Med. & Biol. Eng. & Comput., 1981, 19, 775-776
Timesaving method for segmental pressure measurements
Keywords - -Segmenta l pressure measurement
1 Introduction SEGMENTAL pressure measurements are widely used to evaluate arterial stenosis in the leg.~The pressure ratio
ELECTRICALLY OPERATED SUPPLY
Electrical part \
AUTOMATIC ISPL MANUALLY "HOLD" OPERATED
Fig. 1 Diagram showing the system Jbr segmental pressure measurements
between leg and arm is used to characterise the degree of the disease. Because of variations in the central blood pressure, it is necessary to measure the pressure in the arm and leg simultaneously. (THULES1US, 1978). We measure the pressure in four leg segments and use the average of three values at each level. In the ankle, the pressure is measured in two different arteries. Altogether, this makes 60 measurements for each patient. This is a time-consuming procedure, usually requiring two operators. We therefore use a simplified method, which requires only one operator.
2 Method The patient is resting on a bed during the measurements.
Four cuffs are placed on each leg at the upper thigh, lower thigh, below knee and ankle positions. One cuff is placed on the left arm. The arm and one selectable leg cuff are connected so that they have the same pressure. They can be inflated by a small compressor and deflated by a pre-set nozzle,
The pressure in the cuffs is measured with a Siemens transducer type 746 and amplifier type 863. It is visualised on two AD 2026 digital displays, one for the arm and one for the leg pressure. These convert at a rate of 4 per second and have a 'hold'-mode which makes it possible to freeze the reading by application of an appropriate voltage. The pressure is given in Hg ram. The system is shown in Fig. 1.
The systolic blood pressure in the arm and leg segment is measured by the ultrasound Doppler method. We use two
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First received 9th June and in final form 17th September 1980 0140-0118/81/060775 + 02 SO 1 9 50/0 9 IFMBE: 1981
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LIGHT EMITTING DIODE
Fig. 2 Trigging circuit jbr automatic "~mid'. The light- emitting diode is used to a@lst the triggering /erel
Medica l & Bio logica l Engineer ing & Comput ing November 1981 775
Parks 906 10 MHz Dopplers. One ultrasound transducer is fixed over the radial artery with a strap, and a second one is held over a foot artery by the operator. The velocity output from the radial artery is fed to a triggering circuit which is shown in Fig. 2. This circuit makes the 'arm' display hold the pressure reading when the velocity is greater than a pre-set value. The measurements are performed in the following way: The pressure in the arm and selected leg cuffis elevated above the systolic pressure. The velocity outputs from arm and foot arteries now contain just noise. The triggering circuit is reset so that both displays follow the cuff pressure which is then gradually decreased through the nozzle. The arm systolic pressure is shown on the 'arm' display when the first doppler pulse from the radial artery triggers the circuit. In the foot arteries the signal-to-noise ratio is often so low that automatic trigging is impossible. The operator therefore listens to the doppler output from the foot artery and presses a switch when the first signal is heard. The foot display now shows the leg segment pressure. Both values are recorded, and the procedure is repeated three times in all leg segments of interest.
3 Conclusion The system described above makes it possible to record the
arm and leg pressure nearly simultaneously using only one
operator. One examination takes about half an hour, and we obtain pressure ratios which are almost independent of variations in the central blood pressure. The method is dependent on a good signal from the radial artery and a correctly adjusted triggering level.
J. GILTVEDT R. AASLID
Department of Clinical Physiology University of Trondheim Trondheim, Norway
THULESIUS, O. (1978) Simultane Doppler-Sonographie von Arm und Beingefassen bei arteriellen Okklusionen. In Ultraschall-Doppler Diagnostik in der Anyiologie, KRIESSMANN, A. and BOLLINGER, A. (Eds.), Georg Thieme Verlag, Stuttgart, 48 50.
776 Medical & Biological Engineering & Computing November 1981