Extracting oscillometric pulses from the cuff pressure: does it affect the pressures determined by oscillometric blood pressure monitors?

OBJECTIVE

Oscillometric noninvasive blood pressure measurement devices determine the pressures by analysing the relationship between the pressure in an occluding cuff and low-amplitude pressure pulses (oscillometric pulses) induced in the cuff by the arterial pressure wave. This paper examines the effects on the pulses and oscillometric pulse amplitude envelope of the filters that extract the pulses from the cuff pressure.

METHODS

The cuff pressure and oscillometric pulses extracted by the filter were recorded from a Critikon DINAMAP and a Datex Cardiocap, chosen because of accessibility of the filtered and unfiltered signals. The unfiltered oscillometric pulses were determined by subtracting the cuff pressure from a baseline constructed to represent either the Critikon's step deflation cuff pressure or the Datex's gradual pressure decrease. Waveforms were recorded from a noninvasive blood pressure test simulator and three volunteers.

CONCLUSIONS

The filter alters the shape of oscillometric pulses causing a shift in the oscillometric pulse amplitude envelope drawn from the filtered pulses compared with that drawn from the unfiltered pulses in human subjects, but not the test simulator. The pulse shape distortion is dependent on the filter characteristics and the oscillometric pulse shape. Further work is required to explore whether this may help explain why simulators with artificial waveforms cannot validate noninvasive blood pressure monitors and why noninvasive blood pressure monitors may not be accurate in all patient groups.