Eur Respir J, 1994, 7, 269–273
Printed in UK - all rights reserved
Copyright ERS Journals Ltd 1994
European Respiratory Journal
ISSN 0903 - 1936
Q Qu ua al li it ty y o of f l li if fe e i in n p pa at ti ie en nt ts s w wi it th h c ch hr ro on ni ic c o ob bs st tr ru uc ct ti iv ve e p pu ul lm mo on na ar ry y
d di is se ea as se e i im mp pr ro ov ve es s a af ft te er r r re eh ha ab bi il li it ta at ti io on n a at t h ho om me e
P.J. Wijkstra*, R. Van Altena*, J. Kraan**, V. Otten*, D.S. Postma**, G.H. Koëter**
Quality of life in patients with chronic obstructive pulmonary disease improves after reha-
bilitation at home. P.J. Wijkstra, R. Van Altena, J. Kraan, V. Otten, D.S. Postma, G.H.
Koëter. ERS Journals Ltd 1994.
ABSTRACT: We have developed a rehabilitation programme at home and have
investigated its effects on quality of life (QOL), lung function, and exercise toler-
ance in patients with chronic obstructive pulmonary disease (COPD).
We studied 43 patients with severe airflow obstruction: forced expiratory vol-
ume in one second (FEV1) 1.3±0.4 l (mean±SD), FEV1/inspiratory vital capacity (IVC)
37±7.9%. After stratification, 28 patients were randomly allocated in a home reha-
bilitation programme for 12 weeks. Fifteen patients in a control group received
no rehabilitation. The rehabilitation group received physiotherapy by the local
physiotherapist, and supervision by a nurse and a general practitioner. Quality of
life was assessed by the four dimensions of the Chronic Respiratory Questionnaire
We found a highly significant improvement in the rehabilitation group compared
to the control group for the dimensions dyspnoea, emotion, and mastery. Lung
function showed no changes in the rehabilitation group. The exercise tolerance
improved significantly in the rehabilitation group compared to the control group.
The improvement in quality of life was not correlated with the improvement in
Rehabilitation of COPD patients at home may improve quality of life; this improve-
ment is not correlated with an improvement in lung function and exercise tolerance.
Eur Respir J., 1994, 7, 269–273.
*Asthma Centre Beatrixoord, Haren,
The Netherlands. **Dept of Pulmonary
Diseases, University Hospital Groningen,
Correspondence: P.J. Wijkstra
9751 ND Haren (Groningen)
Keywords: Chronic obstructive pulmonary
quality of life
rehabilitation at home
Received: February 17 1993
Accepted after revision September 19 1993
Supported by a grant from the Nederlands
Astma Fonds (grant no. 89.29) and the
Patients with chronic obstructive pulmonary disease
(COPD) are characterized by an impaired lung function
and a limited exercise tolerance. Medication and reha-
bilitation programmes are generally directed towards relief
of symptoms and improvement of lung function and exer-
cise tolerance. Several studies have shown, however, that
COPD may also lead to an impaired quality of life [1–3].
Health care use by COPD patients appears to be related
even more to an impaired quality of life than to the sever-
ity of the lung disease itself . Therefore, improvement
in quality of life should be one of the aims of treatment
of COPD .
Two general health measurements, the Quality of Well-
being Scale  and the Sickness Impact Profile (SIP) ,
have been used in COPD patients [1–3] in this respect.
However, their use may be limited by a lack of sensi-
tivity to detect changes in health . A disease-specific
questionnaire may be more sensitive, as a higher pro-
portion of its content is pertinent to the disease itself .
However, the most comprehensive disease-specific mea-
surement available in COPD at the time of the study, the
Chronic Respiratory Questionnaire (CRQ) of GUYATT and
co-workers , showed no improvement of quality of
life after inspiratory muscle training in COPD patients
The purpose of the present study was to investigate, in
patients with COPD, whether a more extensive home
rehabilitation programme could show improvement in
quality of life, as measured with the CRQ.
Patients and Methods
We studied 45 COPD patients (all smokers or ex-
smokers) (table 1) with severe airflow limitation. All
patients were in a clinically stable condition (no recent
exacerbations) with optimal drug management. Entry
criteria were: 1) forced expiratory volume in one second
(FEV1) <60% predicted; and 2) FEV1/inspiratory vital
capacity (IVC) <50%; both after two inhalations of 40 µg
ipratropium bromide. Patients with evidence of ischaemic
heart disease, intermittent claudication, musculoskeletal
disorders, or other disabling diseases that could restrict
the rehabilitation programme were excluded. The study
was approved by the Medical Ethics Committee of the
University Hospital of Groningen, and all patients gave
P.J. WIJKSTRA ET AL.
