FIG. 3:  Sleep disordered breathing can be generally divided into two types.  The first is obstructive sleep apnea (OSA), which is the socially interesting kind of apnea that usually occurs in people who are obese.  This apnea is associated with very disruptive snoring and occurs because of collapse of the upper airway during inspiration.  So, the patient is actually trying to inhale, but because of the loss of muscle tone that occurs during sleep, the upper airway (which is striated muscle) tends to collapse on inspiration like a wet paper straw.  At this point the subject wakes, or rather the brain wakes; ie, although the patient is not aware that he or she has woken up, we can tell from a scan of the brain waves that there has been an arousal, and generally after that arousal from sleep there is a resumption of breathing, because there is now a restoration of airway tone. 

The second kind of apnea is central sleep apnea (CSA), which is a quieter kind of apnea.  This is the kind of apnea that we see, for example, in patients with heart failure.  This apnea is also called Cheyne-Stokes respiration (CSR), and it occurs because of loss of respiratory effort.  So for several complex and interacting reasons, the patient actually stops breathing, generally because of a fall in carbon dioxide levels. 

The topic of CSA will be covered by some of the other speakers in this series, particularly in the context of heart failure. This presentation will focus primarily on OSA and its role in cardiovascular disease.