Figure 87-16. A and B: Normal (A) and “peaked pulse” (B) digital photoplethysmographic (PPG) waveforms. A normal waveform

has a rapid upstroke and a sharp apex whereas an obstructive waveform would demonstrate a delayed upstroke and rounded apex.

In a peaked pulse, waveform suggestive of vasospasm, the dichroitic notch slides to high on the systolic downslope of the

waveform.

Figure 87-17. Device for performance of digital hypothermic challenge or Nielsen test. The cuff on the second finger is used to

cool the test finger and measure digital pressure. This allows controlled application of cold to induce a vasospastic response. The

fourth finger is the reference finger. Strain gauges on the finger tips are used to measure the digital pressures. See text.

UPPER EXTREMITY DUPLEX SCANNING

Duplex scanning of the upper extremity is carried out in a manner similar to arterial examination

elsewhere. The origins of the brachial cephalic vessels can be difficult to visualize with duplex scanning.

For examination of the origin of the subclavian artery a 3- or 5-MHz transducer with a small footprint

probe using the sternal notch as a window generally gives the best images. One study found 48 of 50

right subclavian artery origins (96%) and 25 (50%) of 50 left subclavian artery origins could be

visualized by color duplex scanning.55

Criteria for stenosis at the origins of brachial cephalic arteries are slightly different than those used

elsewhere. A PSV ratio of ≥2 indicates stenosis at the origin of a brachial cephalic artery. Stenosis can

also be implied by monophasic flow without actual visualization of a high-velocity jet and by reverse

flow in a vertebral artery. Such additional criteria are necessary to assess the origins of the

brachiocephalic vessels. If only PSV ratios are utilized there would be higher numbers of both falsepositive and false-negative results.55

More distally the upper extremity arteries are relatively superficial and fairly constant in location.

They are best scanned with a higher-frequency probe such as a 7.5- or 10-MHz probe. Either a sector or

linear scan head may be used, but in either case a standoff or mound of acoustical gel is helpful to

visualize the vessel clearly and to assess the flow pattern within it. Color facilitates identification of the

vessels, and tortuosity of the upper extremity arteries may be more easily seen with color flow imaging.

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Stenosis, occlusions, and aneurysms of upper extremity arteries are all readily identified with ultrasound

(Fig. 87-18A–C).

The interpretation of duplex findings in the upper extremity beyond the origins of the vessels is

similar to the interpretation of B-mode images and Doppler signals gathered in other arterial systems.56

Normal waveforms in the upper extremity arteries are usually triphasic. As elsewhere in the arterial

system, stenosis will produce high-velocity jets, poststenotic turbulence, and dampened distal

waveforms. There are, however, at present no specific frequency or velocity criteria with which to

gauge the severity of stenosis in the upper extremity arteries. Some general guidelines are listed in

Table 87-5. The diagnosis of arterial occlusion is made by imaging the artery and using the pulsed

Doppler to show that there is no flow within the lumen.

Figure 87-18. A: Duplex color flow image and velocity waveform with corresponding angiogram in a patient with brachial artery

stenosis (arrow) and symptomatic arm ischemia secondary to a crutch injury. Note the loss of the end-systolic reverse flow

component of the arterial waveform. B: Duplex image of a right axillary artery occlusion secondary to embolism. Note the

occlusive waveform and reconstitution of the artery via a distal branch vessel (arrow). C: Grayscale image of a small subclavian

artery aneurysm.

Table 87-5 Duplex Ultrasound Criteria for Evaluation of Upper Extremity Arterial

Stenosis

For patients with unilateral symptoms who may have a surgically correctable lesion such as a

subclavian artery aneurysm or stenosis, duplex scanning is quite useful.57 The duplex evaluation of

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aneurysms is based upon the B-mode image appearance, with the most important feature being the size

of the enlarged artery and the presence of intraluminal thrombus that may serve as a source of distal

embolization. Presence or absence of flow within the aneurysm can be determined by the Doppler

component.

Duplex scanning may be of use in patients with suspected embolization to identify proximal

aneurysms, but the evaluation should also include echocardiography to look for mural thrombi and

valvular lesions. While duplex scanning alone cannot be used to make the diagnosis of Takayasu

arteritis, it can be a helpful adjunct in following the progression or regression of arterial involvement in

response to treatment.58

VISCERAL ARTERIES

Mesenteric Arteries

Duplex ultrasonography can serve as a valuable noninvasive screening test for splanchnic artery stenosis

in patients with possible chronic mesenteric ischemia and for follow-up of mesenteric artery

reconstructions. Aneurysms and dissections of the visceral arteries can also be identified (Fig. 87-19).

Despite the accuracy of duplex detection of mesenteric artery stenosis, angiographic confirmation of

high-grade stenosis or occlusion of the splanchnic vessels, and appropriate history and physical

examination are still required for the diagnosis of chronic mesenteric ischemia. The examination is

technically difficult and is best performed by vascular technologists with extensive experience in

intraabdominal ultrasound techniques.

