FAQ

We have collected the following information with great care. Some statements are in fact new scientific insights or observations based on practice for which adequate scientific publications do not yet exist. This means that we cannot guarantee the correctness of any of the information.

What is the difference between arteriosclerosis and atherosclerosis?

Unfortunately, in the German-speaking countries both terms are used very simplistically and are in some sources even misused.

Correctly shown in the following illustration: arteriosclerosis (literally, hardening of the arteries) is the generic term for a number of arterial disease, due to wall thickening with consequence of a hardening of the arterial wall with loss of elasticity and lumen narrowing. Strictly speaking, this term includes three different disease forms:

  • The most important form is atherosclerosis, characterized by lipid deposition and formation of fibrous plaques in the intima. In German-speaking countries, a semantic separation of the terms "atherosclerosis" and "arteriosclerosis" is unfortunately not carried out consistently, so that they are often used interchangeably.
  • The medial calcific sclerosis of type Monckeberg with much less clinical significance, characterized by calcium deposits in the media of medium size arteries (persons older than 50 years), often with secondary ossification
  • Arteriosclerosis / hyalinosis, a disease of the small arteries and arterioles, which is usually associated with hypertension and diabetes mellitus.

Source: W. Böcker, Pathologie, Elsevier, Urban & Fischer Verlag, 2008.

What is the ABI?

 

The Ankle Brachial Index (ABI), also referred to as the Ankle-Brachial Pressure Index (ABPI), is the ratio of the blood pressure in the lower legs to the blood pressure in the arms. Compared to the arm, lower blood pressure in the leg is a symptom of blocked arteries (peripheral vascular disease). The ABI is calculated by dividing the systolic blood pressure in the arteries at the ankle and foot by the higher of the two systolic blood pressures in the arms.

Source: http://en.wikipedia.org/wiki/Ankle-Brachial_Index

VascAssist calculates the ABI according to the following algorithm:
right ABI = systolic blood pressure of right ankle / higher of the two arm systolic pressures
left ABI = systolic blood pressure of left ankle / higher of the two arm systolic pressures.

What is the PWV?

The Pulse Wave Velocity is the speed at which the pressure wave travels through the arteries of an organism. This velocity is higher than the speed at which the blood flows.
Because of differences in the wall structure of the arteries the pulse wave velocity varies. In the aorta, because of the elasticity of this blood vessel, the velocity is between 4 and 6 m/S. In the periphery, for example in the limbs, because of the relatively rigid vessel walls (elasticity module), and the smaller lumina with at the same time increased wall thickness, it rises to values between 8 and 12 m/s. In the course of physical modifications due to aging mainly in elastic arteries such as the aorta, elastic connective tissue is replaced by collagen connective tissue. This process results in a raised pulse wave velocity. Pulse wave velocity is also increased in the clinical picture of arteriosclerosis due to the accretion of substances on the walls of the blood vessels with resulting loss of elasticity.
Because of the changes in the vascular system associated with pathological values the measurement of pulse wave velocity can among other things enable statements to be made about mortality by e.g. diabetes mellitus or terminal renal insufficiency and can generally help in the assessment of cardiovascular risk factors.

How does Vascassist work?

See Technology/Principle of operation

What influences ABI and PWV?

ABI is influenced by the pressure drop between heart and ankle arteries. The greater this pressure drop is, the smaller the ABI. As a rule the pressure drop results from atherosclerotic changes, which is why ABI indicates relatively specifically vascular damage of this kind.

In the aorta, because of the elasticity of this blood vessel, the velocity is between 4 and 6 m/S. In the periphery, for example in the limbs, because of the relatively rigid vessel walls (elasticity module), and the smaller lumina with at the same time increased wall thickness, it rises to values between 8 and 12 m/s. In the course of physical modifications due to aging mainly in elastic arteries such as the aorta, elastic connective tissue is replaced by collagen connective tissue. This process results in a raised pulse wave velocity. Pulse wave velocity is also increased in the clinical picture of arteriosclerosis due to the accretion of substances on the walls of the blood vessels with resulting loss of elasticity. 

Are special skills needed to carry out a measurement?

VascAssist is distinguished for its simple and easily learnable operation. Four blood pressure cuffs are applied and pressing a button starts the measurement. In contrast, conventional determination of ABI using an ultrasonic probe requires a high level of experience and knowledge of the anatomy.

Can VascAssist be used on anyone?

Children are excluded from measurements with VascAssist. Otherwise the same restrictions apply as for the measurement of blood pressure. VascAssist’s algorithms are especially designed to deliver reliable and reproducible ABI and baPWV values even in the case of arrhythmias, such as for example extrasystoles. However this does not apply to artifacts caused by movement, to spasms, tremors and extreme arrhythmias. The following list shows generally valid contraindications for the use of a fully automated oscillometric arm and ankle measurement. This is only a selection. The ultimate decision about the suitability of VascAssist for use on a particular patient is at the discretion of the responsible physician.

