Equipment

Several different types of equipment can be used such as mercury strain gauge, laser Doppler, and continuous wave Doppler. PPG is commonly used; with an infra-red probe. Changes in opacity and blood volume are measured in the toe, resulting in a waveform. Here we describe the use of PPG.

Preparation

•  

• Cuff for digital pressure measurements; cuff size approximately 1.5 times the diameter of the digit PPG probe.

• PPG unit or

• hand-held Doppler that can be connected to PPG probe.

   

Measurement conditions

• Quiet surroundings in room with comfortable temperature for the patient, such as 22–24 °C.
• Alcohol, exercise and caffeine should be avoided for 2 hours prior to testing.

• Patient in supine horizontal position, for 10 minutes prior to the measurement.

• Both arms and lower legs should be bare.

• No tight sleeves of shirts and trousers.

• Always use the same sequence of measurements as described below.

Toe-pressure measurement

• Place the digital cuff at the base of the hallux and the PPG probe against distal toe pulp, sufficiently firmly to keep it in place but ensure there is no excess pressure on the digit whilst not inflated.

• Where the hallux cannot be used, the second digit can be used (if a smaller cuff can be placed around the base of the toe).

• Fixate the probe with tape ensuring contact of its entire flat surface against the skin (no external light should enter the underside of the probe) and preventing small movements which will disrupt the waveform.

• Wait until a cyclical signal of the probe appears on the unit’s screen.

• Once a consistent waveform is seen, inflate the cuff to approximately 30 mmHg higher than the point at which the waveform flatlines.

• Deflate the cuff slowly deflated at a rate of 2–3mmHg per second.

• The cuff pressure at the first sign of reappearance of a regular upstroke is equal to the systolic pressure in the artery. Record the result.

• In case of a suboptimal measurement repeat the measurement after a 3 minute waiting period.

• Note: when the resting toe pressure is low (indicating reduced peripheral blood flow), the returning waveform is typically smaller and less clearly distinguishable from baseline.

Brachial artery systolic pressure Measure

• Place cuff around the upper arm.

• Apply the gel over the area of the brachial artery (can be palpated first). Ensure that a clear audible signal is detected.

• Inflate the cuff to supra-systolic values, i.e. about 30 mmHg above the pressure when the signal disappears completely.

• Slowly deflate the cuff at a rate of 2–3mmHg per second until an audible signal re-appears, the cuff pressure at that moment equals the systolic pressure in the artery.

• Record the result.

• Repeat this procedure in the other arm.

  Calculation of TBI The Toe-Brachial Index TBI = toe pressure / highest of the left and right brachial pressures.     A TBI below 0.7 is considered to be abnormal, i.e. indicative for PAD.