The functional hierarchy of coronary circulation: direct evidence of a structure-function relation
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$300 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) 6316 We, 12:15-12:30 (P31) The functional hierarchy of coronary circulation: direct evidence of a structure-function relation G.S. Kassab. Department of Biomedical Engineering, University of California, Irvine, CA, USA The heart muscle is nourished by a complex system of blood vessels that make up the coronary circulation. Here we show that the design of the coronary circulation has a functional hierarchy. A full anatomical model of the coronary arterial tree, containing millions of blood vessels down to the capillary vessels, was simulated based on previously measured porcine morphometric data. A network analysis of blood flow through every vessel segment was carried out based on the laws of fluid mechanics and appropriate boundary conditions. Our results show an abrupt change in cross-sectional area that demarcates the transition from epicardial to intramyocardial coronary arteries (IMCA). Furthermore, a similar pattern of blood flow was observed with a corresponding transition from epicardial to IMCA. These results suggest functional differences between the two types of vessels. An additional abrupt change occurs in the IMCA in relation to flow velocity. Proximal to these vessels the velocity is fairly uniform but drops significantly distal to those vessels towards the capillary branches. This finding suggests functional differences between large and small IMCA. Collectively, these observations suggest a novel functional hierarchy of the coronary vascular tree and provide direct evidence of a structure-function relation. 6953 We, 12:30-12:45 (P32) Coronary wave intensity in humans: effect of changes in microvascular resistance and hemodynamic conditions C. Kolyva, J.A.E. Spaan, B.-J. Verhoeff, J.J. Piek, M. Siebes. Academic Medical Center, Amsterdam, The Netherlands Background: Wave intensity (WI) analysis is uniquely suited to investigate the coronary circulation, where a backward traveling compression wave (BCW) originates in the smallest vessels during early systole. It has been shown in healthy animals that the energy of the BCW depends on cardiac contractility and inversely on microvascular resistance (MR). We applied WI analysis in diseased human coronary arteries and tested these influences in the presence and absence of vasomotor control. Methods: ECG, aortic pressure (Pa), and intracoronary distal pressure (Pd) and flow velocity (v) were recorded at rest and maximal hyperemia induced by IC adenosine. Measurements were obtained in 26 patients before and after revascularization of an epicardial stenosis (stent placement), and in 10 patients at control, during atrial pacing at 120 bpm, and after elevating Pa by 30 mmHg via slow IV phenylephrine infusion at constant HR. End-diastolic Pa divided by the time interval between the ECG R-peak and ED-Pa served as a measure of contractility. WI was computed from ensemble-averaged cycles as (dPd)(dv) and MR = Pd/v. Changes in BCW energy were assessed by the area under the wave. Results: A fall in MR (p<0.001) after distal coronary vasodilation markedly increased BCW at constant contractility for all conditions. Epicardial revascu- larization restored Pd (p<0.001) and further reduced minimal MR by 32% (p<0.002), resulting in a proportional 226% increase in hyperemic BCW (r=0.71, p<0.001). Pacing caused no change in contractility, a 20% decline in baseline MR (p<0.01), and 273% rise in BCW at rest (p<0.001), while during hyperemia BCW rose by 20% although minimal MR increased by 17%. Elevated Pa at constant HR induced a 20% rise in MR and 50% rise in contractility (P< 0.02), resulting in 85% increase in BCW at rest (p<0.01) and 20% increase during hyperemia (p < 0.05). In summary, the energy of BCW was strongly related to coronary conductance at constant contractility, whereas BCW increased with contractility despite a decrease in conductance. Support: NHF grant 2000.090. 7693 We, 12:45-13:00 (P32) Assessment of vasa vasorum density in coronary atherosclerotic lesions by means of contrast enhanced intravascular ultrasound imaging with microbubbles S. Carlier 1, M. Vavuranakis 2, S. O'Malley 3, I. Kakadiaris 3, E. Falk 4, C. Stefanadis 2, M. Naghavi 5. 1Columbia University, New York, USA, 2Hippocration Hospital, Medical School, Athens, Greece, 3Texas Learning and Computation Center, Houston, 4 USA, Skejby Sygehus, Aarhus, Denmark, 5American Heart Technologies, Inc., Houston, USA Distinctive features of plaque vulnerability have been described with intravas- cular ultrasound (IVUS). However, their identification remains a challenge. Pathological studies demonstrated that an increased vasa vasorum (W) density is associated with plaque inflammation and instability. We investigated whether VV could be detected by intravascular ultrasound after intracoronary injection of microbubbles. Oral Presentations Materials and Methods: Five hyperlipidemic pigs (Rapacz-type, presenting a recessive mutation of a low density lipoprotein receptor) and one normal were evaluated in vivo in order to perform histopathological correlation. A total of 17 patients so far with acute coronary syndrome (ACS) have also been studied in the setting of a percutaneous coronary intervention (PCI). IVUS was performed in the three coronary vessels of the pigs but only in a proximal non-culprit lesion in the patients. These lesions were selected based on vulnerability features (echolucent plaque area >40% and positive remodeling). A bolus of echocontrast agent (Optison or Sonoview) was injected through the guiding catheter (1 cc). IVUS images (dicom format) recorded up to 2 minutes post-injection were processed to evaluate the differential enhancement in echogenecity related to microbubbles flowing into W. Results: Significant enhancement of more than 5% could be demonstrated in the echogenicity (E) of the plaque and adventitia in some of the lesions visualized in the pigs and in a majority of the patients. In eight patients the enhancement of E was >50%, in five 20-50% and in four <20%. Correlation with histopathology for the pig study is pending. During the pig experiments, high-speed (400MHz) digitization of the IVUS radiofrequency signal with simultaneously acquired ecg and blood pressure will allow the development of advanced image analysis of ecg-triggered sequences. Conclusion: It appears possible to evaluate the density and perfusion of the vasa vasorum of unstable coronary plaques using IVUS and microbubbles. 