  • Heart-lung machine
  • Venous or arterial vessel access
  • Circulation complications (e.g. shock, tachycardia >240/min)
  • Convulsions
  • Paresis, paraplegia
  • Lymph edema
  • Mamma amputation with removal of the axillary lymph nodes
  • Venous or arterial vessel access
  • Shunt (E.g. dialysis)
  • Skin lesions/wounds at the measurement points

How are the measurement results displayed?

VascAssist itself displays the parameters ABI value left/right and baPWV left/right numerically directly after measurement. The blood pressure values of each of the four limbs are shown clearly on VascAssist’s display.
With the optional VascViewer software more extensive analyses and reports of the results are available to you: see Interpretation of measurement results.

Are the measurement results reproducible?

The human body exhibits physiological fluctuations and the measurement method and technology itself have ranges of tolerance that make exact reproduction of the measurements impossible. Nevertheless in your measurement routine you will find that these inexactitudes have no influence on the diagnostic result. An analyzable trend of the two measurement results ABI and PWV values allow conclusions about vascular damage to be drawn with high accuracy and make VascAssist an indispensable instrument for screening and for early diagnosis of atherosclerosis.

To what extent can the vascular status be judged on the basis of ABI and PWV?

ABI is a relatively reliable parameter for the recognition of PAOD. Reproducible ABI values < 0.95 indicate at least 50% stenosis; reproducible ABI values > 1.39 indicate sclerosis of the tunica media.

The theoretical statement for PWV is: the stiffer the vessels, the higher the pulse wave velocity. However if stenosis is present because of PAOD there can be a reactive dilation of the remaining vessels, which under some circumstances can lead to a reduction of PWV.

One distinctive feature results from VascAssist measurement algorithm: If PWV is calculated based on the troughs of the pulse waves these cannot always be reliably determined. It is therefore more reliable to use the statistically calculated intervals of the pulse wave upward slopes for the PWV calculation. In the case of a pronounced PAOD the pulse waves are increasingly flattened, the distances between the pulse waves are therefore arithmetically larger and the pulse wave velocity arithmetically less. In this case the reduction of the pulse wave velocity measured by VascAssist correlates with the degree of PAOD.

There is an important observation that can be made in connection with VascAssist, particularly when the optional software tool VascViewer is used for analysis: even with ABI values that are still unremarkable, patients for whom PAOD is beginning show conspicuous drops in baPWV. This makes VascAssist a precise diagnostic tool for early diagnosis of PAOD.

What are the standard values for ABI and PWV?

Reproducible ABI values < 0.95 indicate at least 50% stenosis, reproducible ABI values > 1.39 indicate sclerosis of the tunica media.

The standard values for baPWV are heavily dependent on age, blood pressure and gender. Please refer to the VascAssist manual for the necessary information. It includes the relevant nomograms. In VascViewer, the optional analysis software for VascAssist, measurement values are displayed in relation to the standard values.

Our patient couch has a fixed slope of ca. 45%. Is that satisfactory?

Unfortunately not. This would lead to incorrectly increased ankle pressures. Without fail before the measurement the patient should be placed in a horizontal position for ca. 10 min. Measurements on sitting or standing patients deliver false results as well.

The ABI values of our test measurements are unusually high (>= 1.4). Is that normal?

Reproducible ABI values ≥ 1.4 are not normal. There are several possible causes for this situation:

  1. Changes in the vessel structure related to sclerosis of the tunica media.
  2. It is possible that during a demonstration of the equipment measurements were performed on a sitting or standing proband. In this case the hydrostatic pressure relationships are modified, so that the resulting ABI values can no longer be assessed on the basis of recognized, diagnostic thresholds. Also any nervousness because of the medical situation should have subsided. For diagnostic purposes we therefore recommend that two or three ABI measurements be performed after the proband has been lying in a horizontal position for ca. 10 min.
  3. Blood pressure cuffs of an incorrect size were used. (Please refer to the size information printed on the cuffs.)

What is the added value of the baPWV measurement and how can I recognize whether baPWV values are pathological?

The baPWV measurement (brachial ankle Pulse Wave Velocity) can deliver additional input for a diagnosis of PAOD, especially e.g. in cases of diabetes, renal insufficiency or coronary heart disease. In this connection, first of all and dependent on age and blood pressure, the baPWV to be expected is determined (see nomograms), if relevant using external software. BaPWV values which are reproducible and more than ca. 25% above or below this expected value can indicate arteriosclerotic changes. BaPWV body side differences with a reproducible ratio of  >= 1.25 can also frequently indicate arteriosclerotic changes. When interpreting baPWV measurement results it should be considered that there is a systematic difference between pulse wave velocities at various measurement points. So for example the baPWV (brachial ankle PWV) and aoPWV (PWV in the aorta) are approximately related to each other on average by baPWV = 1,2 x aoPWV + 2,5 [m/s].