Interpretation of Mesenteric Duplex Ultrasound Studies

In healthy individuals, fasting arterial waveforms differ in the SMA versus the CA. The arterial

waveforms reflect end-organ vascular resistance. The liver and spleen have relatively high constant

metabolic requirements and are therefore low-resistance organs. As a result, CA waveforms are

generally biphasic, with a peak systolic component, no reversal of end-systolic flow, and a relatively

high end-diastolic velocity (EDV). The normal fasting SMA velocity waveform is triphasic, reflecting the

high vascular resistance of the intestinal tract at rest. There is a peak systolic component, often an endsystolic reverse flow component, and a minimal diastolic flow component (Fig. 87-20A).59

Figure 87-19. Grayscale image of a 2.15-cm hepatic artery aneurysm.

Changes in Doppler-derived arterial waveforms in response to feeding are also different in the CA and

SMA. Because the liver and spleen have basically fixed metabolic demands, there is no significant

change in CA velocity waveform after eating. Blood flow in the SMA, however, increases markedly after

a meal, reflecting a marked decrease in intestinal arterial resistance. The postprandial waveform

changes in the SMA include a near doubling of systolic velocity, tripling of the EDV, and loss of endsystolic reversal of blood flow (Fig. 87-20B).60

Postprandial changes are maximal at 45 minutes after ingestion of a test meal and depend on the

composition of the meal ingested. Mixed nutrient composition meals produce the greatest flow increase

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in the SMA when compared with equal caloric meals composed solely of fat, glucose, or protein.61

Detection of Mesenteric Arterial Stenosis

8 Duplex ultrasound can detect hemodynamically significant stenosis in splanchnic vessels. In a blinded

prospective study of 100 patients who underwent mesenteric artery duplex scanning and lateral

aortography, a PSV in the SMA of 275 cm/s or more indicated a ≥70% SMA stenosis with a sensitivity

of 92%, a specificity of 96%, a positive predictive value of 80%, a negative predictive value of 99%,

and an accuracy of 96% (Fig. 87-21). In the same study, a PSV of ≥200 cm/s identified a ≥70%

angiographic celiac artery stenosis with a sensitivity of 87%, a specificity of 80%, a positive predictive

value of 63%, a negative predictive value of 94%, and an accuracy of 82%.62

Other duplex criteria for mesenteric artery stenosis are also in use. An SMA EDV greater than 45 cm/s

correlates with a ≥50% SMA stenosis with a specificity of 92% and a sensitivity of 100%, whereas a CA

EDV of 55 cm/s or greater predicts a ≥50% CA stenosis with a sensitivity of 93%, specificity of 100%,

and accuracy of 95%.63

Surgical revascularization of the mesenteric arteries is a standard treatment for chronic mesenteric

ischemia. Most often bypass grafts are constructed to the superior mesenteric and/or celiac arteries.

Mesenteric artery bypass grafts can be followed postoperatively with mesenteric artery duplex

scanning. Flow velocities within mesenteric artery bypass grafts vary little with the origin of the graft

(supraceliac or infrarenal aorta or a common iliac artery) and remain stable over time. Serially

increasing velocities over time in a mesenteric bypass likely suggest the development of a graft or

anastomotic stenosis.64

Figure 87-20. A: A normal fasting superior mesenteric artery (SMA) waveform may exhibit reverse flow at the end of systole and

relatively low end-diastolic velocity reflecting relatively high resistance of the intestinal circulation in the fasting state. B:

Postprandial SMA waveform. There has been, in comparison to A, loss of end-systolic reverse flow and an increase in end-diastolic

flow as resistance in the intestinal arterial circulation falls following feeding.

Placement of an intraluminal stent is a viable alternative in many cases to surgical bypass, for the

treatment of mesenteric artery stenosis. Similar to the carotid artery (see above), there is reason to

suspect duplex criteria developed for stenosis in native mesenteric arteries may not be applicable

without modification to stented superior mesenteric arteries. Mesenteric duplex scans pre- and

postplacement of a superior mesenteric artery (SMA) stent have been compared and correlated with

pressure gradients measured at the time of angiography. The data indicate that SMA stenting provides

good anatomic results and significantly reduces angiographically measured pressure gradients. Duplex

measured SMA PSVs are reduced poststent placement but, despite good angiographic results, remain in

most cases above criteria predicting high-grade native artery SMA stenosis.65

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Figure 87-21. Color flow image and duplex-derived SMA waveform in a patient with possible chronic mesenteric ischemia. A

peak systolic velocity of >330 cm/s indicates a high-grade SMA stenosis and is compatible with a clinical picture of chronic

mesenteric ischemia.