14.8. Flow Measurement and Imaging In Vivo and In Vitro with Applications 14.8.1. MRI 5705 Th, 11:00-11:15 (P42) A mathematical tool for quantitative evaluation of medical flow imaging algorithms A. Pashaee, N. Fatouraee. Biological Fluid Mechanics Laboratory, Biomedical Engineering Faculty, Amirkabir University of Technology, Tehran, Iran Using blood flow characteristics (i.e. velocity, pressure, shear stress, stream- line, and volumetric flow rate) provides an effective tool in diagnosis of cardiovascular disease like localization of atherosclerotic plaque, aneurism, and cardiac muscle failure. Noninvasive detection of cardiovascular blood flow characteristics now mostly limited to the measurement of the velocity vector components by the medical imaging modalities. Once the velocity field obtained from the images, other flow characteristics within the cardiovascular system can be determined using algorithms relating them to these velocity components based on some physical constraints. Here we propose a mathematical phantom to accurately evaluate these al- gorithms in different physiological blood flow conditions. The Navier-Stokes equations are used to derive the flow phantom. Solving the governing equa- tions, analytical expressions for the flow characteristics inside the domain are obtained. Features such as pulsatility, incompressibility, and viscosity of fluid in a three dimensional domain are included. The flow characteristics obtained from the phantom are converted into the flow images. These images can be used to evaluate the performance of different flow algorithms. In this study we also present an application of the results obtained from the phantom, as the gold standard value, in the accuracy evaluation of the pressure distribution extracted from the velocity images. The results show that the pressure distribution algorithm has an acceptable accuracy. The presented phantom can be considered as a bench mark test to compare the accuracy of different algorithms. 4818 Th, 11:15-11:30 (P42) Effects of calf compression on the deformation of deep and superficial veins in the lower limb S.P. Downie 1, X.Y. Xu 1, N. Wood 1, D.N. Firmin 2, S. Thorn 3, J.N.H. Wolfe 4. 1Department of Chemical Engineering, 2NHLL CMR Unit, Royal Brompton and Harefield NHS Trust, 3NHLI, International Centre for Circulatory health, 4 and Vascular Surgery, St Mary's Hospital, Imperial College London, UK Lower limb venous disease is prevalent in 5% of the British population and costs the NHS an estimated £500M per year. The use of therapeutic com- pression has remained the standard treatment for hundreds of years. Despite the accumulation of clinical evidence supporting its efficacy there has been little advance in theoretical understanding in terms of the underlying mechanism. It is generally assumed, however, that a reduction in vessel cross section is required to realise the therapeutic effect [1,2]. In this study the effect of compression on vessel geometry is examined with MR imaging (high resolution 3D TrueFISP sequence) in the upper section of the calf. This includes all peroneal and posterior tibial vessels, both saphenous veins and several large superficial veins. From the MR data a 3D model is reconstructed, including skin, fat, fascia, veins, arteries and muscle. This is then used to create a finite element model which may be used to simulate the
Transcript of The functional hierarchy of coronary circulation: direct evidence of a structure-function relation
$300 Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
6316 We, 12:15-12:30 (P31) The funct ional h ierarchy o f coronary circulat ion: direct evidence o f a s t ruc ture- func t ion relat ion G.S. Kassab. Department of Biomedical Engineering, University of California, Irvine, CA, USA
The heart muscle is nourished by a complex system of blood vessels that make up the coronary circulation. Here we show that the design of the coronary circulation has a functional hierarchy. A full anatomical model of the coronary arterial tree, containing millions of blood vessels down to the capillary vessels, was simulated based on previously measured porcine morphometric data. A network analysis of blood flow through every vessel segment was carried out based on the laws of fluid mechanics and appropriate boundary conditions. Our results show an abrupt change in cross-sectional area that demarcates the transition from epicardial to intramyocardial coronary arteries (IMCA). Furthermore, a similar pattern of blood flow was observed with a corresponding transition from epicardial to IMCA. These results suggest functional differences between the two types of vessels. An additional abrupt change occurs in the IMCA in relation to flow velocity. Proximal to these vessels the velocity is fairly uniform but drops significantly distal to those vessels towards the capillary branches. This finding suggests functional differences between large and small IMCA. Collectively, these observations suggest a novel functional hierarchy of the coronary vascular tree and provide direct evidence of a structure-function relation.
