What Is Pulse Volume Recording

Introduction

A Pulse Volume Recording (PVR) is an external exam used by doctors to assess the blood flow in your arms or legs.¹ You may know PVRs by another name, such as arterial duplex, arterial Doppler, segmental pressure study or pulse volume plethysmography. The test is non-invasive, meaning there are no instruments protruding into the body and uses common and easily accessible equipment to form a qualitative result. The product, viewed as a waveform (a curve which shows how a variable, in this case, the artery/blood, moves along time), can aid in the diagnosis of a variety of conditions, along with assessing the progress of treatments and healing after amputations.2 Since being developed in the 1970s by Raines et al. at the University of Michigan,³ it has been used across the globe, most commonly to diagnose peripheral artery disease (PAD), a form of cardiovascular disease.

Basics of PVR

Although PVRs can give stand-alone results, meaning no further testing is required, they are often used in conjunction with the ABI (ankle-brachial index) and plethysmography to evaluate the change in blood flow through different limbs. The equipment includes:

• Blood-pressure cuffs – multiple cuffs are placed at intervals along the limb (not overlapping).
• Transducer – a handheld object which emits ultrasound waves (very high-frequency sound waves) which travel through the body until they are reflected back by different materials, such as the artery walls.
• Oscilloscope – measures and records incoming reflected ultrasound waves and translates them into a waveform depicting the change in distance between the artery and the skin. Usually, just the shape of the curve is needed (qualitative results), but it can also produce quantitative results (measurements).
• Ultrasound gel – reduces the gap in the quality of a material called refractive index, n_i, between the skin and air due to it having a value in between. The lower the difference in n_i values the more ultrasound waves enter the skin, producing a more accurate reading on the oscilloscope.

The waves reflecting off different surfaces allow calculations of the distance between the edge of the body, i.e., the skin, and body parts such as bones, organs and veins. Your heart causes arteries to stretch a little as it beats when the blood is pushed around your body, which is shown in the results from the transducer as well as the blood pressure values. In fact, the two numbers in blood pressure signify these: the lower number is your blood pressure when your heart is resting (diastolic), and the higher number is your blood pressure when your heart beats (systolic).⁴ This transducer/cuff combination thus enables the doctor to gain an insight into the volume of blood and the rate of blood-flow in your arteries. 

Procedure

Initially, blood pressure cuffs are secured around the limb in question at segmental intervals, for example, around the thigh, calf and ankle. They should feel tight before inflation and will be partially inflated to enable accurate measurements of the changing pressure. The ultrasound gel will then be spread over all areas the transducer will cover and, when the cuffs have been inflated, the doctor will move the transducer at intervals down your limb. By measuring at different points of the limb, the doctor gains a clear picture of how the pressure and rate of flow change through the artery. In some cases, the separate cuffs are inflated at different intervals, only when the transducer is being operated ‘down-stream’, or below, the specific cuff. PVR tests usually take between 30 and 60 minutes. 

The difference between blood pressure and volume as you move down the limb is indicative of whether there is any obstruction or thinning of the arteries, known as artery stenosis. For different types of PVR test, you will be in different positions: you may be sitting up, lying down, or even walking on a treadmill depending on what the PVR is referencing. For example, an exercise stress test⁵ is utilised with PVR to assess the leg arteries when people experience unexplained leg pain during exercise. 

Interpretation of results

Analysis of the waveform produced includes how far apart the peaks are and the shape they make on the screen. The rise, fall and peak of the curve should illustrate the dicrotic, or double, heartbeat. For example, a condition such as an artery disease can be recognised by the peak of the curve becoming less sharp. It will also get lower, as well as the double beat becoming less pronounced, making the beats difficult to separate. Often, when used with the ABI, PVRs will assess the difference between blood pressures in the wrists and ankles. Ideally, there should be no difference, so that when the result from your ankle is divided by the result from your wrist you should get a value of 1. If the result is less than 1, meaning your ankle has a lower blood pressure, it signifies the presence of PAD and thus does not usually require further testing. If you have symptoms of PAD but your ankle and wrist have equal blood pressures, further testing is required which includes PVR testing of the lower extremity (leg).

Clinical significance

While PVRs have many applications, they are most frequently used to detect blocked arteries caused by PAD. The difference in blood flow as the scanner moves down the limb, otherwise known as the extremity, can suggest a blockage or narrowing of the artery, usually in the legs. This is caused by a build-up of fatty deposits, or atheroma, along the artery’s walls, restricting the flow of blood. 

PVRs are commonly used for intraoperative monitoring, monitoring during surgery or operations. This can inform the surgeon as to how the patient is responding to the procedure and alert them if there is an issue.³

PVRs can be used to help diagnose and assess a range of conditions other than PAD, such as diabetes and Raynaud’s syndrome. To evaluate Raynaud’s, the PVRs are used to assess the blood flow, or lack of flow, to the extremities. Diabetes can lead to a narrowing or hardening of the arteries, both of which can be evaluated using PVRs. 

Advantages of PVR

Due to the non-invasive nature of the test, there is no aftercare needed. Your doctor may ask you to stop taking medicine in the lead-up to your PVR, such as medications affecting blood pressure, but no other preparation is necessary. This is advantageous as it can be performed with little warning and little-to-no special adjustments are needed. It also makes PVRs very cost-effective, helped by only a small amount of equipment being needed which does not include medication, all of which are standard things to be found in a hospital. They are not, however, items always found in a standard doctor’s office such as a GP clinic, and sometimes require referral to a clinic or hospital. 

One major advantage of PVRs is the lack of effect that vascular calcification has on the results. This is when deposits of minerals build up in veins, usually due to ageing or infections and often resulting in kidney stones. The unaltered result is what sets OVRs aside from other non-invasive methods of diagnosis, which are sensitive to solid articles remaining in arteries. 

Limitations and considerations of PVR

Due to the non-invasive nature of PVRs they are not able to exactly pinpoint the region of interest – where there is a thinning or breakage in the artery. Further, they cannot characterise the severity of the damage if any is found. This can result in further tests being required to find cures or solutions to the issues, such as PET scans. These are invasive tests and require preparation and aftercare to ensure no radioactive damage is done. 

It is also difficult for the scans to be completed continuously through an operation, leading to the current development of a monitoring implant. This would assess the blood flow through the arteries by being inserted to wrap around an artery in the arm or leg, providing long-term results. However, in studies and trials, when removed the implant caused damage to the artery, wholly refuting the point of the results. This technology is still undergoing research and will not be available for wider use in the next few years. 

Summary

PVRs are an excellent tool in the field of vascular disease, having many applications and functions. It is a simple and reasonably quick assessment, requiring little from any patient, and is widely accessible. Due to its resistance to vascular calcification becoming a variable, it is often a go-to for conditions such as diabetes and PAD. However, in the near future it may quickly become outdated as the technologies of implanted devices become more advanced.