Systemic arterial pressure normally falls by less than 10 mmHg during inspiration, but this decline is not palpable at the peripheral pulse. Moderate to severe cardiac tamponade, and occasionally constrictive pericarditis, induce hemodynamic changes that enhance the inspiratory fall in systolic blood pressure. This exaggerated drop in systemic blood pressure during inspiration is termed pulsus paradoxus (waveform 1 and waveform 2).
Although Kussmaul named this phenomenon pulsus paradoxus, the paradox to which he referred was that the pulse palpated on examination is of variable strength, while precordial activity is regular . The name is somewhat misleading, since the direction of change is the same as in normal subjects and is therefore not paradoxical.
Pulsus paradoxus will be discussed here, including its proper measurement, pathophysiology, and clinical conditions in which it may be present. Specific clinical conditions in which pulsus paradoxus may be present are discussed in greater detail separately. (See "Cardiac tamponade".)
MEASUREMENT OF PULSUS PARADOXUS
Severe pulsus paradoxus can be palpated in the radial, brachial, or femoral pulses as a weakening or disappearance of the pulse during inspiration (which is best observed by watching or palpating the rise and fall of the chest). However, in most patients pulsus paradoxus is most readily identified while measuring the blood pressure. It may be necessary to have the patient breathe slowly and deeply to elucidate this finding when pulsus paradoxus is not severe.
To measure pulsus paradoxus, a manually-operated 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. Pulsus paradoxus can be more sensitively quantified by an invasive arterial measurement, and may also be observed by respirophasic variation of the pulse oximetry waveform (waveform 2).