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Frequently Asked Questions

Toe Pressure Measurements Using Photo Plethysmography
Measurements of pressures in the toes are considered useful for the evaluation and practical applications in certain groups of patients, such as those with diabetes mellitus. In normal subjects toe pressures are always found to be lower than ankle pressures and usually lower than brachial systolic pressures. The decrease in systolic pressure between the ankle and the toe is a result of the smaller diameter of the arteries of the feet, which result in damping of the pressure wave and greater resistance.

For information on the Atys SysToe toe automatic pressure meansurement system follow this link


Measurement of toe pressures allows assessment of the occlusive process in those cases in which arterial calcification interferes with the measurement of the more proximal pressures. It is important to carry out the measurements with the patients and their limbs comfortably warm. Pressures measured with cuffs will be overestimated if the cuff is too narrow and may be underestimated if it is too wide. Since a certain length of a digit is needed to apply the sensing device (PPG transducer) distal to the cuff, the 2.5 cm cuff is usually adequate. The lower limit of normal for the toe pressure has been found to be 50 mmHg and 64% of the brachial systolic pressure. For the ankle-toe gradient the upper limit of normal was 70 mmHg.

How to calculate the TBI

Divide the highest toe pressure by the highest brachial pressure. The result is the TBI. 0.65 and 0.7 and above is normal for TBI.

TBI= Toe Systolic Pressure/Brachial Systolic Pressure.

Interpretation (see reference below)

0.64± 0.20 limbs normal
0.52± 0.20 claudication in limbs
0.23± 0.19 limbs with ulcers or ischemic rest pain

A toe systolic pressure greater than 30mm/hg may be an indicator that there is healing potential in a foot with ulcers.


How To Perform a Toe Brachial Index (TBI)

Zierler RE, Sumner DS, "Physiologic Assessment of Peripheral Arterial Occlusive Disease", Chapter 6 Vascular Surgery 4th Edition 1:85-117 WB Saunders CO., Orlando FL 1995

The Hokanson photo plethysmographs consists of dual infrared light-emitting diodes which transmit light into the subcutaneous tissue, and dual receiving diodes to pick up the light reflected from the blood near the skin. The output of the PPG changes as the blood volume near the skin surfaces changes in response to pulse or other causes. The photo sensor is placed on the toe to record pulse changes. When the cuff at the base of the toe is inflated to above systolic level, blanching of the skin occurs and pulsation disappears. During slow deflation of the cuff the first reappearance of the pulse waveform signifies the systolic pressure under the digit cuff.

Digit pulses are much affected by temperature. It is important that the patient be comfortable and extremities be warm.

As with limb cuffs, digit cuffs should be 20% wider than the girth of the digit. Cuff width should equal or exceed the diameter of the toe being tested. A DC2.5cm (2.5 x 9 cm) cuff is recommended. Pressures are measured with the patient in the supine position with the foot supported so that arterial circulation is not restricted.

Procedure:
  1. Attach the photo transducer to the distal pad of the toe with clear double-stick tape. The transducer can also be held in place by a digit cuff (not inflated) or a Velcro strap. (Applying a thin layer of ultrasound gel to the face of the transducer can enhance coupling and light transmission.)
  2. Apply a digit cuff (DC2.5) to the base of the toe.
  3. Inflate the digit cuff above systolic pressure with an Hokanson S300 aneroid sphygmomanometer until the pulse wave form goes flat line due to the cessation of blood flow into the toe. (see example below)
  4. Slowly deflate the cuff and note the systolic pressure on the S300 when pulsation’s appear. The first pulsation is considered the systolic pressure at the level of the cuff.
  5. Compute the toe/brachial index by dividing the toe pressure by the HIGHEST brachial systolic pressure.


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