Sleep apnea

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Sleep apnea



Sleep apnea


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USMLE® Step 1 questions

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Sleep apnea

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USMLE® Step 1 style questions USMLE

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A 34-year-old woman presents to a family medicine clinic with her partner due to excessive day-time fatigue. She feels tired throughout the day despite sleeping for over eight hours nightly. The patient’s partner states that she goes through a pattern of breathing at night, during which she stops breathing, then rapidly hyperventilates. During these episodes, the period of apnea is longer than the period of hyperventilation. The patient currently smokes one pack of cigarettes per day. Her BMI is 26 kg/m2. Vitals are within normal limits. Physical exam is unremarkable. In laboratory polysomnography testing demonstrates six episodes of central apneas per hour of sleep. Which of the following best describes the underlying pathophysiology of this patient’s clinical condition?  

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Obstructive sleep apnea p. 703

pulse pressure in p. 292

pulsus paradoxus in p. 481


Sleep apnea is a sleep disorder which causes irregular breathing and snoring patterns that can ultimately cause apnea, which is where a person momentarily stops breathing altogether. The inability to get restful sleep can also lead to severe exhaustion.

Individuals can have obstructive sleep apnea, central sleep apnea, or features of both. Obstructive sleep apnea is the most common form, and it develops when there’s a blockage of the airways. Now, air has to go from the nose through the nasopharynx into the laryngopharynx, through the larynx and then into the trachea. Somewhere along that path, there might be a blockage in the flow of air.

Allergies might cause swelling in the tissues in the nasopharynx, or there might be swollen adenoid glands or tonsils because of an infection. There might be a severe overbite which pulls the jaw back and blocks the airway. In individuals that are overweight, there could be too much weight in the soft tissues of the neck, which can weigh down the airway especially when a person is lying down.

These problems are most obvious at night because hormonal changes at night cause the muscles around the airway to become slightly less stiff while sleeping. This means that they are less able to keep the airway open, making it more likely to get a bit squashed or obstructed.

Central sleep apnea, on the other hand, refers to the fact that the problem is “central” or related to the central nervous system. This is where the brain intermittently stops making an effort to breathe for 10 to 30 seconds. The apnea can persist for several seconds even after waking up, triggering feelings of panic and further disrupting the sleep cycle.

Central sleep apnea starts with an initial episode of hyperpnea, which is when the brain directs the lungs to start hyperventilating during sleep by increasing the respiratory rate. This rapid breathing causes hypocapnia, a drop in the blood’s carbon dioxide levels.


Sleep apnea is a sleep disorder characterized by brief interruptions of breathing during sleep. These apneic events can occur several times an hour and last from a few seconds to minutes. Symptoms include snoring, daytime sleepiness and fatigue, and morning headaches. There are two main types of sleep apnea: obstructive sleep apnea, caused by a physical blockage of the airway, and central sleep apnea, caused by a failure of the brain to properly control breathing. Older age, obesity, and male sex are the strongest risk factors.


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  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw Hill Professional (2019)
  5. "Meta-analysis: Continuous Positive Airway Pressure Improves Insulin Resistance in Patients with Sleep Apnea without Diabetes" Annals of the American Thoracic Society (2013)
  6. "Obstructive sleep apnoea syndrome and its management" Therapeutic Advances in Chronic Disease (2015)
  7. "Sleep Pathologies in Depression and the Clinical Utility of Polysomnography" The Canadian Journal of Psychiatry (2010)

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