The patients were hospitalized for two days for their
initial evaluation. They were stratified for their FEV1%
predicted (less or more than 45% predicted), their limit-
ing factor in exercise capacity (ventilatory limitation or
nonventilatory limitation), and the maximal workload
(less or more than 70 w) of their cycle ergometer test.
After this stratification, the patients were randomly allo-
cated to a 12 week home rehabilitation programme or to
a control group. Thirty patients entered the rehabilita-
tion group and 15 patients entered the control group.
The following measurements were carried out before, and
12 weeks after, rehabilitation: 1) quality of life; 2) spiro-
metry; and 3) cycle ergometer test.
The patients were supervised by a multidisciplinary
team: pulmonologist, physiotherapist, nurse, and gener-
al practitioner. The study was organized and set up by
one pulmonologist (P.J.W.), who visited all physiothera-
pists, nurses, and general practitioners before the start of
the study to instruct them about the rehabilitation pro-
gramme. The patients visited the physiotherapist twice
a week for 12 weeks.
The physiotherapy programme consisted of conven-
tional physiotherapy (relaxation exercises , and breath-
ing retraining ), upper limb training , target-flow
inspiratory muscle training (IMT) , and exercise train-
ing on a home-trainer according to ALLISON et al. .
The patients started exercise training for 4 min at 60%
of their maximal workload (Wmax) of the cycle ergo-
meter test. The time span was gradually extended to 12
min and the workload to a maximum of 75% of the
Wmax. All exercises were taught by the physiotherapist.
The patients had to practise twice a day for half an hour
at home, according to an individualized protocol. During
this training period of one hour a day, all exercises were
practised. Patients started one day with relaxation exer-
cises and the other day with breathing retraining, and so
on. Every day they practised IMT, upper limb training,
and exercise training on a home-trainer.
In addition to this physical training, the patients were
supervised once a month by a nurse and a general prac-
titioner. The nurse visited the patients at home, and her
task was to give the patients and also family members a
better insight into the possible disabilities and handicaps
due to impairment of the lungs. Information was given
about pulmonary disease, about various strategies for
treatment, how to use the medication, how the patient
could cope with the disease, and the role of a rehabilita-
tion programme in this coping strategy.
The patients also visited the general practitioner once
a month, and his task was to supervise the clinical sta-
tus and maintenance treatment. The control group did
not follow the above mentioned protocol.
Baseline lung function characteristics. Static lung vol-
umes, FEV1, IVC, diffusion capacity, volume-pressure
relationship, and static compliance were measured dur-
ing the initial evaluation. Static lung volumes were deter-
mined in a constant volume whole body plethysmograph
(Masterlab, Jaeger, Würzburg, FRG). FEV1and IVC
were measured by means of a pneumotachograph (Jaeger,
Würzburg, FRG). Diffusion transfer factor for carbon
monoxide divided by alveolar volume (TLCO/VA) was
measured by using the single-breath method. Volume/pres-
sure (V/P) diagrams of the lungs were recorded using an
oesophageal balloon (Jaeger, Würzburg, FRG). Static
compliance was calculated from the V/P diagram. Predicted
values were derived from the European Community for
Coal and Steel (ECCS) .
Quality of life. Quality of life was assessed by the Chronic
Respiratory Questionnaire (CRQ) of GUYATT and co-
workers , which was translated into Dutch. The CRQ
is divided into four dimensions: Dyspnoea, Fatigue,
Emotion, and Mastery. The dimensions Fatigue, Emotion
and Mastery had a good reliability, whilst the dimension
Dyspnoea showed a lower reliability (submitted for pub-
lication). This questionnaire was also shown to be valid
given the good correlation with the dimensions of the
Symptom Checklist  (SCL-90) (submitted for publi-
cation). The CRQ measures both physical and emotional
function. Physical function was investigated by five
items relating to the dimension dyspnoea and by four
items relating to the dimension Fatigue. Assessment of
emotional function, corresponding with the dimensions
Emotion and Mastery, included questions about frustra-
tion, depression, anxiety, panic, and fear of dyspnoea.
