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* From the Institute for Research in Extramural Medicine (EMGO Institute) (Mss. Wijnhoven and Hesselink, and Dr. Penninx), Vrije Universiteit; and the Department of General Practice (Drs. Kriegsman and de Haan), Vrije Universiteit, Amsterdam, The Netherlands.
Correspondence to: Hanneke A. H. Wijnhoven, MSc, Institute for Research in Extramural Medicine (EMGO Institute), Vrije Universiteit, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands; e-mail: HAH.Wijnhoven.emgo{at}med.vu.nl
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Abstract |
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 TOP Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Design: Observational study.
Setting: Dutch general practice.
Patients: We studied 837 asthma patients and 231 COPD patients.
Results: The association between pulmonary function and HRQOL was poor for asthma (ß = 0.10) and COPD (ß = 0.19). Multivariately, in asthma, lower pulmonary function was associated with male gender, region of living, current smoking, use of inhaled short-acting bronchodilators, longer duration of disease, and higher diurnal variation in peak expiratory flow. In COPD, lower pulmonary function was associated with male gender, use of inhaled bronchodilators, more days and nights disturbed by respiratory complaints, not wheezing, and bronchial hyperresponsiveness. Reduced HRQOL was associated most strongly with more days and nights disturbed by respiratory complaints and dyspnea in both asthma and COPD. In asthma, additional associations were found with younger age, lower educational level, region of living, comorbidity, use of inhaled bronchodilators and corticosteroids, wheezing, chronic cough, sputum production, and bronchial hyperresponsiveness. In COPD, lower age, not smoking, chronic cough, and sputum production were associated with reduced HRQOL.
Conclusions: Pulmonary function and HRQOL appear to highlight different aspects of disease severity in asthma and COPD. Therefore, both measures should be taken into account in order to get a complete picture of severity of disease.
Key Words: asthma • COPD • determinants • disease severity • FEV1 • health-related quality of life • pulmonary function
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Another approach of severity assessment that in this last decade is recognized to be important is to assess the subjective influence of the disease on a patient’s quality of life using a health-related quality of life (HRQOL) questionnaire. HRQOL has become an important outcome parameter to assess patients’ subjective experience of the effects of disease and treatment on satisfaction with life. HRQOL can be measured by means of generic or disease-specific questionnaires. Disease-specific questionnaires focus on the influence of characteristics of a particular disease on functioning, while generic questionnaires focus on the influence of general health status on functioning. Several disease-specific questionnaires have been developed for the evaluation of HRQOL in patients with asthma, COPD, or for both diseases.8
Because both HRQOL and FEV1 are regarded as important measures of disease severity in asthma and COPD, intuitively one would expect these entities to be strongly associated. However, weak or no associations at all are found between FEV1 and scores on several generic and disease-specific HRQOL questionnaires in asthma and COPD.9 10 11 12 13 14 15 16
Curtis et al9 reviewed patient and disease characteristics that were associated with HRQOL in COPD patients. In order of strength of association, they are as follows: dyspnea, depression, anxiety, exercise tolerance, FEV1, FVC, age, socioeconomic status, and educational level. In asthma, HRQOL scores were found to be weakly to moderately associated with symptom score, bronchodilator use for the relief of symptoms, morning peak expiratory flow (PEF), bronchial hyperresponsiveness (BHR), educational level, and gender.15 17 18 19
In studies20 21 examining FEV1 as an outcome measure, some similar but also some different determinants were found. Among asthmatic patients, FEV1%pred was found to be associated with severity of symptoms, wheeze, dyspnea, age, and a concurrent diagnosis of chronic bronchitis. However, in a similar population, Teeter and Bleecker22 did not find a significant relationship between any individual symptom (cough, chest tightness, dyspnea, sputum production, nocturnal awakening) and FEV1%pred. In COPD patients, FEV1%pred was found to be moderately associated with the patients’ ratings of dyspnea.23 24 25 Weaver et al26 found FEV1 to be directly associated with exercise capacity but not with dyspnea. Also, Bestall et al27 did not find an association between FEV1%pred and dyspnea in patients with severe COPD.
