Mean blood pressure algorithms

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Abstract
Alternative methods of calculating average blood pressure are examined. It is suggested that the preferred method is calculation of the arithmetic mean if the average value itself is required. However, when blood pressure values arc used to calculate other results, only the instantaneous value is appropriate in all situations. Arithmetic mean blood pressure values may be used with arithmetic mean flow values to calculate resistance, but only if resistance is constant over the interval (laminar flow). To calculate ventricular stroke work, the root mean square averages must be used because in this instance the arithmetic average yields large errors. Most monitors do not use these methods consistently to derive average blood pressure values, thus, the displayed values differ from those obtained from the appropriate calculation. Computational convenience, truncation error in averaging, or true errors in measurement or understanding of the associated physiologic state may account for observed differences. The interpretation of maximum systolic and minimum diastolic pressures with each beat requires additional considerations. Common monitoring algorithms obscure clinically important details, particularly by distorting the relationship between respiratory variation and pulse pressure.

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