Amplitude envelope slopes of oscillometric blood pressure waveforms as defined by amplitude ratios

Oscillometric methods for blood pressure determination use oscillometric waveform amplitudes. A typical waveform amplitude envelope exhibits a rise of amplitudes at cuff pressures above mean arterial pressure and decrease of amplitudes below mean pressure. Amplitude envelope slopes are functions of several hemodynamic variables. An amplitude envelope can be divided into three segments: segment S1 is the portion of the slope at cuff pressures above systolic pressure, segment S2 is the portion at cuff pressures between systolic and mean pressure, and segment S3 is the slope between mean and diastolic pressure. The slope S2 should be less steep than slope S1 or slope S3 because of the blood flow under the cuff and into the distal vasculature. To test this hypothesis, ten subjects were tested using a specialized data acquisition system. Commercial brachial (upper arm) cuff was used. Results (mean values): S1=0.125, S2=0.056, S3=0.093. All ten S2 slopes were less steep than the slopes S1. The results with brachial cuff confirm earlier research showing that blood flow alters radial (wrist) oscillometric waveforms during blood pressure measurement. An algorithm capable of detecting transition from S1 to S2 would determine physiologically correct systolic blood pressure.