Manual of Vascular Medicine

By Marie Gerhard-Herman and Aaron Aday

This practical manual makes clinical vascular medicine easy for the health care provider to master by providing frameworks for each area of diagnosis and a practical approach to necessary testing.  Rather than providing long lists of possible diagnoses for a clinical question, each approach is broken down into a flow chart of the thinking and questions necessary so that only those needed in each situation are utilized. Chapters cover a broad range of topics including arterial and venous testing in the laboratory, thrombophilia, cold disorders of the extremities and lymphatic diseases. 

Manual of Vascular Medicine provides extensive case-based learning for trainees and practicing physicians looking to expand their knowledge in this field that crosses many traditional disciplines. It is therefore of importance to any medical professional managing vascular patients, including cardiovascular and vascular physicians, nephrologists, neurologists, phlebologists, dermatologists, general medical doctors and vascular radiologists.

 

• Language: English
• Publisher: Springer
• Release date: Jun 29, 2020
• ISBN: 9783030447151

Book preview

© Springer Nature Switzerland AG 2020

M. Gerhard-Herman, A. AdayManual of Vascular Medicinehttps://doi.org/10.1007/978-3-030-44715-1_1

1. Noninvasive Vascular Testing

Marie Gerhard-Herman¹   and Aaron Aday²  

(1)

Brigham and Women’s Hospital, Harvard University, Boston, MA, USA

(2)

Vanderbilt University Medical Center, Nashville, TN, USA

Marie Gerhard-Herman (Corresponding author)

Email: [e-mail]

Aaron Aday

Email: [e-mail]

Keywords

WaveformUltrasoundPhysiologic testingMagnetic resonanceComputed tomographyAngiography

Objective

Understand what type of testing is most likely to answer the vascular question.

Vignette

A 50 year old female yoga instructor with history of polymyalgia rheumatica presents with bilateral thigh and calf ache with exertion that goes away with rest.

Physiologic Testing

Techniques of acquisition in physiological testing include segmental pressure measurements, pulse volume recordings (PVRs), continuous wave (CW) Doppler, plethysmography, exercise testing, transcutaneous oximetry, laser Doppler and skin perfusion pressure. One of the most common tests is the ankle-brachial index (ABI), which is used to detect peripheral artery disease (PAD). This test uses sphygmomanometric cuffs, Doppler instruments, and plethysmographic recording devices [1]. After the patient rests for 10 minutes in the supine position, the systolic blood pressure is first measured using a continuous wave Doppler probe and pneumatic cuff in both brachial arteries at rest. The ankle pressure is then measured in both dorsalis pedis and posterior tibial arteries above the medial malleolusafterinflating the cuff to 30 mmHg above the brachial pressure or until the pulse is no longer detectable by Doppler. The ABIs for each extremity are calculated by dividing each of the ankle pressures by the higher of the brachial artery pressures [2]. A normal ABI is between 1.0 and 1.4, whereas an ABI > 0.9 to 1.0 is borderline abnormal. An ABI > 0.90 is considered diagnostic of PAD. An ABI ≥ 1.4 suggests vessels could not be reliably compressed which is often due to vascular calcification artifact and makes interpretation of the pressure measurement unreliable.

The shape of the arterial waveform is evaluated the same way throughout the arterial system (Fig. 1.1). Waveforms are obtained using plethysmography with the cuff inflated to venous occlusive pressure, typically no more than 65 mm Hg. The change in volume in the limb segment throughout the cardiac cycle causes a corresponding change in pressure in the cuff. Pulse waveforms can also be obtained using photoplethysmography, which records reflected infrared light. Waveforms are unaffected by incompressible arteries, and this technique can be useful in individuals with advanced calcific lower extremity arterial disease. Transcutaneous oximetry uses the variations in color absorbance of oxygenated and deoxygenated hemoglobin to determine the blood oxygenation [3]. Normal limb oximetry should be the same in the limb and in the chest. Laser Doppler is another option depends on the light that is scattered from moving blood cells for single point perfusion monitoring.

