Download The Proportional Venn Diagram of Obstructive Lung Disease*

The Proportional Venn Diagram of
Obstructive Lung Disease*
Two Approximations From the United States and
the United Kingdom
Joan B. Soriano, MD; Kourtney J. Davis, PhD; Bobbie Coleman, BSc;
George Visick, PhD; David Mannino, PhD; and Neil B. Pride, MD
Study objectives: The nonproportional Venn diagram of obstructive lung disease (OLD) produced
for the 1995 American Thoracic Society guidelines has not been quantified. We aim to quantify
the proportion of the general population with OLD and the intersections of physician-diagnosed
asthma, chronic bronchitis, and emphysema in the United States and the United Kingdom, and to
examine the relationship to obstructive spirometry.
Design and participants: We analyzed data from the US National Health and Nutrition Examination (NHANES) III survey (1988 to 1994) and the UK General Practice Research Database for
the year 1998.
Results: The areas of intersection among the three OLD conditions produced seven mutually
exclusive disease groups. The asthma-only group was the largest proportion of OLD patients,
accounting for 50.3% and 79.4% of all OLD patients in the United States and the United
Kingdom, respectively, and decreased with increasing age. Overall, 17% and 19% of OLD
patients in the United States and in the United Kingdom, respectively, reported more than one
OLD condition, and this percentage increased with age. According to the spirometry data from
NHANES III, only 37.4% of emphysema-only patients had objective airflow obstruction. The
prevalence of airflow obstruction was significantly higher among participants with combinations
of emphysema and chronic bronchitis (57.7%), with emphysema and asthma (51.9%), and with all
three OLD diseases concomitantly (52.0%).
Conclusion: Concomitant diagnosis of asthma, chronic bronchitis, or emphysema is common
among OLD patients from the general population, particularly in adults aged > 50 years.
(CHEST 2003; 124:474 – 481)
Key words: asthma; COPD; epidemiology; obstructive lung disease; Venn diagram
Abbreviations: ATS ⫽ American Thoracic Society; GOLD ⫽ Global Initiative for Chronic Obstructive Lung Disease;
GP ⫽ general practitioner; GPRD ⫽ UK General Practice Research Database; MEC ⫽ mobile examination center;
NHANES ⫽ National Health and Nutrition Examination Survey; OLD ⫽ obstructive lung disease; OXMIS ⫽ Oxford
Medical Information System; RCT ⫽ randomized controlled trials
chronic bronchitis, and emphysema are
A sthma,
conditions associated with obstructive lung disease (OLD), a leading cause of morbidity and mortality worldwide. Asthma is the most common
chronic condition in children1 but can be diagnosed
*From Worldwide Epidemiology (Drs. Soriano, Davis, and
Visick, and Ms. Coleman), GlaxoSmithKline Research and Development, Research Triangle Park, NC; Air Pollution and
Respiratory Health Branch (Dr. Mannino), Division of Environmental Hazards and Health Effects, National Center for Environmental Health, Centers for Disease Control and Prevention,
Atlanta, GA; and Thoracic Medicine (Dr. Pride), National Heart
and Lung Institute, Imperial College, London, UK.
This study was supported by GlaxoSmithKline Research and
Development.
Manuscript received August 5, 2002; revision accepted February
18, 2003.
at any age. The World Health Report of 19982
estimated that 2.9 million adults die each year of
COPD, a term that typically includes chronic bronchitis and emphysema, and ranked COPD as the
fifth leading cause of mortality worldwide (after
ischemic heart disease, cerebrovascular disease,
acute lower respiratory infection, and tuberculosis)
and as the fifth most prevalent disease (after iron
deficiency anemia, neck and back disorders, goiter,
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (e-mail:
[email protected]).
Correspondence to: Joan B Soriano, MD, Worldwide Epidemiology, GlaxoSmithKline R&D; Greenford Rd, Greenford, Middlesex UB6 0HE, UK; e-mail: [email protected]
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Clinical Investigations
and hypertensive disease) for 1997. International
consensus definitions of asthma3 and COPD, including chronic bronchitis and emphysema,4 are available, but the diagnosis of OLDs is a medical challenge for respiratory specialists and primary care
physicians, even with the availability of spirometry or
a patient history of tobacco use.5
This differential diagnosis is of interest, because
asthma, chronic bronchitis, and emphysema are disorders with a different pathogenesis and prognosis,
and current respiratory guidelines recommend very
different management and drug treatment strategies
for patients with asthma vs those with chronic bronchitis and emphysema. However, it is well-established that individual patients commonly share the
traits of two or even three of these conditions. A
graphic representation of this relationship was first
presented as the nonproportional Venn diagram of
OLD (Fig 1), which was included in the 1995
American Thoracic Society (ATS) COPD guidelines.6 To date, we are not aware of efforts to
quantify this nonproportional Venn diagram. We aim
to quantify the subpopulations of patients with OLD
and the intersections of the diagnoses of asthma,
chronic bronchitis, and emphysema in nationally
representative databases in the United States and the
United Kingdom.
