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Hemodynamic Conditions (hemodynamic + condition)
Selected AbstractsChanges in Vein Dynamics Ranging from Low to High Pressure Levels as a Determinant of the Differences in Vein Adaptation to Arterial Hemodynamic ConditionsARTIFICIAL ORGANS, Issue 7 2007Yanina Zócalo Abstract:, The causes of the regional differences in venous grafts patency rates are partially understood. Differences in vein dynamics during physiological situations could determine differences in veins' capability to face arterial conditions and could contribute to the dissimilar performance of veins as arterial grafts. In vitro pressure and diameter were measured in four different veins during physiological and arterial (graft) pressure conditions. A diameter,pressure transfer function was designed. Compliance, viscous and inertial properties; circumferential stresses and deformation; and buffering function were calculated. Regional differences in veins' dynamics, but not in buffering function were found during physiological and arterial conditions. The back vein (femoral) showed the least changes when submitted to arterial conditions. Arterial conditions represent different changes in vein dynamics depending on the segment considered. The regional differences in vein dynamics, both at physiological and graft conditions, could contribute to explain the dissimilar results of venous grafts. [source] A Novel Subcutaneous Counterpulsation Device: Acute Hemodynamic Efficacy During Pharmacologically Induced Hypertension, Hypotension, and Heart FailureARTIFICIAL ORGANS, Issue 7 2010Carlo R. Bartoli Abstract The miniaturization of mechanical assist devices and less invasive implantation techniques may lead to earlier intervention in patients with heart failure. As such, we evaluated the effectiveness of a novel, minimally invasive, implantable counterpulsation device (CPD) in augmenting cardiac function during impaired hemodynamics. We compared the efficacy of a 32-mL stroke volume CPD with a standard 40-mL intra-aortic balloon pump (IABP) over a range of clinically relevant pathophysiological conditions. Male calves were instrumented via thoracotomy, the CPD was anastomosed to the left carotid artery, and the IABP was positioned in the descending aorta. Hemodynamic conditions of hypertension, hypotension, and heart failure were pharmacologically simulated and data were recorded during CPD and IABP support (off, 1:2, 1:1 modes) for each condition. In all three pathophysiological conditions, the CPD and IABP produced similar and statistically significant (P < 0.05) increases in coronary artery blood flow normalized to the left ventricular (LV) workload. During hypotension and heart failure conditions, however, the CPD produced significantly greater reductions in LV workload and myocardial oxygen consumption as compared with the IABP. A novel 32-mL CPD connected to a peripheral artery produced equivalent or greater hemodynamic benefits than a standard 40-mL IABP during pharmacologically induced hypertension, hypotension, and heart failure conditions. [source] Imaging the future of stroke: I. Ischemia,ANNALS OF NEUROLOGY, Issue 5 2009David S. Liebeskind MD Envisioning the future of stroke appears daunting considering the milestones already achieved in stroke imaging. A historical perspective on the developments in stroke care provides a striking narrative of how imaging has transformed diagnosis, therapy, and prognosis of cerebrovascular disorders. Multimodal imaging techniques such as CT and MRI, incorporating parenchymal depictions, illustration of the vasculature, and perfusion data, can provide a wealth of information regarding ischemic pathophysiology. Key elements of ischemic pathophysiology depicted with imaging include vascular occlusion, compensatory collateral flow, resultant hemodynamic conditions that reflect these sources of blood flow, and the neurovascular injury that ensues. The mantra of "time is brain" has been perpetuated, but this does not provide an entirely accurate reflection of ischemic pathophysiology and imaging insight shows far more than time alone. Maximizing the potential of perfusion imaging will continue to expand the nascent concept that cerebral ischemia may be completely reversible in certain scenarios. Novel modalities provide a fertile ground for discovery of therapeutic targets and the potential to assess effects of promising strategies. Beyond clinical trials, imaging has become a requisite component of the neurological examination