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Manhasset, NY
Dr. Feinsilver is Director, Division of Pulmonary, Critical Care and Sleep Medicine, North Shore University Hospital.
Correspondence to: Steven H. Feinsilver, MD, FCCP, Division of Pulmonary, Critical Care and Sleep Medicine, North Shore University Hospital, 300 Community Dr, Manhasset, NY 11030; e-mail: sfeinsil{at}nshs.edu
In this issue of CHEST (see page 66), Skinner and colleagues from New Zealand attempted to prospectively screen patients admitted to a coronary care unit over a 2-month period using unattended respiratory monitoring during the hours of sleep. The device employed (Embletta; Medcare; Reykjavik, Iceland) is well validated for respiratory monitoring, but does not include EEG monitoring to determine sleep staging, which would have been extremely interesting data as well.
Of 101 consecutively admitted hospital patients, 41 met entry criteria and 29 agreed to participate. Good data were obtained on 26 of 29 patients, a noteworthy success rate, implying this monitoring in the coronary care unit setting may be quite practical. Sleep-disordered breathing was diagnosed in approximately one half. A follow-up study was performed in 18 patients at least 6 weeks after discharge from the hospital; in these patients, 6 did not have the diagnosis of sleep-disordered breathing confirmed, and 1 patient had a new diagnosis.
The authors refer to those subjects whose study findings were initially positive and then did not demonstrate sleep apnea on follow-up studies as "false-positives." It could be argued that these patients were not really false-positives, but demonstrated true sleep-disordered breathing during an acute cardiac illness. Some patients may have had transient left ventricular dysfunction, if not overt congestive heart failure, during their initial illness, and the relationship between heart failure and sleep-disordered breathing is well known. Sleep patterns are enormously changed simply by being in a critical care unit, and sleep deprivation itself worsens sleep-disordered breathing. Finally, the authors point out that patients initially studied in the coronary care unit spent more time in supine sleeping posture, which may also have worsened sleep-disordered breathing.
The limited numbers of patients studied, representing a minority of admissions to this unit, do not allow for a definite estimate of the prevalence of sleep-disordered breathing in these patients with acute cardiac disease, but it is clearly high. This is not entirely surprising. Sleep apnea and coronary disease share risk factors including male gender and obesity. Sleep apnea increases the risk for hypertension,1 and is an independent risk factor for cardiovascular disease, even at relatively modest apnea hypopnea indexes, as shown in the Sleep Heart Health Study.2 Potential or proven mechanisms for this association include sympathetic activation, vascular endothelial dysfunction, oxidative stress, inflammation, hypercoagulability, and metabolic dysregulation, as noted in a recent review.4
The good news is that treating sleep-disordered breathing has the potential to remove this risk factor and to improve outcome in patients with coronary disease. Treatment with continuous positive airway pressure (CPAP) has been shown to reduce both nocturnal and daytime BP in patients with hypertension.456 Sleep-disordered breathing induces nocturnal ST-segment depression,7 which can be reversed by treatment with CPAP.8 Arrhythmias associated with sleep apnea may be expected to improve with treatment; in one study of patients with atrial fibrillation, the risk of recurrence after cardioversion was significantly reduced in those receiving CPAP treatment.9 In patients with congestive heart failure, treatment with CPAP has been shown to have beneficial effects on ejection fraction and functional class, both in patients with obstructive sleep apnea and those with central sleep apnea.1011
The interactions between sleep-disordered breathing and cardiovascular disease appear to be both important and complex. The implications of this are enormous: sleep-disordered breathing is among the most common chronic diseases of middle-aged adults, frequently undiagnosed, and even more frequently untreated. Every cardiac patient does not need polysomnography, but every cardiac patient should at least be asked, "Do you snore?" and "Are you sleepy?"
References
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