Journal of Psychosomatic Research 76 (2014) 146–151

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Journal of Psychosomatic Research

Illness perceptions predict exercise capacity and psychologicalwell-being after pulmonary rehabilitation in COPD patients

Natalie Zoeckler a,⁎, Klaus Kenn b, Kerstin Kuehl a, Nikola Stenzel a, Winfried Rief a

a Department of Clinical Psychology and Psychotherapy, Philipps-University, Marburg, Germanyb Pulmonary Rehabilitation Centre (Schoen Klinik Berchtesgadener Land), Schoenau, Germany

⁎ Corresponding author at: Philipps-University of MPsychology and Psychotherapy, Gutenbergstraβe 18Tel.: +49 6421 2824011; fax: +49 6421 2828904.

E-mail addresses: natalie.zoeckler@staff.uni-marburg.dkkenn@schoen-kliniken.de (K. Kenn), kuehl@staff.uni-mastenzel@staff.uni-marburg.de (N. Stenzel), rief@staff.uni-m

0022-3999/$ – see front matter © 2013 Elsevier Inc. All rihttp://dx.doi.org/10.1016/j.jpsychores.2013.11.021

a b s t r a c t

a r t i c l e i n f o

Article history:

Received 30 June 2013Received in revised form 26 November 2013Accepted 29 November 2013

Keywords:COPDExercise capacityIllness perceptionsPulmonary rehabilitationQuality of life

Objective: Patients' beliefs about their disease have been associated with emotional adjustment and outcomes inseveral severe illnesses. The aim of the present study was to investigate whether illness perceptions beforepulmonary rehabilitation influence exercise capacity and quality of life after rehabilitation in patients sufferingfrom chronic obstructive pulmonary disease (COPD).Methods: Ninety-six patients with COPD (GOLD III/IV) were approached on admission to rehabilitation andreassessed before discharge. Assessment included medical measures of FEV % predicted, and exercise capacity(6 min walk test). Additionally, depressive symptoms (Hospital Anxiety and Depression scale), anxiety (COPDspecific anxiety questionnaire) and quality of life (Short Form 36 health survey (SF-36)) were assessed. Illnessbeliefs were measured by the Revised Illness Perception Questionnaire (IPQ-R).Results: Exercise capacity and psychological well-being (SF-36) of patients improved after rehabilitation

programme, while physical functioning (SF-36) did not change. Additionally, patients showed significantlylower levels of depressive symptoms, COPD specific anxiety and negative perceptions of their illness after pulmo-nary rehabilitation compared to baseline. In the hierarchical multiple regression analyses, after controlling forsocio-demographic data, psychological variables, illness severity and baseline scores of the correspondingvariables, it was shown that illness perceptions before rehabilitation predicted exercise capacity and psychologicalwell-being, both assessed at the end of treatment.Conclusion: COPD patients' perceptions about their illness before rehabilitation influence exercise capacity andquality of life (psychological well-being) after treatment. Therefore it might be relevant to identify and changemaladaptive illness perceptions in order to improve medical and psychological outcome in COPD.

© 2013 Elsevier Inc. All rights reserved.

Introduction

Pulmonary rehabilitation (PR) has become an important treatmentfor patients suffering from chronic obstructive pulmonary disease(COPD), with beneficial effects on exercise tolerance, perceived dyspneaand quality of life [1,2]. Identifying which COPD patients benefit mostfrom pulmonary rehabilitation is not accurately predicted frommedicalmeasures [1]. In recent years, the role of patients' illness perceptionsabout their disease has been highlighted [3]. Patients' negative beliefsof their illness and ability to manage symptoms have been associatedwith negative psychological and medical outcome [4].