It is difficult to compare or summarize results of different studies because there is considerable heterogeneity in outcome measures, instruments used, and study populations included. This makes it difficult to identify determinants associated with FEV1%pred and with HRQOL. Identifying these determinants might give a better understanding of the concept of disease severity in patients with asthma and COPD. This study examines both patient groups separately in order to identify similarities and differences in the determinants of pulmonary function and HRQOL.
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The distinction between asthma and COPD was made by the researcher
using the baseline pulmonary function measurements (see below),
following the 1997 revised guidelines ("standard")29
of the Dutch College of General Practitioners (Nederlands Huisartsen
Genootschap) for the diagnosis of asthma and COPD. Asthma was defined
as follows: (1) a prebronchodilator FEV1%pred of
80%; or (2) a combination of a prebronchodilator
FEV1%pred of < 80%, a reversible obstruction
(increase in FEV1 10 min after administration of
a bronchodilator of > 9% of predicted), and a postbronchodilator
FEV1%pred of 80%. COPD was defined as
follows: a prebronchodilator FEV1%pred of
< 80% combined with an irreversible obstruction (variation in
FEV1 before and after bronchodilation of < 9%
of predicted). Patients with a prebronchodilator
FEV1%pred of < 80%, a reversible obstruction,
and a postbronchodilator FEV1%pred of < 80%
were defined as having a mixed disease (asthma with persisting airway
obstruction). Characteristics of the latter group are presented, but
these patients were excluded from further analyses.
Outcome Variables
The outcome variables measured were FEV1
and HRQOL. FEV1 was measured according to
American Thoracic Society criteria30
before and after
administration of a bronchodilator (salbutamol, 400 µg), using a
hand-held spirometer (SpiroSense; Tamarac Systems; Denver, CO) in the
west study site and east study site, and a dry rolling-seal spirometer
(MasterScreen CS-FRC; Jaeger-Toennies; Hoechberg, Germany) in the
northwest study site. Patients were instructed not to use
bronchodilators on the day of pulmonary function assessment. Personnel
were especially trained by qualified laboratory technicians to perform
the pulmonary function measurements. Spirometers were calibrated daily
with a 3-L syringe (west and east study sites) or a 2-L syringe
(northwest study site). All patients were studied while in a sitting
position wearing a nose clip. Data from the flow-volume curve with the
highest sum of FVC and FEV1 were used for
calculations. FEV1 was expressed as
FEV1%pred, based on gender, height, and age,
using the adult predicted normal values of the European Community for
Coal and Steel.31
HRQOL was measured using the Quality Of Life in Respiratory Illness
Questionnaire of Maille et al,32
which was handed out to
the patients to be completed at home. This written questionnaire was
especially developed and validated for patients with asthma and COPD
treated primarily in general practice, who generally have mildly to
moderately severe disease. It contains 55 items classified into seven
subscales: (1) breathing problems; (2) physical problems; (3) emotions;
(4) situations triggering or enhancing breathing problems; (5) general
activities; (6) daily and domestic activities; (7) and social
activities, relationships, and sexuality. For every item, patients were
asked to answer, on a 7-point Likert-type scale, to what degree they
were troubled because of pulmonary complaints. The response categories
of all items ranged from 1 (not troubled at all) to 7 (very much
troubled). As a measure of reliability, Cronbach’s 
varied from
0.68 to 0.92 for the domain subscales, and was 0.92 for the overall
scale.32
In case of missing data, < 50% of missing
items were allowed per subscale and were substituted, and one missing
subscale was allowed for the calculation of the overall
score.33
Because the distribution of the overall HRQOL
score was skewed in the asthma group (skewness, 1.31; SD, 0.07), this
score was log-transformed for all analyses, which solved this problem.