6953 We, 12:30-12:45 (P32) Coronary wave intensi ty in humans: effect o f changes in microvascular resistance and hemodynamic condi t ions C. Kolyva, J.A.E. Spaan, B.-J. Verhoeff, J.J. Piek, M. Siebes. Academic Medical Center, Amsterdam, The Netherlands
Background: Wave intensity (WI) analysis is uniquely suited to investigate the coronary circulation, where a backward traveling compression wave (BCW) originates in the smallest vessels during early systole. It has been shown in healthy animals that the energy of the BCW depends on cardiac contractility and inversely on microvascular resistance (MR). We applied WI analysis in diseased human coronary arteries and tested these influences in the presence and absence of vasomotor control. Methods: ECG, aortic pressure (Pa), and intracoronary distal pressure (Pd) and flow velocity (v) were recorded at rest and maximal hyperemia induced by IC adenosine. Measurements were obtained in 26 patients before and after revascularization of an epicardial stenosis (stent placement), and in 10 patients at control, during atrial pacing at 120 bpm, and after elevating Pa by 30 mmHg via slow IV phenylephrine infusion at constant HR. End-diastolic Pa divided by the time interval between the ECG R-peak and ED-Pa served as a measure of contractility. WI was computed from ensemble-averaged cycles as (dPd)(dv) and MR = Pd/v. Changes in BCW energy were assessed by the area under the wave. Results: A fall in MR (p<0.001) after distal coronary vasodilation markedly increased BCW at constant contractility for all conditions. Epicardial revascu- larization restored Pd (p<0.001) and further reduced minimal MR by 32% (p<0.002), resulting in a proportional 226% increase in hyperemic BCW (r=0.71, p<0.001). Pacing caused no change in contractility, a 20% decline in baseline MR (p<0.01), and 273% rise in BCW at rest (p<0.001), while during hyperemia BCW rose by 20% although minimal MR increased by 17%. Elevated Pa at constant HR induced a 20% rise in MR and 50% rise in contractility (P< 0.02), resulting in 85% increase in BCW at rest (p<0.01) and 20% increase during hyperemia (p < 0.05). In summary, the energy of BCW was strongly related to coronary conductance at constant contractility, whereas BCW increased with contractility despite a decrease in conductance. Support: NHF grant 2000.090.
7693 We, 12:45-13:00 (P32) Assessment of vasa vasorum densi ty in coronary atherosclerot ic les ions by means of contrast enhanced intravascular u l t rasound imaging with microbubbles S. Carlier 1 , M. Vavuranakis 2, S. O'Malley 3, I. Kakadiaris 3, E. Falk 4, C. Stefanadis 2, M. Naghavi 5. 1Columbia University, New York, USA, 2 Hippocration Hospital, Medical School, Athens, Greece, 3Texas Learning and Computation Center, Houston, 4 USA, Skejby Sygehus, Aarhus, Denmark, 5American Heart Technologies, Inc., Houston, USA
Distinctive features of plaque vulnerability have been described with intravas- cular ultrasound (IVUS). However, their identification remains a challenge. Pathological studies demonstrated that an increased vasa vasorum (W) density is associated with plaque inflammation and instability. We investigated whether VV could be detected by intravascular ultrasound after intracoronary injection of microbubbles.