COPD is a chronic degenerative disease characterised by irreversibleobstruction of the airways [5]. COPD is the fourth leading cause of com-binedmorbidity andmortality [6]. Patients experience acute episodes of

arburg, Department of Clinical, 35032 Marburg, Germany.

e (N. Zoeckler),rburg.de (K. Kuehl),arburg.de (W. Rief).

ghts reserved.

exacerbation including breathlessness (dyspnea), sputum productionor coughing accompanied by a reduction in ability for physical exertion[5]. This condition leads to an overall decline in everyday function andquality of life [7]. Additionally, COPD is associated with a high level ofpsychological distress, like symptoms of depression and general anxiety[8–13]. Psychological repercussions include fear, panic, loss of confi-dence and isolation [14–16]. It was shown that patients with depressivesymptoms reported higher levels in COPD specific anxiety, such as fearof social isolation, dyspnea related fear, fear of physical activity, andfear of progression of disease [17]. The consequences on COPD are in awide range—patients experience restricted ability to perform dailyactivities and fear of dyspnea may lead to avoidance of activities[13,15,17–19].

More recently, the role of illness perceptions and coping responsesin chronic illnesses have been highlighted [3,20,21]. One theoreticalmodel that has addressed how cognitive factors influence illness copingbehaviours and outcomes is the Common Sense Model [21]. This modelidentifies factors involved in the processing of information by a patientregarding their disease, how this information is integrated to provide aview of the illness and how these beliefs guide coping behaviours andoutcomes. Patients create their own beliefs about the identity, time

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course, causes, consequences, emotional reaction and the controllabilityof their illness [3]. These beliefs pertain to the way patients responseand make sense of their disease. Illness beliefs are also expected todevelop and change over the course of illness [22]. Research hasshown that illness perceptions affect coping, functional adaption, andare tied to fear and distress [23–27]. In several studies it was foundthat illness beliefs were predictive for health-related outcomes inchronic illnesses [28–30] and have been associated with non adherenceto rehabilitation [31,32]. Moreover, illness beliefs explained significantamounts of variance in the number of clinical visits, pain, tiredness,and anxiety over a one-year period [33]. Research has shown that illnessperceptions are a better predictor of disability than objective medicalvariables [34].

So far, very few studies have addressed illness perceptions in COPDpatients. One study has shown that patients' beliefs influenced self-management [35] and adherence to participation in PR [36]. Otherstudies have explored the relationship between illness perceptionsand outcome in COPD, showing that beliefs about treatment control,consequences and causeswere associatedwith quality of life and gener-al functioning [28,37]. Further research concerning chronic illnessesdemonstrated how patients' cognitions determined hospitalization,medication use, and quality of life, even after controlling for illnessseverity [28,37–39]. A survey of the contribution of coping and illnessperceptions to outcome in COPD patients found that first-time illnessbeliefs and coping significantly contributed to the prediction of socialfunctioning, mental health, and health perceptions one year later [38].Results of a review concerningCOPDpatients indicate that illness beliefsare associated with disability and psychological outcomes such asdepression and anxiety [40]. Illness severity (e.g. pulmonary function)often fails to predict quality of life and general functioning [40]. Onthe other hand, research illustrates how illness perceptions determinefunctioning and quality of life [41]. Psychological processes are likelyto influence exercise intolerance in COPD patients [1,42]. Previous stud-ies found a significant negative association between anxiety or beliefsabout negative consequences and physical exercise [42–44]. Overall,illness beliefs in patients with chronic respiratory conditions havebeen shown to be important for disability and clinical outcomes aboveand beyond objective physical measures of disease severity [38,45].

Based on the literature it seems that illness perceptions are animportant factor influencing social, medical, behavioural and psycho-logical outcomes in COPD patients. So far there have been no studiesexploring illness perceptions of COPDpatients before a pulmonary reha-bilitation predicting exercise capacity and health-related quality of lifeafter rehabilitation. As physical exercise is an important predictor offunctioning in COPD patients it is relevant to investigate how patients'beliefs might influence exercise capacity. Despite the importance ofphysical exercise, it is a main objective to maintain quality of life inpersons with COPD.

