Why are the systolic and diastolic BP values obtained by the oscillometric (BioZ NIBP) method different from those obtained by the auscultatory (manual) method?
When the BioZ NIBP method is the source for determining BP, the Oscillometric method is used. This method measures the pressure pulse within the cuff in incremental steps and has a maximum value of approximately 1 mmHg, which occurs at the MAP. A sophisticated algorithm is then applied to plot the Oscillometric Envelope of pulse pressure measurements vs. cuff pressure measurements. This oscillometric envelope is used to determine the MAP, SBP and DBP values. The shape of an actual patient Oscillometric Envelope varies from measurement-to-measurement and from individual-to-individual. Therefore, it is quite possible to have different systolic and diastolic pressures for the same measured MAP, as well as different MAPs for the same systolic and diastolic pressures. When using the auscultatory method, the systolic and diastolic pressures are measured and the MAP is traditionally calculated by using the formula: MAP = DBP + (SBP-DBP)/3. This is not the formula used by the BioZ. The formula
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