Table 1. – Baseline characteristics of the study popu-
IVC % pred
RV/TLC % pred
TLCO/VA % pred
All value are expressed as mean±SD. *: p<0.05 unpaired t-
test. FEV1b: forced expiratory volume in one second before
bronchodilation with two inhalations of 40 µg ipratropium bro-
mide; FEV1a: FEV1after bronchodilation; % pred: expressed
as a percentage of the predicted value; FEV1/IVC %: FEV1
expressed as a percentage of the slow inspiratory vital capac-
ity; TLC: total lung capacity; RV: residual volume; Cst: static
lung compliance; TLCO/VA: transfer factor for carbon monoxide
divided by alveolar volume.
Spirometry: FEV1and IVC in the control group were
significantly (p<0.05 and p=0.001, respectively) lower
after 12 weeks compared to baseline (table 3). The change
in IVC was significantly (p<0.05) different between both
REHABILITATION AND QUALITY OF LIFE IN COPD
Patients were asked to rate their physical and emotional
function on a seven point scale. Higher scores repre-
sented better function. During the second administra-
tion of the test (after 12 weeks), the patients were told
their previous answers (from the start of the programme),
as advocated by GUYATT and co-workers .
Spirometry. After 12 weeks, FEV1and IVC were mea-
sured by means of a pneumotachograph.
Cycle ergometer test. Patients respired through a mouth-
piece and wore a noseclip during the incremental symptom-
limited cycle ergometer test (Jaeger, Würzburg, FRG).
Minute ventilation (VE), oxygen uptake (VO2) and car-
bon dioxide output (VCO2) were measured every 30 s from
analysis of the expirate by a computerized system (EOS
Sprint; Jaeger, Würzburg, FRG). Heart rate was moni-
tored simultaneously (Marquette Electronics inc., Milwaukee,
USA), and arterial oxygen saturation (SaO2) was record-
ed continuously by an ear oximeter (Biox IIA, Biox
Technology inc., Colorado, USA). After 1 min of un-
loaded pedalling, work rate increased 10 w every minute.
Patients were instructed to stop when they could not con-
tinue the test any longer due to dyspnoea or general
fatigue. The maximum workload (Wmax) was defined
as the highest work level reached and maintained for a
After checking for a normal distribution, baseline out-
come measures between the two groups were analysed
with unpaired Student's t-test, while the results after 12
weeks were compared with baseline within each group
using a paired t-test. The changes in each variable in the
rehabilitation group compared to the control group were
investigated by the unpaired Student's t-test. Significance
level was set at p<0.05.
Two patients dropped out of the rehabilitation group:
one patient due to a cerebral tumour and one due to arth-
ritis. The rehabilitation group, therefore, consisted of 28
patients and the control group of 15.
Baseline lung function characteristics. These showed no
significant differences between the rehabilitation and the
control group, except for IVC and (RV)/(TLC) % pre-
dicted (table 1). The measurements in both groups con-
cerning quality of life and exercise tolerance were comparable
Quality of life. The dimensions Dyspnoea, Fatigue, Emotion,
and Mastery showed a highly significant (p<0.001) im-
provement after 12 weeks of rehabilitation as compared
to baseline, whilst there was no change in the control
group (table 2). The change in the dimensions Dyspnoea,
Emotion and Mastery was also significantly (p<0.01) dif-
ferent between both groups.
Table 2. – Effects of rehabilitation on quality of life
Baseline12 week12 week
All values are expressed as mean±SD, ***: p<0.001 paired t-
test between baseline and 12 week test; ##: p<0.01 unpaired t-
test between the changes in both groups. Dyspnoea, Fatigue,
Emotion and Mastery: dimensions of the Chronic Respiratory
Cycle ergometer test. The rehabilitation group showed
a significantly (p<0.05) higher Wmax in the cycle ergo-
meter test after 12 weeks than at baseline (table 3). The
rehabilitation group showed an improvement in Wmax
of 10% (70 to 78 W), whilst the exercise tolerance of
the control group decreased by 9%, the difference being
significant (p<0.01). The VO2-symptom limited (VO2-SL)
was also significantly (p<0.05) higher in the rehabilita-
tion group after 12 weeks compared to baseline, whilst
the control group showed a decrease. The change in both
groups was significantly (p<0.05) different.
