The article by White et al (p 1816) reminds us that it is important to differentiate central apnea from obstructive apnea. The physiologic findings during sleep in patients with sleep apnea are not homogenous. A small number of patients have only central apneas, ie, absent respiratory muscle contraction as the cause of the apneas. The vast majority of adult patients with sleep apnea have obstructive apnea or mixed apnea. Obstructive apnea is caused by functional or anatomic obstruction of the upper airway, while, in mixed apnea, episodes begin as central apneas and end as obstructive apneas.
Central sleep apnea has been described in patients who have had disease of the brain stem (eg, bulbar poliomyelitis or encephalitis) and in patients with idiopathic hypoventilation. It is likely that many of the patients with idiopathic hypoventilation have had brain-stem disease. These patients may have severe gas exchange abnormalities and are at the