Paroxysmal nocturnal dyspnea (PND) is best described as

• A. Dyspnea during exercise only
• B. Chronic cough with sputum
• C. Painless shortness of breath at rest
• D. Orthopnea that awakens you from sleep, upright posture resolves breathlessness

Answer: (D)

Paroxysmal nocturnal dyspnea is the sudden, severe shortness of breath that wakes you from sleep due to fluid shifting and pulmonary congestion when you lie flat. When you lie down, venous return to the heart increases, which raises left-sided filling pressures and can trigger pulmonary edema in someone with heart failure. Sitting up or standing upright relieves this by decreasing venous return and improving diaphragmatic mechanics, which reduces the edema and improves breathing. This pattern—nocturnal awakening from breathlessness that improves with an upright posture—is classic for left-sided heart failure with nocturnal pulmonary congestion. It’s not simply dyspnea during exercise, nor a chronic cough with sputum, nor painless shortness of breath at rest; the defining feature is the nocturnal, posture-dependent nature that wakes you and then improves when upright.