Editorial [Hot topic: Sleep Abnormalities in Pulmonary Disease (Guest Editor: Shyamsunder Subramanian)]

Patients with a variety of pulmonary disorders commonly have distinct abnormalities related to sleep. These include poor sleep quality [1] and the development of nocturnal oxygen desaturation [2]. Patients with lung disease commonly develop insomnia - either manifesting as difficultywith initiating or maintaining sleep or both [3]. Sleep is associated with physiologic changes in ventilatory behavior which include changes in ventilatory control and thoracoabdominal muscle activity that are sleep stage specific [4], besides also influencing upper airway dilator muscle activity, resulting in changes in upper airway resistance with sleep onset [5]. These alterations, coupled with the effects of supine body position and its effects on lung volume, [6] become especially significant in patients with chronic lung disease and with limited pulmonary reserve and manifest with distinctive clinical presentations. Patients with co morbid obesity present with a unique set of manifestations commonly related to the presence of obstructive sleep apnea, [7] and in a subset of these patients hypoventilation syndromes characterized by daytime hypercapnea and cor pulmonale [8]. Circadian factors also play a role in determining pulmonary function and this effect is most commonly observed and clinically very relevant in patients with chronic asthma [9]. Nocturnal oxygen desaturation may be either intermittent in relation to sleep-disordered breathing or sustained. A variety of mechanisms contribute to the latter process, and it is especially relevant in patients with parenchymal lung disease such as emphysema [10] as well as in patients with pulmonary vascular disease and pulmonary hypertension [11]. Besides, patients with end-stage lung disease develop chronic hypercapneic respiratory failure and require non-invasive positive pressure ventilation [12] - newer modalities of providing such ventilatory support are gaining ground including average volume assured pressure support ventilation [13]. A variety of factors including low oxygen levels, and ventilatory disturbances, may lead to poor sleep quality in patients with chronic lung disease. Medications used to treat common pulmonary diseases are also seen to have important effects on sleep [14]. Sleep disturbances may lead to daytime fatigue and this in turn may lead patients to adopt poor sleep habits characterized as poor sleep hygiene and thus setting up a vicious cycle that may lead to chronic sleep onset as well as sleep maintenance insomnia. A number of unanswered important questions remain, including determining which factors contribute most, and are best predictive of nocturnal desaturation, and poor sleep quality in patients with chronic pulmonary disease. In addition, it is yet to be determined to what extent poor sleep quality in these patients affects daytime function, including mood, neuro-cognitive function, and overall quality of life, whether interventions such as NPPV are able to predictably improve these parameters, and what is the optimal strategy specific to improving sleep health in patients with pulmonary disease.