Furthermore, this log-HRQOL score was transformed in such a way that a
lower score indicates a reduced quality of life.
Determinants
Patient Characteristics:
Information was obtained on age;
gender; educational level (low [lower vocational education or less],
medium [intermediate secondary or intermediate vocational education],
or high [higher secondary through university education]); and region
of living (east, northwest, west). Comorbidity was defined present if
the patient suffered from any other chronic disease (such as diabetes
mellitus, hypertension, cardiovascular disease, stroke, arthritis, or
malignancies). Cigarette smoking habits were defined by assessing
smoking status (never smoker, former smoker, or current smoker).
Characteristics of Disease:
The duration of the disease (in
years) was assessed by asking the patient when pulmonary complaints had
started. A blood sample was taken for the assessment of allergy, which
was defined as present by a positive Phadiatop test result (Pharmacia
AB; Uppsala, Sweden).34
A 2-week diary chart, including
questions on respiratory symptoms and peak flow assessment, was handed
out to the patient to be completed at home. PEF was measured every
morning and evening three times in the standing position (Personal Best
Peak Flowmeter; Respironics; Pittsburgh, PA). Every day for 2 weeks,
the single best morning and evening PEFs were noted on the diary chart.
Variability in PEF was expressed as the mean diurnal (within-day) PEF
variation:
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Treatment of Disease:
The types of medications (scored as
yes or no) were classified into several subgroups. First,
bronchodilators were classified into the following groups: (1) inhaled
short-acting bronchodilators (ß2-agonists,
anticholinergics); (2) inhaled long-acting bronchodilators
(ß2-agonists); and (3) oral bronchodilators (short-acting
ß2-agonists or theophyllines). Second, preventive
medications were classified as follows: (1) inhaled corticosteroids,
(2) inhaled cromoglycates, or (3) oral corticosteroids (prednisolone,
prednisone).
Statistical Analysis
Data were analyzed using software (Statistical Package for
Social Sciences, version 7.5; SPSS; Chicago, IL). All analyses
were performed separately for the asthma group and the COPD group.
First, all potential determinants were entered separately in bivariate
linear regression models with the prebronchodilator
FEV1%pred and the transformed overall HRQOL
score (tHRQOL) as the respective dependent variables. Subsequently,
multivariate models were constructed using a (manual) backward
selection method, deleting those variables with the highest p values,
until all remaining variables had a p value 
0.10. Because many
patients had missing information on diurnal PEF variation and
days/nights disturbed by respiratory complaints (n = 219), an extra
dummy variable was added to the multivariate model (1 = missing
information on both variables; 0 = others). Patients with missing
information on days/nights disturbed by respiratory complaints
(n = 116) but not on diurnal PEF variation had approximately the same
mean prebronchodilator FEV1%pred, tHRQOL-score,
and diurnal PEF variation as patients with a score of 1 day/night
disturbed and were therefore also classified in this group. The results
from the bivariate regression analyses did not change significantly
after these adaptations. The R2 was
reported as a measure of the percentage of variance in the outcome
parameter explained by the determinants in the model.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In Table 1
, the characteristics of the study group are presented separately for
asthma (n = 837), COPD (n = 231), and mixed disease (n = 67).
Compared to the asthma group, patients with COPD (p 0.05), in
general, were older; were less educated; used inhaled long-acting
bronchodilators, oral bronchodilators, and inhaled or oral
corticosteroids more often; had higher diurnal PEF variations; had more
days/nights disturbed by respiratory complaints; had higher
dyspnea-grades; and had lower tHRQOL scores. Furthermore, compared to
the asthma group, a higher percentage of patients were male, were
(former or current) smokers, were nonallergic, and reported
comorbidity. Patients with mixed disease were comparable to the
COPD group on most characteristics, except that they more often used
inhaled short-acting bronchodilators and presented with higher diurnal
PEF variations (p < 0.05).
