what does elevated peak systolic velocity mean

Introduction. Ability to use duplex US to quantify internal carotid stenoses: fact or fiction? Peak systolic or maximum intra-aneurysmal hemodynamic condition The ICA and ECA can be distinguished by the low-resistance waveforms (higher diastolic flow) in the ICA as compared with the high-resistance waveforms in the ECA (lower diastolic flow) ( Fig. At the time the article was last revised Bahman Rasuli had no recorded disclosures. Angiography, performed on the basis of the patients clinical history, has been the definitive diagnostic procedure to identify significant vertebrobasilar obstructive lesions. N 26 . Up to 20% to 30% of transient ischemic attacks and strokes may be due to disease of the posterior (vertebrobasilar) circulation. Radiopaedia.org, the wiki-based collaborative Radiology resource ESC Scientific Document Group, 2017. [14] In case of discordant grading, after verification of potential error measurements, calcium scoring should be performed as the first-line test. Research grants from Edwards and Abbott. severity based on measurement of peak and mean systolic velocities and shunt , quantification (eg, pulmonary artery flow volume (Qp) to ascending aortic flow volume (systemic flow or Qs) to provide . Transthoracic echocardiography cannot help you solve the problem of AS severity in most cases of discordant grading. Your measurement is Multiples of Median The risk of anemia is highest in fetuses with a pre-transfusion peak systolic velocity of 1.5 times the median or higher. The important points discussed in the present paper can be summarised as follows: Discordant grading is common in clinical practice. The proposed threshold of 35 ml/m is now widely accepted, even if its validation has never been carried out properly. It would therefore seem logical to begin the duplex ultrasound examination in this segment. It can identify a significantly elevated velocity in the proximal subclavian artery (i.e., >300 cm/s), as well as a. what does elevated peak systolic velocity mean Otherwise, the findings must be regarded as suggestive of hemodynamic significance, and confirmation must be sought with other imaging approaches. {"url":"/signup-modal-props.json?lang=us"}, O'Shea P, Rasuli B, Hacking C, et al. A dampened Doppler waveform (parvus: low velocity and tardus: decreased upstroke ) indicates, with a reasonable degree of certainty, that the lesion is severe enough to have hemodynamic significance ( Fig. The two values do typically correlate well with each other. Methods Peak systolic velocity (Doppler ultrasound). Modified from Grant EG, Benson CB, Moneta GL, etal. Flow velocity . Can you tell me what this could possibly mean? However, the standard deviations around each of these average velocity values are quite large, suggesting that Doppler velocity measurements cannot predict the exact degree of vessel narrowing ( Fig. This study will define the optimal Doppler-derived peak systolic velocity (PSV) and velocity ratio (VR) to identify >50% lesions in arteriovenous fistulas (AVF) and arteriovenous grafts (AVG). The solution - The second lesion should be sought. Imaging of segment V2 is most easily accomplished by first obtaining a good longitudinal view of the mid common carotid artery (CCA) at the approximate level of the third through fifth cervical vertebrae. The peak-systolic and end-diastolic velocities ranged from 36 to 74 cdsec (mean, 55 cmlsec) and 10 to 25 cdsec (mean, 16 cm/sec), respectively (Table 1). Correct diagnosis is important because endovascular techniques that make it possible to treat proximal vertebral artery lesions, although still being investigated as to their efficacy, may offer symptom relief to some patients. Peak systolic velocity in the right renal artery is 173 and the left is 178. At angles >60o, the cosine function curves much more steeply,leading to a significant reduction in the accuracy of angle correction, and thus the accuracy of blood velocity indices such as PSV and end-diastolic velocity (EDV)1. Normal aortic velocity would be greater than 3.0m/sec (3.0 meters per second), while a normal mean pressure gradient would be from zero to 20mm Hg (20 millimeters of mercury, which is how blood pressure is measured). At the time the article was created Patrick O'Shea had no recorded disclosures. The human cardiovascular system (CVS) undergoes severe haemodynamic alterations when experiencing orthostatic stress [1,2], that is when a subject either stands up, sits or is tilted head-up from supine on a rotating table.Among the most widely observed responses, clinical