People with sleep apnea syndrome have episodes of blockage of their upper airways during sleep. The condition results in abnormal sleep and low blood oxygen during the night. Sleep apnea is common, occurring in 2% of women and 4% of men. Many people with the syndrome complain of daytime sleepiness, high blood pressure, trouble sleeping at night, or snoring, but they do not know that these symptoms are a result of sleep apnea syndrome. Primary care doctors often fail to detect sleep apnea in their patients. The only way to know for certain whether a person has sleep apnea is to monitor the person's sleep patterns, breathing, and heart function while they are sleeping (sleep studies). Sleep studies are expensive, uncomfortable, and inconvenient because they usually require the patient to spend the night in a special laboratory.