A Study Ex Vivo of the Effect of Epicardial Fat on the HeartLander Robotic Crawler.

A tethered epicardial crawling robot known as HeartLander has been developed for minimally-invasive surgery on the beating heart. The crawler has been tested in vivo many times in a porcine model, a model which provides generally authentic conditions in many ways; however, the pigs tested generally have little epicardial fat, whereas the epicardial fat in human patients will be considerable. As a result, it is necessary to determine the effect of such fat on the performance of the crawler. In one experiment, using fresh ovine hearts ex vivo, clogging of the suction chambers of the crawler during sliding over tissue with active suction was investigated for a variety of thicknesses of epicardial fat. In a second experiment, the maximum traction force during each step was measured when sliding with active suction repeatedly over the same location for a variety of fat thicknesses. The clogging experiment showed accumulation of fat in the suction chamber, with the amount dependent on the state of the epicardial membrane, but the suction line did not clog. The traction experiment showed that traction was maintained in all cases except when the epicardial membrane was excised completely.

Improved traction for a mobile robot traveling on the heart.

This document describes the effects of several design parameters on the traction generated by the suction pads of a mobile robot that walks on the surface of the heart. HeartLander is a miniature mobile robot that adheres to the epicardial surface of the heart using suction, and can travel to any desired location on the heart to administer therapeutic applications. To maximize the effectiveness of locomotion, the gripper pads must provide sufficient traction to avoid slipping. Our testing setup measured the force applied to the gripper pad adhering to ovine epicardial tissue, and recorded overhead video for tracking of the pad and tissue during an extension. By synchronizing the force and video data, we were able to determine the point at which the pad lost traction and slipped during the extension. Of the pads tested, the pad with no suction grate achieved maximum traction. Increasing the extension speed up to 20 mm/s resulted in a corresponding increase in traction. Increasing the vacuum pressure also improved the traction, but the magnitude of the effect was less than the improvement gained from increasing extension speed.

A miniature cable-driven robot for crawling on the heart.

This document describes the design and preliminary testing of a cable-driven robot for the purpose of traveling on the surface of the beating heart to administer therapy. This methodology obviates mechanical stabilization and lung deflation, which are typically required during minimally invasive cardiac surgery. Previous versions of the robot have been remotely actuated through push-pull wires, while visual feedback was provided by fiber optic transmission. Although these early models were able to perform locomotion in vivo on porcine hearts, the stiffness of the wire-driven transmission and fiber optic camera limited the mobility of the robots. The new prototype described in this document is actuated by two antagonistic cable pairs, and contains a color CCD camera located in the front section of the device. These modifications have resulted in superior mobility and visual feedback. The cable-driven prototype has successfully demonstrated prehension, locomotion, and tissue dye injection during in vitro testing with a poultry model.

Preliminary evaluation of a mobile robotic device for navigation and intervention on the beating heart.

This article describes the development and preliminary testing of a mobile robotic device to facilitate minimally invasive beating-heart intrapericardial intervention. The HeartLander robot will be introduced beneath the pericardium via subxiphoid incision, adhere to the epicardium, navigate to any location, and administer therapy under the control of the physician. As compared to current robotic cardiac surgical techniques, this novel paradigm obviates immobilization of the heart and eliminates access limitations. Furthermore, it does not require lung deflation and differential ventilation and thus could enable outpatient cardiac surgery. The current HeartLander prototypes use suction to maintain prehension of the epicardium and wire actuation to perform locomotion. A fiber optic videoscope displays visual feedback to the physician, who controls the device through a joystick interface. The initial prototype demonstrated successful prehension, turning, and locomotion on open-chest, beating-heart porcine models where the pericardium was removed (N = 3). A smaller second-generation prototype with an injection system demonstrated locomotion and myocardial injection of dye, both performed with the pericardium intact (N = 3). These trials illustrate the feasibility of using a miniature mobile robot to navigate upon the beating heart and perform intrapericardial therapy.

Recovery trajectories of vestibulopathic subjects after perturbations during locomotion.

We compared the mediolateral (M/L) responses to perturbations during locomotion of vestibulopathic (VP) subjects to those of controls. Eight subjects with unilateral vestibular loss (100% Reduced Vestibular Response from the caloric test) resulting from surgery for vestibular schwannoma and 11 controls were selected for this study. Despite their known vestibulopathy, all VP subjects scored within the normal range on computerized dynamic posturography Sensory Organization Tests. During gait, subjects were given surface perturbations of the right support-phase foot in two possible directions (forward-right and backward-left) at two possible magnitudes (5 and 10 cm) that were randomly mixed with trials having no perturbations. M/L stability was quantified by estimating the length of the M/L moment arm between the support foot and the trunk, and the M/L accelerations of the sternum and the head. The VP group had greater changes (p < 0.05) in their moment arm responses compared to controls. The number of steps that it took for the moment arm oscillations to return to normal and the variability in the moment arms were greater for the VP group. Differences in the sternum and head accelerations between VP and control groups were not as consistent, but there was a trend toward greater response deviations in the VP group for all 4 perturbation types. Increased response magnitude and variability of the VP group is consistent with an increase in their sensory noise of vestibular inputs due to the surgical lesion. Another possibility is a reduced sensitivity to motion inputs. This perturbation approach may prove useful for characterizing subtle vestibulopathies and similar changes in the human orientation mechanism after exposure to microgravity.