trials have shown accelerated heart rhythm and reduced circulating blood volume (cardiac output . The SRU panel concluded that elevated PSV in the ICA and the presence of flow-limiting plaque are the primary parameters determining the severity of ICA stenosis. The goal of this study is to determine the impact of 12 weeks of Lp299v supplementation (20 million cfu/day vs. placebo) on exercise capacity, circulating biomarkers of cardiac remodeling, quality of life, and vascular endothelial function in humans with heart failure and reduced ejection fraction (HFrEF) who have evidence of residual inflammation based on an elevated C-reactive protein level. during systole), red blood cells exhibit their greatest magnitude of Doppler shift. Peak systolic velocity (Figure 4) increased with advancing gestational age. Longitudinal gray-scale image of a normal vertebral artery segment (, Color Doppler image from the V2 segment of a normal vertebral artery and vein, with the artery color coded red (flow from right to left, toward the brain) and the vertebral vein color coded blue. 13 (1): 32-34. Peak systolic velocity (PSV) and end-diastolic velocity (EDV) were measured in common and internal carotid artery. This can reflect: (1) occlusion or near occlusion of the ICA; (2) contralateral vertebral artery occlusion; or (3) compensatory blood flow because of a subclavian steal in the contralateral vertebral artery. It can be difficult to determine whether symptoms that arise from carotid artery thromboembolic disease are because of generalized decreased perfusion secondary to high-grade carotid artery or vertebrobasilar artery occlusive disease (or both) or come from other sources such as cardiac disease. The diagnosis of stenotic disease affecting other parts of the carotid system may be clinically important and will also be discussed. Methods: This retrospective analysis includes patients with both DUS and fistulogram within 30 days. [6] Among 1,704 patients with a valve area below 1 cm, 24% presented with discordant grading (AVA <1 cm and MPG <40 mmHg). In contrast, in the SEAS trial [5], the authors considered the discordance between AVA and MPG independently of any flow consideration. In 20%-30% of patients, these parameters are discordant (usually AVA <1 cm and MPG <40 mmHg). There is wide variability in the peak systolic velocities seen in normal patients, with a range of 20 to 60cm/s, with an even wider range noted at the vertebral artery origin (also called segment V0). Mean of maximum cerebral velocity readings are obtained, and results are classified . The ACAS (Asymptomatic Carotid Atherosclerosis Study) also showed a reduction in incident stroke for asymptomatic patients with 60% or more stenotic lesions but, like the moderate range of stenoses in the NACSET, there was only a 5.8% reduction over 5 years. All three parameters are consistent with a 70% or greater stenosis according to the Society of Radiologists in Ultrasound (SRU) consensus criteria. Expected flow velocities - Questions and Answers in MRI At the aortic valve, peak velocities of up to 500 cm/sec may be possible. Among patients with discordant grading (AVA <1 cm and MPG <40 mmHg), those with low flow are much less frequent than those with normal flow. Once this image has been obtained, a slight lateral rocking motion of the probe will bring the vertebral artery into view. Did you know that your browser is out of date? Classification of Patients with an Aortic Valve Area <1 cm (and preserved ejection fraction) into Four Groups according to Mean Pressure Gradient (MPG) and Stroke Volume Index (SVI), Figure 2. Normal doppler spectrum. 2010). Systolic BP of 180 or higher means that you're in hypertensive crisis and should call your healthcare provider right away. revisited an interesting approach to ICA ratio measurements where the ratio of the highest PSV at the site of the stenosis was compared with the normalized velocity in the distal ICA. Leye M., Brochet E., Lepage L., Cueff C., Boutron I., Detaint D., Hyafil F., Lung B., Vahanian A., & Messika-Zeitoun D. de Monchy C. C., Lepage L., Boutron I., Leye M., Detaint D., Hyafil F., Brochet E., Lung B., Vahanian A., & Messika-Zeitoun D. Hachicha Z., Dumesnil J. G., Bogaty P., & Pibarot P. Paradoxical low-flow, low-gradient severe aortic stenosis despite preserved ejection fraction is associated with higher afterload and reduced survival. Ultrasound Assessment of the Vertebral Arteries | Radiology Key , and peak TR velocity > 2.8 m/sec. Arterial duplex is utilized by most centers as a second line of testing. The few available studies on the prevalence