A 45-year-old man was referred to the pulmonary function laboratory because of polycythemia (hematocrit of 57%). At the time of referral, he weighs 142 kg (312 pounds) and his height is 175 cm (5 feet, 9 inches). A brief history reveals that he frequently falls asleep during the day. His blood gas values are PaO2, 69 mm Hg; SaO2, 94%; Pco2, 35 mm Hg, and pH, 7.44. A few days later, he is admitted as an outpatient in the hospital's sleep center. He is connected to an ear oximeter and to a portable heart monitor. Within 30 minutes, the patient falls asleep and, within another 30 minutes, his Sao2 decreases from 92% to 47% and his heart rate increases from 92 to 108 beats/min, with two premature ventricular contractions. During this time, his chest wall continues to move, but airflow at the mouth and nose is not detected.
1. How would this patient's test results be interpreted?
2. What is the cause of the polycythemia?
3. How does hypoxia accelerate heart rate?
1. This patient is suffering from what has been known as pickwickian syndrome, a disorder that occurs with severely obese individuals because of their excessive weight. The pickwickian syndrome was named after Joe, the fat boy who was always falling asleep in Charles Dickens' novel The Pickwick Papers. Pickwickian patients suffer from hypoventilation and often suffer from sleep apnea as well. Pickwickian syndrome is no longer an appropriate name because it does not indicate what type of sleep disorder is involved. About 80% of sleep apnea patients are obese and 20% are of relatively normal weight.
2. Polycythemia is the result of chronic hypoxemia from hypoventilation, as well as from sleep apnea.
3. An increase in sympathetic discharge is often associated with sleep apnea and is responsible for the accelerated heart rate.
Martin RJ, ed. Cardiorespiratory Disorders During Sleep. 2nd
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