Given the clear differences in the nature and course of two lung diseases (COPD and NSCLC), and the shown differences in the QoL between the two groups of our patients , where COPD patients demonstrated significantly worse QoL than NSCLC patients across all domains, there was an assumption that the quality of life of their caregivers will also differ. Especially having in mind the already well-demonstrated interdependence between informal caregivers and care recipients’ QoL [12, 20].
Nevertheless, our study did not show a significant difference in most QoL domains and depressive symptoms of the two caregiver groups, but it did show a difference in the domain of general health (GH) and physical health (PHC) measured by the SF-36 (p = 0.003 and p = 0,038, respectively). Thus, COPD caregivers perceived their own general and physical health as inferior to NSCLC caregivers. Self-rated physical (and mental) health is reported to be significantly worse in caregivers of people with advanced COPD when compared to those caring for people with early COPD [21, 22] and all included patients in our study had advanced disease. Another possible explanation for poorer perception of general and physical health of COPD caregivers lies in the fact that there was a significant difference in the average number of comorbidities between the two caregiver groups – more comorbidities were observed in the group of COPD caregivers (NSCLC – 1.46 ± 0.65; COPD – 1.83 ± 1.04; p = 0.037). Also, the average caring duration for COPD patients was 8.27 years, while for NSCLC it was slightly less than 5 months (p = 0.001), probably leading to deterioration of physical health of COPD caregivers over time. On the other hand, our results are in line with results of several other studies which also did not confirm the influence of the disease type on caregiver burden and QoL. It is already known that the patients' illness experience is more related to illness severity than the diagnosis of advanced disease  and all patients in our study sample (COPD and NSCLC) had advanced disease stage. Also, study comparing cancer, CHF and COPD caregivers found similar level of caregiver burden across different patient's diagnoses, suggesting that caregiver burden may not be disease-specific, rather a universal phenomenon of caring for adults with life-limiting diseases . Similarly, study of 139 patient/caregiver dyads (51 living with cancer, 46 living with CHF and 42 living with COPD) demonstrated that diagnosis was not significantly associated with caregiver burden or psychosocial-spiritual outcomes in multivariate models. Authors concluded that caregiver burden is not disease specific, but it is rather a relatively universal experience .
Contrary to the results of our study, which did not show a relationship between the patients and the caregivers' QoL, numerous studies primarily in the oncology field, have shown the adverse impact of poor patients' QoL and depression on caregivers' QoL [9, 12, 13, 24]. Negative impact of declining patients’ QoL on caregivers’ distress level and positive relation between patient and caregiver depression are especially prominent in patients with advanced NSCLC, highlighting the close association between patient and caregiver outcomes [12, 20, 25, 26]. The relation between patients and caregivers' QoL and emotional status has not reported only for patients with cancer but also in other chronic diseases [27, 28]. Data in the literature regarding the impact of COPD patients' QoL on caregivers' QoL are somewhat scarcer. In a study by Pinto RA et al. the QoL of caregivers of COPD patients seems to be negatively associated with low PCS score of the patients measured by SF-36. Thus, the poorer physical health of patients with COPD showed a negative impact on the quality of life of caregivers . On the other hand, patients and their caregivers may have different perceptions of the patient's symptoms and health status . This discrepancy in perception can negatively affect the caregivers and patients’ well-being . In that case patients and family members who care for them do not have to show the interdependence of the same direction and detecting the mutual influence of quality of life can be a challenge. This may be one possible explanation for the results in our study that did not confirm the impact of patients' physical and mental health (QoL) on caregivers' QoL. Two other studies also reported not finding association between patients' QoL and caregivers’ well-being [32, 33] underling the significance of caregiver-related factors.
In our investigation, caregiver-related factors, were most influential on their QoL in both the physical and mental domains for both caregiver groups. In the multivariate model, a higher level of depressive symptomatology in caregivers predicted a poorer QoL in both the physical and mental domains in both caregiver groups: NSCLC (p = 0.001; p = 0.001) and COPD (p = 0.001; p = 0.001). Interestingly, at the same time, the level of depression of the patients they care for, did not show an impact on caregivers' QoL, although their interdependence is well described [11, 20]. Caregiver depression is a well-researched topic. The caregiving process is physically and emotionally demanding and creates a feeling of burden, loneliness and depression in some caregivers, and may be associated with decrease in their QoL and have significant impact on their health, regardless of the type of disease [13, 34]. That is, psychological distress significantly determined the subjective perception of physical and mental health. On the other side, there are studies among informal caregivers that have concluded that helping behavior in a caring context promotes psychological wellbeing .