Relationship between outcome measures. We found no
significant correlation between the baseline score of the
dimensions Dyspnoea, Fatigue, Emotion, and Mastery
and the baseline exercise tolerance for both groups. The
change of the dimensions Dyspnoea, Fatigue, Emotion,
and Mastery did not correlate with the change in exer-
cise tolerance, either for the whole study population, or
for the rehabilitation group alone.
Table 3. – Effects of rehabilitation on lung function and
Baseline12 week 12 week
All values are expressed as mean±SD, *: p<0.05; ***: p=0.001,
paired t-test between baseline and 12 week test; #: p<0.05; ##:
p<0.01 unpaired t-test between the changes in both groups.
Wmax: maximal workload of the cycle ergometer test. for fur-
ther abbreviation see legend to table 1.
Our study shows an improvement in quality of life in
patients with COPD after 12 weeks of rehabilitation at
home. The dimensions Dyspnoea, Fatigue, Emotion,
and Mastery of the Chronic Respiratory Questionnaire
(CRQ) showed a highly significant improvement in the
rehabilitation group, whilst no significant changes were
observed in the control group. The improvement in the
dimensions Dyspnoea, Emotion, and Mastery in the
rehabilitation group was also significantly different com-
pared to the change in the control group. As expected,
spirometry did not improve. Although exercise perfor-
mance improved, this did not correlate with improvement
in quality of life.
In a controlled study, GUYATT and co-workers  also
used the CRQ, but found no change in quality of life
after inspiratory muscle training (IMT) at home. This
finding might have been expected because DEKHUIJZEN
et al.  had already shown that IMT alone did not
influence psychological parameters, although they did not
use the CRQ. On the other hand, they showed that a
combination of IMT and conventional rehabilitation
decreased anxiety and depression. Several other studies
[19–21] have also shown that a comprehensive approach,
i.e. physiotherapy, education, and vocational counselling,
may lead to an improvement in psychological status.
Some studies [19, 20, 22, 23] also showed improvement
in the quality of life, but they did not assess it system-
atically by means of a valid questionnaire. Studies that
showed an improved quality of life by using valid ques-
tionnaires, like the CRQ, were mostly carried out in a
clinical setting without a control group [5, 9, 24]. On
the other hand, studies [19, 21, 25, 26] that investigated
the effects of a comprehensive rehabilitation programme
at home did not assess the change in quality of life. Our
study is the first to show that a comprehensive pro-
gramme of rehabilitation carried out in a home care set-
ting improves both exercise tolerance and quality of life,
as compared to a control group.
An important question remaining is whether this improved
quality of life, as assessed by the CRQ, is of clinical rel-
evance. GUYATT and co-workers  defined improve-
ment in quality of life as an increase of at least four points
in the raw score for physical function (Dyspnoea and
Fatigue) or emotional function (Emotion and Mastery),
with a total improvement of at least four points. It was
their impression, after extensive clinical experience with
the CRQ , that patients with an increase of at least
four points find their quality of life improved, whilst
patients with a score below four points find their quality
of life unchanged. Although the definition of GUYATT
and co-workers  of an improved quality of life is some-
what arbitrary, we think that the total improvement of 14
points for the dimensions Dyspnoea, Fatigue, Emotion
and Mastery in our study is clinically relevant.
JONES et al.  and GUYATT  advocated the use of
disease-specific questionnaires to assess quality of life.
Therefore, in our study we used the Chronic Respiratory
Questionnaire (CRQ), which proved to be precise, valid,
and sensitive . Although we found that the dimension
Dyspnoea had a lower reliability compared to the other
dimensions, it was shown to be sensitive to change in
this study. Therefore, we agree with GUYATT and co-
workers that the CRQ is a reliable and valid tool to mea-
sure quality of life. The CRQ determines both physical
and emotional function, which encompasses the term qual-
ity of life . The use of the CRQ was investigated by
MORGAN , who concluded that the questionnaire has
the capacity to identify changes after intervention, in
patients with COPD.
We also measure physiological functions. In accor-
dance with most studies we found no improvement in
lung function in the rehabilitation group. On the other
hand, the control group showed a significant decrease in
both FEV1and IVC after merely 12 weeks. This unex-
pected finding is in contrast with a study by MCGAVIN et
al. , who found no changes in their control group.
Although the patients in the rehabilitation group, in con-
trast with the control group, visited their general practi-
tioner once a month, this was only to supervise their
clinical status according to a checklist. The maintenance
treatment in both groups did not change during these 12
weeks, and patients in both groups received oral corti-
costeroids and antibiotics for an exacerbation in a stan-
dardized way. There was no difference in the number
of exacerbations during 12 weeks between both groups.
