Cardiac adrenergic neuronal activity, sleep apnea, and potential therapeutic role of nocturnal ventilatory assistance in patients with heart failure

Excerpt

Breathing disorders during sleep are common. Patients with congestive heart failure (CHF) and systolic dysfunction have a high prevalence of sleep disorder breathing.1^–7 This is mainly in the form of Cheyne Stokes breathing and central sleep apnea (CSA). CSA is characterized by a dysregulated and insufficient drive for breathing during sleep, resulting in repetitive episodes of insufficient ventilation and inadequate gas exchange. There are frequent episodes of hyperventilation followed by apnea associated with a drop in O₂ saturation, sleep fragmentation, and arousals. Another form of sleep disorder or obstructive sleep apnea (OSA) is also common in general population.8^–10 This mainly comprises of episodes of increased resistance and obstruction in the upper airways, a rise in negative intra-thoracic pressure, ineffective ventilation, hypoxia, and arousals. A major distinction between CSA and OSA is an insufficient respiratory drive in the former, whereas there is ineffective respiratory drive in the later. OSA is more commonly seen in the overweight patients and in those with increased neck circumference. Both forms of sleep apnea cause daytime drowsiness and poor quality of life. Whereas both forms of sleep apnea have distinct mechanism, nevertheless, both result in disturbance of sleep architecture, episodes of hypoxia, sympathetic activation, daytime drowsiness, and have been associated with systemic hypertension, pulmonary hypertension, supraventricular and ventricular arrhythmias, left ventricular remodeling, and adverse cardiovascular events. There is a significant degree of overlap between the two types of sleep apnea. Both forms of sleep apnea are diagnosed by the detection of episodes of apnea or hypopnea (AHI) on a sleep study. Detection of ≥15 episodes of apnea or hypopnea per hour during sleep study is used as a threshold for the diagnosis of sleep apnea. When ≥ 50% of the episodes of AHI are central in origin, this is arbitrarily classified as CSA. The prevalence of CSA has been estimated to be in over one-third of patients with CHF. Both forms of sleep apnea have attracted a lot of investigative and therapeutic interest. Continuous positive airways pressure-assisted ventilation (CPAP) is the most common form of respiratory assistance used in patients with OSA, whereas adaptive servo ventilation (ASV) is the most commonly used ventilatory assistance in patients with CSA.1,3,7 The later is an algorithm driven close loop ventilator system designed to maintain normal breathing pattern in patients with CSA. Different manufactures use different algorithms in their adaptive ventilator devices, but they all achieve the same goal of maintaining a normal breathing pattern in patients with CSA. …