A 63-year-old man undergoes a sleep study, during which he is closely observed for a full night. Several physiologic parameters, such as oxygen saturation, heart rhythm, cerebral electrical activity, respiratory airflow, and movements of the chest and upper abdominal walls, are continuously recorded. The following graph depicts a recording obtained over a period of several minutes: Which of the following is the most likely cause of the observed findings?

Question

A 63-year-old man undergoes a sleep study, during which he is closely observed for a full night.  Several physiologic parameters, such as oxygen saturation, heart rhythm, cerebral electrical activity, respiratory airflow, and movements of the chest and upper abdominal walls, are continuously recorded.  The following graph depicts a recording obtained over a period of several minutes:  Which of the following is the most likely cause of the observed findings?

Quizplus · Accepted Answer

This patient with prolonged pauses in airflow despite continued thoracic and diaphragmatic activity has obstructive sleep apnea (OSA). OSA, the most common sleep-related breathing disorder, is characterized by recurrent obstruction of the upper airway. During sleep, there is relaxation of the oropharyngeal and/or soft palate musculature. In patients with OSA, this results in a functional airway collapse that produces periods of reduced (hypopnea) or absent (apnea) airflow despite continued breathing efforts. Apneic episodes may last anywhere from 10 seconds to >1 minute, resulting in hypoxia and hypercapnia. This eventually triggers chemoreceptors in the carotid body and brainstem, leading to transient arousal and resumption of breathing. Patients may not be aware of apnea, but bed partners commonly report loud snoring with intermittent episodes of silence. This pattern occurs hundreds of times per night, leading to poor sleep quality and chronic fatigue. Risk factors for OSA include obesity, large neck circumference, and reduced oropharyngeal diameter (eg, enlarged tonsils or tongue, retro- or micrognathia). (Choice A) Patients with advanced heart failure may exhibit Cheyne-Stokes breathing, a cyclic breathing pattern in which apnea is followed by gradually increasing then decreasing tidal volumes (crescendo-decrescendo) until the next apneic period. (Choice B) Reduced lung compliance in pulmonary fibrosis limits tidal volume (TV) per breath. Patients exhibit rapid, shallow breathing (without apnea) to restore minute ventilation (TV × respiratory rate) and minimize the work of breathing. (Choice C) Neuromuscular weakness (eg, Guillain-Barré syndrome) results in reduced thoracic and diaphragmatic muscle activity with rapid, shallow breathing; recurrent apnea does not occur. (Choice D) Severe diabetic ketoacidosis can result in Kussmaul breathing (ie, deep, rapid breathing with associated increased thoracic and diaphragmatic activity). It occurs as a respiratory compensation for severe metabolic acidosis. Educational objective: Obstructive sleep apnea, the most common sleep-related breathing disorder, is characterized by recurrent obstruction of the upper airways. Relaxation of the oropharyngeal and/or soft palate musculature during sleep results in a functional collapse of the airway, producing periods of reduced (hypopnea) or absent (apnea) airflow despite continued breathing efforts. __________ References: Obstructive sleep apnea syndrome: a literature review. (http://www.ncbi.nlm.nih.gov/pubmed/25747430)

A 63-Year-Old Man Undergoes a Sleep Study, During Which He