Same heart and different sleep? A brief review of the association between sleep apnea syndrome and heart failure based on two clinical cases

The research in the field of sleep medicine has increased during the whole twentieth century, principally for the involvement of sleep-related disordered breathing (SDB) in cardiovascular disease. If sleep encompasses about a third of one’s life, the reasons are mostly linked to its effects on the cardiovascular and respiratory systems. Sleep is a physiological phenomenon characterized by changes in the human body leading to a state of quiescence of the cardiovascular, respiratory and metabolic systems [1]. The importance of these events becomes more evident if we consider what happens in their absence, that is, during SDB syndromes. These syndromes include habitual snoring, sleep apnea, Cheyne-Stokes breathing syndrome and sleep hypoventilation syndrome [2]. Sleep apnea syndromes are characterized by several apneic events during the night, which consist in absence of the airflow or its reduction by more than 90% lasting more than 10 seconds, with consequent oxyhemoglobin desaturation and arousal [2]. These events provoke microawakening and sleep fragmentation that represent, along with hypoxemia, important harmful triggers on the cardiovascular system. In fact, SDB presents as a highly prevalent comorbidity in patients with heart failure (HF); both diseases are related to each other in a bidirectional way through multiple mechanisms: apneic events raise cardiac afterload, and at the same time impaired cardiac function itself may contribute to the development ofsleep apnea. HF is a clinical syndrome characterized by signs or symptoms due to the inability of the heart to provide a normal tissue perfusion: the failing cardiac pump is not able to maintain an adequate output for this task. Typical features of HF are represented by shortness of breath, resting or exertion dyspnea, fatigue, fluid retention leading to pulmonary congestion or ankle swelling, and objective evidence of a structurally or functionally abnormal heart at rest [1,3].