Guido Danieli

Left ventricle load impedance control by apical VAD can help heart recovery and patient perfusion: a numerical study.

The aim of this work is to investigate the dependence between left ventricular load impedance control by an apical ventricular assist device (VAD) and the consequent benefits for pathological heart recovery. A pathological left ventricle with 34% contractility has been simulated in the assisted and nonassisted conditions. By means of an extended Kalman filter, left ventricular pressure-volume loops have been partially estimated and ventricular as well as circulatory quantities inferred. The heart operation mode, based on cardiac energetic criteria, is imposed by controlling the VAD filling phase. In the assisted condition, results show that the left ventricle end-diastolic volume, left atrial pressure, and wall stress all decrease; stroke volume, ejection fraction, ventricular efficiency, aortic pressure, and cardiac output all increase. Benefits are also evident for the right ventricle and systemic and pulmonary circulation. The strategy outlined in this work also shows that good results for heart recovery are achievable and a possible way to improve the functional properties of commercial pulsatile VADs.

Left Ventricle Afterload Impedance Control by an Axial Flow Ventricular Assist Device: A Potential Tool for Ventricular Recovery

Ventricular assist devices (VADs) are increasingly used for supporting blood circulation in heart failure patients. To protect or even to restore the myocardial function, a defined loading of the ventricle for training would be important. Therefore, a VAD control strategy was developed that provides an explicitly definable loading condition for the failing ventricle. A mathematical model of the cardiovascular system with an axial flow VAD was used to test the control strategy in the presence of a failing left ventricle, slight physical activity, and a recovering scenario. Furthermore, the proposed control strategy was compared to a conventional constant speed mode during hemodynamic changes (reduced venous return and arterial vasoconstriction). The physiological benefit of the control strategy was manifested by a large increase in the ventricular Frank-Starling reserve and by restoration of normal hemodynamics (5.1 L/min cardiac output at a left atrial pressure of 10 mmHg vs. 4.2 L/min at 21 mmHg in the unassisted case). The control strategy automatically reduced the pump speed in response to reduced venous return and kept the pump flow independent of the vasoconstriction condition. Most importantly, the ventricular load was kept stable within 1%, compared to a change of 75% for the constant speed. As a key feature, the proposed control strategy provides a defined and adjustable load to the failing ventricle by an automatic regulation of the VAD speed and allows a controlled training of the myocardium. This, in turn, may represent a potential additional tool to increase the number of patients showing recovery.

Hybrid test bench for evaluation of any device related to mechanical cardiac assistance.

Hydraulic mock circulatory systems have low flexibility to allow tests of different cardiovascular devices and low precision when a reference model must be reproduced. In this paper a new bench is described. It combines the computer model of the environment in which the device will operate and the electro-hydraulic interfaces by which device and computer are connected. A models library provided with basic functions allows implementing many layouts of the bench, which in turn depend both on the device properties and the desired experiment. In case of an apical LVAD evaluation, the bench can reproduce right and left ventricles, pulmonary and systemic circulations, inlet and outlet LVAD cannulas. An interface forces the instantaneous calculated flow at the VAD input and feeds back the measured pressure to the computer; another interface works in a similar -but complementary- way at the VAD output. The paper focuses on the operating principle of the electro hydraulic interfaces which represent a relevant component of the bench, on the RT-Linux-based software architecture, on the models of the basic elements of the bench. A patent is under preparation. At the moment, only a portion of the bench has been developed. It consists of a piston-cylinder mechanism, which mimics the elastance-based mechanism of a natural ventricle, and a hydraulic circuit representing the arterial load according to a modified windkessel model and the venous return according to the Guytons model. The pump is driven by a real-time simulation of the cardiovascular system. This preliminary layout allowed testing the piston-cylinder mechanism, its control, and the software. This electro-hydraulic interface has been used to reproduce a pulsatile pump working in different modes. The hybrid model approach can support the development of new cardiac assist devices from their computer model to their manufacture.

A modified elastance model to control mock ventricles in real-time: numerical and experimental validation.

This article describes an elastance-based mock ventricle able to reproduce the correct ventricular pressure-volume relationship and its correct interaction with the hydraulic circuit connected to it. A real-time control of the mock ventricle was obtained by a new left ventricular mathematical model including resistive and inductive terms added to the classical Suga-Sagawa elastance model throughout the whole cardiac cycle. A valved piston pump was used to mimic the left ventricle. The pressure measured into the pump chamber was fed back into the mathematical model and the calculated reference left ventricular volume was used to drive the piston. Results show that the classical model is very sensitive to pressure disturbances, especially during the filling phase, while the modified model is able to filter out the oscillations thus eliminating their detrimental effects. The presented model is thus suitable to control mock ventricles in real-time, where sudden pressure disturbances represent a key issue and are not negligible. This real-time controlled mock ventricle is able to reproduce the elastance mechanism of a natural ventricle by mimicking its preload (mean atrial pressure) and afterload (mean aortic pressure) sensitivity, i.e., the Starling law. Therefore, it can be used for designing and testing cardiovascular prostheses due to its capability to reproduce the correct ventricle-vascular system interaction.

