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Efficient PAD diagnosis by automatic measurement of ankle-brachial index and pulse wave velocity.

The ankle-brachial index (ABI) is regarded as extremely reliable indicator of symptomatic and asymptomatic peripheral arterial disease (PAD) and is…

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Simple handling for routine use, also by support personnel.

The great advantage of VascAssist is that it is very simple to handle. This makes it ideal in routine use…

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Significant diagnostic results – reliable early identification of occlusive diseases, also when asymptomatic.

 

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Multiple target audiences and application areas in many areas of medicine, health promotion, research, science and business.

 

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Interpretation of the measurement results

Significant diagnostic results – reliable early identification of occlusive diseases, also when asymptomatic.

The following information was compiled with the greatest care and to our knowledge corresponds with the generally recognized status of medical learning. However, divergent opinion or changes in the accepted school of thought can result in other possibilities of interpretation of the measurements. Error on our part cannot be excluded. For these reasons we cannot take responsibility for the correctness and reliability of any of the information contained in this document. The responsible physician alone is responsible for diagnoses and therapy decisions made on the basis of VascAssist measurement results.
Please use our Forum to discuss your own experience with and opinions about the interpretation of the measurement results. In that way you contribute to the improvement of the diagnostic quality of VascAssist and share your knowledge with many other VascAssist users.

ABI and PWV

With its two measurement procedures for ankle brachial index measurement and pulse wave velocity measurement the VascAssist equipment offers a range of valuable diagnostic possibilities:

  • Measurement of blood pressure on arms and legs. The measurements take place sequentially on the right and then on the left, in each case simultaneously for arm and ankle.
  • Determination of pressure differences between the sides, right arm/left arm and right ankle/left ankle.
  • Determination of the ankle brachial index for right and left, in the following abbreviated to "ABI".
  • Determination of the pulse wave velocity (baPWV = brachial ankle PWV) as an absolute value in m/s, in the following abbreviated to "baPWV" or just "PWV".
  • Display of the pulse pressure curves with the associated PC software VascViewer. Recognition of arrhythmia and deformations of pulse curves caused by stenoses.

ABI and baPWV are two parameters that complement each other ideally and that enable a far-reaching or differential diagnosis regarding atherosclerosis and existing or developing vascular stenosis. To visualize the two parameters in a suitable form a four-quadrant diagram has been developed in which the ABI is entered on the horizontal axis and the PWV on the vertical axis. There are two markers for the ABI and the associated PWV measurements, one for the left ABI/PWV pair and one for the right ABI/PWV pair.

The ABI value measured by VascAssist can be entered directly into the diagram independent of the proband data, while the PWV, as we know, depends on gender, age and blood pressure.  The PWV must therefore first be standardized. The VascViewer software with the connected online service performs this. The algorithm used is based on the results of a large-scale Japanese study [1] and enables the baPWV measurement to be shown as a percent divergence from the corresponding normal values.

The comparability of the data is thus given independent of the proband demography. Only "on the edges", i.e. for probands significantly younger than 30 or more than 70 years old, there can be statistical outliers, so that for healthy young probands very low PWV values may occur that must not be regarded as significant, although they diverge clearly from the norm.

 

The VascViewer measurement protocol

vascvieweren

The VascViewer software measurement protocol uses the four-quadrant representation of ABI and PWV. The yellow markers are for the left and the green markers for the right ABI/PWV pair.

ABI is shown horizontally with a range of values from 0 to 2. The value 0.9 is shown with a vertical dotted line marking the border to assuredly pathological ABI values. In addition both the borderline of 1 to what is assuredly not pathological is marked and also the border to sclerosis of the tunica media (ABI > 1.35).

The PWV divergences from norm are shown vertically with values from -100% to +100%, with 0% divergence from norm as the middle line. The dashed horizontal lines at +15% and –25% are empirical values (representing the normal range) based on about 500 VascAssist measurements taking account of the diagnoses and case histories of the probands.

Each of these limits is of course to be regarded as "soft". Errors of measurement, physiological variation in blood pressure and PWV and also insufficient preparation of the proband can lead to limits being exceeded without it in fact being medically relevant. Therefore to achieve the most exact results possible and to identify measurement errors multiple readings are unavoidable.

The green area, i.e. the area without pathological findings, is limited by the lower ABI value of 1 and the upper value of 1.35 and for the normal divergence of PWV by +15% and –25%.

