Upright versus supine MRI: effects of body position on craniocervical CSF flow

Background Cerebrospinal fluid (CSF) circulation between the brain and spinal canal, as part of the glymphatic system, provides homeostatic support to brain functions and waste clearance. Recently, it has been observed that CSF flow is strongly driven by cardiovascular brain pulsation, and affected by body orientation. The advancement of MRI has allowed for non-invasive examination of the CSF hydrodynamic properties. However, very few studies have addressed their relationship with body position (e.g., upright versus supine). It is important to understand how CSF hydrodynamics are altered by body position change in a single cardiac phase and how cumulative long hours staying in either upright or supine position can affect craniocervical CSF flow. Methods In this study, we investigate the changes in CSF flow at the craniocervical region with flow-sensitive MRI when subjects are moved from upright to supine position. 30 healthy volunteers were imaged in upright and supine positions using an upright MRI. The cranio-caudal and caudo-cranial CSF flow, velocity and stroke volume were measured at the C2 spinal level over one cardiac cycle using phase contrast MRI. Statistical analysis was performed to identify differences in CSF flow properties between the two positions. Results CSF stroke volume per cardiac cycle, representing CSF volume oscillating in and out of the cranium, was ~ 57.6% greater in supine (p < 0.0001), due to a ~ 83.8% increase in caudo-cranial CSF peak velocity during diastole (p < 0.0001) and extended systolic phase duration when moving from upright (0.25 ± 0.05 s) to supine (0.34 ± 0.08 s; p < 0.0001). Extrapolation to a 24 h timeframe showed significantly larger total CSF volume exchanged at C2 with 10 h spent supine versus only 5 h (p < 0.0001). Conclusions In summary, body position has significant effects on CSF flow in and out of the cranium, with more CSF oscillating in supine compared to upright position. Such difference was driven by an increased caudo-cranial diastolic CSF velocity and an increased systolic phase duration when moving from upright to supine position. Extrapolation to a 24 h timeframe suggests that more time spent in supine position increases total amount of CSF exchange, which may play a beneficial role in waste clearance in the brain.

Echocardiographic parameters of left ventricular non-systolic function predict length of stay following coronary artery bypass graft -- a prospective observational study

Background: Abnormal left ventricular (LV) echocardiographic parameters during non-systolic phase, with or without a diagnosis of heart failure, is a common finding that can be easily diagnosed by intra-operative transesophageal echocardiography (TEE). However, its association with duration of hospital stay after coronary artery bypass (CAB) is unknown. Objective: To determine if Abnormal left ventricular (LV) echocardiographic parameters during non-systolic phase is associated with length of hospital stay after coronary artery bypass surgery (CAB). Method: Prospective observational study at a single tertiary academic medical center Result: Median time to hospital discharge was significantly longer for subjects with abnormal left ventricular (LV) echocardiographic parameters during non-systolic phase (9.1/IQR 6.6-13.5 days) than those with normal LV non-systolic function (6.5/IAR 5.3-9.7days) (P< 0.001). The probability of hospital discharge was 34% lower (HR 0.66/95% CI 0.47-0.93) for subjects with abnormal LV function even during non-systole despite a normal LV systolic function, independent of potential confounders, including a baseline diagnosis of heart failure Conclusions and Relevance: In patients with normal systolic function undergoing CAB, non-systolic LV dysfunction is associated with prolonged duration of postoperative hospital stay. This association cannot be explained by baseline comorbidities or common post-operative complications.

A Dissipation Function–Based Method for Calculating the Energy Loss of Intracranial Aneurysms

At present, the energy loss (EL) mechanism of intracranial aneurysm (IA) rupture is explored based on the global EL calculated by Bernoulli equation, but the details of EL are still unclear. This study aimed to explore the temporal and spatial characteristics of EL of IAs and reveal its mechanism. A novel method for calculating the EL of IAs based on dissipation function (DF) was proposed. DF was derived from the differential form of the energy equation and reflected the irreversible conversion from mechanical energy to internal energy caused by the friction between the fluid micelles. Eight sidewall IAs located at the posterior communicating segment of the internal carotid artery were collected; the three-dimensional (3D) geometric models of IAs were established employing image segmentation and 3D reconstruction. Computational fluid dynamics was applied to obtain hemodynamic parameters of IAs. The temporal and spatial characteristics of EL of IAs were achieved utilizing our proposed method. The simulation results indicated that EL occurred mainly in the boundary layer and the region adjacent to high-velocity inflow jet, EL increased rapidly during cardiac systole and reached its maximum at end-systolic phase and then decreased gradually during diastole until the end of cardiac cycle. The proposed method achieved some improvements over the traditional Bernoulli equation–based method by acquiring the temporal and spatial characteristics of EL, and it could provide insights into the EL of IAs and contribute to further rupture mechanism investigation.

