Abstract
BACKGROUND: Pulsus paradoxus (PP) represents increased fluctuation of systolic pressure during the respiratory cycle. PP increases in pathologic conditions, including asthma and other obstructive airways diseases. Respiratory waveform variation (RWV) represents arterial-waveform baseline variability resulting from intra-pleural pressure changes during the respiratory cycle in the presence of airway obstruction. It is not known whether RWV influences manual PP measurement using a sphygmomanometer and stethoscope. METHODS: We performed an observational study in six healthy adults. Participants performed tidal-breathing through a breathing apparatus with pre-determined inspiratory (0-45.6 cm H(2)O) and expiratory (0-24.4 cm H(2)O) resistance levels for a total of 23 data sets per participant. PP was measured from continuous radial artery pressure recordings as the absolute difference between maximum and minimum systolic pressure levels during a complete respiratory cycle. RESULTS: In this study, PP values measured without applied airway resistance exceeded 10 mmHg, the traditional definition of PP, in five of the six participants. Manual measurement of PP would not be possible at greater RWV because the maximum diastolic pressure exceeded minimum systolic pressure during RWV. CONCLUSIONS: PP in normal adults may exceed 10 mmHg, and RWV may be of sufficient magnitude to preclude manual PP measurement.