In addition to depression in our caregiver sample, in the multivariate model older age proved to be an independent predictor of poorer physical QoL in NSCLC caregivers (p = 0.001), and in COPD caregivers the presence of comorbidity predicted poorer physical QoL (p = 0.031). Both observations, that older and sicker caregivers who at the same time experiencing mental and emotional strain and have reported more problems in the area of physical health, are in line with the already known risk factors for caregivers’ physical health . Caregivers of patients with COPD in our study were a particularly vulnerable group since the presence of comorbid diseases predicted poorer physical health, and the care period was significantly longer – 8.27 years versus only 6 months for NSCLC caregivers. They also were approximately 10 years older than NSCLC caregivers. Thus, the decline in the physical health of those caring for seriously ill patients intensifies with the caring duration and the progression of the disease .
Interestingly, in our research, the mental well-being of caregivers (MCS), in addition to depressive symptomatology, was also influenced by the duration of unemployment. Although the duration of unemployment of the NSCLC caregivers were significantly longer than of COPD caregivers (12,54 (± 11,38) vs 6,11 (± 8,29) years), longer unemployment duration was shown to be independent predictive factor for worse mental functioning in both caregiver groups (p = 0.019; p = 0.020, respectively). Socio-economic factors and especially employment status have complex impact on the caregiving experience and the previous literature shows very mixed results in this regard. From potential benefits when caregivers are employed (higher income levels with positive influence on physical and emotional health , buffering for dissatisfaction in one of the roles – higher level of satisfaction with diverse social interactions and consequently fewer negative psychological symptoms ) to significant disadvantages of being an employed caregiver (reduced work responsibilities, termination of employment in order to cope with caregiving responsibilities , the psychological strain due to the simultaneous performance of multiple roles .
The data on the impact of the employment status on the physical and mental health of NSCLC and COPD caregivers are very scanty. Still, our results can be interpreted in line with results of recent study of dementia caregivers Liu Y et al, where caregivers who were not employed experienced increasing role overload (subjective feelings of being overwhelmed by care-related responsibilities) over time. Especially because in underdeveloped countries, unemployment generally implies the existence of financial disadvantage, and the above-mentioned study demonstrated that greater financial strain was associated with higher levels of role overload in general. Authors concluded that changes in caregivers' employment status may have complex association with their feelings of stress over time . Similarly, several studies of informal caregivers of adults with mental illness reported significant negative effects of unemployment on caregivers' mental health and QoL [43, 44].
This study has several limitations. Although, study included respectable number of caregiver-patient dyads, they are recruited in tertiary care centre which impedes generalization of our results to the whole community. The accessibility of health services to patients with advanced diseases and their caregivers in remote areas can be significantly restricted. The cross-sectional study design prevents assessment of changes in QoL over time, particularly considering the different illness trajectories and duration of caregiving experience. Hence, our results can be biased because significantly longer caregiving duration of COPD caregivers. Further, to assess the presence of depressive symptoms, we used BDI as a screening tool, not a diagnostic instrument, and the frequency of depressive disorders has not been precisely determined.
In underdeveloped countries providing organized support to informal caregivers is a challenge. The context of insufficiently available dedicated palliative care can significantly frame the burden placed on caregivers. In such circumstances, the task of providing support to informal caregivers of patients with chronic lung disease in advanced stage is often taken over by respiratory physicians. Unfortunately, this support provided by physicians is very limited and consultative in its nature. Therefore, for developing models of support is necessary to take into account the needs of different caregiver groups and on the other side also lack of well-organized palliative care. Our research identified as particularly vulnerable caregiver group the one that cared for patients with COPD, as COPD caregivers perceived their own general and physical health significantly worse compared to NSCLC caregivers. Also, more depressed caregivers and those with a longer duration of unemployment (regardless of the disease type) reported poorer quality of life and represented a groups with greater support needs. Since the type of disease is not an essential determinant of caregiver’s quality of life, a caregiver support model should be developed within general practice and home-based care rather than as a component of specialized palliative care in secondary and tertiary care facilities, taking into account particularly vulnerable groups of informal caregivers. Bearing in mind that a recently published study demonstrated very different approaches to caregiving in three developed EU countries (France, Germany, Italy), highlighting the need for future studies to explore the country-specific context of caregiving we believe that special attention should be paid to caregiving research in underdeveloped countries with still inadequately implemented palliative care.