVC, the mean TLC increased from 97.1% of predicted to 99.1% and 108.2%, respectively (P values between the three groups < .001). The mean RV percentage of predicted increased from 102.3% to 109.4% to 145.4% (P values between the three groups < .001). Air trapping progressively worsened between the three groups with the mean % predicted RV/TLC ratio increasing from 105.4% to 110.1% to 133.0% (P values between the groups < .001). If an isolated reduction in the FEV3/FVC ratio is a finding of only mild airways disease, then one would expect to see only small but significant differences in the markers for mild hyperinflation and air trapping.

The mean Dlco corrected for hemoglobin showed a significant decline comparing the group with no obstruction, to when only the FEV3/FVC ratio was reduced, and comparing the latter group to when the FEV1/FVC was reduced (81.9% vs 78.3% vs 68.1%, P < .001). Whether the Dlco was corrected for hemoglobin or not gave similar results (Table 2).

An FEV1/FVC ratio below the 95% CI of predicted normal is the recommended standard of the ATS/ERS for identifying airways obstruction on spirometry. There has been confusion caused by conflicts with other recommendations such as the GOLD (Global Initiative for Chronic Obstructive Lung Disease) guidelines, which are based on observational evidence that an FEV1/FVC ratio below 70% is indicative of COPD.19,20 There has also been a plethora of literature using % predicted values based on opinions from observations rather than statistical analysis when interpreting other measurements, such as the FEF25-75, in which the CIs are extremely wide with major overlap between normal and disease states.4

The FEV3/FVC ratio is an often neglected and more sensitive tool for identifying early or mild airways disease than other commonly reported values.2 This study demonstrates that patients with only a reduced FEV3/FVC have significant physiologic differences compared with those with normal ratios consistent with the early development of air trapping (higher RV/TLC), hyperinflation (higher RV and TLC), and impairment of the gas exchanging surface (lower Dlco). The significance of these findings is further supported by these subjects having a lower mean FEV1, and complements past research showing that a reduced value correlates with a smoking history.2

The total number of patients in which the reduced FEV3/FVC was the only abnormality was not insignificant, consisting of 16% to 17% of the patients with airways obstruction. As a group, their mean lung volumes and Dlco were still within the normal range. This potentially could be useful information when evaluating smokers in whom otherwise we would report their spirometry as being normal. Because there was no age difference between the reduced FEV3/FVC group compared with those with more severe obstruction, this may suggest they have a less progressive form of COPD or less advanced disease.

The FEV1/FVC is considered the standard for identifying airway obstruction. Finding 456 subjects in the reduced FEV1/FVC group that had a normal FEV3/FVC (Table 5), we calculated the sensitivity and specificity of the FEV3/FVC ratio for those with no restriction on TLC as well as all subjects (both > 90%). The positive predicted values were 82% and 83% with negative predicted values of > 95%. This analysis is valid if the FEV3/FVC is measuring the same abnormality as the FEV1/FVC. A more important question is whether the FEV3/FVC is measuring a different, additional, or overlapping physiologic abnormality than the FEV1/FVC. Table 6 shows that the FEV3/FVC identifies a greater percentage of obstructed patients than the FEV1/FVC (92% vs 83%). These findings were similar whether looking at subjects with or without restriction on TLC.

Table Graphic Jump Location
Table 5 —Comparing FEV3/FVC to FEV1/FVC

Assuming FEV1/FVC is the gold standard for obstruction. See Table 1 legend for expansion of abbreviation.

a 

95% confidence limits.

Table Graphic Jump Location
Table 6 —If the FEV1/FVC and FEV3/FVC Are Both Measures Of Obstruction, Which Test Picks Up a Greater Proportion of the Obstructed Patients?

See Table 1 legend for expansion of abbreviation.

There have been numerous studies trying to find more sensitive and specific ways to measure airflow obstruction, substituting one value for another (for example, substituting the FEV3/FVC or FEV1/FEV in 6 s for the FEV1/FVC). Recent articles have suggested this may not be the correct approach because it assumes these ratios are measurements of the same thing. There may be reasons for one being normal while the other is abnormal. These studies suggest using these values in concordance with the FEV1/FVC rather than as a substitute. For example, an isolated reduction of the FEV1/FEV in 6 s can identify subjects with significant hyperinflation, air trapping, and diffusing impairment that is masked by having relatively shorter expiratory times (8 s) than what one sees in patients with COPD (15 s), and consideration should be given for more extensive testing.21 This approach has also been suggested for the FEV3/FVC ratio as well.22

Other factors may be involved in the discordance between these values, such as the effects of aging on these measurements and the performance of the test.

The FEV3/FVC should be recommended as a routine measurement on spirometry in addition to the FEV1/FVC ratio, and become a standard for identifying subjects with milder airways obstruction and lung injury when the FEV1/FVC ratio is normal.

Author contributions: Dr Morris had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Dr Morris: contributed to the design of the study, defined the hypothesis, created the database, worked with the statistician, wrote and revised the manuscript.