Materials and Methods
Data Sources
We analyzed data from the US National Health and Nutrition
Examination (NHANES) III survey, conducted from 1988 to
1994, and the UK General Practice Research Database (GPRD)
for the year 1998.
The NHANES III was a cross-sectional, multistage probability
sample (n ⫽ 33,994) that was representative of the total noninstitutionalized civilian population of the United States, and
surveys were conducted from 1988 to 1994.7,8 Information about
the medical history of respiratory symptoms and diagnoses of
respiratory conditions were obtained by questionnaire interview
for all participants aged ⱖ 17 years and through a proxy interview
with a household adult for those aged ⬍ 17 years. Spirometry
data were obtained for participants aged ⱖ 8 years following the
recommendations and standards of the ATS (n ⫽ 22,431). Analysis of NHANES III data incorporated sampling weights, in
accordance with a probability sampling design, in order to obtain
estimates of disease prevalence that reflect the total noninstitutionalized, civilian US population.
The GPRD is an automated medical record database of
primary care covering a total population of ⬎ 3 million inhabitants (approximately 5%) of the population in England and
Wales.9,10 Several studies have demonstrated that the study base
is a representative sample of the UK general population, with an
almost identical gender and age structure as the one provided by
the Office of Population Census and Statistics. General practitioners (GPs) from the participating surgeries enter all significant
morbidity for each individual patient into the computer record.
All diagnoses and procedures communicated to the GP as a result
Figure 1. Nonproportional Venn diagram of COPD showing
subsets of patients with chronic bronchitis, emphysema, and
asthma. The subsets comprising COPD are shaded. Subset areas
are not proportional to the actual relative subset sizes. Asthma is
by definition associated with reversible airflow obstruction, although in variant asthma special maneuvers may be necessary to
make the obstruction evident. Patients with asthma whose airflow
obstruction is completely reversible (ie, subset 9) are not considered to have COPD. Because in many cases it is virtually
impossible to differentiate patients with asthma whose airflow
obstruction does not remit completely from persons with chronic
bronchitis and emphysema who have partially reversible airflow
obstruction with airway hyperreactivity, patients with unremitting
asthma are classified as having COPD (ie, subsets 6, 7, and 8).
Chronic bronchitis and emphysema with airflow obstruction
usually occur together (subset 5), and some patients may have
asthma associated with these two disorders (ie, subset 8). Individuals with asthma who have been exposed to chronic irritation,
as from cigarette smoke, may develop chronic productive cough,
which is a feature of chronic bronchitis (ie, subset 6). Such
patients often are referred to in the United States as having
asthmatic bronchitis or the asthmatic form of COPD. Persons
with chronic bronchitis and/or emphysema without airflow obstruction (ie, subsets 1, 2, and 11) are not classified as having
COPD. Patients with airway obstruction due to diseases with
known etiology or specific pathology, such as cystic fibrosis or
obliterative bronchiolitis (subset 10), are not included in
this definition. Reprinted with permission from the American
Thoracic Society.6
of a hospital or other specialist visit (ie, inpatient, outpatient, or
in an accident and emergency unit) must be recorded when the
GP is informed. The diagnosis, symptoms, procedure or investigation, referrals, and their outcome must be entered into the
relevant sections of the medical record. In this report, estimates
are presented for patients who attended their GP, were given a
diagnosis of asthma or COPD, and were registered throughout
1998. Pulmonary function data are not systematically or routinely
available.
