Address of Corresponding Author

Respiration 2006;73:203-208 (DOI: 10.1159/000088681)

 Outline

• Key Words
• Abstract
• Introduction
• Patients and Methods
• Study Design
• Patients
• Physiological Measurements
• Health-Related Quality of Life Questionnaires
• Level of Social Support and Emotional Distress
• Analysis
• Results
• Patients
• Univariate Regression Analysis
• Multiple Regression Analysis
• Discussion
• Limitations of the Study
• Acknowledgement
• References

• Author Contacts
• Article Information
• Publication Details
• Drug Dosage / Copyright

  Key Words

• Pneumoconiosis
• Pneumoconiosis, quality of life
• Pneumoconiosis, Hong Kong community-dwellers
• St. George's Respiratory Questionnaire

  Abstract

Background: There have been few data on the health-related quality of life (HRQOL) in patients with pneumoconiosis. HRQOL is an important aspect of daily living in patients with industrial diseases. Objectives: To investigate the HRQOL and factors that contribute to the impairment of HRQOL in patients with pneumoconiosis. Methods: 297 patients with pneumoconiosis were recruited from a community-based case registry. The HRQOL was measured with the St. George's Respiratory Questionnaire (SGRQ). Pulmonary function, comorbidity and psychosocial variables were also assessed. Patients' mood state was evaluated with the Geriatric Depression Scale (GDS). Results: The mean SGRQ symptom, activity, impact and total scores were 38.0 ± 19.3, 44.5 ± 21.9, 34.2 ± 17.9 and 39.4 ± 17.4, respectively. These figures were lower than those reported in patients with chronic obstructive pulmonary disease who attended chest clinics. The GDS score (r = 0.38), forced expiratory volume in 1 s predicted (FEV₁% predicted;r = -0.33) and comorbidity (r = 0.21) were the most important predictors of the HRQOL. Conclusions: Besides lung functions, chest clinicians should consider the impact of mood symptoms and comorbidity on the HRQOL in the management of patients with pneumoconiosis.

Copyright © 2006 S. Karger AG, Basel

 Introduction

The major goal in the care of patients with pneumoconiosis is to improve their health-related quality of life (HRQOL), since cure is still impossible. Health status questionnaires have found their widest application in clinical trials where they are used to provide a measure of the overall symptomatic benefit from a treatment, together with an index of whether the effect was worthwhile [1]. However, only a few attempts have been made to identify the factors that are related to the different aspect of HRQOL in patients with pneumoconiosis. Chang et al. [2] evaluated the HRQOL in 50 patients with non-specific interstitial lung diseases whom were recruited from a chest clinic. They found that patients' HRQOL was related to the lung function, exercise tolerance and dyspnea score. The sample size of the above study was small and there was a possible referral bias. In addition, the diagnostic distribution of the sample was heterogeneous with 66 and 20% of the subjects having idiopathic pulmonary fibrosis and sarcoidosis, respectively. Furthermore, certain important determinants of the HRQOL such as the mood state [3] and comorbidity [4] were not assessed.

The HRQOL has been extensively researched in chronic obstructive lung disease (COPD). Well-known determinants of the HRQOL in patients with COPD are lung functions [5], respiratory symptoms [6], exercise tolerance [1] and mood symptoms [3].

The most common cause of pneumoconiosis in Hong Kong is silicosis [7], which is behind 93% of all cases of pneumoconiosis [8]. Since the introduction of the statutory pneumoconiosis compensation scheme in 1981, more than 3,700 patients have been identified [8]. Although pneumoconiosis is a potentially preventable disease, more than 100 new cases are reported each year in Hong Kong, which has about 7 million inhabitants [9]. Pneumoconiosis causes disability; in year 2000, 2,010 patients received HKD 174 million of compensation [8].

The objective of this study was toexamine the HRQOL and factors that contribute to the impairment of HRQOL in patients with pneumoconiosis.

 Patients and Methods

 Study Design

A clinical sample of Hong Kong community-dwellers who sought compensation for pneumoconiosis was recruited and examined by physiological and psychological tests and a disease-specific HRQOL measure.