Given the apparent clinical relevance of illness beliefs in patientswith COPD the aim of the present studywas to examine the relationshipbetween illness perceptions, exercise capacity and health-related qual-ity of life. The hypothesis was that illness perceptions assessed beforerehabilitation would predict exercise capacity and self-reported qualityof life after pulmonary rehabilitation programme.

Method

Participants

COPDpatientswere recruited froma centre of pulmonary rehabilita-tion (Schoen Klinik Berchtesgadener Land, Germany). Patients diag-nosed with a severity grade of III or IV (according to the GlobalInitiative for Chronic Obstructive Lung Disease (GOLD criteria)) wereinvited to participate in this study. A total of 106 COPD patients wereinformed, 7 persons declined to participate and 3 had to be excludedfor reasons of illness exacerbation. Thus, the final sample consisted of

96 patients. Exclusion criteria for patientswere serious illness exacerba-tion or another severe acute illness (myocardial infarction, tumour).Eighty-one percent of the patients used long-term oxygen treatment,and 27.1% were listed for lung transplantation.

Procedure

This study has received ethical approval by the Bavarian StateMedical Association. Patients completed informed consent proceduresand participants were asked to fill out psychological questionnaires,and questionnaires including socio-demographic data (age, sex, educa-tion, marital status, length of diagnosis, smoking status, and pack years)after admission at the centre and before entering the rehabilitationprogramme. Additionally, baseline assessment included a pulmonaryfunction test (FEV as a percentage of the predicted value), and a classi-fication of disease severity (GOLD criteria) according to internationalguidelines [46]. Higher GOLD grade represents worse lung function.All patients underwent height and weight measurements and a fieldexercise test (6 min walking test) [47]. Additional medical data wastaken from the patient file. After the rehabilitation programme, partici-pants were asked to fill in the questionnaires and the 6 min walk testand FEV measures were repeated.

Measures

Illness perception

The Revised Illness Perception Questionnaire (IPQ-R) [48] wasadministered to assess the patients' beliefs of their illness before reha-bilitation programme. This is a widely used quantitative measure,whichhas been applied to several illnesses. The IPQ-R has demonstratedgood internal reliability, retest reliability and predictive validity.

The IPQ-R comprises nine subscales: timeline (chronic time courseand cycling time course; e.g., “My illness will last a short time”), conse-quences (e.g., “My illness is a serious condition”), timeline cyclical(e.g., “My symptoms come and go in cycles”), personal control(e.g., “There is a lot which I can do to control my symptoms”), treat-ment control (e.g., “My treatment can controlmy illness”), illness coher-ence (e.g., “I don't understand my illness”), emotional representations(e.g., “My illnessmakesme feel afraid”), identity, and cause. The identity(.20) and cause scale (.24) were not included in the current analysesbecause the subscales showed low internal consistency of Cronbach'salpha. For the other subscales Cronbach's alpha ranged from .71 to .92.Subscales are measured by 32 five-point Likert scale items. Mean sub-scale scores were computed with higher scores indicating greaterendorsement of the given construct.

Health-related quality of life

The Short Form 36 health survey (SF-36) [49] is a general quality oflife instrument. The questionnaire consists of 36 questions that mea-sures eight dimensions of health: physical functioning, role limitationsdue to physical health problems, bodily pain, social functioning, generalmental health, role limitations due to emotional problems, vitality, andgeneral health perceptions. The SF-36 dimensions are scored separatelyand transformed to a 0–100 scale. The dimension scores can be aggre-gated in two scores: physical functioning and psychological well-being. Higher scores indicate a better health status. The questionnairehas shown satisfactory validity and reliability in COPD patients [50].