The red area includes all ABI measurements less than 0.9. Here it is typical that through the vascular stenosis the pulse wave velocity is dramatically reduced, even when the risk anamnesis of the proband would lead one to expect stiffened vessels with high PWV values. A PWV above the norm with ABI < 0.9 almost never occurs, so a marker in the white area is to be regarded as a measurement error.

The transition from the green area to the red area is very interesting for early diagnosis. Here a vascular constriction is often indicated early by a drop in the PWV, sometimes much earlier than the drop of ABI under the value of 1.0.

As not all constellations and connections can be represented in the diagram, in the following section the currently known connections between measurement results (observations) and possible causes are shown in a table.

 

VascAssist – Measurement results: observations, verification and possible causes


Primary observation

Further observations

Verification

Possible causes

1

High blood pressure in arms and legs

ABI and PWV if anything unremarkable

Multiple measurement until the proband is at rest. As measurements are sequential from right to left, initial agitation that has not yet settled can lead to higher blood pressure on the right.

·       Hypertonia

·       Nervousness because of the medical situation

·       State after physical effort

2

Blood pressure side differences in the arms [2]

Differences systolic > 20 mmHg or diastolic > 10 mmHg

Multiple measurement until the proband is at rest.

·       Atherosclerosis

·       Subclavian stenosis in the arm with lowered blood pressure

3

Significant side differences in leg blood pressures

ABI ≥ 1

Multiple measurement until the proband is at rest.

·       Precision of measurement, proband not at rest

4

ABI > 1.35

High blood pressure values in the legs

Proband must lie down as flat as possible

·       Sclerosis of the tunica media, arteriosclerosis

·       Measurement error because proband not horizontal

5

ABI ≥ 1

PWV near norm,

Pulse pressure curve unremarkable

Multiple measurement

·       No PAOD

6

ABI 0,91 – 1

PWV 20% to 40% under norm [4],

Pulse pressure curve flattened for leg in question

Multiple measurement

·       PAOD possibly developing

7

ABI 0,71 – 0,9 [3]

PWV 20% to 60% under norm [4],

Pulse pressure curve flattened for leg in question

Multiple measurement

·         Light PAOD

8

ABI 0,41 – 0,73 [3]

PWV 40% to 60% under norm [4],

Pulse pressure curve severely flattened for leg in question

Multiple measurement

·        Medium PAOD

9

ABI ≤ 0,43 [3]

PWV more than 50% under norm [4],

Pulse pressure curve very severely flattened for leg in question

Multiple measurement

·        Severe PAOD

10

Raised PWV on one or on both sides and in addition ... →

... blood pressure difference between sides in arms, pulse pressure curve for arm flattened

Multiple measurement

·       Subclavian stenosis

11

PWV more than 30% under norm [5]

Pulse pressure curve flattened for leg or legs in question

Multiple measurement

·       Beginning or established stenosis, PAOD

12

PWV more than 20% above norm on both sides, but ... →

... no significantly low or divergent blood pressure(s) in the arms

Multiple measurement

·       General atherosclerosis without stenosis of aorta or legs

13

High PWV difference between sides, one side above norm, other side below norm

ABI > 1, possibly small differences of ABI between sides

Multiple measurement

·       General atherosclerosis
stenosis starting in one leg with low PWV

14

Despite multiple measurement ABI values not reproducible or undeterminable

Very irregular pulse pressure curves

Check that blood pressure cuffs are correctly applied and that cuff size is suitable

·       Heavy cardiac arrhythmia, heavy vascular damage due to advanced atherosclerosis

15

Arrhythmic pulse characteristics in the pulse pressure curve

ABI and/or PWV partly difficult to reproduce

Irregularities present in all four curves (both legs, both arms)

·       Cardiac arrhythmia

 

Sources

[1] Akira YAMASHINA, Hirofumi TOMIYAMA et al. Nomogram of the Relation of Brachial-Ankle Pulse Wave Velocity with Blood Pressure. Hypertens Res Vol. 26, No. 10 (2003): 801-806

[2] Clarc CE and Powell RJ. The differential blood pressure sign in general practice: prevalence and prognostic value. Family Practice 2002; 19: 439-441

[3] Diehm C, Darius H, Pittrow D, Allenberg JR, 2005: Knöchel-Arm-Index. Dtsch. Ärztebl. 102, A 2310-3

[4] VascAssist experience data

[5] Metz D, Beobachtungen über lokale Veränderungen der Pulswellengeschwindigkeit bei peripheren Durchblutungsstörungen: Klinische Wochenschrift, Heft 33/34, Sept. 1954