Chronic obstructive pulmonary disease (COPD) is characterized by the presence of a limitation to airflow that is not completely reversible and is associated with an abnormal inflammatory response to gases or inhaled toxic particles, mainly tobacco 12. COPD is currently the fourth cause of morbidity and mortality in the developed world 1. The IBERPOC study, carried out in 7 different geographical areas with nearly 5000 patients, has shown that in Spain the prevalence of COPD in the general population aged between 40 and 69 years is 9.1%, and is a first-order public health problem 3. This condition originates approximately 10–12% of primary care consultations and 35–40% of those of pneumology, and causes 35% of definitive occupational disabilities and 7% of hospital admissions 4.

As the condition progresses, patients with COPD experience a progressive deterioration and disability, which lead to a worsening in their health-related quality of life (HRQoL). However, it has been confirmed that the evaluation alone of the severity of COPD, measured by the degree of reduction of the forced expiratory volume in one second (FEV₁), does not provide sufficient information to establish the health condition perceived by the patients. The interest for HRQoL measurement in patients with COPD has grown in recent years. The fact that HRQoL is the result of the interaction of multiple physical, psychological and social factors, unique for each individual, can justify this interest from the scientific community 5. Each of these domains can be measured with the objective of establishing the performance or health condition and the subjective perception of health. The HRQoL can be quantified through various health evaluation questionnaires, both general and specific, widely validated 6. The former covers a broad range of dimensions, enable the comparison between groups of patients with different diseases, and facilitate the detection of problems or unexpected effects 7. One of them is the Short Form 36 (SF-36) questionnaire 8, that has an abbreviated version (SF-12) 910. Since one of the main objectives of the treatment of COPD is to improve the general health condition 1, it is important to identify possible factors determining the HRQoL of these patients. Some of these have been identified previously 11. Relationships have been shown between HRQoL during acute exacerbation of chronic bronchitis with post-exacerbation functional status, hospital readmission for acute exacerbation or COPD and mortality 1213141516.

The objective of this study was to assess the HRQoL of a group of patients with stable COPD followed in primary care and to identify the associated determinant factors.

The number of physicians participating in the study was 2,377, which enabled to recruit a total of 10,711 patients (75.6% men, 24.4% women), with a mean age of 67.1 years (SD 9.66), and a mean body mass index of 27.6 (4.0) kg/m². Table 1 shows the sociodemographic and clinical characteristics of the sample studied. The mean FEV₁ value was 35.9 ± 10.0%. The severity of the disease was mild in 35.5% of the cases, moderate in 53.4%, and severe in 11.2%. The concomitant conditions most frequently detected were hypertension (47.7%), hypercholesterolemia (41.3%), anxiety (22.2%), heart disease (18.8%), gastroduodenal ulcer (17.4%), diabetes (16.9%), and depression (12.8%). With regard to the use of health resources in the previous year, the mean values were: visits to primary care physician 6.66 (SD 5.71), visits to pneumologist 1.43 (SD 1.52), visits to emergency rooms 1.60 (SD 2.71), and hospital admissions 0.50 (SD 1.17).

The mean PCS-12 and MCS-12 scores were 36.0 ± 9.9 and 48.3 ± 10.9, respectively. As compared to the reference population, patients with COPD had a reduction of PCS-12, regardless of sex, age range or degree of airflow obstruction. However, a significant decrease was only seen in MCS-12, vs the reference population, in women and patients with severe COPD, with no differences in this parameter related to age (Figure 1). Figure 2 shows the relationship between quality of life, sex, and degree of airflow obstruction. With regard to the PCS-12, significant differences were only detected between men and women in patients with moderate COPD. With regard to MCS-12, differences were found between the two sexes in patients with mild and moderate COPD, but not in patients with severe COPD.

The use of oxygen therapy was associated with a significant reduction of the quality of life, in both PCS-12 and MCS-12. Table 2 shows the distribution of the mean scores of both parameters based on the use of oxygen therapy and the variables related to utilization of health resources.

PCS-12 was correlated positively to FEV₁ (r = 0.38, p < 0,001), however the correlation with the mental component (MCS-12) was lower (r = 0.12). Tables 3 and 4 show the factors determining physical and mental components of the HRQoL, respectively. The determinant factors of MCS-12 were sex, FEV₁, use of oxygen therapy, and number of visits to emergency rooms and hospital admissions. The PCS-12 was also determined by age, Body Mass Index and educational level. Smoking was not significantly related to any of the components of HRQoL.

This study shows that patients with stable COPD have, as compared to the reference population, a reduction of PCS-12, even in the initial stages, though they only show a reduction in MCS-12 in the most advanced phases of the disease. The determinant factors of both components of HRQoL include sex, FEV₁, use of oxygen therapy and number of visits to emergency rooms and hospital admissions. In addition, the age, educational level and body mass index are also variables that influence the PCS-12.