It is known that lung function deteriorates in COPD, but
the decline in FEV1averages about 50 ml·yr-1. At
this moment, we have no explanation for the large decrease
in lung function in our control group. Follow-up of the
patients has to show whether this finding is due to change
or a real observation.
Our study showed a minor, but significant improve-
ment in exercise capacity on the cycle ergometer test,
although lung function did not improve. This finding is
compatible with rehabilitation studies in a clinical setting
[14, 31], and with a home rehabilitation programmes [25,
26]. Because the patients in the rehabilitation group
trained at home on a home-trainer, this increase in exer-
cise capacity might be due to familiarization with the
bicycle, in contrast to the control group. However, not
only the Wmax but also VO2-SL improved in the reha-
bilitation group. The combination of an increased Wmax
and VO2-SL must be considered to be influenced by moti-
vation and effort , and not only an increased effi-
ciency due to familiarization. At the same time, there is
a decrease in maximal workload in the control group
which might be explained by their fall in lung function.
However, we did not find a correlation between the fall
in lung function and the decrease in exercise capacity in
the control group. As far as we know, no other study
has found this correlation either.
The increase in exercise tolerance was not associated
with an improved quality of life, suggesting that a sub-
jective parameter, such as quality of life, is not influ-
enced by exercise tolerance. On the other hand, GUYATT
and co-workers  did find a correlation between the
improvement in the dimension Dyspnoea and the im-
proved exercise tolerance after a rehabilitation pro-
gramme. However, GUYATT and co-workers  assessed
exercise capacity by a 6 min walk test, whilst we used
P.J. WIJKSTRA ET AL.
REHABILITATION AND QUALITY OF LIFE IN COPD
cycle ergometer test. At the same time, GUYATT and co-
workers  had already shown in a previous study that
Dyspnoea correlated with the walking distance and not
with cycle ergometer tests.
In summary, our study showed that rehabilitation at
home leads to an improved quality of life in COPD
patients, which is not associated with an improvement in
lung function or exercise tolerance. The improvement of
quality of life is probably due to the comprehensive care
of the rehabilitation programme and not only to a part of
it. However, our study investigated only quality of life
immediately after rehabilitation at home. An important
question remains, namely how long this improvement of
quality of life will last. Therefore, further long-term reha-
bilitation studies, including assessment of quality of life,
need to be carried out.
Acknowledgement: The authors thank the lung function
laboratory staff of Beatrixoord for their technical assistance
in the performance of this study. They also thank H.A.A.M.
Gosselink and R.V.M. Chadwick-Straver of the Department
of Physiotherapy, University Hospital of Amsterdam (VU),
for their translation of the CRQ into Dutch.
1. McSweeny AJ, Grant I, Heaton RK, Adams KM, Timms
RM. Life quality of patients with chronic obstructive
pulmonary disease. Arch Intern Med 1982; 142: 473–478.
Prigatano GP, Wright EC, Levin D. Quality of life and
its predictors in patients with mild hypoxemia and chron-
ic obstructive pulmonary disease. Arch Intern Med 1984;
Schrier AC, Dekker FW, Kaptein AA, Dijkman JH. Quality
of life in elderly patients with chronic nonspecific lung
disease in family practice. Chest 1990; 98: 894–899.
Traver GA. Measures of symptoms and life quality to
predict emergent use of institutional health care resources
in chronic obstructive airways disease. Heart Lung 1988;
Guyatt GH, Berman LB, Townsend BA. Long-term out-
come after respiratory rehabilitation. Can Med Assoc J
1987; 137: 1089–1095.
Kaplan RM, Atkins CJ, Timms R. Validity of a well-
being scale as an outcome measure in chronic obstruc-
tive pulmonary disease. J Chron Dis 1984; 37: 85–95.
Bergner M, Bobbitt RA, Carter WB, Gilson BS. The
Sickness Impact Profile: development and final revision
of a health status measure. Med Care 1981; 19: 787–805.
Jones PW, Quirk FH, Baveystock CM, Littlejohns P.
A self-complete measure of health status for chronic
airflow limitation. Am Rev Respir Dis1992; 145: 1321–1327.