Case Definitions
Definitions of OLD in each database differ. NHANES III was
a survey, and the questionnaire part of the survey asked participants about self-reported physician-diagnosis of three conditions
(ie, asthma, chronic bronchitis, and emphysema). A positive
response to the single question “Has a doctor ever told you that
you have emphysema?” was sufficient to define emphysema. But,
for asthma and chronic bronchitis, positive responses to the
following two questions were necessary to define a current
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CHEST / 124 / 2 / AUGUST, 2003
475
condition: “Has the doctor ever told you that you have [asthma or
chronic bronchitis]?” and ”Do you still have it?“ A participant
could be classified as having all three conditions.
The GPRD system uses the Oxford Medical Information
System (OXMIS) and READ coding system (the first three digits
of the OXMIS number corresponds, in most cases, to the first
three digits of the International Classification of Diseases, eighth
revision, codes). Physician-diagnosed asthma, chronic bronchitis,
and emphysema were defined as any individual who was labeled
with one or more of the OXMIS/READ codes that were compatible with their respective diagnoses during calendar year 1998.
This permitted the use of terms like COPD without reference to
chronic bronchitis or emphysema.11,12 Acute bronchitis was
excluded from the algorithm. The choice of GPRD OXMIS/
READ codes was recorded by each individual GP without
instructions or guidelines. Direct codes for COPD were defined
as overlapping chronic bronchitis and emphysema in the Venn
diagrams.
Spirometry in NHANES III
Lung function testing was conducted on participants aged ⱖ 8
years by a trained technician in a mobile examination center
(MEC). Testing also was conducted at the home of participants
aged ⱖ 60 years who were unwilling or unable to come to the
MEC. Before testing, screening questions were asked to determine medical safety exclusions (ie, those who had undergone
chest or abdominal surgery within 3 weeks or had experienced
heart problems [myocardial infarction or heart attack, angina or
chest pain, and congestive heart failure]) within 6 weeks before
attending the MEC. Airflow obstruction was defined as stage 1
according to the following Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines: FEV1, ⬍ 80% of predicted (based on gender, age, and height); FEV1/FVC ratio,
⬍ 70%.4 As children aged ⱕ 7 years did not have spirometry
measurements recorded in NHANES III, estimates of airflow
obstruction were weighted to the sample of participants aged ⱖ 8
years for whom spirometry had been measured.
Statistical Analysis
The prevalence for each condition per gender and age group is
presented for the United States and the United Kingdom separately.
Values have been extrapolated to the total population in each
country using the NHANES III sample weights for the United
States and using the Office of National Statistics data for the United
Kingdom. Each graphic representation in Figures 2 to 5 was
calculated by applying simple proportional euclidean geometry, with
the area of the circle representing the exact population size. The
areas of intersection of circles represent the percentage of
overlap of two or three OLD conditions. Analyses were conducted using a statistical software package (SAS, version 8.0; SAS
Institute; Cary, NC).
Results
The descriptive characteristics of NHANES III
and GPRD participants with OLD are presented in
Table 1. Patients were stratified into seven mutually
exclusive disease groups by age and sex for each
study population. Patients with asthma, in whom
diagnoses had been made with or without other
OLD conditions, were younger than COPD patients.
The combination of asthma with chronic bronchitis,
but not with emphysema, was associated with
younger age.
In the US NHANES III total population, the
prevalence of current asthma was 5.5%, the prevalence of current chronic bronchitis was 3.2%, and
the prevalence of ever having had emphysema was
1.5%. In the UK GPRD total population, the prevalence of current asthma was 2.3%, the prevalence of
current chronic bronchitis was 0.5%, and the prevalence of current emphysema was 0.5% (Fig 2). The
asthma-only group was the largest group of OLD
patients, accounting for 4.3% and 2.2%, respectively,
of the United States and United Kingdom general
populations; that is, 50.3% and 79.4%, respectively,
of all OLD patients. Seventeen percent of OLD
patients in the United States had more than one
OLD condition, and 2.8% had all three conditions
simultaneously. The UK figures were 19.1% and
3.6%, respectively. The areas of intersection among
the three OLD conditions differed by data source
and country (Fig 2).
