Which one of the following does not cause pulsus paradoxus?
**Core Concept**
Pulsus paradoxus is a clinical phenomenon characterized by an excessive fall in systolic blood pressure (greater than 10 mmHg) during inspiration, typically observed in conditions that affect the respiratory system or the cardiovascular system. It is often associated with conditions that lead to an increased intrathoracic pressure variation during breathing.
**Why the Correct Answer is Right**
Pulsus paradoxus is commonly observed in conditions such as severe asthma, chronic obstructive pulmonary disease (COPD), and cardiac tamponade. In these conditions, the increased intrathoracic pressure variation during inspiration leads to a significant decrease in cardiac output and subsequently, a fall in systolic blood pressure.
**Why Each Wrong Option is Incorrect**
**Option A:** Cardiac tamponade is a classic cause of pulsus paradoxus. The increased pressure in the pericardial sac leads to a decrease in cardiac output during inspiration, resulting in a fall in systolic blood pressure.
**Option B:** Severe asthma is another common cause of pulsus paradoxus. The increased airway resistance and hyperinflation of the lungs lead to a significant increase in intrathoracic pressure variation during inspiration.
**Option C:** Chronic obstructive pulmonary disease (COPD) is also associated with pulsus paradoxus. The hyperinflation of the lungs and the increased airway resistance lead to a decrease in cardiac output during inspiration.
**Clinical Pearl / High-Yield Fact**
Pulsus paradoxus is often a sign of a severe underlying condition that requires immediate attention. It is essential to recognize this clinical phenomenon and promptly investigate the underlying cause.
**Correct Answer: D. Constrictive pericarditis**