Guyatt GH, Berman LB, Townsend M, Pugsley SO,
Chambers LW. A measure of quality of life for clinical
trials in chronic lung disease. Thorax 1987; 42; 773–778.
Guyatt G, Keller J, Singer J, Halcrow S, Newhouse M.
Controlled trial of respiratory muscle training in chronic
airflow limitation. Thorax 1992; 47: 598–602.
Jacobson E. In: Progressive relaxation. Chicago, University
of Chicago Press, 1938.
Casciari RJ, Firshter RD, Harrison A, Morrison JT,
Blackburn C, Wilson AF. Effects of breathing retrain-
ing in patients with COPD. Chest 1981; 79: 393–398.
Ries AL, Ellis B, Hawkins RW. Upper extremity exer-
cise training in chronic obstructive pulmonary disease.
Chest 1988; 93: 688–692.
14.Dekhuijzen PNR, Beek MM, Folgering HT, Van Herwaarden
CL. Psychological changes during pulmonary rehabili-
tation and target-flow inspiratory muscle training in COPD
patients with a ventilatory limitation during exercise. Int
J Rehabil Res 1990; 13 (2): 109–117.
Allison JA, Samios R, Anderson SD. Evaluation of exer-
cise training in patients with chronic airway obstruction.
Phys Ther 1981; 61: 1273–1277.
Quanjer PH, ed. Standardized lung function testing.
Report of working party for "Standardization of Lung
Function Tests". European community for Coal and Steel,
Luxembourg. Bull Eur Physiopathol Respir 1983; 19
(Suppl. 5): 1–95.
Derogatis LR, Cleary PA. Confirmation of the dimen-
sional structure of the SCL-90: a study in construct valid-
ity. J Clin Psychol 1977; 33: 981–989.
Guyatt GH, Townsend M, Keller JL, Singer J. Should
study subjects see their previous responses: data from a
randomized 18 control trial. J Clin Epidemiol 1989; 42:
Haas A, Cardon H. Rehabilitation in chronic obstructive
pulmonary disease. A five year study of 252 male patients.
Med Clin North Am 1969; 53: 593–606.
Petty TL, Nett LM, Finigan MM, et al. A comprehen-
sive care program for chronic airway obstruction. Ann
Intern Med 1969; 70: 1109–1120.
Agle DP, Baum GL, Chester EH, Wendt M. Multi-
discipline treatment of chronic pulmonary insufficiency.
1. Psychologic aspects of rehabilitation. Psychosom Med
1973; 35 (1): 41–49.
Cherniack RM, Handford RG, Svanhill E. Home care of
chronic Respiratory Disease. J Am Med Assoc 1969; 208:
Petty TL. Ambulatory care for emphysema and chronic
bronchitis. Chest 1970; 58: 441–448.
Bebout DE, Hodgkin JE, Zorn EG, Yee AR, Sammer EA.
Clinical and physiological outcomes of a university hos-
pital pulmonary rehabilitation program. Respir Care 1983;
McGavin CR, Gupta SP, Lloyd EL, McHardy JR. Physical
rehabilitation for the chronic bronchitic: results of a con-
trolled trial of exercises in the home. Thorax 1977; 32:
Strijbos JH, Koëter GH, Meinesz AF. Home care
rehabilitation and perception of dyspnea in chronic ob-
structive pulmonary disease patients. Chest 1990; 97:
Guyatt G. Measuring health status in chronic airflow
limitation. Eur Respir J 1988; 1: 560–564.
Berger M. Measurement of health status. Med Care 1988;
5 (23): 696–704.
Morgan MDL. Experience of using the CRQ (Chronic
Respiratory Questionnaire). Respir Med 1991; 85 (Suppl.
Anthonisen NR, Wright EC, Hodgkin JE. Prognosis in
chronic obstructive pulmonary disease. Am Rev Respir
Dis 1986; 133: 14–20.
Cockcroft GH, Saunders MJ, Berry G. Randomized con-
trolled study of rehabilitation in chronic respiratory dis-
ability. Thorax 1981; 36: 200–203.
Casaburi R. Exercise training in Chronic Obstructive
Lung Disease. In: Casaburi R, Petty TL, eds. Principles
and Practice of pulmonary rehabilitation. Philadelphia,
W.B. Saunders Co., 1993; pp. 204–224.
Guyatt GH, Thompson PJ, Berman LB, et al. How should
we measure function in patients with chronic lung dis-
ease? J Chronic Dis 1985; 38: 517–524.