The women in our study had lower HRQoL levels than men, both in the physical and mental component of quality of life. Several authors have reported that women usually suffer more respiratory symptoms than men 20, which could partly justify this finding. Furthermore, it has been demonstrated that, after adjusting for smoking, women show a higher risk of hospital admission for COPD than men 21.

Most previous studies have detected a mild to moderate association between the different areas of HRQoL and the degree of airflow obstruction 22232425262728. In our study, a higher correlation has been found with the physical vs the mental component of HRQoL. Thus, it seems that the effects of COPD on health are not only mediated by the severity of the airflow limitation. For instance, it has been shown that the health condition perceived by the patients correlates better with the degree of dyspnea 2930 or with the distance walked in the walking test 31 than with FEV₁. The patients who obtain better results in these parameters report a limitation to fulfill their activities and the disease has less impact in their daily life.

The influence of hypoxemia and oxygen therapy on the HRQoL of patients with COPD has been assessed in previous studies. Some of them have found no relationship between HRQoL and the presence of respiratory failure 3233. On the contrary, we have observed that the use of oxygen therapy is a predictive factor independent from the health condition perceived by the patients. Similar results have been obtained in other studies. Thus, Okubadejo et al. 34 demonstrated, through a multivariate model, the existence of a relationship between HRQoL and the severity of hypoxemia. More recently, Ferreira et al. 35 have also demonstrated a marked worsening of HRQoL in patients with COPD receiving long-term oxygen therapy, with greater influence on physical and social function dimensions. Several reasons have been proposed to justify the trend of the patients to reject the treatment with oxygen therapy. These include the negative expectation linked to the use of an apparatus for long time periods to maintain health, the noise caused by the device, the mobility restriction resulting of its use, and the limitation involved by the fact that the patient must be confined at home most of the time 333637.

Acute worsening is a common adverse event in the natural history of patients with COPD. It is the most common reason for medical visits, hospital admissions, and death in these patients 38. Furthermore, there is an increasing evidence of the impact of these events on the health condition of patients with COPD. Thus, it has shown that patients suffering more than three annual acute worsening of COPD had a significantly greater impairment in their quality of life than those with a lower number of acute worsening 3940. Furthermore, Fan et al. 41 have shown that HRQoL is a predictive factor independent from hospitalization and mortality in these patients. In our study it has been also detected that the visits to emergency rooms and hospital admissions for acute worsening of the disease in the last year influence significantly the quality of life of patients with COPD, affecting both the physical and mental component.

The influence of age on HRQoL in patients with COPD is controversial. Some studies have detected no association between the two parameters 42 and others have demonstrated it through a logistic regression analysis that is an independent factor 2343. In our study we have only found a relationship with the physical component of quality of life, but not with the mental. The same has happened with other parameters such as the educational level of the patients evaluated. It is possible that subjects with a higher educational level have a greater purchasing power and have more material resources and, on the contrary, those with a lower level belong to the most disadvantaged classes, complaining later of health problems, have a higher environmental exposure, and the percentage of smokers among them is higher 43.

There is no agreement on the relationship between BMI and HRQoL. There seems to be an association between a poor nutritional status and quality of life worsening in patients with COPD, particularly those with emphysema 44. Our results confirm that there is an association, though it is only demonstrated with the mental component of quality of life. The same has happened in another recent study, which only found a relationship with emotional function, though it was weak 43. On the contrary, other authors have not evidenced any influence of bodyweight on the HRQoL of the patients with COPD 2945.

Some limitations may have influenced the results of this study. First, we have used a generic questionnaire to measure HRQoL, less sensitive than the specific tools. However, the large sample size of our study enables to compensate this effect and give validity to our model. Second, all the patients were from primary care, so the results may not be extrapolable to all patients with COPD. However, a recent study evaluating this has found no relationship between HRQoL and the healthcare level 29.

In conclusion, the HRQoL of the patients with COPD is in part related to some parameters, including sex, airflow limitation, use of oxygen therapy and number of acute worsening and hospital admissions. However, these factors do not predict overall the high variability of HRQoL. Despite this, their measurement enables to identify the patients with a greater disability and enhances the assessment of the effects of various interventions on a standard basis.

Javier Rejas Gutierrez and Antonio Martin Centeno are employees at Pfizer Spain and Elena Gobartt Vázquez is employee at Boehringer Ingelheim SA. The other authors have not any conflict of interest with Pfizer or Boehringer Ingelheim SA. This study has been funded by an unrestricted grant from Pfizer Spain and Boehringer Ingelheim SA.

PCG, JRG, MGC, AGM and RJG have made substantive intellectual contributions to conception and design, acquisition of data and analysis and interpretation of data. PCG, JRG, JMD, AGM, and EGV have been envolved in drafting the manuscript and revising it critically for important intellectual content. All authors have given final approval of the version to be published.