USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 71-year-old Caucasian man is brought to the emergency department by his wife. The wife mentions that this is the second time she notices important breathing pauses while her husband sleeps. The patient's medical history is relevant for a recent hospitalization due to decompensated heart failure and an ischemic stroke 2 years ago. He currently takes low-dose aspirin, metoprolol, and furosemide. Upon further interrogation, the patient reports "lacking air" and extreme daytime tiredness. On physical examination, the patient looks pale. Auscultatory findings reveal a progressively faster breathing followed by breathing apneas. His temperature is 36.7°C (98.2°F), pulse is 91/min, respirations are 18/min, blood pressure is 130/61 mm Hg. Laboratory findings reveal a high carbon dioxide saturation of blood after awakening. Which of the following best explains this patient's findings?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
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.
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 of the tissue 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 becomes 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 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.
When the carbon dioxide falls below a certain threshold, the body slips into a state of apnea, making no effort to breathe and taking in no oxygen.
This causes the carbon dioxide levels to rise back to normal levels and then, as the apnea persists, they keep rising to which is called hypercapnia.
The really high carbon dioxide levels triggers hyperpnea again, and the cycle starts all over.
Essentially, the respiratory system is going rapidly back and forth between two states, first making no effort to breathe and then hyperventilating, with no in-between.