Doppler ultrasound (one kind of diagnostic ultrasound) uses the “Doppler Principle” to assess two items: First, whether structures, generally blood, are moving towards or away from the probe, and secondly, its relative velocity.

What is it?

Transcutaneous oximetry is a measure of oxygen levels through the patient’s skin, as a measure of tissue healability. As such, this information is useful to a vascular surgeon and other health care providers who may consider opening vessels into the ankle and the foot (angioplasty) or other procedures to help with the vascular rehabilitation process.

Why?  Who needs this test?

Diabetic patients with ‘medial calcinosis’, which identifies the presence of non-compressible calcium deposits occurring inside the vessel (preventing the patient from getting accurate ankle-brachial index measurements of blood flow). The accuracy of tcpO2 is not hampered by vessel calcification and hence, transcutaneous oximetry is a much better test to determine healability.

How is it done?

Transcutaneous oximetry requires a machine called a transcutaneous oximeter, which connects to various sensors placed on the patient’s body. This set up is very similar to that of an electrocardiogram. The transcutaneous oximeter then collects the oxygen measurement from the sensors.

Where is it done?

Transcutaneous oximetry is performed at some non-invasive vascular laboratories where Doppler ultrasounds are done as well. In particular, diabetic patients who have “small vessel disease”, use this process to create an “oxygen map”, which indicates sites of oxygen delivery near the targeted wound (e.g. commonly the toes and heel).

1. Open occluded (clogged) vessels known as angioplasty, which is a non-surgical procedure where a thin tube, known as a catheter, manually widens a blocked artery.

2. Support opened vessels from a collapse with the insertion of a stent.  A stent, which looks like a cylindrical synthetic tube, is placed in the artery permanently to keep it widened.

An ankle brachial pressure index, also known as an ABPI/ABI, is the measure of the change in blood pressure of the arteries supplied in the legs. The ABI is measured when the patient is lying down at two points on the body, the arm and the ankle.

To calculate the highest ankle reading, the highest arm reading is divided by the ankle reading. The following range considers of discrepancies due to the distance the blood has to travel.

Please note an ABI less than 0.5 (pain) is generally associated with pain, and an ABI less than 0.2 is associated with severe ischemia and gangrene.

Ankle-brachial index may not be a useful measure for diabetics, as the blood vessels in diabetics are commonly calcified and are not compressible. Hence, ABI readings for diabetics often results in false negative readings so alternative measures are recommended for patients with diabetes.

Calcification in the arteries of the lower leg is common in diabetes and can result in false readings. This is because calcification causes the vessels to be not easily compressed by the blood pressure cuff.

 In that case we can sometimes perform more accurate “toe pressure” measurements by attaching a small blood pressure cuff.

Toe pressures can be technically challenging in some cases (e.g. ulcer on toe or no toes present).