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Figure 1.1

Criteria for normal to abnormal waveform shape

Because the ABI uses pressure measurements at the ankle, it integrates flow disturbances in all segments of the limb arterial bed. However, in many cases it is also useful to detect the anatomic level at which these disturbances occur, particularly in individuals with a history of lower extremity arterial intervention. This can be achieved in a non-invasive manner with segmental Doppler pressure (SDP) measurements, which use the same principles of the ABI to compare limb pressures at the proximal thigh, distal thigh, calf, and ankle levels to the higher of the two brachial artery pressures (Fig. 1.2). Pressure decrements between levels indicate disease between cuff levels.

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Figure 1.2

Segmental Doppler pressure and pulse volume recording. In this physiologic study the pressure at each level of the legs is seen in the box. Thigh systolic pressure cannot be accurately determined due to compressibility artifact, seen as pressure > 220 mmHg. There is a drop in pressure between the upper and lower calves; this indicates infrapopliteal stenoses are present. The bilateral ankle brachial index (ABI) less than 0.90 is diagnostic of peripheral artery disease. The pulse volume waveforms are seen at each level in the right and left column. The waveforms widen and amplitude decreases in the infrapopliteal region, consistent with obstructive disease

Exercise testing can be used to clarify whether leg symptoms are related to PAD [4]. Ankle pressures are taken before and after exercise. The ankle pressures are obtained starting with the symptomatic leg, followed by the highest brachial pressure. A decrease in ABI to < 0.90 or decrease in ABI of more than 20% immediately following exercise is diagnostic for PAD.

Ultrasound

Images are acquired through sending and receiving sound wave bundles known as pulses. The ultrasound transducer frequency determines the ideal depth of imaging [5]. Higher frequencies are superior for more superficial structure and low frequencies are ideal for deep structure. The structure of interest should be perpendicular to the ultrasound beam to obtain the brightest image. This is readily achieved in vascular imaging because the neck, extremity, and visceral vessels generally lie parallel to the surface of the skin. Unfortunately, dense objects, such as plaque with calcium deposits, do not permit sound waves to penetrate and cause acoustic shadowing [6].

Vascular ultrasonography evaluates flow velocity using Doppler shift frequencies by insonating the vessel at an angle that is 30–60° to flow (Fig. 1.3). The returning frequency will shift, either positively or negatively, depending on the direction of blood flow. The concentric or laminar blood flow is disturbed at branching points or in the presence of abnormal walls. The spectral waveform provides information about flow at the site of interrogation as well as proximal and distal to that site (Fig. 1.4). The frequency shift data can also be displayed as color Doppler, and aliasing occurs at the site of stenosis when the flow velocity exceeds the Nyquist limit (i.e., when the Doppler frequency shift exceeds one half the pulse repetition frequency). Color aliasing occurs at the site of stenosis when the flow velocity exceeds the Nyquist limit (i.e., when the Doppler frequency shift exceeds one half the pulse repetition frequency).

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Figure 1.3

Doppler angle used to determine flow velocity. B mode gray scale imaging is obtained with transducer perpendicular to the blood vessel. The insonation beam angles away from 90 degrees in order to obtain velocity. The standard is an angle of 60° between the insonation beam and the blood flow channel. Components of the Doppler equation given in the picture are: Fd = Doppler shift, Fo = Carrier frequency, V = Blood flow velocity, c = Speed of sound

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Figure 1.4

Spectral Waveform Proximal and Distal to Arterial Stenosis. Spectral waveform (A) is first obtained proximal to a stenosis. There is a mild delay in upstroke suggesting more proximal disease. Peak systolic velocity is normal at 50 cm/s (B1). Peak systolic velocity increases at the site of stenosis to 350 cm/s. this indicates high grade stenosis at