The Lost Connection between Sleep Disorders and Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease or COPD has become a common problem nowadays. COPD has been defined by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) as a disease characterised by airflow limitation that is not fully reversible. It is composed of three other illnesses: emphysema, an anatomically defined condition characterised by destruction and enlargement of the lung alveoli; chronic bronchitis, a clinically defined condition with chronic cough and phlegm; and small airways disease, a condition in which small bronchioles are narrowed. COPD has become so common that it is said to be the fourth leading cause of death; it affects 16 million people in the United States alone. This is why factors contributing to COPD have to be investigated and treated as soon as possible.

Unknown to many, one of the factors affecting COPD is sleep. We recall that sleep has several effects on breathing such as changes in central respiratory control, lung mechanics and muscle contractility. These mechanisms may not have an adverse effect on healthy people but may have effects on those with COPD such as significant hypoxaemia and hypercapnia. In COPD patients, hypoventilation is already pronounced in the awakened state and further intensifies during sleep, when there is a collapse in the airways due to obstruction. Also, it is to be noted that sleep problems are one of the most common symptoms of COPD patients. In COPD patients, there are problems initiating or maintaining sleep, increased light sleep and reduced REM sleep, frequent sleep stage shifts and micro-arousals.

A recent review published in The European Respiratory Review (September 2013 issue) discusses the pathophysiological basis of sleep and breathing disturbances in patients with COPD. It reviews the overlap syndrome where COPD and obstructive sleep apnoea (OSA) coexist, and finally discusses the management of sleep-related disorders in patients with COPD.

In this review, the pathophysiology of sleep-related breathing disturbances with COPD is explained. These include alterations in respiratory mechanics and ventilatory control during sleep. It is said that people who are hypoxaemic during wakefulness may be prone to have disproportionately greater falls in oxygen saturation at night. Also, hypoxemia in COPD is due to the increased physiological dead space in COPD, which leads to an even greater decrease in alveolar ventilation with lower tidal volumes than in normal subjects.

Also, sleep quality is often impaired in patients with COPD, which is likely to be an important factor in the chronic fatigue, sleepiness and overall impairment in quality of life reported by patients. It seems that in patients with mild obstructive airways disease, there is little impact on sleep quality. However, as COPD becomes more severe, there are an increasing number of sleep complaints with possibly more deleterious physiological effects.

In summary, patients with COPD are victims to a range of sleep-related abnormalities that include poor sleep quality and sleep disordered breathing with associated hypoxaemia. Thus, clinical attention should be given to sleep problems in these patients so that their quality of life may improve.

The full review is located in this link:

http://err.ersjournals.com/content/22/129/365.long

Reference:

McNicholas WT, Verbraecken J, Marin JM. Sleep disorders in COPD: the forgotten dimension. Eur Respir Rev. 2013 Sep 1;22(129):365-75.

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