Carotid stenosis and plaque formation

The risk of ischemic stroke increases proportionately to the severity of carotid stenosis (Table 6.2), and randomized carotid endarterectomy (CEA) clinical trials have shown that patients with severe carotid stenosis benefit from CEA combined with medical therapy compared to medical therapy alone 20-22 . Since less invasive interventions to prevent stroke such as angioplasty and stenting are emerging 23 , it is extremely important to carefully apply the results of the clinical trials into...

Larger gate shows spectral broadening due to sampling of the nearwall flow

Arrows represent velocity vectors. Faster moving blood is present in the midstream of parabolic flow. determines the so-called compliance flow 5 , During the deceleration phase of systole, the arterial wall moves inward, forcing the layers closer together. This inward movement and crowding of the cell layers causes the cells to move at a narrow range of velocities in the center stream. During diastole, the resting phase of the cardiac cycle with the lowest blood...

Intracranial stenosis

Cranial Stenosis

Middle cerebral artery (MCA) stenosis Primary findings include a focal significant mean flow velocity increase (MFV > 80 cm s), and or peak systolic velocity increase (PSV > 140 cm s), and or inter-hemispheric MFV difference of > 30 cm s in adults free of abnormal circulatory conditions 14,174-185 . A proximal M2-distal Ml MCA stenosis is present if the velocity increase is found at 40-50 mm 186 . A proximal Ml MCA stenosis is usually found at 55-65-mm depths in adults 187 . Chimowitz et...

Arterial bifurcation and flow distribution

Arterial stenosis or occlusion display flow features predicted by the principles governing resistance and velocity only when the lesion is single, short in length and located at segments with no bifurcations. The brain attempts to compensate for arterial lesions by utilizing multiple bifurcations and regulatory mechanisms that redistribute flow around the obstruction. To bring the flow around the lesion, the brain vessels neighboring the obstruction dilate to create a pressure gradient between...

Intrinsic cardiac determinants of blood flow

Cardiac output (CO) is defined as the amount of blood that is pumped by the left ventricle into the aorta each minute. Normally in adults, the volume of blood pumped by the left ventricle each minute is 4-8 L, with an average cardiac output of approximately 5 L min. Cardiac output varies according to body size because of this, cardiac index (CI) is a measure that is used to estimate the proportion of blood flow to body surface area (BSA) Normal values for CI are 2.8-4.2 L min m2 an average CI...

How to read waveforms

Transcranial Ultrasound Waveform

The flow waveform represents time dependence of blood flow velocity on cardiac activity 12 . Waveform recognition during Doppler examination starts with hearing the flow signal followed by visual analysis of the signal appearance on screen. Steps to optimize flow signals depend largely on this immediate recognition of the waveform and sonographer skills. Reading any ultrasound findings starts with orientation on screen and identification of machine settings. For Doppler examination, these...

Arterial vasospasm and hyperemia

Arterial vasospasm is a complication of subarachnoid hemorrhage SAH , which becomes symptomatic in more than 25 of patients leading to a delayed ischemic deficit DID 204 . DID usually occurs when vasospasm results in a severe lt 1 mm intracranial arterial narrowing, producing flow depletion with extremely high velocities 205 , Vasospasm may affect proximal stems and distal branches of intracranial arteries, with the most common locations being the MCA terminal ICA, bilateral ACA and basilar...

Collateral patterns and flow direction

TCD can directly detect the following collateral channels 222-226 1 anterior cross-filling via the anterior communicating artery 2 posterior communicating artery and The intracranial collateral channels are dormant under normal circulatory conditions. A collateral channel opens when a pressure gradient develops between the two anastomosing arterial systems. TCD can detect some of these collateral pathways reversed OA, anterior cross-filling via AComA, and PComA flow either Figure 6.18 A...

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Waveform Catheter

Cardiovascular patient assessment. In Kinney MR, Dunbar SB, Brooks-Brunn JA, Molter N, Vitello-Ciccciu JM, eds. AACN Clinical Reference for Critical Care Nursing, St. Louis Mosby, 277-318. in Table 4.2. Insertion of a CVP line or pulmonary artery PA catheter provides the clinician with an improved ability to directly measure preload parameters in an accurate manner. Because invasive catheters require use of transducers to convert mechanical pressures to...

Subclavian steal syndrome

Subclavian Steal Syndrome

Subclavian steal is a hemodynamic condition of reversed flow in one vertebral artery to compensate for a proximal hemodynamic lesion in the unilateral subclavian artery 289 , Thus, blood flow is diverted or 'stolen' from the brain to feed the arm. Subclavian steal is usually an accidental finding since it rarely produces neurologic symptoms. If the patient is asymptomatic, it is called 'subclavian steal phenomenon' and it usually indicates a widespread atherosclerosis in aortic branches. If...

Relationship between systemic and intracranial hemodynamics

Icp Waveform Interpretation

The brain is metabolically dependent on a continuous supply of oxygen and glucose which are delivered at a Figure 4.9 Intracranial pressure ICP waveform. ICP waveform with respiratory fluctuation note drop in pressure due to decreased cardiac output during inspiratory phase. Unlike thoracic pressures which fluctuate artificially with intrathoracic respiratory pressure changes, measurement at end-expiration is not used in the calculation of ICP, as both Inspiratory and expiratory pressures...

Questions

Transcranial Doppler Image Right Mca

Identify the arteries and brain structures shown in Figure 3.2. Question 2. The change in color assignment of the distal middle cerebral artery MCA flow location 1, Figure 3.2 represents A Aliasing B Range ambiguity C Stenosis D Tortuousity E Reversal Question 3. Figure 3.3 provides keys to vessel identification using transcranial color flow imaging. The appearance of the distal right MCA in a color flow image in Figure 3.3 is likely due to A Range ambiguity B Branching C...

Principles of blood flow

The circulatory system is a closed circuit made up of two major components, the systemic and pulmonary circulation. An understanding of blood flow through these circuits must be supported by discussion of the physical characteristics of blood, and the interrelationship of pressure, resistance and flow. Manipulation of pressure and resistance variables within the cardiovascular system directly affects blood flow parameters, and serves as the basis for clinical hemodynamic augmentation. Blood...

TCD examination technique

Basilar Artery Doppler

A single-gate spectral transcranial Doppler TCD was introduced by Rune Aaslid in 1982 to non-invasively assess cerebral hemodynamics 1 , The four 'windows' for insonation Figure 2.1 are temporal, orbital, suboccipital and submandibular 2 , The transtemporal approach allows velocity measurements in the middle MCA , anterior ACA , posterior PCA and communicating arteries 1-5 . The transorbital approach is used to insonate the ophthalmic artery OA and internal carotid artery ICA siphon. The...

Doppler spectral analysis

The Doppler spectral display contains the diagnostic information similar to 'non-image-guided' TCD. However, TCCS allows angle correction and the velocity values will be different from a non-image-guided TCD that assumes a zero angle of insonation 16,17 . The TCCS display should document the peak systolic velocity, the maximum mean flow velocity, end-diastolic velocity, the resistance index RI and the pulsatility index PI . It is important to 1 use adequate Doppler power to allow penetration...

The cardiac cycle

Arterial Waveform

The cardiac cycle represents the sequential electrical and mechanical events that occur within a single heart beat, namely systole and diastole. At normal heart rates approximately two-thirds of the cardiac cycle consist of diastolic events, allowing for muscle relaxation and filling of the ventricles. Figure 4.1 illustrates the events of the cardiac cycle and corresponding pressure changes associated with blood flow through the heart. Ventricular systole consists of three phases. In phase 1,...