 Patients

In Hong Kong, workers with a history of silica dust exposure seeking compensation are assessed by the Pneumoconiosis Medical Board, which consists of three medical practitioners. The diagnosis of pneumoconiosis is based on a relevant occupational history involving significant exposure to silica-containing dust and radiological changes consistent with pneumoconiosis. The Pneumoconiosis Compensation Fund Board keeps a register of all confirmed cases of pneumoconiosis. Staff of the Pneumoconiosis Compensation Fund Board interviews patients in community centers annually to make sure they still survive and have received the monthly allowance regularly. Reassessment of patients' degree of disability is not performed in the annual interview. In 2003, 1,442 patients were interviewed, a figure representing 75% of all registered patients with pneumoconiosis in Hong Kong. 421 patients who were scheduled for their annual interviews were randomly selected by computer-generated random numbers and invited to participate in the study.

The following socio-demographic and medical data were collected:name, age, gender, education, smoking status, occupation, duration of occupation related to pneumoconiosis, body mass index (BMI) and the presence of concomitant medical diseases (comorbid conditions).

The study protocol was approved by the Clinical Research Ethics Committee of the Chinese University of Hong Kong. Written consent was obtained from all participating patients.

 Physiological Measurements

A research assistant (RA), trained by a physician in pulmonary rehabilitation (C.M.L.), performed a spirometry examination with a portable spirometer (Micro Medical Ltd). The ambient temperature ranged from 27 to 31°C. The data obtained in the blow with the largest forced expiratory volume in 1 s (FEV₁) of at least three maneuverswas recorded and analyzed. Response to bronchodilators was not measured. Patient's height and weight was measured and the predicted values of lung function parameters were calculated from Asian population norms.

 Health-Related Quality of Life Questionnaires

The same RA administered the St. George's Respiratory Questionnaire (SGRQ) [6] to assess the HRQOL. The SGRQ is a disease-specific, HRQOL instrument designed for, and commonly applied in, patients with COPD. It has been validated in patients with interstitial lung disease [2]. The SGRQ has three components: (1) symptom, measuring respiratory symptoms; (2) activity, measuring impairment of mobility or physical activity, and (3) impact, measuring the psychosocial impact of disease. Scores for each of these components and the total score are on a 100-point scale. Higher scores correspond to worse HRQOL. It has a Chinese version validated in Hong Kong (SGRQ-HK) and the weightings applied in this study were derived from a Chinese population [10].

 Level of Social Support and Emotional Distress

The Chinese version of the Lubben Social Network Scale (LSNS) [11] was administered by the RA to measure social support. LSNS consists of 10 questions. Scores for individual items range from 0 to 5; the higher the score, the better the social network. There are questions which evaluate an individual's family network, e.g. 'How many relatives do you see or hear from at least once a month?', network of friends, e.g. 'How many close friends do you see or hear from at least once a month?', confidant relationship, e.g. 'When you have an important decision to make, do you have someone you can talk to about it?', helping others, e.g. 'Does anybody rely on you to do something for them each day?' and living arrangement, e.g. 'Do you live alone or with other people?'. The Chinese version of LSNS has been validated in Hong Kong and has been employed to examine social support in local elderly [12].

The RA also administered the Chinese version of the 15-item Geriatric Depression Scale [13] to all participating patients to measure the severity of depressive symptoms. Although the GDS was originally designed for elderly population, it has been shown to be a valid and reliable instrument in adult patients [14] because age has no effect on the total GDS score [15].

 Analysis

Data are reported as mean ± SD unless specified otherwise. Demographic data of the included and excluded patients were compared using the Student's t test and Fisher's exact test. Descriptive statistics were computed for each of the analyzed variables. Pearson's correlation coefficient and Spearman's were calculated to study the relationship between the SGRQ scores and other variables.

One multiple linear regression was prepared for each of the SGRQ symptom, activity, impact and total scores. For each of these regression models, the following predictor variables were entered if these variables met a criterion of p value 0.10 in bivariate models: age, education, smoking status, number of comorbid conditions, duration of occupation related to pneumoconiosis, average forced vital capacity predicted (FVC%), FEV₁/FVC% and LSNS score. The following variables were entered into the models regardless of their p value: the FVC% and GDS scores. The correlations between the variables were also examined. If the correlation between any pairs of the variables was 0.50, one of them was removed from the final model, to avoid multi-colinearity. Statistical significance was set at the p < 0.05 level. All statistical tests were performed using the SPSS version 11.0.

 Results

 Patients

Recruitment of patients with pneumoconiosis took place from September to November 2003. Of the 421 patients selected, 297 (70.5%) participated while 124 (29.5%) were excluded from the study; there was no significant difference between the included and excluded groups in terms of proportion of male patients (100.0 vs. 96.0%, p = 0.167) and age (65.1 ± 10.7 vs. 64.2 ± 11.0, t = 0.784, p = 0.433).

