Pulsus Paradoxus
Systemic arterial pressure measured via an intraarterial cannula normally falls up to 10 mmHg during inspiration, but this decline is not palpable at the peripheral pulse. Moderate and severe cardiac tamponade induce hemodynamic changes that enhance the inspiratory fall in blood pressure. This exaggerated fall in systemic blood pressure during inspiration constitutes pulsus paradoxus. Although Kussmaul named this phenomenon pulsus paradoxus, the paradox to which he referred was that the pulse is intermittently irregular while precordial activity is regular. The name is somewhat misleading, however, since the direction of change is the same as normal and is therefore not paradoxical in the sense usual in medical terminology.
To measure pulsus paradoxus, a sphygmomanometer is employed for blood pressure measurement in the standard fashion except that the cuff is deflated more slowly than usual. During deflation, the first Korotkoff sounds are audible only during expiration, but with further deflation, Korotkoff sounds are heard throughout the respiratory cycle. The difference between the systolic pressure at which the first Korotkoff sounds are heard during expiration and the pressure at which they are heard throughout the respiratory cycle quantifies pulsus paradoxus.
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