Depression

Depressive symptoms were assessed before and after rehabilitationusing the depression scale of the Hospital Anxiety and DepressionScale (HADS) [51]. This is a validated seven-item rating scale designedto screen for clinically significant states of depression in medical

Table 1Demographic and clinical characteristic of study sample

Variables COPD-patients (n = 96)

Age (years) 61.2 ± 8.8Gender (F:M) 41:55 (42.7%: 57.3%)Marital statusMarried 71 (74%)Single or divorced 25 (26%)

Body mass index (BMI) 24.4 ± 5.4COPD severity (GOLD)III 26 (27.1%)IV 70 (72.9%)

Exercise capacity (metres) 267 ± 116Smoking (pack years) 43.4 ± 22.9FEV % pred. 33.5 ± 12.5Length of diagnosis (years) 8.3 ± 6.1

Data presented as n, mean ± SD.Abbreviations: FEV % pred., forced expiratory volume in 1 s expressed in percentagepredicted; Exercise capacity, 6 minute walk test (6MWT) in metres; smoking (packyears), packs smoked per day × years as a smoker.

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outpatients. The items are scored on a four-step scale ranging from 0(not at all) to 3 (verymuch). The depression scale is scored by summingthe responses and the score ranges from 0 to 21, with higher scoresreflecting more depressive symptoms. The questionnaire was devel-oped to measure mood disorders in a medical outpatient populationand therefore the HADS excludes confounding somatic symptoms.

COPD specific anxiety

The COPD specific anxiety questionnaire (CAF) [52] is a diseasespecific instrument for patients suffering from pulmonary disease. Itmeasures COPD related anxiety. The questionnaire consists of 27 itemsdivided into four subscales: fear of social isolation, dyspnea related tofear, fear of physical activity, and fear of progression of disease. Theitems are scored on a five-step scale ranging from 0 (never) to 4(always). Due to the high intercorrelations (ranged from r = 0.74 tor = 0.91) of the CAF subscales the sum score was selected, with higherscores indicating higher levels of COPD specific anxiety. The CAF consti-tutes a reliable and valid measure to assess COPD-related fears.

Illness severity (pulmonary function test)

Illness severity was assessed by a pulmonary function test. Spirome-try and body-plethysmography (Master Screen Body, Jaeger GmbH,Hoechberg, Germany) were performed, according to internationalguidelines. Forced expiratory volume in 1 s (FEV ) was measured andthe predicted values were calculated. FEV per litre and FEV as a per-centage of the predicted value (FEV % predicted) were used as a mea-sure of lung functioning.

Exercise capacity (6 min walk test)

The 6 min walk test (6MWT) was used for determining functionalcapacity (once at baseline) and changes in functional capacity (onceat follow-up) according to international standards of the AmericanThoracic Society. The 6MWT is a practical test that requires a continuouscorridor. Itmeasures the distance a patient canwalk on aflat surface in aperiod of 6 min. In order to assure high quality, patients were testedtwice by the same trained person without a “warm-up” period. Beforestarting the test, patients rested in a chair for 10 min. Additionally,only standardized phrases for encouragement (e.g. “you are doingvery well”) were used (participants were asked to walk as far and asfast as they could and to cover as much distance as possible). Encour-agement was used every minute.

Data analysis

SPSS version 19.0 was used to carry out statistical analysis of data.First, independent samples t-test and χ2-test were applied to comparemeans and proportions between male and female, and between thetwo groups of COPD patients (GOLD III/IV). In order to determinedescriptive statistics for the pre- and post-rehabilitation values, weused dependent t-tests. Relations between the independent variablesand outcome measures were analyzed using the Pearson correlationcoefficients. Hierarchical multiple linear regression analyses were usedto investigate whether baseline illness perceptions predicted exercisecapacity, psychological and physical functioning at follow-up abovesocio-demographic data, depressive symptoms, COPD specific anxietyand FEV % predicted (illness severity). Single missing values were im-puted using multiple imputations with NORM version 2.03. Multipleimputation provides a strategy for dealing with missing data. Insteadof filling in single values for each missing data, this procedure replaceseach missing value with a set of plausible values that represent theuncertainty about the right value to impute. Data screening in thisstudy revealed the following missing data: 6 missing values for CAF at

baseline, 3 missing values for HADS at baseline, 1 for SF-36, 2 missingvalues for CAF at follow-up, 7 for IPQ-R and 5 for HADS.