and the natural history of vertebral artery atherosclerotic stenosis show that most lesions, 90% or more, occur at the vertebral artery origin. The minimum and maximum flow rates for the temporal window of interest were based on the cycle-averaged mean velocity in the Middle Cerebral Artery (MCA), and the peak systolic flow velocity in the MCA as predicted by a 30% damped older-adult flow waveform (Hoi et al. People with elevated blood pressure are likely to develop high blood pressure unless steps are taken to control the condition. The diagnostic strata proposed by the Consensus Conference of the SRU (0% to 49%, 50% to 69%, and 70% but less than near occlusion) represent practical values that are clinically relevant and consistent with the NASCET. Duplex Ultrasound of the Mesenteric Vessels | Thoracic Key There is no obvious cut point to indicate an ideal threshold. showed that, in most patients, the systolic velocity decreases in the CCA as one goes from proximal to distal within the vessel. Download Citation | . Doppler waveforms can be consistently obtained at both vertebral artery intervertebral segments and the right vertebral origin. Low resistance vessels (e.g. The side-to-side ratio was calculated by dividing contralateral flow parameter by ipsilateral one measured by using carotid ultrasonography. This Doppler waveform gives qualitative information and, once angle corrected, quantitative information on local hemodynamics. Velocity magnitude and wall shear stress (WSS) were calculated during one cardiac cycle. They are usually classified as having severe AS. In one study, PSV and ICA/CCA PSV ratios performed almost identically with regard to the identification of ICA stenoses greater than 70% when compared with angiography ( Fig. Peak Systolic Velocity - an overview | ScienceDirect Topics Sex-Related Discordance Between Aortic Valve Calcification and Hemodynamic Severity of Aortic Stenosis: Is Valvular Fibrosis the Explanation? Not using other views leads to the underestimation of AS severity in 20% or more of patients. The recent recommendation on echocardiographic assessment of AS from the European Association of Cardiovascular Imaging and the American Society of Echocardiography [1] does not provide a definite answer, but underlines the fact that measurement of the LVOT at the annulus level provides higher measurement reproducibility and ensures that diameter and pulse Doppler are measured at the same anatomical level. The ICA Doppler spectrum typically shows a low-resistance pattern. The SRU consensus data represent a compromise between sensitivity and specificity and are based on cut points validated against ACAS/NASCET-based angiographic measurements of stenosis severity ( Table 7.2 ; Figs. 7. The ICA is usually posterior and lateral to the ECA. Specific cut-points based on the arteriographic correlative studies need to use the NASCET/ACAS measurement approach ( Fig. [7] Although attractive, such methodology suffers from important bias. 331 However, these devices are often heavy and uncomfortable to use, with 64% patient discontinuation rates at 2 years 332 Trials among individuals with diabetes showed that vacuum . Subaortic stenosis produces a high-velocity jet and a mean transvalvular pressure gradient (TMPG), and LVOT systolic blood flow disorder forms rich and complex vortex dynamics . Reappraisal of Flow Velocity Ratio in Common Carotid Artery to Predict Left ventricular outflow tract velocity time integral (LVOT VTI) is a measure of cardiac systolic function and cardiac output. Intervention is recommended in symptomatic patients with proven severe AS and low gradient, as for patients with classic severe AS. What's the difference between Peak & Mean Velocity? (A) The approximate locations of the V1 and V2 segments of the vertebral artery are shown. Calculation of the AVA relies on the measurement of three parameters; error measurement may occur in all three. 