Patients with chronic obstructive pulmonary disease (COPD) experience poorer sleep quality than those without the disease, say the authors of an Irish study.
Furthermore, the efficiency of patients' sleep was independently related to daytime arterial oxygen pressures, a finding that could lead to new therapeutic interventions.
The study, published in Respirology, included 106 COPD patients who were all former or current heavy smokers. All patients underwent polysomnography and the results were compared with previously published findings from two groups of controls, totaling 217 people, who were of a similar age and did not have COPD.
The authors found that, compared with controls, patients with COPD experienced poorer sleep. For example, they took 37 minutes on average to get to sleep compared with 19 minutes and 15 minutes in the control groups; they spent 66% of their time in bed asleep, compared with 86% and 75% in the control groups; and they had 17 minutes of stage 1 sleep on average compared with 4 minutes and 6 minutes in the control groups.
Multiple regression analyses showed that PaO2 (awake arterial oxygen tension) independently predicted sleep efficiency, such that patients in the lowest quartile of PaO2 spent 60% of their time in bed asleep compared with 69% among patients in the highest quartile of PaO2.
Interestingly, nighttime oxygen saturation was not associated with sleep efficiency, which the authors say could be because poor sleep quality reduced sleep-induced hypoventilation among patients.
The authors say that previous studies have shown that hypoxia can significantly affect neurotransmitter levels, such as those that regulate sleep and arousal.
"Continuous hypoxaemia in patients with COPD may impact on neurotransmitter levels such as serotonin and through these mechanisms contribute to poor sleep efficacy," write Walter McNicholas (St Vincent's University Hospital, Dublin, Ireland) and colleagues.
However, they say that the addition of oxygen therapy in order to improve sleep quality remains controversial. "Sleep quality is determined by several factors and further studies on this topic are necessary to fully evaluate the relationship. This may identify therapeutic interventions that might improve the overall quality of life in COPD patients."
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