Reasons for exclusion were absence from the annual interview (n = 81, 65.3%), refusal to participate in the study (n = 36, 29.0%), deafness (n = 4, 3.2%) and female patients (n = 4, 3.2%). The final sample had the following characteristics: 247 (83.2%) were married, 255 (85.9%) cohabited with their family, 228 (76.8%) were retired; their mean education level was 3.2 ± 2.9 years (range 0-11 years, median 3.0 years (i.e., approximately attended school until the age of 9)); 178 (59.9%) were ex-smokers, 81 (27.3%) were current smokers and 38 (12.8%) were non-smokers; 46 (15.5%) were currently employed. There were 99 patients with age <60, among whom 44 (44.4%) were retired, 36 (36.4%) were currently employed and 19 (19.2%) were unemployed. The four most common previous occupations were caisson worker (n = 84, 28.3%), stone-cutting machine attendant (n = 75, 25.2%), stone splitter (n = 53, 17.8%) and jade worker (n = 11, 3.7%). The mean period of time spent on these jobs was 25.1 ± 10.9 years. The mean number of comorbid conditions was 0.9 ± 1.0 (range 0-6, median 1); the most common comorbid disorders were musculoskeletal and cardiovascular diseases.

The mean GDS score of all participating patients (n = 297) was 7.3 ± 3.8, the mean BMI was 23.0 ± 3.4 and the mean LSNS score was 27.0 ± 9.9. The SGRQ symptom, activity, impact and total scores were 38.0 ± 19.3, 44.5 ± 21.9, 34.2 ± 17.9 and 39.4 ± 17.4, respectively.

Twenty-six patients did not have spirometry data because of refusal of (n = 12) or poor effort/technique (n = 14) in performing the spirometry examination. The mean FVC% of the remaining 271 patients was 68.1 ± 20.3%, their forced expiratory volume in 1 s predicted FEV₁% and FEV₁/FVC% was 59.7 ± 20.0 and 91.6 ± 21.4%, respectively, indicating a restrictive functional pattern in this group of pneumoconiosis subjects.

 Univariate Regression Analysis

Pearson correlations for the SGRQ scores are shown in table 1. The SGRQ total score correlated best with the SGRQ impact score. The correlations between the SGRQ symptom, activity, impact and total scores and the FEV₁%, FVC%, GDS and comorbidity were modest. The LSNS score correlated with the SGRQ total and impact scores whereas the level of education correlated with the SGRQ total and symptom scores. The age and duration of occupation related to pneumoconiosis ('occupation' in the following) correlated with the SGRQ activity score only. The duration of occupation also correlated with age (r = 0.31, p < 0.001) and comorbid diseases (r = 0.25, p < 0.001). The BMI and smoking status were not correlated with any of the SGRQ scores.

Table 1. Pearson correlations and Spearman's between the St. George's Respiratory Questionnaire (SGRQ) symptom, activity, impact and total scores and other outcome variables (n = 297)

 Multiple Regression Analysis

The correlation between FVC% and FEV₁ was 0.79, therefore FEV₁ was removed from the regression model. Most of the variance for the SGRQ symptom, activity, impact and total scores was explained by the GDS score as well as the FVC% (table 2). Comorbidity predicted the SGRQ impact and total scores, age predicted the activity score and FEV₁/FVC% predicted the symptom score. The coefficients of comorbid conditions were 2.45 and 2.63 for SGRQ impact and total scores, respectively. No correlation was found between education, LSNS score and duration of occupation and the SRGQ scores.

Table 2. Results of the stepwise multiple regression analyses with the SGRQ symptom, activity, impact and total scores as dependent variables (n = 271)

 Discussion

This is the first systematic investigation of HRQOL in a large community sample of patients with pneumoconiosis. As expected, the SGRQ total score related most strongly to other SGRQ scores. The correlations between the SGRQ symptom, activity and impact scores were moderate. The SGRQ total score of our sample was similar to that found in patients with non-specific interstitial lung disease [2] but somewhat lower than the figures of 46-54 reported in COPD patients attending chest clinics [3, 5, 16]. We could not locate any study on the HRQOL in patients with COPD or asthma that used SGRQ and involved a community sample.

In the univariate analysis, the correlations between the spirometric parameters and the SGRQ scores were not high. In fact, it would be inappropriate to expect high correlations with any specific aspect of pneumoconiosis, since the SGRQ is designed to address a wide range of different effects of the disease [1]. Certain SGRQ scores correlated with education, social support, FVC, age and duration of occupation.