In the subpopulation of participants aged ⱖ 50
years, the prevalence of current asthma was 5.1%,
the prevalence of current chronic bronchitis was
5.8%, and the prevalence of ever having had emphy-
Table 1—Descriptive Characteristics of NHANES III and GPRD Participants With OLD, Extrapolated to the US
and UK Populations for all Ages
NHANES III
Characteristics
No. (%)
Asthma only
10,710,843 (4.27)
Chronic bronchitis only
4,612,955 (1.84)
Emphysema only
2,300,062 (0.92)
Asthma ⫹ chronic bronchitis
2,255,186 (0.90)
Asthma ⫹ emphysema
318,211 (0.13)
Chronic bronchitis ⫹ emphysema
441,481 (0.18)
Asthma ⫹ chronic bronchitis ⫹ emphysema
596,376 (0.24)
Total country population
251,097,002 (100.0)
GPRD
Mean
Female, No. (%) Age, yr
5,939,434 (2.37)
3,048,853 (1.21)
851,042 (0.34)
1,435,115 (0.57)
153,064 (0.06)
162,951 (0.07)
181,616 (0.07)
28.6
42.8
63.3
38.2
65.2
68.4
61.4
34.3
No. (%)
1,277,297 (2.16)
15,822 (0.03)
9,223 (0.02)
3,037 (0.01)
1,125 (0.00)
244,634 (0.41)
57,850 (0.10)
59,237,000 (100.0)
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Mean
Female, No. (%) Age, yr
669,942 (1.13)
8,248 (0.01)
3,412 (0.01)
1,912 (0.00)
487 (0.00)
108,051 (0.18)
30,068 (0.05)
29.7
59.0
67.3
55.1
66.9
69.4
66.2
37.6
Clinical Investigations
Figure 2. Proportional Venn diagram of OLD in the United States (NHANES III surveys from 1988
to 1994) and United Kingdom (GPRD 1998) for all ages.
sema was 5.0% in the US NHANES III survey. In
the UK GPRD subpopulation of participants aged
ⱖ 50 years, the prevalence of current asthma was
1.6%, the prevalence of current chronic bronchitis
was 1.1%, and the prevalence of current emphysema
was 1.1% (data not shown). The seven mutually
exclusive disease groups of this proportional Venn
diagram also can be displayed as stacked bars, for
comparison by gender and age (Fig 3). The relative
size of the asthma-only group decreased with increasing age, both in women and men in the United
States and the United Kingdom. In the NHANES
III data, probably because acute bronchitis could
have been misclassified as chronic bronchitis in some
cases via the self-reported questionnaire, combinations of chronic bronchitis with asthma or chronic
bronchitis alone appeared at very young ages. Emphysema was reported consistently from age 50 years
onward. Combinations of two of the three OLD
conditions occurred among 21.2%, 31.4%, and
14.4%, in those patients in the age groups of 60 to 69
years, 70 to 79 years, and ⱖ 80 years, respectively.
By contrast, in the UK GPRD, emphysema and
chronic bronchitis are virtually nonexistent diagnoses
before 50 years of age. After age 50 years, the
frequent diagnoses of chronic bronchitis and emphysema together as COPD gave little room for chronic
bronchitis-only or emphysema-only diagnoses.
Therefore, combinations of two of the three OLD
conditions occurred among 41.5%, 58.8%, and
65.5% of patients in the age groups of 60 to 69 years,
70 to 79 years, and ⱖ 80 years, respectively.
Finally, according to the spirometry data of
NHANES III, US OLD participants with chronic
bronchitis or emphysema, with or without a concomitant diagnosis of asthma, differed widely regarding
the prevalence of airflow obstruction among patients
with a diagnosis of emphysema only, with only 37.4%
of patients having airflow obstruction confirmed by
spirometry. The prevalence of airflow obstruction
was significantly higher among participants with
combinations of emphysema and chronic bronchitis
(57.7%), with emphysema and asthma (51.9%), and
with all three OLD diseases concomitantly (52.0%).
Among all NHANES III participants with airflow
obstruction, accounting for 4.8% of the general
population, 58.3% reported no diagnosis of any of
the three OLD conditions (Fig 4). The patterns of
airflow obstruction prevalence were confirmed when
the analysis was restricted to participants aged ⱖ 50
years (Fig 5). The prevalence of airflow obstruction
in the seven mutually exclusive areas were as follows:
asthma only, 26.5%; chronic bronchitis only, 29.6%;
emphysema only, 45.5%; asthma plus chronic bronchitis, 55.8%; asthma plus emphysema, 48.7%;
chronic bronchitis plus emphysema, 59.7%; and
asthma plus chronic bronchitis plus emphysema,
49.0%. Still, 9.3% of the NHANES III population
who were ⬎ 50 years of age had objective airflow
obstruction without any respiratory diagnoses.
