A 39-year-old man is brought to the emergency department after immediately collapsing at the finish line when he completed a marathon. Although he was unable to stand or walk, the patient did not lose consciousness. He says he has run multiple marathons in the past without any problems. Medical history includes mild intermittent asthma. He uses albuterol as needed and last took it a week ago. Temperature is 38C (100.4F), blood pressure is 98/52 mm Hg, pulse is 118/min, and respirations are 22/min. The patient is alert and oriented and does not report any pain. Neurologic examination is normal. Which of the following is the most likely cause of this patient's collapse?

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11ec25c8_d1d4_e59c_bc81_0ba55e62cf00_MD0003_00 This patient who collapsed after running a marathon but did not lose consciousness most likely has exercise-associated postural hypotension (EAPH). EAPH is thought to occur due to physiologic adaptations in endurance athletes, who have significantly higher cardiac output than unconditioned individuals due to hypertrophy and hyperplasia of the left ventricle (ie, athlete's heart). During strenuous exercise, skeletal muscles, particularly in the lower extremities, exert significant pressure on the venous system, which increases venous return to the heart. When an athlete abruptly stops exercising (eg, finishes a marathon), the muscles are no longer exerting pressure, and venous return dramatically decreases. The sudden decrease in cardiac preload fails to meet increased cardiac demand and results in transient postural hypotension and collapse. This condition may be compounded by inhibition of the baroreflex and dehydration, which often occur with intense exercise. Unlike many other causes of exercise-associated collapse (eg, exertional heat stroke, sweat-induced hyponatremia), patients with EAPH remain alert with normal mental status. Collapse or inability to walk is typically associated with a sensation of lightheadedness or dizziness. Core temperature may be normal or mildly elevated (as in this patient) from prolonged exercise. Management of EAPH is primarily supportive; patients should be placed in Trendelenburg position and offered oral hydration. (Choice A) Although severe asthma exacerbations can cause tachypnea, and hypoxia or hypercarbia may result in altered mentation with collapse, patients are expected to develop severe dyspnea and wheezing. (Choice B) Cardiac arrhythmia is a rare but potentially fatal cause of collapse in athletes. However, cardiac arrhythmia typically occurs during exercise, not immediately afterward; patients may lose consciousness (unlike this patient who collapsed without losing consciousness); and arrhythmia would not explain the patient's inability to stand or walk. (Choice D) Exertional heat stroke presents with elevated core temperature (>40 C [104 F]) associated with altered mental status (eg, confusion, syncope, seizure). Although this patient's core temperature is mildly elevated, his mental status is normal, making this diagnosis unlikely. (Choice E) Exertional hyponatremia results from excessive fluid intake (weight gain). It presents with confusion, headache, and swollen hands after prolonged heat exposure during an athletic event; a resultant seizure may induce collapse. This patient's normal mental status and consciousness make this diagnosis unlikely. Educational objective: Exercise-associated postural hypotension occurs in conditioned athletes and is caused by the sudden decrease in venous return after cessation of exercise, which fails to meet increased cardiac demand. It is characterized by collapse (with no loss of consciousness) immediately after completion of exercise. References: Exercise-associated collapse: an evidence-based review and primer for clinicians. (http://www.ncbi.nlm.nih.gov/pubmed/21948122)

A 39-Year-Old Man Is Brought to the Emergency Department After