Auscultatory and oscillometric methods of ambulatory blood pressure monitoring, advantages and limits: a technical point of view.

Two methods of indirect blood pressure (BP) measurement are currently used for ambulatory blood pressure measurement (ABPM): the auscultatory and oscillometric methods. The auscultatory method is based on the detection of Korotkoff sounds issued from the acoustic transudcer signal. Its main advantages are (1) similarities with usual clinical measurement of BP; and (2) accurate detection of systolic and diastolic pressures on the appearance and disappearance of sounds. The main disadvantages of this method are (1) artefacts due to movements; and (2) difficulties in signal analysis due to physiological variations of the Korotkoff sound patterns or poor signals. Difficulties can be overcome by appropriate signal processing (K2 recognition), noise rejection and/or ECG gating. This may allow relatively accurate BP measurement during mild exercise. With the oscillometric method, air volume variations in the cuff are detected during deflation. The maximum oscillation is related to the mean arterial pressure. The systolic and diastolic BP are determined by an algorithmic interpretation of the shape of oscillometric amplitudes as well as the heart rate. The main advantages are (1) possibility of BP measurement when the Korotkoff signal is poor; (2) measurement of the mean arterial BP; and (3) no need of a microphonic sensor. The main disadvantages are (1) some oscillometric curves are difficult to read accurately; (2) oscillometry is very sensitive to movements due to the bandwidth of the signals, so the arm must be immobile; and (3) the accuracy of the systolic and diastolic BP depends on the algorithm used. These two methods are complementary and should ideally be associated in the same device.