Please note that this is an indirect method of measuring blood pressure, not a direct one such as where a catheter placed in an artery is attached to a pressure transducer. This approach produces more accurate measurements, but involves increased risk to the subject and is far less convenient.
With the auscultatory method the appearance will usually predict the systolic pressure plus or minus a few mmHg when carried out by an experienced individual. Diastolic pressure is less accurately measured by this method. Some investigators believe the diastolic pressure is indicated by the muffling, some by the disappearance. The degree of accuracy for diastolic pressure determination is no better than +/- 5 mm of Hg. This is unfortunate because the diastolic pressure is the more important pressure in terms of establishing the mean pressure and the afterload on the heart.
In some cases three numbers are given for the blood pressure, the appearance number (e.g. 120 mm Hg), the muffling number (e.g. 80 mm Hg), and the disappearance number (e.g. 75 mm Hg); thus, 120 / 80 / 75, rather than the 120 / 80 which we are used to seeing.
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