Contrary to dire predicitions, technological advances have not devalued physical diagnosis. The observing eye, the palpating hand, and the listening ear continue to perform useful diagnostic functions. In fact, their value has been enhanced by correlative data obtained from sophisticated techniques. Thus, what may have been only an "educated" guess can become an authenticated indicator, and a mere association can be transformed into an understandable manifestation of a pathologic process.
One such valuable simple diagnostic physical sign with an expanding range of usefulness is pulsus paradoxus. Detectable by palpation, but more often only by measuring the arterial blood pressure, the inspiratory drop of the peak systolic pressure in excess of 10 mm Hg was first observed a century ago by Kussmaul1 in association with constrictive pericarditis and pericardial effusion. This sign has since become the hallmark of cardiac compression.
Fifty years after Kussmaul's report, Katz and Gauchat2 noted