**4. Discussion**

This study investigated the global trend of 3242 research publications regarding interventions to increase QoL of patients with COPD. It was found that the publications of research related to in topic increased annually and gradually, and most of the contribution came from high income countries (HICs). Mental health issues and non-pharmacological therapy, including exercise, home care, self-care education, noninvasive ventilation, and oxygen therapy were common approaches. Current findings emphasize the importance of research that focuses on the effects of non-pharmacological therapy, which should be considered to increase QoL of people living with COPD. Additionally, mental health problems among people living with COPD have received more focus, especially in the last five years.

Notably, but unsurprisingly, a high number of research were conducted by authors from HICs than that of LMICs although more than 90% of COPD-related deaths occur in LMICs [53]. This work supports the conclusion of previous studies, which confirmed the main contribution of HICs in diabetes research [54] or HIV/AIDS research [55]. This phenomenon may be explained by the fact that risk factor prevention has not been fully recognized by the LMICs' governments and populations, including using biomass fuels indoors for cooking [56] or occupational exposure [57]. Moreover, many LMICs faced the barriers in research and implication planning, such as information and communication technology limitations [58], lack of human resources and finance, and scientific findings [59]. Therefore, the support of HICs and actively joining in collaboration network with HICs are critical to LMICs [60].

Chronic obstructive pulmonary disease is a chronic disorder, which requires a long-term treatment with complementary and alternative therapy to reduce exacerbation and improve patients' QoL [61]. Our finding were in line with the results of previous studies, which emphasized that pharmacological therapy [62], exercise [63], non-invasive ventilation [64], and oxygen therapy [65] increase the QoL of people living with COPD. In our study, the number of papers mentioning pharmacological treatment was in the top five of highest volume of work by LDA. It showed the concern of researchers and physicians on this therapy to control the symptoms in stable COPD as well as improve QoL of people suffered COPD. It confirmed the results of some papers which emphasize the effectiveness of pharmacotherapy in controlling symptoms to decrease recurrence and seriousness of exacerbations and improve QoL [66,67]. However, this topic rose at a lower level in the last five years compared with non-pharmacy therapies, such as mental health, or rehabilita. The results might be explained by the efficiency of the alternative therapies in improving the quality of life, controlling symptoms in daily life and when exacerbations occur [68], and reducing the frequency of hospitalization [69].

Furthermore, the topics receiving the most attention in the last five years were comorbidities and mental health issues in patients with COPD. A previous study showed that about one-third of patients living with COPD with depression or anxiety did not received appropriate treatment [50]. The comorbid condition of mental illness can increase the risk of exacerbations, reduce QoL, and raise the chance of mortality [70,71]. Thus, mental health illness should receive further piority, which may help to increase QoL among patients living with COPD [72].

The results provide some evidence to enhance designing interventions, health research, and policy. Most of the death cases related to COPD happened in LMICs, yet, most of the studies were conducted in HICs. The health research capacity in LMICs is lower than that of HICs could be explained by (1) the limitation of infrastructure and capacity [73], (2) a lack of investment funding in universities and research institutions, low wages for researchers [74], and (3) a lack of clear national research priorities [74]. Therefore, LMICs need to (1) actively create collaboration research networks with HICs and (2) prepare the national research priorities under the circumstance of understanding the local context. Moreover, the LMICs' national health research priorities should be considered when international organizations or donors from HICs invest in LMICs. Secondly, we call for multidisciplinary collaboration of researchers and physicians among research areas, especially between psychological and respiratory physiologists since the complexity of this disease and negatives effects of depression and anxiety to patients with COPD.

Several limitations of this study should be mentioned. Firstly, WOS was the only database used in the analysis. However, for a large number of papers for analysis, there was a high possibility that these articles were in other databases, including PubMed and Scopus. Secondly, only English publications were included. Thus, it was more likely that our study did not reflect the trend in COPD research where English is not used. Finally, only titles and abstracts were used for topic modeling. However, by applying a different level of data and alternative method, the trends and hidden themes of the research studies could be discovered [74].
