Kreg G. Gruben

A Preliminary Study of Cardiopulmonary Resuscitation by Circumferential Compression of the Chest with Use of a Pneumatic Vest

BACKGROUND More than 300,000 people die each year of cardiac arrest. Studies have shown that raising vascular pressures during cardiopulmonary resuscitation (CPR) can improve survival and that vascular pressures can be raised by increasing intrathoracic pressure. METHODS To produce periodic increases in intrathoracic pressure, we developed a pneumatically cycled circumferential thoracic vest system and compared the results of the use of this system in CPR (vest CPR) with those of manual CPR. In phase 1 of the study, aortic and right-atrial pressures were measured during both vest CPR (60 inflations per minute) and manual CPR in 15 patients in whom a mean (+/- SD) of 42 +/- 16 minutes of initial manual CPR had been unsuccessful. Vest CPR was also carried out on 14 other patients in whom pressure measurements were not made. In phase 2 of the study, short-term survival was assessed in 34 additional patients randomly assigned to undergo vest CPR (17 patients) or continued manual CPR (17 patients) after initial manual CPR (duration, 11 +/- 4 minutes) had been unsuccessful. RESULTS In phase 1 of the study, vest CPR increased the peak aortic pressure from 78 +/- 26 mm Hg to 138 +/- 28 mm Hg (P < 0.001) and the coronary perfusion pressure from 15 +/- 8 mm Hg to 23 +/- 11 mm Hg (P < 0.003). Despite prolonged unsuccessful manual CPR, spontaneous circulation returned with vest CPR in 4 of the 29 patients. In phase 2 of the study, spontaneous circulation returned in 8 of the 17 patients who underwent vest CPR as compared with only 3 of the 17 patients who received continued manual CPR (P = 0.14). More patients in the vest-CPR group than in the manual-CPR group were alive 6 hours after attempted resuscitation (6 of 17 vs. 1 of 17) and 24 hours after attempted resuscitation (3 of 17 vs. 1 of 17), but none survived to leave the hospital. CONCLUSIONS In this preliminary study, vest CPR, despite its late application, successfully increased aortic pressure and coronary perfusion pressure, and there was an insignificant trend toward a greater likelihood of the return of spontaneous circulation with vest CPR than with continued manual CPR. The effect of vest CPR on survival, however, is currently unknown and will require further study.

Constrained Cartesian motion control for teleoperated surgical robots

This paper addresses the problem of optimal motion control for teleoperated surgical robots, which must maneuver in constrained workspaces, often through a narrow entry portal into the patients body. The control problem is determining how best to use the available degrees of freedom of a surgical robot to accomplish a particular task, while respecting geometric constraints on the work volume, robot mechanism, and the specific task requirements. We present a method of formulating desired motions as sets of task goals in any number of coordinate frames (task frames) relevant to the task, optionally subject to additional linear constraints in each of the task frames. Mathematically, the kinematic control problem is posed as a constrained quadratic optimization problem and is shown to be computable in real time on a PC. We will present experimental results of the application of this control methodology to both kinematically deficient and kinematically redundant robots. Specifically, we will discuss the control issues within the context of a representative set of tasks in robot-assisted laparoscopy, which includes (but is not limited to) teleoperated navigation of a laparoscopic camera attached to a surgical robot. A system based on this control formalism has been used in preclinical in vivo studies at the Johns Hopkins University Medical Center and the early experience with the system will be summarized.

System for mechanical measurements during cardiopulmonary resuscitation in humans

A computer-based mobile data acquisition system that was designed and built for measurement of the mechanical properties of the human chest and the resultant vascular pressures are discussed. During manual cardiopulmonary resuscitation (CPR), a short cylindrical module was placed between the rescuers hands and the patients chest. This module, which was attached to an easily manipulated position-sensing arm, measured force and acceleration at the sternum. Three-dimensional position and orientation of the module were measured, as well as the component of the applied force which was perpendicular to the sternum. The central venous and aortic pressures were measured by high-fidelity pressure transducers. All transducer signals were recorded by digital computer. Real-time feedback of sternal force and displacement and vascular pressures was provided to the rescue team via chart recordings. An audible signal was produced as an aid in maintaining the desired compression rate and duration. The systems mobility permitted rapid implementation at any hospital location.<<ETX>>

Control and evaluation of a 7-axis surgical robot for laparoscopy

This paper describes the control and ergonomic evaluation of a ceiling mounted (or support frame suspended) 7-axis surgical robot (HISAR) for laparoscopic camera navigation. A key feature of the robot is that it incorporates a passive wrist for natural compliance with the port of entry into the patient. The use of a previously reported constrained Cartesian controller is motivated and demonstrated, and the results of successfully applying this control methodology to the manipulator are presented. The significance of the control strategy is the ease with which control of passive axes, the fulcrum constraint, and the motion inversion effect created by the fulcrum are accommodated. We also report on the results of laboratory evaluations of the arm in terms of its work volume, ergonomic factors, ease of control, and overall design within the context of laparoscopic camera control.

