ABSTRACT
Central sleep apnea (CSA) syndromes consist of a heterogeneous group of disorders in which respiratory effort is diminished or absent because of withdrawal of central respiratory drive (1,2). These disorders can be classified into a hypercapnic and a non-hypercapnic group on the basis of awake PaCO2. In the hypercapnic group, they have an already blunted respiratory drive that is further reduced during sleep, resulting in central sleep apnea usually from syndromes such as central alveolar hypoventilation or neuromuscular weakness. In the nonhypercapnic group, central sleep apnea is induced when arterial PaCO2 levels are below the PaCO2 apnea threshold, leading to cessation in ventilatory effort, which can occur in such disorders as congestive heart failure (CHF), neurological diseases, and high-altitude periodic breathing (1). But it may also be seen in the absence of any underlying medical illness, which is called idiopathic central sleep apnea or primary central sleep apnea (1,3).
