FAQ about ABI Machines

ABI Machine is an instrument designed to perform the vascular physiological assessment in patients to identify vascular problems in the legs.
FAQ about ABI Machines

In this session, we will discuss frequently asked questions about Ankle Brachial Index (ABI) machines, focusing on ABI measurements.  

What is Measured During an ABI Test?

During an ABI test, the sonographer attempts to find the ABI, which is the ratio between systolic ankle pressure and systolic brachial pressure.
To measure this ratio, the examiner wraps a pressure cuff around the ankles and brachials and inflates it past the presumed systolic pressure. Then, the examiner will use a Doppler (or PPG) sensor to measure distal to the pressure cuff. This method is the primary tool to determine systolic pressure. During cuff occlusion, the Doppler signal flattens out or disappears. When the pressure cuff is deflated, blood flow starts to flow again, and the Doppler signal appears again, indicating the point of systole.

ABI Test Results at Rest and Post Exercise
ABI Test Results at Rest and Post Exercise

Which Doppler Probe Frequency to Use During the ABI Test?

The best Doppler measurements of blood flow in the peripheral arteries are obtained with handheld ultrasound probes with a frequency of 8MHz. In some special cases, 10MHz probes can provide better measurements when the vessels are superficial. On the contrary, 4MHz probes can be used when the vessels are deeper, but for most practical cases, the 8MHz and 10MHz probes are perfect for ABI testing. 

As a side note, the Falcon vascular machine is the only complete high-end vascular system that offers the range of all Doppler frequencies.  

Which Pressure Cuff Size to Use for ABI Measurements?

The recommended cuff size for ABI is 10.
Size 10 is the standard and most common size of the pressure cuff for both the ankle and brachial sites.
During an ABI procedure, the pressure cuffs are placed on both upper arms and around both ankles of the patient. The larger pressure cuff of size 12 is typically used for the thigh. Smaller pressure cuff sizes are used for measuring the pressure index at the foot metatarsal or the digit and toes.

What is an ABI Machine?

ABI is measured with dedicated ABI machines. The type of ABI equipment ranges from very basic and low-end devices to high-end vascular diagnostic devices. For example, the Falcon physiologic machine is considered the best high-end vascular device for many reasons, including offering a complete set of vascular diagnostic tests. 

In addition to ABI measurements, the best physiologic machines also allow measuring:

  • Segmental Blood Pressures, 
  • The Toe Brachial Index, 
  • Full spectral ultrasound Doppler, 
  • A range of photoplethysmographic measurements with PPG sensors, 
  • Pulse Volume Recordings (PVR), 
  • Skin temperature, and 
  • A wide range of vascular specialty tests. 

Low-end ABI machines are often based on oscillometric pressure technology, which is not clinically approved. It also lacks spectral doppler analysis, and does not support specialty test protocols, sophisticated reporting possibilities, or required institute networking options.   

Can ABI Measurements be Performed with the Oscillometric Method?

Yes, oscillometric blood pressure measurements are in widespread use for the measurement of brachial pressures. However, they are not clinically accepted in most places for ankle pressure measurements. 

While oscillometric ABI measurements are very simple to perform, their clinical reliability is still in question. Typically, oscillometric ABI machines are very basic and do not include various vascular diagnostic functions that are useful for complete physiologic diagnosis.

Oscillometric vs. Doppler for ABI Test

What is the Best Design for an ABI Machine?

Ideally, the design of an ABI machine must allow for patient examinations to continue even if a pump or valve fails. Typically all ABI machines include air pumps, electronic valves, pressure sensors, and tubing. When there is a problem with any of these components, the ABI equipment is not functional until serviced. 

Specifically, the Falcon vascular diagnostic system is the only advanced ABI machine based on the IPU technology (Independent Pneumatic Unit). With this special pneumatic technology, each pressure channel is completely independent. Thus, if one channel fails for any reason, the remaining pressure channels can continue working normally. This design allows continuing with patient examinations without missing a beat until the failing pressure channel is repaired.  

Which Machines Perform ABI and SBP Measurements?

Segmental Blood Pressure measurements, including the Ankle Brachial Index and the Toe Brachial Index, are performed with dedicated vascular diagnostic equipment, such as the Falcon vascular system. 

Such an ABI machine is expected to clearly display the inflation and deflation process of the pressure cuff and automatically mark the suggested systolic blood pressure on the Doppler or PPG signal. 

In addition, the best segmental pressure machine is expected to support pressure tests with both Doppler and PPG sensors. 

Finally, High-end vascular diagnostic systems automatically calculate and display the pressure indices at each measured location.  

Is a PVR Machine the Same as an ABI Machine?

The term PVR machine is frequently used to describe the standard ABI machine. PVR measurements are important for the proper vascular diagnosis of patients. Therefore, many use the term PVR machine or PVR system to describe the complete physiologic device.

What is the Price of an ABI Machine?

The price of a good ABI machine that is capable of a complete vascular physiologic examination is between 20k and 50k USD.
Typically, the price depends on many factors, including the number of pneumatic pressure channels and the supportive accessories and sensors such as the Doppler probes, PPG sensors, and a skin temperature sensor. The price also depends on the country in which it is sold due to various local conditions.

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