Blood flow studies

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Alternative names
Duplex/Doppler ultrasound

Definition
Blood flow studies measure blood flow and pressure. A duplex study uses Doppler ultrasound to estimate blood flow through arteries or veins. Plethysmography measures changes in blood volume in a blood vessel.

How the test is performed

For the Duplex/Doppler ultrasound:
Clothing is removed from the area being tested, and a probe with a conductive gel (like vasoline) on the tip is placed on various points along the blood vessel in question. The information is relayed to the ultrasound monitor to be viewed and recorded.

For a plethysmography:
Blood pressure is first taken in both arms.

Clothing is removed from the arm or leg being tested. The patient lies on his or her back. A blood pressure cuff is applied to the limb being tested. It is inflated until the pulsatile flow is no longer heard. Then the pressure is released from the cuff until the flow returns. The blood pressure when flow returns is recorded and the information is transmitted to a computer which records and interprets the information.

The blood pressure cuff may be moved to other positions on the same or other extremities during the test. After the readings are taken, the patient may be re-tested while in another position such as sitting or standing.

How to prepare for the test
Clothing over the extremity being tested will be removed just before the test. Medications being used that can alter blood flow will be recorded before the test. In general, there is no other special preparation necessary for these tests.

For infants and children:
The preparation you can provide for this test depends on your child’s age and experience. For specific information regarding how you can prepare your child, see the following topics:

• infant test or procedure preparation (birth to 1 year)
  
• toddler test or procedure preparation (1 to 3 years)
  
• preschooler test or procedure preparation (3 to 6 years)
  
• schoolage test or procedure preparation (6 to 12 years)
  
• adolescent test or procedure preparation (12 to 18 years)

How the test will feel
For the plethysmography, the blood pressure cuff will constrict the arm or leg, but there is no pain. The gel used for the duplex ultrasound may feel cold when it is placed on your skin.

Why the test is performed
These are noninvasive (external) tests used to determine if there is significant disease in either arteries or veins, if adequate blood is reaching an extremity, to evaluate trauma to a blood vessel, or to monitor patients with arterial reconstruction or grafts. These tests can also detect blood clots.

Normal Values
As part of a duplex ultrasound, the doctor may calculate an ABI or ankle-brachial index. This number is obtained by dividing the Doppler or systolic pressure of the ankle by the pressure in the arm. A value of 0.9 or greater is normal. Your doctor will also evaluate the flow of blood in the vessels with the ultrasound.

What abnormal results mean

An ABI of less than 0.5 is associated with peripheral vascular (arterial) disease.

Other abnormal blood flow patterns can be seen with:

• Deep venous thrombosis
  
• superficial thrombophlebitis
  
• communicating vein thrombophlebitis

These tests, or tests like them, may also be performed for additional conditions:

• Raynaud’s Phenomenon
  
• stroke secondary to carotid dissection or carotid artery stenosis

What the risks are
There are no special risks associated with these tests.

Special considerations
Most Doppler ultrasounds use a duplex/Doppler probe to enable the technician to both view the vessels (regular ultrasound) as well as assess the blood flow through them (Doppler imaging).

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