Results

Demographic and clinical characteristics of participants

Participants had a mean age of 61.2 years (SD = 8.8). Forty-two percent (n = 41)were female (Table 1). Seventy-seven percent (n = 74) had received an educationaltraining, 9.4% (n = 9) had graduated from high school, 7.3% (n = 7) had some collegeor technical school degree, and 5.2% (n = 5) had graduated from college. A large per-centage of participants were ex-smokers (86.5%, n = 83), with six patients stillcurrently smoking. For further details see Table 1. There were no significant differ-ences between male and female regarding demographic and clinical characteristicsexcept age (t = −1.99, p b .05) and pack years (t = −4.07, p b .01).

Twenty-six participants (27.1%) suffered from COPD grade III (severe), 70 (72.9%)participants suffered from grade IV (very severe), and themean length of time since diag-nosis was 8.3 years (SD = 6.2). Mean FEV % predicted was 33.5 (SD = 12.5). There wereno significant differences between the participants suffering from grade III or grade IVregarding demographic and clinical characteristics. Since there were no differencesfound, the two groups were merged together in further analyses.

Patients functioning after pulmonary rehabilitation

Descriptive statistics for the predictor and outcome variables (pre- and post-rehabilitation values) are presented in Table 2. In the present sample, patients showedsignificantly less depressive symptoms, less COPD specific anxiety and lower levels of neg-ative perceptions of their illness (IPQ-R) after PR compared to baseline. There were alsosignificant changes in exercise capacity and follow-up self-reported levels of psychologicalfunctioning (SF-36). However, there were no significant changes in reported physicalfunctioning (SF-36).

In order to examine the associations between illness perceptions (IPQ-R subscales),exercise capacity (6 min walk test), health related quality of life (SF-36), age, gender,depressive symptoms (HADS), COPD specific anxiety (CAF) and FEV1% pred. (illness sever-ity), the Pearson correlations were examined (see Table 3).

Results showed that exercise capacity was lower in patients who saw their illness ashaving a cyclical timeline and in patients who reported higher levels of fear, anger anddistress (emotional representation). Higher COPD specific anxiety before PR was signifi-cantly correlated with lower levels in walk distance after rehabilitation. Observed lungfunction (FEV % pred.) showed a negative relationship to exercise capacity.

Lower levels in depression and COPD specific anxiety were significantly correlatedto higher psychological well being (SF-36) after PR. Furthermore, cyclical time course,consequences and emotional representation were negatively correlated to psychologicalwell-being.

Additionally, the belief that COPD would not be related to serious consequences andhigh treatment control beliefs was associated to higher reported physical functioning(SF-36) after PR. COPD specific anxiety showed a negative relationship to physical func-tioning. All observed relations showed medium effect sizes. There was no significantrelationship between age, gender and outcome variables.

Illness perceptions and health-related outcomes after pulmonary rehabilitation

All subscales of the illness perceptions questionnaire-revised (IPQ-R) form a coherentgroup of subscales. In order to gain insight in illness perceptions in general, the IPQ-R sumscore was computed, with higher scores indicating a more negative perception of theillness. The sum score was chosen due to the high collinearity between the subscales(ranged from −0.26 to 0.89), as applied elsewhere [53]. The largest correlations were

Table 2Descriptive statistics for predictor and outcome variables (pre- and post-rehabilitationvalues) using dependent t-tests

Pre-rehabilitationmean (SD)

Post-rehabilitationmean (SD)

t p

Depression (HADS) 7.54 (4.63) 6.25 (4.35) 5.43 b .01⁎⁎

COPD specific anxiety(CAF)

38.93 (14.59) 36.34 (14.90) 3.38 b .01⁎⁎

IPQ-R sum score 111.35 (9.18) 100.74 (9.13) 13.22 b .01⁎⁎

Exercise capacity 266.43 (116.76) 287.84 (122.20) −2.64 .010⁎⁎

Psychological well-being(SF-36)

45.02 (12.37) 47.99 (14.22) −1.52 .037⁎

Physical functioning(SF-36)

28.60 (6.97) 29.80 (9.03) −2.12 .131

⁎ p b .05.⁎⁎ p b .01.