Discussion
Our analysis highlights the problem of the differential diagnosis among OLDs, particularly in older
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CHEST / 124 / 2 / AUGUST, 2003
477
Figure 3. Proportion of patients with asthma, chronic bronchitis, emphysema, or any combination of
the three conditions, by age and gender in the United States (NHANES III surveys from 1988 to 1994)
and United Kingdom (GPRD 1998).
adults and the elderly. By analyzing large samples of
patients from the general population in the United
States and the United Kingdom, we demonstrated
that a substantial number of patients are diagnosed
with two or even all three OLD conditions concomitantly. By analyzing the NHANES III spirometry
data, we observed that diagnoses of asthma, chronic
bronchitis, and emphysema are present with and
without demonstrable airflow obstruction.
Some limitations of our research deserve discussion. The GPRD does not include reliable information on respiratory function, as pulmonary function is
not routinely assessed at the primary care level in the
United Kingdom or elsewhere, and the information
on tobacco use is not complete. The NHANES III
self-reported measurement of current chronic bronchitis by interview questionnaire may have included
some misclassified cases of acute bronchitis, which
would lead to the overestimation of this disease.
Some strengths of our results are the large study
sample sizes, the demonstrated quality control of
NHANES III spirometry,13 and the analyses in two
nationally representative populations. As explained
previously, the comparison of results from NHANES
III and GPRD had to be done indirectly. NHANES
III participants were asked about “ever” and “current” physician-diagnosed conditions, while the
GPRD analysis was based on OLD diagnoses recorded directly by GPs, with a wide range of possible
terms, over a 12-month period. A patient revisiting
the GP might not have a diagnosis recorded again
that year. Therefore, one potential reason for the
lower absolute UK rates relative to the US rates
might be a technical artifact. The apparently more
than double frequency of OLD conditions that was
found in NHANES III compared to the GPRD has
to be interpreted cautiously. These estimates should
not be considered in absolute terms but in relative
terms, as the percentages of each population sample.
The most likely major explanation of this difference
is the self-reported nature of physician-diagnosed
conditions in NHANES III and the potential for
misclassification of bronchitis as chronic bronchitis.
However, the GPRD results are no less relevant
than those from NHANES III. The GPRD is a
real-life source of information, and, as it directly
records many thousands of physician diagnoses
rather than relying on the self-reporting of these
diagnoses as in NHANES III, so it should provide a
more accurate estimate of disease burden. Therefore, the GPRD likely produced smaller estimates of
disease burden with greater specificity.
We can speculate on the reasons for why the
differential diagnosis of asthma vs COPD is still
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Clinical Investigations
Figure 4. Proportional Venn diagram of OLD and airflow obstruction in the United States (NHANES
III surveys from 1988 to 1994) in participants aged ⱖ 8 years. Open circles within each area represent
the proportion of OLD patients with objective airflow obstruction according to spirometry measurements. Note that there are eight open circles, one for each of the seven mutually exclusive conditions
plus one on the right that represents participants with airflow obstruction who did not receive an OLD
diagnosis.
difficult, including the following: (1) the consideration of conditions as part of a continuum; (2) the
consideration of different conditions with strong
overlapping features (similar to diabetes mellitus
being insulin-dependent or non-insulin-dependent);
(3) no incentive to differentiate whether treatment
and prognosis are the same; (4) lack of clear guidelines from “experts” as to how the distinction can be
Figure 5. Proportional Venn diagram of OLD and airflow obstruction in the United States (NHANES
III surveys from 1988 to 1994) in participants aged ⱖ 50 years. Open circles within each area represent
the proportion of OLD patients with objective airflow obstruction according to spirometry measurements. Note that there are eight open circles, one for each of the seven mutually exclusive conditions
plus one on the right that represents participants with airflow obstruction who did not receive an OLD
diagnosis.
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CHEST / 124 / 2 / AUGUST, 2003
479
made in clinical practice; or (5) uncertain criteria
used by the physician to classify the patient as having
asthma, chronic bronchitis, or emphysema.
The controversy on how to label OLDs has been
around for decades,14 debating whether it is generalized OLD, chronic nonspecific lung disease,
COPD, or another term that fits the best. The
so-called Dutch hypothesis on the interrelationship
of OLD, initially described by Orie15 in 1961, stated
that asthma and bronchial hyperreactivity predispose
patients to develop COPD later in life, and this
theory has not yet been ruled out. Practical implications in this debate are relevant because the management guidelines for asthma and COPD differ.