An Experimental Comparative Study on Non-Circular Gears and CAM Transmissions for a Blood Pumping System

In this paper, we have reported results of experimental activity for a characterization of mechanical transmissions with gears or cams. The study has been focused on specific transmission characteristics that are related to a mechanical blood pumping design. In particular, experimental tests have been analyzed to understand benefits and drawbacks for using non-circular gears and polynomial cams in pure mechanical transmissions with limited motion regulation but with specific prescribed motion law.Copyright

The Twin Forceps: A New Instrument for SILS

In the last ten years, the single incision laparoscopic surgery (SILS) is gaining more interest than the traditional laparoscopic surgery (LAP). Many studies make a comparison between the performances of the SILS and the LAP. The results show that the single incision laparoscopic surgery reduces pain, length of period of postoperative hospitalization, and loss of blood. This technique is also able to reduce the infection sites. In spite of many advantages, SILS reveals some problems: laparoscopic instruments triangulation and small workspace. The surgeon has to be more skillful to make a surgery in SILS because the surgeon has only three laparoscopic instruments and only one hole in the abdomen cavity. In this paper, a novel laparoscopic instrument to help the surgeon during a SILS operation is presented. This instrument is innovative forceps with double graspers. Different designs of this instrument are presented, with the final one which greatly simplifies both construction and operation. The initial experience in the laboratory with the innovative instrument is presented. The surgeon experienced in laparoscopic surgery and with the help of assistants performed a training program based on predetermined task performed in simulation box (laparoscopic box-trainer).

EXPERIMENTAL VALIDATION OF A SPECIAL LOCKING DRUM BRAKE FOR ROBOTIC APPLICATIONS

The paper presents the development of a novel type of drum brake capable of locking a joint exploiting the effect of self excitation characteristic of this type of brake. A theoretical analysis based on the Reye assumption on wear is first presented, were conditions for self excitement are determined. An initial version of the brake was designed and tested, but it was soon discovered that actuation with solenoids was not appropriate. A second version was then developed where solenoids were replaced by a small motor and reducer placed inside the brake itself, but the resulting drum was too big for the application. Finally a version were the motor and reducer were placed outside the drum was designed. An ad hoc experimental test bed was built using a Maxon motor to control rotation and toque of the drum and to allow an initial wear of the ferodo in order to obtain compliant surfaces. Finally an electronic control of the brakes has been developed.Copyright

ROSA – RObotic System for Angioplasty

This paper describes an innovative robotic system designed to perform transcatheter angioplasty, that can be used in a number of different applications. It is based on a very simple system, including both a measuring unit, called Master, that is the one on which the physician directs the operations, and an actuation device, called Slave, located near to the patient, that actively reproduces the movements commanded by the operator at the passive Master unit. Both systems require a small additional element that takes direct contact with guides and catheters and needs therefore to be sterile on the Slave unit. The system has been designed adding also the possibility of using an alternative Master station equipped with two joysticks and a series of knobs and can drive up to three different Slaves, one dedicated to the guiding catheter, the second and third to balloon catheters and relative guide wires, that may be used also in couple. Two patents have already been presented on this topic.

Upper and Lower Limbs Rehabilitation: DARTAGNAN, An Alternative Solution to Exoskeletal Robots

This article deals with a new robot for rehabilitation, DARTAGNAN, able to work in active or passive modes, on upper and lower human limbs. The presented robot has an hybrid serial/parallel structure with 6 degree of freedoms and a self-balanced mechanical structure. Although it is not an exoskeleton, DARTAGNAN behaves as such thanks to the customized software and to specific end-effectors, which can be appropriately connected to the forearm or lower leg. Thanks to the force/torque sensor the robot is able to treat the patient limb allowing him/her to (i) feel no effort in passive following mode, (ii) feel a specific effort in passive resistive mode or (iii) to actuate directly the limb in case of force deficit or spasticity for the active mode, while performing the exercise. Moreover, one of features of the robot is the possibility to directly calculate the limbs anthropometric parameters without the need of manual measurements to be set up before each treatment.

Design and Development of an Optical System for 3D Direct Detection of Dental Arch Model From the Patient’s Mouth

This paper describes a 3D scanning system based on an active vision method using structured light in order to obtain the CAD model of a dental arch. Presently, dental prosthesization requires long times in between detecting the shape of the dental arch, plaster model generation, scanning of it, prosthesis preparation, and implant. The situation is even worse when use of dental implants is required, while early loading of the implants is considered a positive solution. For this reason many devices are actually presented for the intra oral determination of the shape of dental prostheses and inserts. These devices however are able to detect limited portions of the dental arch, since they must be hand held by the doctor. This work presents a new device able to detect with high precision the entire dental arch.