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observedbetween the treatment control and timeline scale (r = −0.85) and between thetreatment control and personal control scale (r = 0.89). In order to test our hypothesisthat illness beliefs before pulmonary rehabilitation predict exercise capacity and health-related quality of life (psychological well-being and physical functioning) after rehabilita-tion, three hierarchicalmultiple regression analyseswere conducted. For the three regres-sionmodels, variables were entered in two steps. In the first step, potentially confoundingvariables were entered: socio-demographic variables (age, gender), clinical variables(illness severity, depression, COPD specific anxiety) and baseline levels of the outcomevariables (exercise capacity and quality of life (psychological-well-being, physical func-tioning)). A summary of the hierarchical multiple regression analyses is shown in Table 4.

Exercise capacity

Results from the multiple hierarchical regression analyses showed that in the firststep, COPD specific anxiety and baselinewalk distancewere the only significant predictorsof exercise capacity after pulmonary rehabilitation, explaining 65% of the variance inoutcome. We chose to include the IPQ-R sum score (internal consistency = .82). Thesum score was computed after reversing the illness control and coherence scales.Including the IPQ-R sum score in the second step, added an amount of 12% of variance(β = − .426, R2 = .772, p b .01). Baseline level of exercise capacity remained a significantpredictor. This model showed that negative perceptions about patients' illness beforerehabilitation were associated with exercise capacity after rehabilitation, even aftercontrolling for baseline exercise capacity.

Quality of life: psychological well-being

In a first step, depression and levels of self-reported psychological well-being beforepulmonary rehabilitation explained 36% of the variance in psychological well-being afterrehabilitation. The IPQ-R sum score added 21% of variance (β = − .560, R2 = .573,p b .01). In other words, patients' beliefs about a negative impact of their illness beforetreatment were related to poorer self-reported psychological well-being after the rehabil-itation programme.

Table 3Correlations between predictor variables (baseline) and outcomes after rehabilitation(follow-up)

Exercise capacity(6 min walk test)

Psychologicalwell-being(SF-36)

Physical functioning(SF-36)

Chronic time courseª .040⁎ .006 −.148Cyclical time courseª −.292⁎⁎ −.285⁎⁎ −.165Consequencesª −.168 −.418⁎⁎ −.279⁎⁎

Personal controlª −.102 −.173 .138Treatment controlª −.080 −.091 .265⁎⁎

Illness coherenceª −.003 −.105 .179Emotional representationª −.266⁎⁎ −.526⁎⁎ −.063Age −.150 .006 −.130Gender −.155 −.042 .094Depression −.096 −.446⁎⁎ −.120COPD specific anxiety −.313⁎⁎ −.473⁎⁎ −.268⁎⁎

FEV1% pred. .267⁎⁎ .128 .150

Abbreviations: FEV % pred., forced expiratory volume in 1 s expressed in percentagepredicted.⁎ p b .05.⁎⁎ p b .01.a IPQ-R subscales.

Quality of life: physical functioning

In contrast, the pattern of physical functioning after rehabilitation programme wasdifferent. Results from the hierarchical multiple regression showed that in the first step,COPD specific anxiety (β = − .235, p b .05) and baseline level of physical functioning(β = .522, p b .01) explained 37% of the variance. Including the IPQ-R sum score in thesecond step did not predict physical functioning after rehabilitation (ΔR2 = .017,p N .05). Measures of illness perceptions did not contribute significantly to the model.These results should consider the fact that physical functioning did not change overtherapy, and therefore baseline scores explain major parts of the rehabilitation results.

