Indicators of obstructive sleep apnea
A complete evaluation to diagnose sleep apnea is best done in an overnight sleep center. There, technicians can record your breathing, heart rate, brain waves and other measurements. You'll find out if the apnea is mild, moderate or severe.
FLOW-VOLUME LOOP -- A sawtooth appearance on the flow-volume loop was previously thought to be a specific indicator of obstructive sleep apnea. It is now recognized as a nonspecific marker of upper airway obstruction found in patients with upper airway burns, laryngeal dyskinesia, and neuromuscular and extrapyramidal disorders affecting the upper airway. Analysis of flow ratios is also not helpful.
POLYSOMNOGRAPHY -- The diagnosis of obstructive sleep apnea is best established by overnight polysomnography. However, the test does have limitations. Patients with infrequent episodes of apnea (fewer than 100 a night) were found on successive testing to have a highly variable number of episodes when compared with patients with more frequent episodes (more than 100 a night). Another possible confounding factor is the time a patient spends on his or her back during the test; patients with severe apnea may have a near normal test if they spend more time sleeping on the side.
In addition to being used to confirm the diagnosis, overnight polysomnography is done to assess the severity of physiologic disturbances, the need for therapy, and the response to nasal continuous positive airway pressure (CPAP).
Overnight polysomnography is time-consuming and cumbersome. Recently, an ambulatory device that monitors oxygen saturation, heart rate, snoring, and body position has been found to have high sensitivity and specificity for sleep apnea. This device has been proposed as a low-cost screening tool.
MULTIPLE SLEEP-LATENCY TESTING -- Multiple sleep-latency testing is an objective measurement of daytime hypersomnolence. The subject is allowed 20 minutes to fall asleep on several occasions (usually four to six) during the day. The time required to fall asleep (ie, latency to stage 1 or 2 sleep) is determined by electroencephalographic monitoring. A mean latency of 5 to 10 minutes indicates mild to moderate hypersomnolence, whereas latency of less than 5 minutes indicates severe hypersomnolence.
Complications A number of complications are associated with obstructive sleep apnea, including respiratory failure and death.
MORTALITY -- Untreated patients with an apnea index above 20 have a higher mortality rate than those with an index of 20 or less. The survival rate is higher in patients treated with either nasal CPAP or tracheotomy.
AUTOMOBILE ACCIDENTS -- Patients with obstructive sleep apnea have an automobile accident rate that is seven times that of persons without the syndrome.
HYPERTENSION -- The prevalence of daytime systemic hypertension in patients with sleep apnea is about 50%. Although several studies have implicated the syndrome in the development of hypertension, especially in morbidly obese young patients, more recent studies have found that the high prevalence of hypertension in snorers is linked more to obesity and age than to obstructive sleep apnea.