Sleep-disordered breathing and chronic heart failure

BACKGROUND: Chronic heart failure, a common cause of morbidity and mortality, is frequently associated with sleep-disordered breathing, which may be detrimental through a variety of haemodynamic, autonomic and vascular mechanisms. Whilst associated with increased morbidity and mortality, sleep-disordered breathing is often unrecognised and yet presents a potential therapeutic target in patients with chronic heart failure.OBJECTIVES: The aims of the thesis were, in patients with stable symptomatic chronic heart failure treated with optimal contemporary heart failure therapy: first, to determine prospectively the prevalence of sleep-disordered breathing; second, to compare the clinical characteristics of those patients with sleep-disordered breathing to those without sleep-disordered breathing; third, to assess the accuracy and clinical utility of a limited sleep study system, compared with polysomnography, for diagnosing sleep-disordered breathing; and finally, fourth, to establish whether treatment of obstructive sleep apnoea with nocturnal continuous positive airway pressure improves subjective and objective measures ofheart failure severity.METHODS: Patients with stable symptomatic chronic heart failure were screened for sleep-disordered breathing by home sleep study. Daytime sleepiness was assessed by Epworth Sleepiness Scale and heart failure severity by symptom class, left ventricular ejection fraction and serum N-terminal pro-brain natriuretic peptide concentrations. In a subset ofpatients, synchronous in-laboratory limited sleep studies and polysomonography, and home limited sleep studies, were performed prospectively. Patients with obstructive sleep apnoea and stable symptomatic chronic heart failure were randomised to nocturnal auto-titrating continuous positive airway pressure or sham for six weeks each in crossover design. Study co-primary endpoints were changes in peak VO2 and six minute walk distance and secondary endpoints changes in left ventricular ejection fraction, VE/VCO2 slope, neurohormonal markers and quality of lifeRESULTS: In the era of modern therapy, sleep-disordered breathing is common in patients with stable symptomatic chronic heart failure, predominantly obstructive in aetiology, without clear relationship to heart failure severity and is difficult to diagnose because ofmajor overlap in symptomatology. Limited sleep studies compare well diagnostically to polysomnography when tested under identical patient and environmental conditions but less so when tested in the home setting. Auto-titrating continuous positive airway pressure improves daytime sleepiness in patients with obstructive sleep apnoea and chronic heart failure but not other subjective or objective measures of heart failure severity.CONCLUSIONS: Sleep-disordered breathing is difficult to detect clinically in patients with chronic heart failure, and as such, the diagnosis is reliant on accurate sleep studies. However, the clinical utility of limited sleep studies in detection and diagnosis of sleep-disordered breathing is restricted by a number of technical and situational factors which are exacerbated in patients with chronic heart failure. The potential therapeutic benefits of continuous positive airway pressure in patients with obstructive sleep apnoea and chronic heart failure are achieved by alleviation of obstructive sleep apnoea rather than by improvement in cardiac function; however, efficacy of continuous positive airway pressure therapy may in part be limited by poor patient tolerability and compliance