554 research outputs found
Arterial hemodynamics and wave analysis in the frequency and time domains: an evaluation of the paradigms
Assessment of coronary endothelial function using blood oxygenation level dependant cardiovascular magnetic resonance imaging (BOLD-CMR) in a canine model
USING THE RESERVOIR WAVE APPROACH TO STUDY THE HORIZON EFFECT
INTRODUCTION Differing theories and models have been explored in the field of arterial hemodynamics in an effort to better understand how the blood flows in the body. The existence of discrete reflection sites remains a source of disagreement. As a wave proceeds along an artery, any local change in impedance will result in partial reflection. Thus, because of the great complexity of the arterial system, it has been suggested that no distinct reflector sites should exist. On the other hand, there is recent experimental evidence using the reservoir-wave approach (RWA) that implies discrete positive and negative reflection sites. The pattern of wave propagation and reflection is plausible, as are the modifications produced by pharmacologic interventions [1]. The classical, frequency-domain, âimpedance analysisâ approach uses Fourier analysis to break down pressure and flow waveforms into summations of sinusoids, resulting in an impedance spectrum [2]. The RWA is a novel alternative, positing that measured pressures and flows are the instantaneous sums of âexcessâ (wave-related) and reservoir (volume-related) components [2]. The âHorizon Effectâ (HE) [3] implies that a reflector site can never be reached no matter how far into the periphery one measures (Figure 1). As such, it supports the idea that there are no distinct reflector sites. Measuring peripheral pressure and flow and using the RWA, the purpose of this study was to evaluate the HE and the question of fixed reflector sites. METHODS Eight anesthetized pigs were catheterized and pressure and flow were measured simultaneously at 4 locations: the aortic root and the brachial, carotid and renal arteries. Pharmacologic interventions were used to manipulate propagation and reflection patterns. MatLab (The MathWorks Inc., Natick, MA) was used to calculate the reservoir pressure, the local wave speed and to carry out wave intensity analysis (WIA) to obtain the forwards and backwards components of pressure. RESULTS Analysis has been completed on 4 of the 8 animals studied. Each showed minimal backward wave activity at the aortic root and in the carotid artery. However, in the brachial and renal arteries, no backward waves could be detected. DISCUSSION AND CONCLUSIONS Backward waves were scarcely detected in the periphery using either the RWA or classical analysis. This may suggest that the pig model was inappropriate to study the HE. Porcine anatomy does not allow measurement at remote peripheral sites and reflection sites cannot be studied if no reflections are to be found. Further analysis of the data is needed before more definitive conclusions can be made
On the Mechanics Underlying the Reservoir-Excess Separation in Systemic Arteries and their Implications for Pulse Wave Analysis
Several works have separated the pressure waveform p in systemic arteries into reservoir pr and excess pexc components, p = pr + pexc, to improve pulse wave analysis, using windkessel models to calculate the reservoir pressure. However, the mechanics underlying this separation and the physical meaning of pr and pexc have not yet been established. They are studied here using the time-domain, inviscid and linear one-dimensional (1-D) equations of blood flow in elastic vessels. Solution of these equations in a distributed model of the 55 larger human arteries shows that pr calculated using a two-element windkessel model is space-independent and well approximated by the compliance-weighted space-average pressure of the arterial network. When arterial junctions are well-matched for the propagation of forward-travelling waves, pr calculated using a three-element windkessel model is space-dependent in systole and early diastole and is made of all the reflected waves originated at the terminal (peripheral) reflection sites, whereas pexc is the sum of the rest of the waves, which are obtained by propagating the left ventricular flow ejection without any peripheral reflection. In addition, new definitions of the reservoir and excess pressures from simultaneous pressure and flow measurements at an arbitrary location are proposed here. They provide valuable information for pulse wave analysis and overcome the limitations of the current two- and three-element windkessel models to calculate pr
Endoscopic Therapy for Pancreatic Fluid Collections: A Definitive Management Using a Dedicated Algorithm
Background/Aims Endoscopic ultrasonography (EUS)-guided drainage is the preferred approach for infected or symptomatic pancreatic fluid collections (PFCs). Here, we developed an algorithm for the management of pancreatitis complicated by PFCs and report on its effcacy and safety. Methods Between September 2011 and October 2017, patients were prospectively managed according to the algorithm. PFCs were classified as poorly organized fluid collections (POFCs), pancreatic pseudocysts (PPs), or walled-off pancreatic necrosis (WOPN). Clinical success was defined as a decrease in PFC size by â„50% of the maximal diameter or to â€2 cm. Results A total of 108 patients (62% male; mean age, 53 years) were included: 13 had POFCs, 43 had PPs, and 52 had WOPN. Seventytwo patients (66%) required a pancreatic duct (PD) stent, whereas 65 (60%) received enteral feeding. A total of 103 (95%) patients achieved clinical success. Eight patients experienced complications including bleeding (n=6) and surgical intervention (n=2). Patients with enteral feeding were 3.4 times more likely to achieve resolution within 60 days (p=0.0421), whereas those with PD stenting was five times more likely to achieve resolution within 90 days (p=0.0069). Conclusions A high PFC resolution rate can be achieved when a dedicated algorithm encompassing EUS-guided drainage, PD stenting, and early enteral feeding is adopted
Assessment of coronary endothelial function using blood oxygenation level dependant cardiovascular magnetic resonance imaging (BOLD-CMR) in a canine model
to systemic vascular resistance windkessels windkessel: relation of arterial and venous Systemic venous circulation. Waves propagating on a
Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation
<p>Abstract</p> <p>Background</p> <p>As myocardial oxygenation may serve as a marker for ischemia and microvascular dysfunction, it could be clinically useful to have a non-invasive measure of changes in myocardial oxygenation. However, the impact of induced blood flow changes on oxygenation is not well understood. We used oxygenation-sensitive CMR to assess the relations between myocardial oxygenation and coronary sinus blood oxygen saturation (SvO<sub>2</sub>) and coronary blood flow in a dog model in which hyperemia was induced by intracoronary administration of vasodilators.</p> <p>Results</p> <p>During administration of acetylcholine and adenosine, CMR signal intensity correlated linearly with simultaneously measured SvO<sub>2 </sub>(<it>r</it><sup>2 </sup>= 0.74, <it>P </it>< 0.001). Both SvO<sub>2 </sub>and CMR signal intensity were exponentially related to coronary blood flow, with SvO2 approaching 87%.</p> <p>Conclusions</p> <p>Myocardial oxygenation as assessed with oxygenation-sensitive CMR imaging is linearly related to SvO<sub>2 </sub>and is exponentially related to vasodilator-induced increases of blood flow. Oxygenation-sensitive CMR may be useful to assess ischemia and microvascular function in patients. Its clinical utility should be evaluated.</p
Generation of local magnetic fields at megahertz rates for the study of domain wall propagation in magnetic nanowires
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