Biomedical subjects

Robert D Howe

Publications and source records attributed to Robert D Howe.

7 recordsLinked to original sources

PubMed2005

Three-dimensional echo-guided beating heart surgery without cardiopulmonary bypass: atrial septal defect closure in a swine model.

OBJECTIVE: In this study, we tested 3 techniques of atrial septal defect closure under real-time 3-dimensional echocardiography guidance in a swine model. METHODS: The operations were conducted under the sole guidance of a modified real-time 3-dimensional echocardiography guidance system with a x4 matrix transducer (Sonos 7500, Philips Medical Systems, Andover, Mass). Eighteen swine were anesthetized, and after median sternotomy, the echo probe was applied directly to the surface of the right atrium. To create an atrial septal defect, balloon atrial septostomy and atrial septal defect enlargement were performed. Subsequently, 3 different techniques of atrial septal defect closure were attempted: group I, direct suture closure; group II, closure of the atrial septal defect using the Amplatzer device (AGA Medical Corp, Golden Valley, Minn); and group III, patch closure of the atrial septal defect (n = 6 each). RESULTS: Real-time 3-dimensional echocardiography guidance provided sufficient spatial resolution and a satisfactory frame rate to provide a "virtual surgeon's view" of the relevant anatomy during the entire procedure. All atrial septal defects were enlarged, and the mean final size was 8.5 +/- 1.8 mm. Atrial septal defect closure was successfully accomplished with all the 3 surgical techniques examined. In groups I and III, the needles (1-3 sutures) and staples (6-12 staples) penetrated the tissue and patch material consistently, whereas in group III, the Amplatzer atrial septal defect device was easily deployed. There was no incident device/staple embolization or air introduction. Neither intraoperative 2-dimensional color Doppler echocardiography nor postmortem macro-evaluation revealed any residual shunts. CONCLUSIONS: Beating heart atrial septal defect closure under real-time 3-dimensional echocardiographic guidance is feasible and, unlike catheter-based devices, applicable for any type of secundum atrial septal defect.

Animals↗

PubMed2005

Effects of perfusion on the viscoelastic characteristics of liver.

Accurate characterization of soft tissue material properties is required to enable new computer-aided medical technologies such as surgical training and planning. The current means of acquiring these properties in the in vivo and ex vivo states is fraught with problems, including limited accessibility and unknown boundary conditions in the former, and unnatural behavior in the latter. This paper presents a new testing method where a whole porcine liver is perfused under physiologic conditions and tested in an ex vivo setting. To characterize the effects of perfusion on the viscoelastic response of liver, indentation devices made force and displacement measurements across four conditions: in vivo, ex vivo perfused, ex vivo post perfused, and in vitro on an excised section. One device imposed cyclic perturbations on the liver's surface, inducing nominal strains up to 5% at frequencies from 0.1 to 200 Hz. The other device measured 300 s of the organ's creep response to applied loads, inducing nominal surface stresses of 6.9-34.7 kPa and nominal strains up to 50%. Results from empirical models indicate that the viscoelastic properties of liver change with perfusion and that two time constants on the order of 1.86 and 51.3s can characterize the liver under large strains typical of surgical manipulation across time periods up to 300 s. Unperfused conditions were stiffer and more viscous than the in vivo state, resulting in permanent strain deformation with repeated indentations. Conversely, the responses from the ex vivo perfusion condition closely approximated the in vivo response.

Animals↗

PubMed2005

Measurement of vocal fold collision forces during phonation: methods and preliminary data.

Forces applied to vocal fold tissue as the vocal folds collide may cause tissue injury that manifests as benign organic lesions. A novel method for measuring this quantity in humans in vivo uses a low-profile force sensor that extends along the length and depth of the glottis. Sensor design facilitates its placement and stabilization so that phonation can be initiated and maintained while it is in place, with minimal interference in vocal fold vibration. In 2 individuals with 1 vibrating vocal fold and 1 nonvibrating vocal fold, peak collision force correlates more strongly with voice intensity than pitch. Vocal fold collision forces in 1 individual with 2 vibrating vocal folds are of the same order of magnitude as in previous studies. Correlations among peak collision force, voice intensity, and pitch were indeterminate in this participant because of the small number of data points. Sensor modifications are proposed so that it can be used to reliably estimate collision force in individuals with 2 vibrating vocal folds and with changing vocal tract conformations.

Biomechanical Phenomena↗

PubMed2004

Three-dimensional echocardiography-guided beating-heart surgery without cardiopulmonary bypass: a feasibility study.