Regulation of coronary flow

This chapter describes the regulation of coronary blood flow. The left ventricle generates the systemic arterial blood pressure that is required to maintain coronary blood flow. The coronary circulation is unique among regional vascular beds in that its perfusion is impeded during the systolic phase of the cardiac cycle by the surrounding contracting cardiac muscle. Systolic contraction increases left ventricular wall tension and compresses the intramyocardial microvessels, thereby impeding coronary arterial inflow. This compression is not uniformly distributed across the left ventricular wall, resulting in a redistribution of blood flow from the subendocardium to subepicardium.

Effect of non-linear leaflet material properties on aortic valve dynamics - A coupled fluid-structure approach

Due to complex structure of aortic valve (AV) leaflets and its strong interaction with the blood flow field, realistic and accurate modeling of the valve deformations comes with many challenges. In this study, we aimed to investigate the effect of AV material properties on the valve deformations, by implementing different non-linear properties of the AV leaflets in three different material models. In the computations, we captured the dynamics between the leaflet deformations and blood flow field variations by using an iterative implicit fluid-structure interaction (FSI) approach. By comparison of the FSI simulation results of these three models, the effects of hyperelasticity and anisotropy on the valve deformations have been studied in detail. The simulation results reveal the fact that the material characteristics strongly affect the deformation characteristics of the leaflets in the systolic phase. The material anisotropy stabilizes the leaflet movements during the systolic phase, which helps decreasing the flutters of the leaflets during the peak jet blood flow. Similarly, it has been observed that the hyperelastic behavior yields an increase in the valve opening area during systolic phase which prevents the risk of excessive work of the heart due to high pressure difference. Furthermore, simulation results indicate that the stress levels in hyperelastic model are much lower, compared to the stress levels in linear elastic one. This suggests that the non-linear material character of the leaflets decreases the risk of calcification.

Right and left ventricle native T1 mapping in systolic phase in patients with congenital heart disease

Background T1 mapping is emerging as a powerful tool in cardiac magnetic resonance (CMR) to evaluate diffuse fibrosis. However, right ventricular (RV) T1 mapping proves difficult due to the limited wall thickness in diastolic phase. Several studies focused on systolic T1 mapping, albeit only on the left ventricle (LV). Purpose To estimate intra- and inter-observer variability of native T1 (nT1) mapping of the RV, and its correlations with biventricular and pulmonary function in patients with congenital heart disease (CHD). Material and Methods In this retrospective, observational, cross-sectional study we evaluated 36 patients with CHD, having undergone CMR on a 1.5-T scanner. LV and RV functional evaluations were performed. A native modified look-locker inversion recovery short-axis sequence was acquired in the systolic phase. Intra- and inter-reader reproducibility were reported as complement to 100% of the ratio between coefficient of reproducibility and mean. Spearman ρ and Mann–Whitney U-test were used to compare distributions. Results Intra- and inter-reader reproducibility was 84% and 82%, respectively. Median nT1 was 1022 ms (interquartile range [IQR] 1108–972) for the RV and 947 ms (IQR 986–914) for the LV. Median RV–nT1 was 1016 ms (IQR 1090–1016) in patients with EDVI ≤100 mL/m2 and 1100 ms (IQR 1113–1100) in patients with EDVI >100 mL/m2 ( P = 0.049). A significant negative correlation was found between RV ejection fraction and RV–nT1 (ρ = −0.284, P = 0.046). Conclusion Systolic RV-nT1 showed a high reproducibility and a negative correlation with RV ejection fraction, potentially reflecting an adaptation of the RV myocardium to pulmonary valve/conduit (dys)-function.