enabling tailored stroke therapy with the use of detailed neuroimaging modalities. In this first article on ischemia, the focus is on the most recent imaging advances and exploring aspects of cerebral ischemia where imaging may yield additional therapeutic strategies. A subsequent article will review recent and anticipated imaging advances in hemorrhage. These thematic overviews underscore that imaging will undoubtedly continue to dramatically shape the future of stroke. Ann Neurol 2009;66:574,590 [source] Experimental Study of a New Method for Early Detection of Vascular Access Stenoses: Pulse Pressure Analysis at Hemodialysis NeedleARTIFICIAL ORGANS, Issue 2 2010Koen Van Canneyt Abstract Hemodialysis vascular access (VA) stenosis remains a frequent complication. However, early detection is challenging and costly. The aim of this in vitro study was to assess a new detection method based on pulse pressure analysis at the hemodialysis needle. A silicon model of a radiocephalic arteriovenous fistula was built in a mock loop. Pressure profiles were measured at the arterial hemodialysis needle and in the proximal feeding artery. Stenoses (50 and 25% diameter reduction) were created proximal to the anastomosis (proximal artery) and distal to the arterial needle (distal vein and proximal vein). The pulse pressure (PP) at the needle was divided by the PP at the feeding artery to obtain a dimensionless ratio, %PP. Experiments were conducted at different blood flow (500,1200 mL/min) and heart rates (60,90 beats/min) to test this new index over a wide range of hemodynamic conditions. In the control model (no stenosis), %PP was 20.26 ± 4.55. A proximal artery 50% stenosis significantly decreased %PP to 7.69 ± 2.08 (P < 0.0001), while the presence of 50% stenosis in the distal (36.20 ± 2.12) and proximal (32.38 ± 2.17) vein led to significantly higher values of %PP (P < 0.0001). For stenosis of 25% diameter reduction in the proximal artery, the %PP decreased to 15.45 ± 2.13 (P = 0.0022) and the %PP increased with a 25% stenosis in the distal vein to 26.71 ± 3.01 (P = 0.0003) and in the proximal vein to 26.53 ± 2.67 (P = 0.0004). This in vitro study shows that the analysis of the PP at the dialysis needle is useful for early detection and localization of hemodialysis VA stenosis, independent of heart rate and flow level. [source] Experimental Setup to Evaluate the Performance of Percutaneous Pulmonary Valved Stent in Different Outflow Tract MorphologiesARTIFICIAL ORGANS, Issue 1 2009Riccardo Vismara Abstract Percutaneous pulmonary valve implantation is a potential treatment for right ventricular outflow tract (RVOT) dysfunction. However, RVOT implantation site varies among subjects and the success of the procedure depends on RVOT morphology selection. The aim of this study was to use in vitro testing to establish percutaneous valve competency in different previously defined RVOT morphologies. Five simplified RVOT geometries (stenotic, enlarged, straight, convergent, and divergent) were manufactured by silicone dipping. A mock bench was developed to test the percutaneous valve in the five different RVOTs. The bench consists of a volumetric pulsatile pump and of a hydraulic afterload. The pump is made of a piston driven by a low inertia programmable motor. The hydraulic afterload mimics the pulmonary input impedance and its design is based on a three element model of the pulmonary circulation. The mock bench can replicate different physiological and pathological hemodynamic conditions of the pulmonary circulation. The mock bench is here used to test the five RVOTs under physiological-like conditions: stroke volume range 40,70 mL, frequency range 60,80 bpm. The valved stent was implanted into the five different RVOT geometries. Pressures upstream and downstream of the valved stent were monitored. Flow rates were measured with and without the valved stent in the five mock RVOTs, and regurgitant fraction compared between the different valved stent RVOTs. The percutaneous valved stent drastically reduced regurgitant flow if compared with the RVOT without the valve. RVOT geometry did not significantly influence the flow rate curves. Mean regurgitant fractions varied from 5% in the stenotic RVOT to 7.3% in the straight RVOT, highlighting the influence of the RVOT geometry on valve competency. The mock bench presented in this study showed the ability to investigate the influence of RVOT geometry on the competence of valved stent used for percutaneous pulmonary valve treatment. [source] | ||||||||||