Dr Coz: contributed to the design of the study, researched literature, worked with the statistician on the statistical analysis, and assisted in revising the manuscript.

Dr Starosta: contributed to the design of the study, researched literature, worked with the statistician on the statistical analysis, and assisted in writing and revising the manuscript.

Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

ATS

American Thoracic Society

Dlco

diffusing capacity of lung for carbon monoxide

ERS

European Respiratory Society

FEF25-75

forced expiratory flow between 25% and 75% of FVC

IC

inspiratory capacity

NHANES III

National Health and Nutrition Examination Survey III

RV

residual volume

SVC

slow vital capacity

TLC

total lung capacity

Leuallen EC, Fowler WS. Maximal midexpiratory flow. Am Rev Tuberc. 1955;72(6):783-800. [PubMed]
 
Hansen JE, Sun X-G, Wasserman K. Discriminating measures and normal values for expiratory obstruction. Chest. 2006;129(2):369-377. [CrossRef] [PubMed]
 
US Department of Health and Human Services (DHHS) National Center for Health Statistics. Third National Health and Nutrition Examination Survey, 1988-1994: NHANES III Raw Spirometry Data File. Hyattsville, MD: Centers for Disease Control and Prevention; 2001.
 
Knudson RJ, Lebowitz MD. Maximal mid-expiratory flow (FEF25-75%): normal limits and assessment of sensitivity. Am Rev Respir Dis. 1978;117(3):609-610. [PubMed]
 
Morris AH, Kanner RE, Crapo RO, Gardner RM. Clinical Pulmonary Function Testing: A Manual Of Uniform Laboratory Procedures.2nd ed. Salt Lake City, UT: Intermountain Thoracic Society; 1984.
 
Crapo RO, Morris AH, Gardner RM. Reference spirometric values using techniques and equipment that meet ATS recommendations. Am Rev Respir Dis. 1981;123(6):659-664. [PubMed]
 
McFadden ERJ Jr, Linden DA. A reduction in maximum mid-expiratory flow rate. A spirographic manifestation of small airway disease. Am J Med. 1972;52(6):725-737. [CrossRef] [PubMed]
 
Kuperman AS, Riker JB. The predicted normal maximal midexpiratory flow. Am Rev Respir Dis. 1973;107(2):231-238. [PubMed]
 
Beus ML, Gardner RM, Crapo RO. Hazards of using the FEF25-75% as an indicator of obstructive lung disease [abstract]. Am Rev Respir Dis. 1981;123(4 pt 2):102.
 
American Thoracic Society. Lung function testing: selection of reference values and interpretative strategies. Am Rev Respir Dis. 1991;144(5):1202-1218. [CrossRef] [PubMed]
 
Miller MR, Crapo R, Hankinson J, et al; ATS/ERS Task Force. General considerations for lung function testing. Eur Respir J. 2005;26(1):153-161. [CrossRef] [PubMed]
 
Miller MR, Hankinson J, Brusasco V, et al; ATS/ERS Task Force. Standardisation of spirometry. Eur Respir J. 2005;26(2):319-338. [CrossRef] [PubMed]
 
Wanger J, Clausen JL, Coates A, et al. Standardisation of the measurement of lung volumes. Eur Respir J. 2005;26(3):511-522. [CrossRef] [PubMed]
 
Macintyre N, Crapo RO, Viegi G, et al. Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J. 2005;26(4):720-735. [CrossRef] [PubMed]
 
Pellegrino R, Viegi G, Brusasco V, et al. Interpretive strategies for lung function tests. Eur Respir J. 2005;26(5):948-968. [CrossRef] [PubMed]
 
Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. population. Am Rev Respi Crit Care Med. 1999;159(1):179-187. [CrossRef]
 
Crapo RO, Morris AH, Clayton PD, Nixon CR. Lung volumes in healthy nonsmoking adults. Bull Eur Physiopathol Respir. 1982;18(3):419-425. [PubMed]
 
Miller A, Thornton JC, Warshaw R, Anderson H, Teirstein AS, Selikoff IJ. Single breath diffusing capacity in a representative sample of the population of Michigan, a large industrial state. Predicted values, lower limits of normal, and frequencies of abnormality by smoking history. Am Rev Respir Dis. 1983;127(3):270-277. [PubMed]
 
Global initiative for chronic obstructive lung disease: global strategy for diagnosis, management, and prevention of chronic pulmonary disease. Global Initiative for Chronic Obstructive Lung Disease website. www.goldcopd.org. Accessed September 30, 2012.
 
Hansen JE, Sun X-G, Wasserman K. Spirometric criteria for airway obstruction: use percentage of FEV1/FVC ratio below the fifth percentile, not < 70%. Chest. 2007;131(2):349-355. [CrossRef] [PubMed]
 
Morris ZQ, Huda N, Burke RR. The diagnostic significance of a reduced FEV1/FEV6. COPD. 2012;9(1):22-28. [CrossRef] [PubMed]
 
Lam DC, Fong DYT, Yu WC, et al. FEV3, FEV6 and their derivatives for detecting airflow obstruction in adult Chinese. Int J Tuberc Lung Dis. 2012;16(5):681-686. [PubMed]
 

Figures

Tables

Table Graphic Jump Location
Table 1 —Comparison Results for Demographic Data Excluding Subjects With Restriction on TLC

Categorical data are given as fraction (%) of group. (C) = χ2 test; TLC = total lung capacity.

a 

Statistically significant, P < .017.