Discussion

The purpose of the present study was to examine the relevance ofillness perceptions in patients with COPD before the start of pulmonaryrehabilitation as a predictor of exercise capacity and quality of life, bothafter rehabilitation. Our results show that patients' view about theirown disease before the beginning of rehabilitation plays an importantrole. It was demonstrated that, after controlling for socio-demographicvariables, psychological variables and illness severity, patients' illnessbeliefs predicted exercise performance and psychological well-beingat the end of rehabilitation in COPD patients, thus confirming ourhypothesis.

For the two outcome variables (exercise capacity and psychologicalwell-being), the contribution of variance made by illness perceptionswas moderate for exercise, and substantial for well-being. In previousstudies it was demonstrated that illness beliefs are associated with out-come in chronic illnesses in general [28–30]. Additionally, our finding isconsistent with previous studies that found COPD patients' views abouttheir illness associated with psychological and functional variables[28,37,38]. In this study as well as in other studies negative illnessperception was related to impaired functioning, disability, and qualityof life [28,40]. A number of studies have shown that when patientshold generally negative illness perceptions about their illness (e.g. alarge number of symptoms associated with the condition, more severeattributed consequences, longer timeline beliefs) these perceptionsare associated with increased future disability and a slower recovery,independent of the initial medical severity of the condition [33,38,54].For all dependent variables in our study, a large amount of variance,especially in the case of exercise capacity, was explained by the investi-gated variables, which underlines the significance of the selected pre-dictors. Depressive symptoms as well as COPD specific anxiety weresignificant predictors in the regression models. This supports previousfindings of the importance of psychological factors in COPD patients inaddition to socio-demographic data and illness severity for the predic-tion of functioning and health-related quality of life [11,38,55,56].

The correlational analyses revealed that especially participants'perception about the cyclical time line of illness, the expected conse-quences and being emotionally affected were important dimensions.Patients who perceived their disease to have very severe consequenceson their daily lives reported lower levels of psychological well-beingand physical functioning after the ending of pulmonary rehabilitation.Furthermore, COPD patients who experienced several emotions attrib-uted to their illness, such as fear and depression, reported lower levelsof psychological well-being and showed poorer performance in 6 minwalk distance after rehabilitation. In line with other studies, higherdepression was related to lower mental health-related quality of life[11,18]. Additionally, higher baseline levels of COPD specific anxietywere associated with worse results in exercise capacity. This finding isin accordance with other research underlining the importance ofCOPD specific anxiety in patients suffering from pulmonary disease[17,52]. Besides, illness severity was related to exercise capacity,demonstrating that COPD patients who suffer from a severe medicalcondition performed worse on the 6 min walk test. The strength ofassociations wasmedium sized and is consistent with existing previousresearch showing the impact of illness perceptions on health-relatedquality of life and functioning in COPD patients [41–44].

Table 4Hierarchical multiple regression analyses

Outcome variables after rehabilitation

Exercise capacity Psychological well-being (SF-36) Physical functioning (SF-36)

Model Predictors β R2 R2 adjusted β R2 R2 adjusted β R2 R2adjusted

Step 1 .653⁎⁎ .630⁎⁎ .359⁎⁎ .315⁎⁎ .366⁎⁎ .324⁎⁎

Age −.056 −.064 −.114Gender −.042 −.100 .149FEV1% pred. .102 .134 .005Depression .099 −.229⁎ .132COPD specific anxiety −.210⁎ −.215 −.235⁎

Baseline levelª .711⁎⁎ .284⁎⁎ .522⁎⁎

Step 2 .772⁎⁎ .754⁎⁎ .573⁎⁎ .539⁎⁎ .384 .335Age −.091 −.134 −.093Gender −.001 −.059 .137FEV1% pred. .059 .100 .013Depression .088 −.269⁎ .140COPD specific anxiety .036 .082 −.322⁎

Baseline levelª .791⁎⁎ .241⁎⁎ .526⁎⁎

IPQ-R sum score −.426⁎⁎ −.560⁎⁎ .159

Abbreviations: FEV % pred., forced expiratory volume in 1 s expressed in percentage predicted.⁎ p b .05.⁎⁎ p b .01.a Baseline level of exercise capacity, psychological well-being and physical functioning.