Oral Presentat ions
Materials and Methods: Five hyperlipidemic pigs (Rapacz-type, presenting a recessive mutation of a low density lipoprotein receptor) and one normal were evaluated in vivo in order to perform histopathological correlation. A total of 17 patients so far with acute coronary syndrome (ACS) have also been studied in the setting of a percutaneous coronary intervention (PCI). IVUS was performed in the three coronary vessels of the pigs but only in a proximal non-culprit lesion in the patients. These lesions were selected based on vulnerability features (echolucent plaque area >40% and positive remodeling). A bolus of echocontrast agent (Optison or Sonoview) was injected through the guiding catheter (1 cc). IVUS images (dicom format) recorded up to 2 minutes post-injection were processed to evaluate the differential enhancement in echogenecity related to microbubbles flowing into W. Results: Significant enhancement of more than 5% could be demonstrated in the echogenicity (E) of the plaque and adventitia in some of the lesions visualized in the pigs and in a majority of the patients. In eight patients the enhancement of E was >50%, in five 20-50% and in four <20%. Correlation with histopathology for the pig study is pending. During the pig experiments, high-speed (400MHz) digitization of the IVUS radiofrequency signal with simultaneously acquired ecg and blood pressure will allow the development of advanced image analysis of ecg-triggered sequences. Conclusion: It appears possible to evaluate the density and perfusion of the vasa vasorum of unstable coronary plaques using IVUS and microbubbles.
14.8. Flow Measurement and Imaging In Vivo and In Vitro with Applications
14.8.1. MRI
5705 Th, 11:00-11:15 (P42) A mathematical tool for quant i tat ive evaluat ion o f medical f low imaging a lgor i thms A. Pashaee, N. Fatouraee. Biological Fluid Mechanics Laboratory, Biomedical Engineering Faculty, Amirkabir University of Technology, Tehran, Iran
Using blood flow characteristics (i.e. velocity, pressure, shear stress, stream- line, and volumetric flow rate) provides an effective tool in diagnosis of cardiovascular disease like localization of atherosclerotic plaque, aneurism, and cardiac muscle failure. Noninvasive detection of cardiovascular blood flow characteristics now mostly limited to the measurement of the velocity vector components by the medical imaging modalities. Once the velocity field obtained from the images, other flow characteristics within the cardiovascular system can be determined using algorithms relating them to these velocity components based on some physical constraints. Here we propose a mathematical phantom to accurately evaluate these al- gorithms in different physiological blood flow conditions. The Navier-Stokes equations are used to derive the flow phantom. Solving the governing equa- tions, analytical expressions for the flow characteristics inside the domain are obtained. Features such as pulsatility, incompressibility, and viscosity of fluid in a three dimensional domain are included. The flow characteristics obtained from the phantom are converted into the flow images. These images can be used to evaluate the performance of different flow algorithms. In this study we also present an application of the results obtained from the phantom, as the gold standard value, in the accuracy evaluation of the pressure distribution extracted from the velocity images. The results show that the pressure distribution algorithm has an acceptable accuracy. The presented phantom can be considered as a bench mark test to compare the accuracy of different algorithms.
4818 Th, 11:15-11:30 (P42) Effects o f calf compress ion on the deformat ion o f deep and superf ic ia l veins in the lower l imb S.P. Downie 1 , X.Y. Xu 1 , N. Wood 1 , D.N. Firmin 2, S. Thorn 3, J.N.H. Wolfe 4. 1Department of Chemical Engineering, 2NHLL CMR Unit, Royal Brompton and Harefield NHS Trust, 3 NHLI, International Centre for Circulatory health,
4 and Vascular Surgery, St Mary's Hospital, Imperial College London, UK
Lower limb venous disease is prevalent in 5% of the British population and costs the NHS an estimated £500M per year. The use of therapeutic com- pression has remained the standard treatment for hundreds of years. Despite the accumulation of clinical evidence supporting its efficacy there has been little advance in theoretical understanding in terms of the underlying mechanism. It is generally assumed, however, that a reduction in vessel cross section is required to realise the therapeutic effect [1,2]. In this study the effect of compression on vessel geometry is examined with MR imaging (high resolution 3D TrueFISP sequence) in the upper section of the calf. This includes all peroneal and posterior tibial vessels, both saphenous veins and several large superficial veins. From the MR data a 3D model is reconstructed, including skin, fat, fascia, veins, arteries and muscle. This is then used to create a finite element model which may be used to simulate the