Table Graphic Jump Location
Table 2 —Comparison Results for Degree of Obstruction Excluding the Patients With Low TLC

Numeric data are given as mean ± SD. DL = diffusing capacity; ExpT = expiratory time; Hb Adj = hemoglobin adjusted; IC = inspiratory capacity; RV = residual volume; sGaw = specific conductance; SVC = slow vital capacity; (T) = two-sample t test; (W) = Wilcoxon rank sum test; Wt = weight. See Table 1 legend for expansion of other abbreviation.

a 

Statistically significant, P < .017.

Table Graphic Jump Location
Table 3 —Comparison Results for Degree of Obstruction Using All of the Patients (Including Reduced TLCs)

Categorical data are given as fraction (%) of group; numeric data are given as mean ± SD. See Table 1 and 2 legends for expansion of abbreviations.

a 

Statistically significant, P < .017.

Table Graphic Jump Location
Table 4 —Comparison Results for Degree of Obstruction Without Restriction Based on TLC

Categorical data are given as fraction (%) of group, numeric data are given as mean ± SD. See Table 1 and 2 legends for expansion of abbreviations.

a 

Statistically significant, P < .017.

Table Graphic Jump Location
Table 5 —Comparing FEV3/FVC to FEV1/FVC

Assuming FEV1/FVC is the gold standard for obstruction. See Table 1 legend for expansion of abbreviation.

a 

95% confidence limits.

Table Graphic Jump Location
Table 6 —If the FEV1/FVC and FEV3/FVC Are Both Measures Of Obstruction, Which Test Picks Up a Greater Proportion of the Obstructed Patients?

See Table 1 legend for expansion of abbreviation.

References

Leuallen EC, Fowler WS. Maximal midexpiratory flow. Am Rev Tuberc. 1955;72(6):783-800. [PubMed]
 
Hansen JE, Sun X-G, Wasserman K. Discriminating measures and normal values for expiratory obstruction. Chest. 2006;129(2):369-377. [CrossRef] [PubMed]
 
US Department of Health and Human Services (DHHS) National Center for Health Statistics. Third National Health and Nutrition Examination Survey, 1988-1994: NHANES III Raw Spirometry Data File. Hyattsville, MD: Centers for Disease Control and Prevention; 2001.
 
Knudson RJ, Lebowitz MD. Maximal mid-expiratory flow (FEF25-75%): normal limits and assessment of sensitivity. Am Rev Respir Dis. 1978;117(3):609-610. [PubMed]
 
Morris AH, Kanner RE, Crapo RO, Gardner RM. Clinical Pulmonary Function Testing: A Manual Of Uniform Laboratory Procedures.2nd ed. Salt Lake City, UT: Intermountain Thoracic Society; 1984.
 
Crapo RO, Morris AH, Gardner RM. Reference spirometric values using techniques and equipment that meet ATS recommendations. Am Rev Respir Dis. 1981;123(6):659-664. [PubMed]
 
McFadden ERJ Jr, Linden DA. A reduction in maximum mid-expiratory flow rate. A spirographic manifestation of small airway disease. Am J Med. 1972;52(6):725-737. [CrossRef] [PubMed]
 
Kuperman AS, Riker JB. The predicted normal maximal midexpiratory flow. Am Rev Respir Dis. 1973;107(2):231-238. [PubMed]
 
Beus ML, Gardner RM, Crapo RO. Hazards of using the FEF25-75% as an indicator of obstructive lung disease [abstract]. Am Rev Respir Dis. 1981;123(4 pt 2):102.
 
American Thoracic Society. Lung function testing: selection of reference values and interpretative strategies. Am Rev Respir Dis. 1991;144(5):1202-1218. [CrossRef] [PubMed]
 
Miller MR, Crapo R, Hankinson J, et al; ATS/ERS Task Force. General considerations for lung function testing. Eur Respir J. 2005;26(1):153-161. [CrossRef] [PubMed]
 
Miller MR, Hankinson J, Brusasco V, et al; ATS/ERS Task Force. Standardisation of spirometry. Eur Respir J. 2005;26(2):319-338. [CrossRef] [PubMed]
 
Wanger J, Clausen JL, Coates A, et al. Standardisation of the measurement of lung volumes. Eur Respir J. 2005;26(3):511-522. [CrossRef] [PubMed]
 
Macintyre N, Crapo RO, Viegi G, et al. Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J. 2005;26(4):720-735. [CrossRef] [PubMed]
 
Pellegrino R, Viegi G, Brusasco V, et al. Interpretive strategies for lung function tests. Eur Respir J. 2005;26(5):948-968. [CrossRef] [PubMed]
 
Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. population. Am Rev Respi Crit Care Med. 1999;159(1):179-187. [CrossRef]
 
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