9.3 ). Unable to process the form. Following the stenosis the turbulent flow may swirl in both directions. Carotid endarterectomy and stenting are also effective in managing symptomatic patients with high-grade carotid stenosis. Similar cut-points had also been validated against angiography and produced a sensitivity of 95.3% and specificity of 84.4%. Ultrasound imaging of the arterial system - AME Publishing Company Discordant grading is defined based upon the observation that one parameter suggests a moderate AS while the other suggests a severe AS. Arterial wave dynamics preservation upon orthostatic stress: a THere will always be a degree of variation. The velocity criteria apply when atherosclerotic plaque is present and their accuracy can be affected by: ICA/CCA PSV ratio measurements may identify patients that for hemodynamic reasons (low cardiac output, tandem lesions, etc. This artery segment is typically quite straight, with minimal tortuosity and does not have any significant diameter changes. Also, examining the waveform is even more important than usual in this case. The peak systolic phase jet flow impacts the aortic valve flaps, leading to harm, scarring, excess flaps, . The patient is supine and the neck is slightly extended with the head turned slightly to the opposite side. The resistive indexes calculated from the peak-systolic and end- Sickle cell disease is a disorder of the blood caused by abnormal hemoglobin which causes distorted (sickled) red blood cells.It is associated with a high risk of stroke, particularly in the early years of childhood. Peak A-wave velocity is normally 0.2 ms/s to 0.35 m/s. Find local offices and events - National Kidney Foundation behavior changes (in children) Get medical help right away, if you have any of the symptoms listed above. Previous studies have shown the importance of internal carotid plaque characterization (see Chapter 6 ). In these circumstances, AVA should be adjusted for BSA, with the threshold being 0.6 cm/m. However, Hua etal. 2023 European Society of Cardiology. Professor David Messika-Zeitoun, Bichat Hospital, 46 rue Henri Huchard, 75018 Paris, France. Kamperidis V., van Rosendael P. J., Katsanos S., van der Kley F., Regeer M., Al Amri I., Sianos G., Marsan N. A., Delgado V., & Bax J. J. Messika-Zeitoun D., Aubry M. C., Detaint D., Bielak L. F., Peyser P. A., Sheedy P. F., Turner S. T., Breen J. F., Scott C., Tajik A. J., & Enriquez-Sarano M. Cueff C., Serfaty J. M., Cimadevilla C., Laissy J P., Himbert D., Tubach F., Duval X., Lung B., Enriquez-Sarano M., Vahanian A., & Messika-Zeitoun D. Aggarwal S. R., Clavel M. A., Messika-Zeitoun D., Cueff C., Malouf J., Araoz P. A., Mankad R., Michelena H., Vahanian A., & Enriquez-Sarano M. Simard L., Cote N., Dagenais F., Mathieu P., Couture C., Trahan S., Bosse Y., Mohammadi S., Page S., Joubert P., & Clavel M. A. Clavel M. A., Messika-Zeitoun D., Pibarot P., Aggarwal S. R., Malouf J., Araoz P. A., Michelena H. I., Cueff C., Larose E., Capoulade R., Vahanian A., & Enriquez-Sarano M. Baumgartner H., Falk V., Bax J. J., De Bonis M., Hamm C., Holm P. J., Lung B., Lancellotti P., Lansac E., Munoz D. R., Rosenhek R., Sjogren J., Tornos Mas P., Vahanian A., Walther T., Wendler O., Windecker S., & Zamorano J. L. Bichat Hospital and University Paris VII, Paris, France; Barts Heart Centre, St. Bartholomews Hospital, West Smithfield, London,United Kingdom. [4] The Mayo Clinic group has provided us with important data regarding the prevalence of the different subsets. Tortuosity also may render angle-corrected Doppler velocity measurements unreliable. Moderate (50% to 69%) internal carotid artery (, Receiver Operating Characteristic (ROC) curves for three Doppler velocity measurements to detect 70% or greater internal carotid artery (ICA) stenosis: peak systolic velocity (PSV =, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), on Ultrasound Assessment of Carotid Stenosis, Ultrasound Assessment of Carotid Stenosis, Carotid Sonography: Protocol and Technical Considerations, Normal Findings and Technical Aspects of Carotid Sonography, Ultrasound Assessment of Lower Extremity Arteries, Ultrasound Assessment of the Vertebral Arteries. Aortic-valve stenosis--from patients at risk to severe valve obstruction. What are the symptoms of a blocked renal artery? PDF Acr-nasci-spr Practice Parameter for The Performance and Interpretation Blood flow velocity waveforms of the fetal pulmonary artery and the Avoiding simple pitfalls such as mitral annular, aortic wall and coronary ostia calcifications, the method is highly reproducible. ESC/EACTS guidelines for the management of valvular heart disease. 