Huntleigh DA100PB, Service Manual, Page: 26 / 73

Operating Principles
771402-2 dopplex ABIlity Service Manual
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7.1 Cuff Inflation & Deflation Control
The Ability includes a small compressor that provides air for cuff inflation. As there are effectively eight
pneumatic channels (four occlude and four detect), valves are included to direct the air to the appropriate
channels at the appropriate time. These are all controlled by the internal application software.
7.2 Brachial occlusion cuff chambers
The highest pressure that each occlusion chamber is inflated to during a measurement is referred to as the cuff
terminal pressure. The brachial cuff terminal pressure is not fixed, but varies depending on the patient’s
estimated brachial systolic blood pressure. An algorithm estimates the systolic pressure during cuff inflation,
and the cuff terminal pressure for that test is set to 30 mmHg higher (up to an absolute maximum of 230mmHg).
This ensures that the arterial blood flow is completely occluded, without inflating to excessively high pressures.
7.3 Ankle occlusion cuff chambers
For the ankle occlusion chambers, the cuff terminal pressure (for the first inflation) is fixed at 180 mmHg. A
software neural network algorithm analyses the detect chamber signal, and determines if the initial inflation
pressure of 180mmHg was sufficient. If not, the occlusion cuff is deflated, and re-inflated to a terminal pressure
of 230 mmHg. If this second inflation is found to be inadequate the neural network reports this as out of range.
The same neural network identifies if the detect signals are of poor quality, for example if the patient moves
excessively, and reports the outcome at the end of the test.
7.4 All detect chambers
At the beginning of each test, all chambers, including occlusion chambers are inflated to 45 mmHg, and
maintained at this pressure for around ten seconds. During this period, the AC signals from the ankle occlude
chamber pressure sensors is recorded. This signal is referred to as the Pulse Volume Recording (PVR) and
can be displayed on the LCD and printed on the hard copy output if required.
When the PVR signal recording phase is complete, the ABPI test commences, starting with the brachial systolic
pressure measurements, and from this point onwards, until the test is completed, all four cuff detect chambers
are maintained at 45 mmHg. At this pressure, the detect chambers do not occlude blood flow, and the pressure
sensor signals contain information relating to the blood flow in the vessels under each chamber.
7.5 Systolic Pressure Determination
The systolic pressure is determined by a software algorithm that analyses the pressure signals in the detect
cuffs during controlled deflation of the occlusion chambers. These changes relate to the changes in blood
volume that occur during this phase. In some cases, interfering influences such as patient movement disturb
the very small pressure signals, and systolic pressure determination is not achievable. In such cases, the
instrument reports this by displaying an appropriate message, and a repeat of the test is suggested.
7.6 System Faults
During a measurement, the software algorithms continuously monitor the instantaneous cuff pressures, and if a
fault is detected such as a cuff air leak, an error message is displayed. A full list of error messages is given in
the user manual.