Three-dimensional structure of the flow inside the left ventricle of the human heart

The laboratory models of the human heart left ventricle developed in the last decades gave a valuable contribution to the comprehension of the role of the fluid dynamics in the cardiac function and to support the interpretation of the data obtained in vivo. Nevertheless, some questions are still open and new ones stem from the continuous improvements in the diagnostic imaging techniques. Many of these unresolved issues are related to the three-dimensional structure of the left-ventricular flow during the cardiac cycle. In this paper we investigated in detail this aspect using a laboratory model. The ventricle was simulated by a flexible sack varying its volume in time according to a physiologically shaped law. Velocities measured during several cycles on series of parallel planes, taken from two orthogonal points of view, were combined together in order to reconstruct the phase averaged, three-dimensional velocity field. During the diastole, three main steps are recognized in the evolution of the vortical structures: i) straight propagation in the direction of the long axis of a vortex-ring originated from the mitral orifice; ii) asymmetric development of the vortex-ring on an inclined plane; iii) single vortex formation. The analysis of three-dimensional data gives the experimental evidence of the reorganization of the flow in a single vortex persisting until the end of the diastole. This flow pattern seems to optimize the cardiac function since it directs velocity towards the aortic valve just before the systole and minimizes the fraction of blood residing within the ventricle for more cycles

Fluid dynamics of aortic root dilation in Marfan syndrome

Aortic root dilation and propensity to dissection are typical manifestations of the Marfan Syndrome (MS), a genetic defect leading to the degeneration of the elastic fibres. Dilation affects the structure of the flow and, in turn, altered flow may play a role in vessel dilation, generation of aneurysms, and dissection. The aim of the present work is the investigation in-vitro of the fluid dynamic modifications occurring as a consequence of the morphological changes typically induced in the aortic root by MS. A mock-loop reproducing the left ventricle outflow tract and the aortic root was used to measure time resolved velocity maps on a longitudinal symmetry plane of the aortic root. Two dilated model aortas, designed to resemble morphological characteristics typically observed in MS patients, have been compared to a reference, healthy geometry. The aortic model was designed to quantitatively reproduce the change of aortic distensibility caused by MS. Results demonstrate that vorticity released from the valve leaflets, and possibly accumulating in the root, plays a fundamental role in redirecting the systolic jet issued from the aortic valve. The altered systolic flow also determines a different residual flow during the diastole.Comment: Accepted versio

Technology applications

A summary of NASA Technology Utilization programs for the period of 1 December 1971 through 31 May 1972 is presented. An abbreviated description of the overall Technology Utilization Applications Program is provided as a background for the specific applications examples. Subjects discussed are in the broad headings of: (1) cancer, (2) cardiovascular disease, (2) medical instrumentation, (4) urinary system disorders, (5) rehabilitation medicine, (6) air and water pollution, (7) housing and urban construction, (8) fire safety, (9) law enforcement and criminalistics, (10) transportation, and (11) mine safety

Cascade Control of a Hydraulic Prosthetic Knee

A leg prosthesis test robot with hydraulic knee actuator is modeled and tested with closed loop control simulation. A cascade control architecture is designed for the system, the outer loop is controlled by a robust passivity-based controller (RPBC) and the inner loop is controlled by an optimization method. The control algorithm provides knee angle tracking with an RMS error of 0.07 degrees. The research contributes to the field of prosthetics by showing that it is possible to find effective closed loop control algorithm for a newly proposed hydraulic knee prosthesis. The simulations demonstrate the efficiency of RPBC\u27s ability to control complex, nonlinear and multivariable system with plant variability and parameter uncertainty. Dynamic equations for the hydraulic knee actuator are derived from bond graph, an optimization method is used to solve the inversion problem. Low-pass filters are implemented to eliminate signal chatter. Necessary modifications of knee actuator parameters are discussed and recommended to achieve better tracking performance

Cascade Control of a Hydraulic Prosthetic Knee

A leg prosthesis test robot with hydraulic knee actuator is modeled and tested with closed loop control simulation. A cascade control architecture is designed for the system, the outer loop is controlled by a robust passivity-based controller (RPBC) and the inner loop is controlled by an optimization method. The control algorithm provides knee angle tracking with an RMS error of 0.07 degrees. The research contributes to the field of prosthetics by showing that it is possible to find effective closed loop control algorithm for a newly proposed hydraulic knee prosthesis. The simulations demonstrate the efficiency of RPBC\u27s ability to control complex, nonlinear and multivariable system with plant variability and parameter uncertainty. Dynamic equations for the hydraulic knee actuator are derived from bond graph, an optimization method is used to solve the inversion problem. Low-pass filters are implemented to eliminate signal chatter. Necessary modifications of knee actuator parameters are discussed and recommended to achieve better tracking performance