P1409 Sizing of mitral annuloplasty rings using three-dimensional transoesophageal echocardiography

Funding Acknowledgements Department funding Background Mitral valve repair is preferred to valve replacement in cases of degenerative mitral regurgitation (MR) due to the lower risk of valve-related complications and operative mortality. In mitral valve repair, annuloplasty is associated with better clinical outcomes. Sizing of the annuloplasty ring with a ring sizer, which should be performed in the end-systolic phase, is performed in diastole during hyperkalaemia cardioplegic arrest. Three-dimensional transoesophageal echocardiography (3D-TEE) allows measurement of the mitral valve while the heart is beating, which is beneficial since the mitral valve size changes throughout the cardiac cycle. Purpose To investigate whether 3D-TEE measurements of the mitral valve are effective for preventing recurrent mitral regurgitation (MR) in patients who undergo mitral valve repair for degenerative MR. Methods This study retrospectively reviewed 139 patients who underwent mitral annuloplasty for degenerative MR. After 47 patients were excluded, 92 patients were analysed. The inter-commissural (IC) distance and anterior leaflet height of the A2 segment of the mitral valve were measured by 3D-TEE at the end-systolic phase. The annuloplasty ring size and type were selected by surgeons using specific ring sizers. We investigated the association of the IC distance with the size of implanted annulus ring and differences between the size of implanted annulus ring and the IC distance. We also compared the IC distance, the A2 height, and the ratio of A2 height to IC distance between patients with and without recurrent mild-to-moderate MR for 36 months. Results There was a significant correlation between the size of the mitral annuloplasty ring and the IC distance (R²=0.7023, p &lt; 0.001). The variety between implanted annulus ring size and IC distance measured by 3D-TEE was shown in Figure1. Eight cases had mild or greater recurrent MR. There was a significant difference in the ratio of A2 height to IC distance between patients with and without recurrent MR (p = 0.006). The A2 height was greater in patients with recurrent MR, but this difference was not significant (p = 0.059). Conclusions There was a significant correlation between the size of the mitral annuloplasty ring and the IC distance. Our results demonstrated a higher ratio of A2 height to IC distance in patients with recurrent MR. Abstract P1409 Figure1

Fluid–Solid Interaction Analysis on Iliac Bifurcation Artery: A Numerical Study

Atherosclerosis, which is commonly seen at regions with low wall shear stress (WSS) level in bifurcations, is a kind of fibro-fatty plaque accumulated on arterial walls. Aortic and iliac bifurcations have the highest proportion of patients among all atherosclerosis cases, thus it is necessary to numerically analyze the flow distribution and predict plaque positions in these bifurcations. Furthermore, using fluid–solid interaction (FSI) method could obtain a more exact flow pattern in arteries. In this study, a patient-specific model of aortic and iliac bifurcations was simulated with both FSI and rigid-wall cases. We analyzed the vessel deformation, WSS and flow distribution of this model. Computed tomography (CT) angiography was used in our study to create patient-specific model of aorto-iliac arteries. Real material properties and pulsatile fluid boundary conditions were applied in solid and fluid zones, respectively. We performed FSI and ordinary computational fluid dynamics (CFD) simulations with AYSYS 15.0 software (ANSYS Inc., Canonsburg, PA), and compared the diameter change, WSS and flow field between these two results. The diameter change between systolic phase and diastolic phase is 8–9% on abdominal aorta, and 3% on external and internal iliac arteries. The compliance of vessels corresponds to in-vivo observations. At peak systolic phase, the average WSS obtained in FSI simulation is 10% lower than in rigid-wall result, area of low-WSS region ([Formula: see text]) also increases by 78%. Wall deformation has a greater impact on WSS of those vessels with larger diameter, but hardly changes the shear level in smaller branches. Our result also shows that iliac bifurcations reveal more complicated secondary flow in systolic phase, comparing to other vessels, and stenosed iliac artery has more severe secondary flow than healthy artery. We obtained a feasible method for hemodynamic FSI research. The material parameters, boundary conditions and mesh could be used for further simulations, while the WSS and flow distribution may support clinical diagnosis and treatment. We concluded that compliance is a must-consider factor for simulating an accurate wall shear stress, because the vessel deformation in FSI simulation will significantly change the distribution of low-WSS zones. Moreover, more complicated secondary flow is detected in iliac arteries because it may interact between bifurcations. Stenosis in artery may also have a blocking effect on downstream blood flow.

Intra-aortic Balloon Pump—Current Status

Cardiac failure is an ever-growing public health concern confronted by both developed and developing nations of the world. Intra-aortic balloon pump (IABP) is a circulatory assist device that is used to support a failing left ventricle. IABP is designed to augment myocardial perfusion by increasing coronary blood flow during diastolic phase of the cardiac cycle and unloading the left ventricle during systolic phase. Intraoperative IABP is extremely useful when facing difficulty to wean from cardiopulmonary bypass. Until the controversy is resolved, personal experience and decision of the physician and patient circumstances may form the basis for the IABP use in a clinical setting with acute left ventricular failure.