The baPWV is often confused with the aortic pulse wave velocities (e.g. aoPWV, cfPWV, hfPWV). However in the baPWV measurement the legs are included, which are more frequently affected by PAOD. Even if this understanding has not yet found its way into the worldwide-recognized standards for evaluation of PAOD to the same extent as ABI, there is every indication that similarly sensitive diagnoses are possible using these criteria as for the measurement of ABI, and in individual cases even before the ABI becomes pathological. The baPWV always delivers valuable additional information, above all in cases of doubt when the ABI values lie in the diagnostic borderline area.

With the help of the VascViewer software an even clearer graphical representation in diagram form of one pair or of several ABI and baPWV measurements can be given. When determining both ABI and baPWV we strongly recommend that at least two, better three, measurement are performed. This should ensure that effects such as nervousness in the medical situation or physiological blood pressure fluctuations are excluded as far as possible.

Can’t the equipment detect when I assign the same Patient ID twice?

As it is basically possible to carry out multiple measurements on the same patient on one or on successive treatment days, the responsibility for the input of the correct Patient ID lies with the user. VascAssist cannot "know" whether the same patient is to be measured again or whether there has been an input mistake.

What happens when I attach the blood pressure cuffs the wrong way round despite the clear labels?

It is often possible to derive the side on which limbs are affected by arteriosclerotic changes from the side on which pathological ABI or baPWV values occur. Exchanging right for left would lead to the corresponding incorrect interpretation. This would however be detected in the course of the confirmation using imaging that is mandatory before medical intervention. The exchange of arm and ankle blood pressure cuffs could be more disadvantageous as this could lead to false-positive or false-negative results. However, because of the conical form of the ankle cuffs, a practiced user quickly detects a swap of arm and ankle cuffs.

Shouldn’t there really be an "official" briefing?

For Germany:
The obligation to have a briefing and an initial on-the-spot functional test exists only for products within the scope of MPBetreibV, Attachment 1. This does not apply to the PAOD monitor VascAssist.

For other countries:
Please refer to your regional laws for medical products.

What maintenance activities are necessary?

The necessary maintenance activities can be found in the Users Handbook. On inquiry you can also receive detailed instructions from us. As a rule it is a matter of metrological controls and of technical safety controls every two years and after repair activities.

Please refer to your regional laws for medical products.

Which blood vessels is the pressure taken from when the ankle measurement is performed?

The ankle cuff detects the blood vessel with the higher pressure; this is either the Arteria tibialis posterior or the Arteria dorsalis pedis.
Because of the measuring principle it is not possible to show the pressures of both blood vessels at the same time.

How should the ankle cuff be positioned?

The ankle cuff should be positioned above the ankle as far from the body as possible, with the marking placed over the artery Arteria tibialis posterior.

Fußmanschette
Why should the screening for early detection of PAD be done with VascAssist instead of the conventional Doppler determination of ABI?

Both measurement methods are suitable for the determination of the ABI. With VascAssist however, there are some advantages:

  • The determination of the ankle pressure by Doppler requires a lot of user experience. The results may therefore include an element of subjectivity. A measurement device such as VascAssist provides a standardized method of measurement, however, with good reproducibility.
  • A fully automatic measuring device helps to save valuable time, since the actual measurement can be performed independently. The operation and use of VascAssist can thus be easily delegated to assistants.
  • VascAssist determines ABI for both halves of the body in one measurement, so you have additional time savings.
  • With its oszillometric method VascAssist records all the arteries of the leg equally. The pressure determination with the manual Doppler covers only individual vessels. In this way, the Doppler method can create a false picture of the stenotic situation. For a non-specific assessment of the entire vascular status in terms of screening VascAssist is therefore better.
  • With VascAssist you have a further parameter to differentiate the diagnostic accuracy for POAD and for arterial stiffness: the pulse wave velocity.
  • The recording, storing and processing of results together with the pulse pressure values leads to an improvement in terms of quality assurance. Transmission errors caused by manual, handwritten reading documentation of measurements can be avoided.

When I compare the ABI results between VascAssist and Doppler measurements, I can see differences. Why is that?

Those are different methods of measurement, which should, in principle, deliver the same value. Nevertheless, there are reasons for differences:

  • Doppler measurement determines the pressure in a single artery, while the oscillometric method with VascAssist refers to all the arteries of the leg at ankle level. If you select a non-stenotic artery for Doppler measurement and the others are stenotic then the measurement values are different.
  • Physiological changes in the reading of successive measurements. Even pure blood pressure measurements, performed several times, are not fully reproducible.
  • Small measurement error in either process can at worst lead to obvious differences.