RENAL ARTERIES

Duplex scanning of the renal arteries is useful in evaluating for renal artery stenosis in patients with

possible renal vascular hypertension and can also be used to detect renal artery aneurysms (Fig. 87-22),

as well as provide a measure of the health of the renal parenchyma.

Indirect Assessment of Renal Artery Stenosis

Indirect methods to assess renal artery stenosis evaluate interlobar arteries. Decreased acceleration

times and/or presence of tardus/parvus waveforms (waveforms with delayed or slowed upstrokes) may

suggest the presence of a main renal artery stenosis. These techniques are quicker and easier to perform

than direct examination of the main renal artery but have been not widely validated. Improved

visualization of main renal arteries with modern duplex scanners has made indirect methods of assessing

the main renal artery essentially obsolete. These techniques are even less accurate in patients with

bilateral stenosis and are not applicable in patients with a single patent renal artery.

Figure 87-22. Grayscale image of a large renal artery aneurysm in the hilum of the kidney.

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Figure 87-23. Renal artery waveform in a patient with severe hypertension. The high peak systolic velocity is compatible with a

high-grade renal artery stenosis.

Direct Assessment of Renal Artery Stenosis

Normal renal arteries have a PSV less than 180 cm/s and low-resistance waveforms reflecting the high

metabolic demands of the kidney. A ratio of the PSV in the renal artery to that in the aorta (renal–aortic

ratio, RAR) of ≥3.5 indicates a ≥60% diameter-reducing renal artery stenosis (84% to 88% sensitivity,

97% to 99% specificity, 94% to 98% positive predictive value) (Fig. 87-23).66 A PSV of ≥200 cm/s has

also been suggested to indicate a ≥60% renal artery stenosis whereas a velocity in the renal artery of

>185 cm/s has been suggested to indicate a less than 60% renal artery stenosis. Therefore a renal

artery can be considered normal when PSV is <180 cm/s and the RAR is <3.5. With a PSV >180 cm/s

and a RAR <3.5, the renal artery can be considered to have a <60% stenosis. RARs of >3.5 indicate

>60% renal artery stenosis regardless if the renal artery PSV is less than or more than 180 cm/s.67

When the EDV exceeds 150 cm/s, data suggest a >80% renal artery stenosis.68 The same criteria have

been used to evaluate the patency of renal arterial reconstructions, but similar to stented carotid and

mesenteric arteries may need modification for stented renal arteries.69

Predicting Success of Renal Artery Interventions

EDVs tend to be lower in patients with renal insufficiency, indicating decreased diastolic flow and

suggesting increased parenchymal resistance to blood flow. Decreased parenchymal diastolic velocities

may therefore suggest renal parenchymal disease (Fig. 87-24). Many patients, 20% to 40%, treated with

renal artery angioplasty and stenting or open surgical reconstructions do not have postprocedure blood

pressure or renal function improvement. An estimate of resistance to flow within the renal parenchyma

can be made by comparisons of EDV and PSVs of renal artery waveforms obtained from renal

parenchymal arteries. The so-called resistive index (RI) is calculated as follows:

RI = [1 - (EDV/PSV)] × 100

In effect a high RI, >0.7 is bad, suggesting renal parenchymal disease whereas a low RI is good,

indicating healthy renal parenchymal tissues. Evaluation of parenchymal resistance has been suggested

as a possible preprocedure predictor of clinical success of renal artery interventions.70 Abnormal

parenchymal resistance may also be a marker of renal allograft dysfunction or rejection (Fig. 87-25).

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Figure 87-24. The absence of end-diastolic flow in the left renal artery indicates severe parenchymal disease of the left kidney.

VENOUS DISEASE

Acute Deep Venous Thrombosis

Physical examination is not sensitive or specific for the detection of acute deep venous thrombosis

(DVT).71 Prior to the acceptance and widespread use of venous duplex scanning, impedance

plethysmography (IPG) was employed as the initial noninvasive test for patients with suspected acute

lower extremity DVT. IPG is a reasonably sensitive (87%) and specific (up to 100%) test for proximal

(above knee) lower extremity DVT in symptomatic patients.72–74 However, lower sensitivities for

proximal DVT (65%) have been reported in studies that exclude clinical outcomes and only report in

comparison to venography. IPG may not detect nonocclusive proximal DVT, occlusive proximal DVT

present in parallel venous systems, such as duplicated femoral or popliteal veins, and cannot detect DVT

isolated to the calf veins.75,76 While IPG is still sometimes used for clinical situations felt to require

serial evaluations of the proximal veins, the limitations noted above make it a substandard examination

for routine clinical assessment of lower extremity DVT.77 Currently, color flow duplex scanning

performed by skilled operators provides the most practical and cost-effective method for assessment of

DVT of the lower and upper extremity veins as well as for detection of thrombosis in superficial veins.

Figure 87-25. There is very little diastolic flow in the renal artery of the transplanted kidney consistent with rejection or primary

allograft dysfunction.

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