Higher level of education predicts better HRQOL in patients with COPD [3, 17]. Perhaps higher educational level may be linked to better coping strategies resulting in better HRQOL [18]. Graydon and Ross [19] reported that social support influenced the functioning in patients with COPD. Ninot et al. [20] recommended that psychosocial support should be a part of any pulmonary rehabilitation program for patients with COPD.

FVC predicts HRQOL in patients with interstitial lung disease [2] and COPD [5]. Chang et al. [2] found that the correlation between SGRQ scores and FVC ranged from -0.31 to -0.45 in 50 pneumoconiosis patients attending a chest clinic. Similarly, Engstrom et al. [5] reported that the correlation between SGRQ total score and FVC was -0.44 in 68 outpatients with COPD. In the present study, duration of occupation was associated with higher SGRQ activity score, possibly through the effect of age and comorbidity, as the latter two variables remained significant in the subsequent multivariate analysis. Interestingly, age only correlated with SGRQ activity score. The literature concerning the effect of age on HRQOL in patients with COPD is conflicting as both positive [3] and negative results have been reported [5, 21]. Similarly to what was reported in patients with COPD [5, 21], we did not find any relationship between sex and HRQOL.

The multivariate regression analysis showed that besides lung function, depressive symptoms and comorbidity were also important in predicting the HRQOL. The correlation between the FVC and HRQOL was low, similar to the figures of 0.14-0.41 reported in patients with interstitial lung disease [2] and COPD [1, 5], suggesting that some patients may have very poor health despite mild spirometric impairment [1].

The correlation between depressive symptoms and the SGRQ scores in the present study (0.30-0.41) were lower than the figures of 0.51-0.62 reported in outpatients with COPD [5, 19,21,22,23,24]. Differences in the sampling method (community vs. specialist clinic patients) may explain these differences. Factors behind depressive mood in pneumoconiosis such as fatigue [16] and coping strategies [25] should be further investigated. Clinicians taking care of patients with pneumoconiosis should pay attention the early detection, treatment and prevention of depression.

Comorbid conditions are common in patients with interstitial lung diseases [2]. Concurring with our findings, Wijnhoven et al. [4] reported that comorbid diseases significantly contributed to all domains of HRQOL in patients with COPD. Van Manen et al. [26] suggested that impairment in social and emotional functioning in patients with COPD did not seem to be related to COPD, only to comorbid pathologies.

 Limitations of the Study

The study has the following limitations. First, the cross-sectional design of the study could not establish the direction of causality of the predictors of the HRQOL. Second, some of the putative HRQOL predictors such as the arterial saturation [22], exercise tolerance [1], body composition [27], fatigue [16], level of anxiety [6, 23], coping strategies [18, 25] and administration of respiratory drugs [3] have not been examined. Third, chest X-ray data were not available and it was uncertain what proportion of patients had progressive disease. Fourth, formal index of comorbidy such as the Cumulative Illness Rating Scale [28] had not applied to assess its role. Furthermore, potentially influential comorbid diseases such as tuberculosis or rheumatoid arthritis have not been explored. Fifth the final multiple regression model only explained 25% of the variance in SGRQ score at best. This percentage is low in comparison with similar studies [5], possibly due to the omission of several known correlates of HRQOL such as the 6-min walking distance, carbon monoxide transfer factor and anxiety symptoms.

In conclusion, the lung function, mood symptoms, and comorbidity were found to be the three most important determinants of HRQOL in patients with pneumoconiosis.

 Acknowledgement

The study was supported by a research grant from the Pneumoconiosis Compensation Fund Board of Hong Kong.

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  Author Contacts

Dr. W.K. Tang
Department of Psychiatry, Shatin Hospital
Shatin, NT, Hong Kong, SAR (China)
Tel. +852 2636 7760, Fax +852 2647 5321
E-Mail tangwk@cuhk.edu.hk

  Article Information

Received: January 12, 2005
Accepted after revision: April 28, 2005
Published online: September 29, 2005
Number of Print Pages : 6
Number of Figures : 0, Number of Tables : 2, Number of References : 28

  Publication Details

Respiration (International Journal of Thoracic Medicine)

Vol. 73, No. 2, Year 2006 (Cover Date: March 2006)

Journal Editor: Bolliger, C.T. (Cape Town)
ISSN: 0025-7931 (print), 1423-0356 (Online)

For additional information: http://www.karger.com/RES

  Drug Dosage / Copyright

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