Cognitive function in patients with severe chronic obstructive pulmonary disease (COPD): A cross-sectional study

Chronic obstructive pulmonary disease (COPD) is characterized by persistent lung function impairment, primarily airflow limitation resulting from conditions like obstructive bronchitis or emphysema. Globally, COPD was the third leading cause of death in 2017, with 3.2 million fatalities. Smoking is a primary cause, but air pollution and socioeconomic factors also play roles.

Patients with COPD often experience comorbidities such as cardiovascular disease, diabetes, anxiety and depression, influencing disease severity and prognosis. Obstructive sleep apnea (OSA) is also a known comorbidity, described as the "overlap syndrome" (OS) when observed in patients with COPD. Another comorbidity, cognitive impairment (CI), has been described to have an impact on clinical outcomes and morbidity in patients with COPD. CI may involve impaired abilities of perception, attention or memory and affects daily functioning, leading to diminished quality of life, decreased adherence to prescribed treatments such as medication, oxygen therapy and behavioral interventions, along with an increased risk of exacerbations. However, the prevalence estimates of CI in patients with COPD vary widely, with reported rates ranging from 10.4% to 77%. The link between COPD and CI remains unclear. Various factors, characteristics and comorbidities associated with patients with COPD might also be associated with CI and may influence the association between COPD and CI.

This thesis aimed to assess cognitive function in severe COPD, determining CI prevalence and its associations with various factors. The study explored the impact of OSA on cognitive function and evaluated the potential benefits of treating OSA. By understanding these associations, the goal is to improve patient care and tailor treatments for patients with severe COPD.

Study I found that 40% of COPD patients met criteria for CI, but there was no significant difference in CI prevalence between patients and age-matched nonCOPD controls. Patients had lower scores in visuospatial function, reduced stability in reaction time and impaired attention and perception compared to controls. In patients with COPD, CI was associated with older age, more severe self-perceived COPD symptoms, and poorer driving outcomes.

In Study II, patients with severe COPD reported elevated levels of anxiety, depression and stress compared to controls, but no significant differences in psychological symptoms were observed between patients with and without CI. While stress predicted reduced attention, overall psychological factors did not significantly contribute to cognitive function variance beyond sociodemographic and physical factors in COPD.

In Study III, 63% of severe COPD patients were diagnosed with symptomatic OSA, with 1 in 5 having moderate to severe OSA. Patients with moderate to severe OSA exhibited a higher risk of CI, particularly in attention and reaction time. Treatment for OSA demonstrated potential benefits by improving shortterm memory in patients with OS.

In conclusion, the development of CI in patients with COPD is complex and involves a multitude of factors that all may contribute to CI. However, age emerges as the predominant predictor of CI. The lack of consensus in defining and assessing CI underscores the importance of developing standardized guidelines, ensuring a more consistent and universally applicable approach for the benefit of clinical practice. This thesis advocates for routine OSA screening in severe COPD patients, challenging existing assumptions and emphasizing the potential benefits of early detection, but further studies are needed to validate our findings.