(Study type: Ultrasound; related body system: Circulatory system.)

Ultrasound (US) procedures are diagnostic, noninvasive, and relatively inexpensive. They take a short time to complete, do not use radiation, and cause no harm to the patient. High-frequency sound waves of various intensities are delivered by a transducer, a flashlight-shaped device, pressed against the skin. The waves are bounced back off internal anatomical structures and fluids, converted to electrical energy, amplified by the transducer, and displayed as images on a monitor. Color Doppler US can be used with the duplex method, whereby red and blue are assigned to represent the direction of blood flow, and the intensity of the color is an indication of velocity. Using the duplex scanning method, arterial leg US records sound waves to obtain information about the arteries of the lower extremities from the common femoral arteries and their branches as they extend into the calf area. The amplitude and waveform of the pulses are measured, resulting in a two-dimensional image of the artery. Blood flow direction, velocity, and the presence of flow disturbances can be readily assessed, and for diagnostic studies, the technique is done bilaterally. The sound waves hit the moving red blood cells and are reflected back to the transducer corresponding to the velocity of the blood flow through the vessel. The result is the visualization of the artery to assist in the diagnosis (i.e., presence, amount, and location) of plaque causing vessel stenosis or occlusion and to help determine the cause of claudication. Arterial reconstruction and graft condition and patency can also be evaluated.

In arterial Doppler studies, arteriosclerotic disease of the peripheral vessels can be detected by slowly deflating blood pressure cuffs that are placed on an extremity such as the calf, ankle, or upper extremity. The systolic pressure of the various arteries of the extremities can be measured. The Doppler transducer can detect the first sign of blood flow through the cuffed artery, even the most minimal blood flow, as evidenced by a swishing noise. There is normally a reduction in systolic blood pressure from the arteries of the arms to the arteries of the legs; a reduction exceeding 20 mm Hg is indicative of occlusive disease (deep vein thrombosis) proximal to the area being tested. This procedure may also be used to monitor the patency of a graft, status of previous corrective surgery, vascular status of the blood flow to a transplanted organ, blood flow to a mass, or the extent of vascular trauma.

The ABI can also be assessed during this study. This noninvasive, simple comparison of blood pressure measurements in the arms and legs can be used to detect peripheral arterial disease (PAD). A Doppler stethoscope is used to obtain the systolic pressure in the dorsalis pedis and the posterior tibial artery. The higher of the two ankle pressures is then divided by the higher of the brachial systolic pressures acquired after taking the blood pressure in both of the patients’ arms. This normal range of this index is 1 to 1.4. When the index falls below 0.5, blood flow impairment is considered severe. Patients should be scheduled for a vascular consult for an abnormal ABI. Patients with diabetes or kidney disease, and some older adult patients, may have a falsely elevated ABI due to calcifications of the vessels in the ankle causing an increased systolic pressure. The ABI test approaches 95% accuracy in detecting PAD. However, a normal ABI value does not absolutely rule out the possibility of PAD for some individuals, and additional tests should be done to evaluate symptoms. The toe-brachial index (TBI) may be performed in such cases, where the ABI is greater than 1.4 and PAD is suspected. The TBI is calculated by dividing the systolic pressure of the toe by the brachial systolic pressure from the arm with the higher pressure; normal is equal to or greater than 0.65.