Paroxysmal nocturnal dyspnea – Cardiology MCQ – Answer

Paroxysmal nocturnal dyspnea usually occurs: 
Correct answer: c) 2 – 4 hours after onset of sleep
Patient wakes up with breathlessness and sits up or even stands. It is relieved over a few minutes. Paroxysmal nocturnal dyspnea is different from orthopnea which occurs soon after assuming the supine position and is relieved by sitting up. Orthopnea has no relation to sleep. Onset of paroxysmal nocturnal dyspnea is delayed after onset of sleep as it takes some time for the peripheral edema fluid to get absorbed and translocate to the lungs. Sympathetic withdrawal during sleep is also a proposed mechanism. Paroxysmal nocturnal dyspnea occurs in left heart failure (both in acute left ventricular failure and left ventricular inflow obstruction like mitral stenosis).
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