9.5 ), using combined gray-scale and color Doppler imaging, to assess blood flow hemodynamics in the proximal artery segment. Graph demonstrating the relationship between average peak systolic velocity (PSV) (y-axis) and percentage luminal narrowing as determined by contrast angiography using, North American Symptomatic Carotid Endarterectomy Trial (NASCET) method of measurement (x-axis). If the diagnosis of severe AS is established (and if the patient is symptomatic), intervention should be promptly considered. To an extent, an increased degree (%occlusion) of stenosis corresponds to increased PSV and EDV 4. The more reliable approach to assessing the vertebral artery is to visualize it near the mid portion of the cervical spine, at the V2 segment of the vertebral artery, as it courses cranially through the foramina to the transverse processes of C 6 to C 2 ( Fig. The majority of stenotic lesions occur in the proximal internal carotid artery (ICA); however, other sites of involvement in the carotid system may or may not contribute to significant neurologic events. Thus, extremely low LVOT VTI may predict heart failure patients at highest risk for mortality. Large, multicenter trials both in North America and Europe confirmed the effectiveness of CEA in preventing stroke in patients with ICA stenoses compared with optimized medical therapy. Peak transmitral flow velocity in late diastole (peak A) was significantly higher, whereas peak transmitral flow velocity in early diastole (peak E), deceleration time (DT), and the ratio of early to late diastolic filling were significantly lower, in TS patients. Prof. David Messika-Zeitoun , On a Doppler waveform, the peak systolic velocity corresponds to each tall "peak" in the spectrum window 1. To get the best experience using our website we recommend that you upgrade to a newer version. The right kidney is 12.2cm in length, the left kidney is 12.3cm. Echocardiographic assessment of the severity of aortic valve stenosis (AS) usually relies on peak velocity, mean pressure gradient (MPG) and aortic valve area (AVA), which should ideally be concordant. In 20%-30% of patients, these parameters are discordant (usually AVA <1 cm and MPG <40 mmHg). In addition, ulcerated plaque that demonstrates a focal depression or break within the plaque is also more prone to plaque rupture and subsequent embolic event ( Fig. The association of carotid atherosclerotic disease with symptomatic cerebrovascular disease (i.e., transient ischemic attacks), amaurosis fugax, and stroke, is well established. The following criteria are associated with at least a 50% diameter stenosis of the vertebral artery: peak systolic velocity above a threshold of between 108 and 140cm/s, depending on the series, more consistent criteria of peak systolic velocity ratio of 2.0 or more in a nontortuous segment. Trials combining CEA with statin therapy started on hospital admission for surgery showed a decrease in neurologic events such as ischemic stroke and decreased mortality after CEA. Peak systolic velocity (PSV)is an index measured in spectral Doppler ultrasound. To assess whether these patients truly present with severe AS, the calcium score should be measured using computed tomography (thresholds are 2,000 AU in males and 1,250 AU in females). This can be quantified using the pulmonary velocity acceleration time (PVAT). A normal sized aorta has a valve area of approximately 3.0cm2 (3.0 centimeters squared) and 4.0cm2. Secondary parameters such as elevated EDV in the ICA and elevated ICA/CCA PSV ratios further support the diagnosis of ICA stenosis. RVSP - Right Ventricular Systolic Pressure MyHeart Aortic valve stenosis: evaluation and management of patients with In stepwise selection of polynomial terms, the linear, quadratic, and cubic correlations of .38, .17, and .22 for N and .45, .24, and .03 for C were found to be significant ( P <.02). Ultrasound diagnosis of vertebral artery origin stenosis is complicated by the frequent occurrence of considerable tortuosity in the proximal 1 to 2cm of the vertebral artery ( Fig. The inferior mesenteric artery has a waveform similar to the superior mesenteric artery with high resistance. Although the so-called NASCET method may not truly reflect the degree of luminal narrowing at the site of stenosis, this method has the advantage of minimizing interobserver error. High flow velocity causes Reynolds number to increase beyond a critical point, resulting in turbulent flow which manifests as spectral broadeningon Doppler ultrasound 3. . Introduction to Vascular Ultrasonography. Visualization of the vertebral artery is easiest in the V2 segment, the segment that extends from vertebral bodies C 6 to C 2 . Blood flow velocity (which is what the test measures) is not exactly constant every time you measure. This is confirmed by a high-velocity measurement made on an angle-corrected Doppler waveform. a. potential and kinetic engr. In the vast majority (21% of the overall population), the flow was normal, while low flow was observed in only 3% of the total population. In addition, the Doppler blood flow velocities should always be compared with the degree of plaque, if present. Usefulness of the right parasternal view and non-imaging continuous-wave