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0.05): higher diurnal PEF
variation (ß = - 0.21), male gender (ß = - 0.14), longer
duration of disease (ß = - 0.14), current smoking
(ß = - 0.13), and use of inhaled short-acting bronchodilators
(ß = - 0.10). Living in the west was associated with a higher
prebronchodilator FEV1%pred (ß = 0.15). The
percentage of variance in prebronchodilator
FEV1%pred explained by the determinants in the
reduced multivariate model was 16%. When tHRQOL was added, no
significant improvement of the model was observed (data not presented
in Tables).
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0.05) in the multivariate model: use of inhaled long-acting
bronchodilators (ß = - 0.31), use of inhaled short-acting
bronchodilators (ß = - 0.16), more days/nights disturbed by
respiratory complaints (ß = - 0.15), male gender
(ß = - 0.14), and BHR (ß = - 0.13). A significantly higher
prebronchodilator FEV1%pred was found for those
who ever wheezed (ß = 0.19). The percentage of variance in
prebronchodilator FEV1%pred explained by the
determinants in the reduced multivariate model was 36%. By adding
tHRQOL to the model, the variance explained increased to 38%
(ß = 0.13; data not presented in Tables).
In the asthma group, a lower tHRQOL score was multivariately found to
be most strongly associated with dyspnea (ß = - 0.28) and more
days/nights disturbed by respiratory complaints (ß = - 0.27).
Furthermore, associations (p 0.05) were found with wheezing most
days and nights (ß = - 0.14), BHR (ß = - 0.12), being
younger (ß = 0.11), chronic cough (ß = - 0.11), use of
inhaled short-acting bronchodilators (ß = - 0.11) and
corticosteroids (ß = - 0.07), living in the east
(ß = - 0.10) or west (ß = - 0.09), comorbidity
(ß = - 0.08), and sputum production (ß = - 0.08). A higher
educational level was associated with a higher tHRQOL score
(ß = 0.09). The percentage of variance in tHRQOL explained by the
determinants in the reduced multivariate model was 43%. The model was
not improved by adding prebronchodilator
FEV1%pred (data not presented in Tables).
For COPD, days/nights disturbed by respiratory complaints
(ß = -0.32) and dyspnea (ß = - 0.27) were (multivariately)
found to be most strongly associated with a lower tHRQOL score. The
following characteristics were also associated (p 0.05) with a
lower tHRQOL score: sputum production (ß = - 0. 17), chronic
cough (ß = - 0.14), and younger age (ß = 0.15). Current
smoking was associated with a higher tHRQOL score (ß = 0.18). The
percentage of variance in tHRQOL explained by the determinants in the
reduced multivariate model was 45%. No significant contribution of
prebronchodilator FEV1%pred to this model was
found (data not presented in Tables).
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Discussion |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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One striking finding is that in both asthma and COPD, male gender was (bivariately) associated with a lower pulmonary function and a better HRQOL. This is in accordance with results from a study done by Osborne et al,19 who found that men with asthma reported a better quality of life than women. After we adjusted for other determinants in the multivariate model, the gender effect became nonsignificant for HRQOL. The fact that gender remains a significant determinant of pulmonary function even when the model is adjusted for other relevant determinants might indicate that men are more affected by their disease, resulting in lower pulmonary function (as a percentage of predicted) compared to women. Also Osborne et al19 found that men with asthma have a lower prebronchodilator FEV1%pred.