However, a growing number of researchers and
clinicians consider that respiratory disease is a continuum from childhood to adulthood, and that
asthma leads to chronic OLD becoming COPD in
the elderly. Indeed, many physicians treat adult
chronic asthma patients and COPD patients with
similar drugs. In our study, it was not possible to
establish any difference between the GPs and pulmonologists as to how the diagnoses were made. All
entries in the GPRD were from GPs only, as the
GPRD is a database of primary care doctors only,
while NHANES III is a survey of self-reported
diagnoses and conditions by the participants. Regrettably, in these two countries and elsewhere, OLD is
diagnosed too often without spirometry findings. It
may be timely to remind primary care physicians that
they should accurately assess the airway status of
their patients. It takes only a few minutes to inquire
about medical history, to examine patients’ lungs, to
confirm their impression with spirometry followed
by a course of appropriate therapy, and finally to
educate patients on the correct use of inhalers.
Overall, only about half of the patients who reported
a COPD-compatible diagnosis in the NHANES III
survey had abnormal spirometry findings corresponding to grade 1 (or higher) of the GOLD
guidelines.4 If the diagnosis was based on spirometry
as well as clinical features, the distribution of the
various COPD diagnoses would alter considerably
(Fig 4). Our finding that US NHANES III participants with an emphysema-only diagnosis had a lower
prevalence of objective airflow obstruction than did
participants with concomitant emphysema and
asthma or chronic bronchitis might seem to be
counterintuitive. If these results are confirmed in
other studies, the current practice in COPD randomized controlled trials (RCTs) of excluding patients who have been diagnosed with concomitant
COPD and asthma, or COPD patients who have
some asthmatic component (ie, positive results of a
bronchodilator test or methacholine challenge, or
atopy) might be artificial and would not represent
the spectrum of OLD patients represented in the
community. Asthma RCTs usually recruit patients
who are extremely young, do not smoke, and have
mild disease, and whose condition are completely
reversible. Conversely, COPD RCTs tend to recruit
patients who are old, smoke, and have severe disease,
and whose conditions are largely irreversible and
include emphysema. Therefore, “mixed” patients are
not recruited into RCTs. Physicians often have difficulties in labeling patients as having COPD or
asthma among those in the large group of aging,
chronic OLD patients with a history of cigarette
smoking and an asthmatic component. Indeed,
evidence-based medicine cannot be conducted in
patients with combined asthma and COPD, who,
according to our research, account for as much as
half of the OLD population aged ⱖ 50 years.
In contrast to investigators and respiratory researchers, GPs often have applied Occam’s razor,
treating all OLD patients the same by administering
inhaled corticosteroids and bronchodilators, but with
some difference in the usage of anticholinergic
agents, theophylline, cromones, and, of course, oxygen.16,17 This practical approach has made the subdivision of OLDs irrelevant for most doctors, except
for those investigators studying etiology, prognosis,
or treatment response in detail.
Further research to better characterize the subgroup of patients with objective airflow obstruction
but without any respiratory diagnosis (3.1%) [Fig 4]
is needed.18 At least in North America, primary care
physicians are still reluctant to consider the diagnosis
of COPD, even when confronted by a middle-aged
former smoker with chronic cough and dyspnea,
especially among women.19 The newly established
Burden of Lung Disease3 initiative within GOLD
aimed to obtain population data on respiratory symptoms, diagnosed conditions, and lung function in
patients of different ages and multiple geographic
regions will help to quantify the magnitude of these
subpopulations.
Finally, we consider our presentation of proportional Venn diagrams to be original. Our diagram
allows us to represent the percentage of patients with
abnormal spirometry data in all seven groups, which
is not possible with the original ATS version.6 The
Venn diagram first appeared in a book written by
John Venn at Cambridge in 1866. The idea of a
universe box was added later by Charles Dodgson,
alias Lewis Carroll, at Oxford in 1891. Usually, these
diagrams consist of circles of the same size, so that
they were only symbolic of the groups they represented and did not indicate in any way their relative
magnitudes. Proportional Venn diagrams are always
possible using triangles instead of circles but they
lack the clarity and elegance of circles.
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Clinical Investigations
We conclude that the concomitant diagnosis of
asthma, chronic bronchitis, or emphysema is common among OLD patients from the general population, accounting for as much as half of the OLD
population who are aged ⱖ 50 years.
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