Doppler transducer for the evaluation of the severity of aortic stenosis in the modern area. Peak systolic velocities Prior to intervention the PSV ECA in both groups was similar, 161.7 cm/s (CAS) versus 150.9 cm/s (CEA). The first two parameters are directly measured using continuous wave Doppler, while the last one is calculated based on the continuity equation and measurement of the left ventricular outflow tract (LVOT) diameter, LVOT time-velocity integral (TVI) and aortic TVI. In near occlusion (>99%), flow velocity indices become unreliable (may be high, low or absent) 4. . Methods Echocardiographic images were collected and post processed in 227 ACS patients. Elevated Elevated blood pressure is when readings consistently range from 120-129 systolic and less than 80 mm Hg diastolic. Flow velocity may vary based on vessel properties and pathological changes 3,4. RVSP basically is the pressure generated by the right side of the heart when it pumps. For that reason, ICA/CCA PSV ratio measurements may identify patients who, for hemodynamic reasons (e.g., low cardiac output, tandem lesions), have velocities that fall outside the expected norm for either PSV or EDV. doppler ultrasound examination of fetal. Peak Velocity is the highest velocity attained during the same concentric lift phase. Thus, in the rest of the article we will use the MPG. The ratio on the right is 1.6 between the renal artery and the aorta and the left is 1.8. external carotid artery, limb arteries) are characterized by early reversal of diastolic flow, and low or absent EDV 4. 7.7 ). The normal peak systolic velocity (PSV) in peripheral lower limb arteries varies from 45-180 cm/s (30). B., Egstrup K., Kesaniemi Y. Assessment of Upper Extremity Arterial Disease | Radiology Key All rights reserved. As a result of improved high-resolution ultrasound imaging of the carotid arteries with supplemental imaging from MRA or CTA, the role of conventional angiography as a diagnostic technique has significantly decreased. Spectral Doppler image confirms marked velocity elevation: PSV = 581 cm/s, end diastolic velocity ( EDV ) = 181 cm/s, and the PSV ratio is 8.2. Correlation of Peak Systolic Velocity and Angiographic - Stroke When considering an individual patient, the great variation in the PSV and EDV in any population must be taken into consideration. S: peak systolic tissue doppler velocity; PECS: peak endocardial circumferential strain; PWWCS: peak whole . Magnetic resonance angiography (MRA) and computed tomographic angiography (CTA) have shown high accuracy, with duplex ultrasound having moderate accuracy, for the diagnosis of vertebral-basilar disease. In the 1990s, many large, well-controlled, multicenter trials both in North America and Europe confirmed the effectiveness of CEA in preventing stroke in patients with ICA stenoses as compared with optimized medical therapy. However, stenoses in other carotid artery segments such as the distal ICA (an area not typically well seen on routine carotid ultrasound), the common carotid artery (CCA), or the innominate artery (IA) may be equally significant. Jander N., Minners J., Holme I., Gerdts E., Boman K., Brudi P., Chambers J. Aortic Stenosis Grades of Severity as Assessed Using Echocardiography and Computed Tomography (calcium scoring). Intervention is recommended in symptomatic patients with proven severe AS, as in classic severe AS. B., Edvardsen T., Goldstein S., Lancellotti P., LeFevre M., Miller F. Jr., & Otto C.M. John Pellerito, Joseph F. Polak. Patients often present with nonlocalizing symptoms such as blurred vision, ataxia, vertigo, syncope, or generalized extremity weakness. Introduction. David Messika-Zeitoun1, MD, PhD; Guy Lloyd2, MD, FRCP. where they found a ratio of 2.2 to have the best accuracy for stenosis of 50% or more. (C) Magnetic resonance angiogram (MRA) shows a high-grade origin stenosis (, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), on Ultrasound Assessment of the Vertebral Arteries, Ultrasound Assessment of the Vertebral Arteries, Ultrasound Assessment of Lower Extremity Arteries, The Role of Ultrasound in the Management of Cerebrovascular Disease, Anatomy of the Upper and Lower Extremity Arteries, Dizziness or vertigo (accompanied by other symptoms). Elevated velocities can also be found with entities other than significant stenosis such as in young athletes, in high cardiac output states, in vessels supplying arteriovenous fistulas or arterial venous malformations, and in patients with carotid stenting. 15, If the elevated thoracic pressure is maintained, blood pressure will be insufficient to support .