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It remains unclear why the baseline IPQ-R sum score did not predictphysical functioning after rehabilitation. In a meta-analytic review ofthe Common Sense Model of illness representations [4] it was shownthat physical functioning is related to illness perceptions. One reasonfor our result could be the large influence of baseline scores of the phys-ical functioning scale; another reason could be the rather small samplesize which does not provide sufficient statistical power to detect smalleffects.

Our findings demonstrate that COPD patients' illness beliefs beforerehabilitation influence outcomes of the 6 min walk test and quality oflife after completing a pulmonary rehabilitation. This shows thatpatients' improvements might not depend solely on the rehabilitationprogramme, but also on patients' perceptions about their disease. Thefindings of our study have important clinical implications for the treat-ment of COPDpatients. It is necessary to identifymaladaptive views andmisconceptions of patients as early as possible in order to improve out-come. Previous research has shown that positive illness beliefs wereassociated with better health related outcomes [3]. The first study tosuccessfully use interventions based on illness beliefs in a clinicalsample found that an illness perception-based intervention producedseveral enhanced outcomes including reduction of symptoms and earli-er return towork inmyocardial infarction patients [57]. Atkins et al. [58]applied a cognitive behavioural programme where illness perceptionswere the core target already in 1984, which led to significant improve-ments in exercise capacity and quality of life in COPD patients. This sug-gests that illness perceptions may be successfully altered by cognitiveinterventions at the beginning of pulmonary rehabilitation and thatthis approach may be useful to improve adjustment and functioning.Additionally, it could be helpful for patients to reduce depressive symp-toms by cognitive interventions during the rehabilitation programme,as it was shown that COPD patientswith depressive symptoms reportedhigher levels of COPD specific anxiety [17], which leads to reducedphysical activity. Our study indicates that COPD patients need interven-tions targeted at changing maladaptive illness beliefs.

The present studywas one of the first studies to examine the impactof illness perceptions on pulmonary rehabilitation in a longitudinaldesign. Nonetheless, the study has limitations which should be consid-ered while interpreting the results. First, the study was conducted in asingle setting. The participants included in this studywere participatingin a pulmonary rehabilitation programme, and were not a representa-tive sample of COPD patients. Patients mostly suffered from COPDgrade IV (72.9%) and the relatively high rate of oxygen use in this

study may limit the generalizability of the results (81.2% used long-termoxygen therapy). Therefore, further studies should examine illnessperceptions in less disabled samples such as those receiving outpatienttreatments. Although longitudinal data provide stronger evidenceof causal relation, they cannot rule out alternative causal models. Wetried to minimize the probability of alternative explanations by addingbaseline scores of outcome, socio-demographic data, psychological var-iables and illness severity.

Notwithstanding these limitations, this is one of the first longitudi-nal studies investigating the influence of patients' view about theirillness on later objective exercise tolerance and self-reported qualityof life in COPDpatients. In conclusion,we have shown empirical supportfor the fact that perceptions regarding COPD and its treatment are im-portant factors influencing outcome. Therefore patients' illness beliefsshould be taken into consideration in order to improve treatment inCOPD patients.

Conflict of interest statement

The authors declare that they have no conflicts of interest in theresearch.

Acknowledgments

We are extremely grateful to the staff of Schoen Klinik BerchtesgadenerLand for supporting this study.

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