[Indirect blood pressure measurement with a two-probe-ultrasound system (author's transl)].

A two-probe-ultrasound system is described as an example of the indirect measurement of blood pressure. Possible errors of the indirect method as well as attempts of improvement are shown. To receive a separate detection of the systolic, respectively the diastolic pressure, one probe of the two-probe system is fixed to the arteria radialis, the other to the arteria brachialis. The determination of the "Nulkriterium" (coincidence of the pneumatic cuff pressure and the arterial pressure) can be performed either by the investigator or automatically. The measuring systems shows the following advantages: 1. Use of a more reliable "Nulkriterium" (measurement of hypotonic blood pressure values which could no longer be measured by means of the Riva-Rocci/Korotkoff-procedure; no auscultatoric gap appeared at about 20 000 single measurements). 2. No falsification of systolic values by suprasystolic noises (two-probe principle; measurement of the systolic blood pressure by means of a probe outside the region of the pneumatic cuff). 3. Errors which come up by the expectation of the investigator or by the reading of the manometer can be avoided dependent on the mode of the system. The automatic measurement (dynamical compression, selection of frequencies, electronic threshold, delayed ECG coincidence) led to no satisfactory results, especially referring to the diastolic values. Principle criteria, however, come up which should be fulfilled with the construction of an automatic system of indirect blood pressure measurement. A better automatic measurement may be expected, if instead of the "threshold principle" used here a signal analysis is performed by microprocessors. The example of an intraarterial measurement of blood pressure demonstrates the phenomenon of a "mock auscultatoric gap" because of the spontaneous variability of the arterial pressure decreasing for a short time faster than the pneumatic cuff pressure.