Applications of aerospace technology in the public sector

Current activities of the program to accelerate specific applications of space related technology in major public sector problem areas are summarized for the period 1 June 1971 through 30 November 1971. An overview of NASA technology, technology applications, and supporting activities are presented. Specific technology applications in biomedicine are reported including cancer detection, treatment and research; cardiovascular diseases, diagnosis, and treatment; medical instrumentation; kidney function disorders, treatment, and research; and rehabilitation medicine

Cascade Control of a Hydraulic Prosthetic Knee

A leg prosthesis test robot with hydraulic knee actuator is modeled and tested with closed loop control simulation. A cascade control architecture is designed for the system, the outer loop is controlled by a robust passivity-based controller (RPBC) and the inner loop is controlled by an optimization method. The control algorithm provides knee angle tracking with an RMS error of 0.07 degrees. The research contributes to the field of prosthetics by showing that it is possible to find effective closed loop control algorithm for a newly proposed hydraulic knee prosthesis. The simulations demonstrate the efficiency of RPBC\u27s ability to control complex, nonlinear and multivariable system with plant variability and parameter uncertainty. Dynamic equations for the hydraulic knee actuator are derived from bond graph, an optimization method is used to solve the inversion problem. Low-pass filters are implemented to eliminate signal chatter. Necessary modifications of knee actuator parameters are discussed and recommended to achieve better tracking performance

A parallel interaction potential approach coupled with the immersed boundary method for fully resolved simulations of deformable interfaces and membranes

In this paper we show and discuss the use of a versatile interaction potential approach coupled with an immersed boundary method to simulate a variety of flows involving deformable bodies. In particular, we focus on two kinds of problems, namely (i) deformation of liquid-liquid interfaces and (ii) flow in the left ventricle of the heart with either a mechanical or a natural valve. Both examples have in common the two-way interaction of the flow with a deformable interface or a membrane. The interaction potential approach (de Tullio & Pascazio, Jou. Comp. Phys., 2016; Tanaka, Wada and Nakamura, Computational Biomechanics, 2016) with minor modifications can be used to capture the deformation dynamics in both classes of problems. We show that the approach can be used to replicate the deformation dynamics of liquid-liquid interfaces through the use of ad-hoc elastic constants. The results from our simulations agree very well with previous studies on the deformation of drops in standard flow configurations such as deforming drop in a shear flow or a cross flow. We show that the same potential approach can also be used to study the flow in the left ventricle of the heart. The flow imposed into the ventricle interacts dynamically with the mitral valve (mechanical or natural) and the ventricle which are simulated using the same model. Results from these simulations are compared with ad- hoc in-house experimental measurements. Finally, a parallelisation scheme is presented, as parallelisation is unavoidable when studying large scale problems involving several thousands of simultaneously deforming bodies on hundreds of distributed memory computing processors

Intelligent Controls for a Semi-Active Hydraulic Prosthetic Knee

We discuss open loop control development and simulation results for a semi-active above-knee prosthesis. The control signal consists of two hydraulic valve settings. These valves control a rotary actuator that provides torque to the prosthetic knee. We develop open loop control using biogeography-based optimization (BBO), which is a recently developed evolutionary algorithm, and gradient descent. We use gradient descent to show that the control generated by BBO is locally optimal. This research contributes to the field of evolutionary algorithms by demonstrating that BBO is successful at finding optimal solutions to complex, real-world, nonlinear, time varying control problems. The research contributes to the field of prosthetics by showing that it is possible to find effective open loop control signals for a newly proposed semi-active hydraulic knee prosthesis. The control algorithm provides knee angle tracking with an RMS error of 7.9 degrees, and thigh angle tracking with an RMS error of 4.7 degrees. Robustness tests show that the BBO control solution is affected very little by disturbances added during the simulation. However, the open loop control is very sensitive to the initial conditions. So a closed loop control is needed to mitigate the effects of varying initial conditions. We implement a proportional, integral, derivative (PID) controller for the prosthesis and show that it is not a sufficient form of closed loop control. Instead, we implement artificial neural networks (ANNs) as the mechanism for closed loop control. We show that ANNs can greatly improve performance when noise and disturbance cause high tracking errors, thus reducing the risk of stumbles and falls. We also show that ANNs are able to improve average performance by as much as 8 over open loop control. We also discuss embedded system implementation with a microcontroller and associated hardware and softwar

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 192

This bibliography lists 247 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1979