We chose to include region of living as a potential determinant in all models in order to adjust for the possible influence of different instruments used to assess pulmonary function. Because the spirometer used in the northwest differed from the one used in the other two regions, we expected to see differences regarding the level of pulmonary function when comparing this region with the other two regions. Although all bivariate coefficients were in the same direction, supportive of the idea that the spirometers used in the east and west might systematically produce higher levels of pulmonary function, multivariate results were less consistent. Only asthma patients living in the west, but not in the east, had a significantly higher pulmonary function. One possible explanation might be that in this region, patients receive a diagnosis earlier in their disease course. However, regional differences regarding pulmonary function must be interpreted carefully, because we cannot be sure that observed differences were not caused by different measurement conditions. The finding that living in the east and west was associated with a reduced HRQOL in asthma patients even after correction for other determinants might be caused by a different attitude toward disease between the different regions. This is an important finding to keep in mind when, for the purpose of epidemiologic studies, HRQOL is assessed in patients recruited from different areas.
In asthma, current smoking was associated with a lower level of pulmonary function, which underlines the importance of smoking cessation in asthma patients. The finding that former smoking, not current smoking, was associated with a lower pulmonary function level in COPD patients might be explained by a "healthy smokers effect." Relatively healthy smokers are less motivated to quit smoking, while patients who do quit because of their disease (former smokers) are less healthy (have lower pulmonary function). In COPD, current smoking was associated with a better HRQOL, which may also be explained by the fact that patients who did not quit smoking (yet) are those with a less severe stage of disease. This finding is in contrast with findings of Prigatano et al,36 in which COPD patients who continued smoking had a significantly lower quality of life than those who quit smoking.
Presence of allergy and wheezing was weakly associated with lower pulmonary function in asthma patients. Reverse associations were found in COPD patients, which might indicate that COPD patients who present with asthmatic features (such as wheezing and allergy) have better pulmonary function levels than other COPD patients; however, it should be kept in mind that this also might be the result of a not-entirely-correct separation in an asthma, COPD, and mixed-disease group.
In this study, we found diurnal PEF variation to be higher in COPD patients than in asthma patients. This is in contrast with the idea that because patients with asthma have a more variable pulmonary obstruction, they also have a higher diurnal PEF variation.1 One possible explanation for this finding might be that some misclassification of asthma or COPD patients has occurred. In both asthma and COPD, a higher diurnal PEF variation was found to be associated with a lower level of pulmonary function. In a study done by van Schayck et al,37 a higher diurnal PEF variation was predictive of a more rapid decline in pulmonary function in COPD patients, but no association was found in asthma patients.
In asthma patients, no associations were found between pulmonary function level and symptoms such as cough, sputum production, and days and nights disturbed by respiratory complaints. Weak associations were found with wheezing and dyspnea. This is in line with results from other studies that also found weak associations with wheezing21 22 and dyspnea,21 but no associations with cough, sputum production, and nocturnal awakening.22 Also, in COPD, no associations between pulmonary function level and symptoms were found, except for days and nights disturbed by pulmonary complaints and wheezing (wheezing in the opposite direction of expected). Although symptoms were poorly associated with pulmonary function, in this study they were the strongest determinants of HRQOL in both asthma and COPD. The explained variance of HRQOL, including all determinants in a multivariate model, was around 45% for both disease groups. Approximately the same percentage was found in another multivariate analysis from a cross-sectional study,38 in which up to 50% of the variance in HRQOL could be explained by a range of measures, including, among others, cough, wheezing, and dyspnea.
In summary, pulmonary function appears to be poorly associated with respiratory symptoms and complaints in both asthma and COPD. HRQOL, however, which shows poor association with pulmonary function, does associate with respiratory symptoms and complaints. It seems that both pulmonary function and HRQOL highlight different aspects of disease severity and are both valuable in determining the actual disease state. This is in accordance with Ferrer et al,39 who suggested that both pulmonary function and HRQOL should be used to evaluate patients with COPD. Also, Bailey et al40 concluded that asthma severity appears to be multidimensional. This is important to consider not only when patients are seen in general practice, but when disease severity of patients with asthma or COPD is assessed in epidemiologic studies.
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Footnotes |
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Received for publication April 7, 2000. Accepted for publication November 14, 2000.
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