Identification of dynamic mechanical parameters of the human chest during manual cadiopulmonary resuscitation

Timely cardiopulmonary resuscitation (CPR) is often unsuccessful. The outcome can be improved by a better understanding of the relationship between the force applied to the sternum and the resulting hemodynamic effects. The first step in this complex chain of interactions is the mechanical response of the chest wall to cyclical compressions. A dynamic mechanical model of the chest response was formulated, and a method of identification of the model parameters based on force, displacement, and acceleration data acquired during cyclical compressions was developed. The elasticity, damping, and equivalent mass of the human chest were estimated with a constrained nonlinear least-mean-square identification technique. The method was validated on data acquired from a test apparatus built for this purpose. The model fit was measured with the normalized chi-square statistic on residuals obtained between recorded force and force predicted by the model. In the analysis of one human chest, the elasticity was found to be nonlinear and statistically different during compression and release.<<ETX>>

A remote center of motion robotic arm for computer assisted surgery

We have designed a robotic arm based on a double parallel four bar linkage to act as an assistant in minimally invasive surgical procedures. The remote center of motion (RCM) geometry of the robot arm kinematically constraints the robot motion such that minimal translation of an instrument held by the robot takes place at the entry portal into the patientApos;s body. In addition to the two rotational degrees of freedom comprising the RCM arm, distal translation and rotation are provided to manoeuver the instrument within the patients body about an axis coincident with the RCM. An XYZ translation stage located proximal to the RCM arm provides positioning capability to establish the RCM location relative to the patients anatomy. An electronics set capable of controlling the system, as well as performing a series of safety checks to verify correct system operation, has also been designed and constructed. The robot is capable of precise positional motion. Repeatability in the ±10 micron range is demonstrated. The complete robotic system consists of the robot hardware and an IBM PC-AT based servo controller connected via a custom shared memory link to a host IBM PS/2. For laparoscopic applications, the PS/2 includes an image capture board to capture and process video camera images. A camera rotation stage has also been designed for this application. We have successfully demonstrated this system as an assistant in a laparoscopic cholecystectomy. Further applications for this system involving active tissue manipulation are under development.

Optimal motion control for teleoperated surgical robots

This paper addresses the problem of optimal motion control for teleoperated surgical robots, which must maneuver in constrained workspaces. The control problem is determining how best to use the available degrees of freedom of a surgical robot to accomplish a particular task, while respecting geometric constraints on the work volume, robot mechanism, and the specific task requirements. We present a method of formulating desired motions in the task space (task space goals) as instances of a quadratic optimization problem, optionally subject to additional linear constraints. The control formalism applies both to kinematically deficient as well as kinematically redundant mechanisms. Specifically, we discuss the problem as it relates to a representative set of tasks in teleoperated navigation of a laparoscopic camera attached to a surgical robot.

Comparison of two manipulator designs for laparoscopic surgery

Two kinematically dissimilar robots for laparoscopic surgery have been designed and built through a collaborative effort between IBM Research and the Johns Hopkins University School of Medicine. The two mechanisms represent two distinct design approaches and a number of different engineering design decisions. In this paper we describe the mechanical design and kinematic structure of the two robots and report on the results of laboratory evaluations of the two mechanisms. The two systems are compared in terms of safety, ergonomics, ease of control, accuracy, and mechanical stiffness. In each of the categories we attempt to separate the impact of the particular design decisions made in the construction of each mechanism from the more general issue of the fundamental potential and limitations of each of the design approaches towards satisfying the particular design criterion. Based on our experience, we offer some conclusions and recommendations regarding the design of surgical robots for laparoscopy.

Foot force direction control during leg pushes against fixed and moving pedals in persons post-stroke.

The component of foot force generated by muscle action (F(m)) during pedaling in healthy humans has a nearly constant direction with increasing force magnitude. The present study investigated the effect of stroke on the control of foot force. Ten individuals with hemiparesis secondary to a cerebral vascular accident performed pushing efforts against translationally fixed and moving pedals on a custom stationary cycle ergometer. We found that while F(m) direction remained constant with increasing effort in both the fixed- and moving-crank conditions for both limbs, the orientation of that force component differed between limbs. The non-paretic limb produced the same F(m) orientation as seen previously in healthy humans. However, relative to the non-paretic limb, the paretic limb force line-of-action was shifted away from the hip and closer to the knee in the sagittal-plane for both pedal motion conditions. In the frontal plane, the paretic limb force line-of-action was shifted laterally, closer to parallel to the midline, for both pedal motion conditions. These shifts were consistent with previously reported lower limb muscle weakness and alterations in muscle activation observed during pedaling tasks following stroke. The finding of similar orientations for static and dynamic pushing efforts suggests that limb posture could be a trigger for relative muscle activation levels. The preservation of a constant direction in F(m) with increasing force magnitude post-stroke, despite an orientation shift, suggests that control of lower limb force may be organized by magnitude and direction and that these two aspects are differentially affected by stroke.

Force direction pattern stabilizes sagittal plane mechanics of human walking.

The neural control and mechanics of human bipedalism are inadequately understood. The variable at the interface of neural control and body mechanics that is key to upright posture during human walking is the force of the ground on the foot (ground reaction force, F). We present a model that predicts sagittal plane F direction as passing through a divergent point (DP) fixed in a reference frame attached to the person. Four reference frames were tested to identify which provided the simplest and most accurate description of F direction. For all reference frames, the DP model predicted nearly all the observed variation in F direction and whole body angular momentum during single leg stance. The reference frame with vertical orientation and with origin on the pelvis provided the best combination of accuracy and simplicity. The DP was located higher than the CM and the predicted F produced a pattern of torque about the CM that caused body pitch oscillations that disrupted upright posture. Despite those oscillations, that torque was evidence of a stability mechanism that may be a critical component enabling humans to remain upright while walking and performing other tasks.