BACKGROUND: There is no current acceptable approach for intracardiac beating-heart interventions. We have adapted real-time 3-dimensional echocardiography with specialized instrumentation to facilitate beating-heart repair of atrial septal defects and mitral valve plasty to investigate the feasibility of real-time 3-dimensional echocardiography-guided cardiac surgery. METHODS: In experiment I a modified real-time 3-dimensional echocardiography system with x4 matrix transducer was compared with 2-dimensional echocardiography in the performance of common surgical tasks. Completion times, deviation from an ideal trajectory, and an echogenic target were measured. In experiment II porcine atrial septal defects were closed with an original semiautomatic suturing device (n = 4) and with a 5-mm endoscopic stapler and a pericardial or polytetrafluoroethylene patch (n = 4). In experiment III a pulsatile porcine mitral valve model was developed, and suture placement through the anterior and posterior mitral leaflets was performed (n = 8). During all experiments, the operator was blinded to the target and operated on only with ultrasonic guidance. RESULTS: In experiment I, compared with 2-dimensional echocardiographic guidance, completion times improved by 21% ( P <.01) with high-trajectory accuracy, and suture deviation was significantly smaller (2-dimensional echocardiography, 5.4 +/- 2.7 mm; 3-dimensional echocardiography, 1.7 +/- 0.7 mm; P <.05) in real-time 3-dimensional echocardiography-guided tasks. In experiments II and III in both atrial septal defect closure and mitral valve plasty, real-time 3-dimensional echocardiography provided satisfactory images and sufficient anatomic detail for suturing and patch deployment. All surgical tasks were successfully performed with accuracy. CONCLUSIONS: Real-time 3-dimensional echocardiography provides adequate imaging and anatomic detail to act as a sole guide for surgical task performance. These initial experiments demonstrate the feasibility of beating-heart direct or patch closure of atrial septal defects and mitral valve plasty without cardiopulmonary bypass.

Animals↗

PubMed2003

Truth cube: establishing physical standards for soft tissue simulation.

Accurate real-time models of soft tissue behavior are key elements in medical simulation systems. The need for fast computation in these simulations, however, often requires simplifications that limit deformation accuracy. Validation of these simplified models remains a challenge. Currently, real-time modeling is at best validated against finite element models that have their own intrinsic limitations. This study develops a physical standard to validate real-time soft tissue deformation models. We took CT images of a cube of silicone rubber with a pattern of embedded Teflon spheres that underwent uniaxial compression and spherical indentation tests. The known material properties, geometry and controlled boundary conditions resulted in a complete set of volumetric displacement data. The results were compared to a finite element model analysis of identical situations. This work has served as a proof of concept for a robust physical standard for use in validating soft tissue models. A web site has been created to provide access to our database: http://biorobotics.harvard.edu/truthcube/ (soon to be http://www.truthcube.org).

Animals↗

PubMed2003

Application of robotics in congenital cardiac surgery.

Over the past 5 years, robotic systems that combine advanced endoscopic imaging with computer-enhanced instrument control have been used for both coronary revascularization and intracardiac procedures in adults. In addition, endoscope positioning systems and articulated instruments with a robotic wrist mechanism have further expanded the potential applications for robotics in cardiac surgery. In pediatric cardiac surgery, potential applications can be divided into simple scope manipulation versus the use of 3-dimensional imaging and a robotic wrist for dissection and reconstruction. A voice-controlled robotic arm for scope manipulation can facilitate current pediatric thoracoscopic procedures such as ligation of patent ductus arteriosus and division of vascular rings. By using an advanced imaging system along with a robotic wrist, more complex extracardiac and even intracardiac procedures can be performed in children. Examples include coarctation repair, septal defect repair, and mitral or tricuspid valvuloplasty. Furthermore, with adequate intracardiac imaging, a robot-assisted off-pump approach to intracardiac pathology is conceivable. New real-time 3-dimensional echocardiography now offers sufficient resolution to enable such procedures, while the addition of instrument tracking, haptic feedback, and novel tissue fixation devices can facilitate safe and reliable intracardiac repair without extracorporeal circulation.

Cardiac Surgical Procedures↗

PubMed2003

Real-time three-dimensional ultrasound for guiding surgical tasks.

OBJECTIVE: As a stand-alone imaging modality, two-dimensional (2D) ultrasound (US) can only guide basic interventional tasks due to the limited spatial orientation information contained in these images. High-resolution real-time three-dimensional (3D) US can potentially overcome this limitation, thereby expanding the applications for US-guided procedures to include intracardiac surgery and fetal surgery, while potentially improving results of solid organ interventions such as image-guided breast, liver or prostate procedures. The following study examines the benefits of real-time 3D US for performing both basic and complex image-guided surgical tasks. MATERIALS AND METHODS: Seven surgical trainees performed three tasks in an acoustic testing tank simulating an image-guided surgical environment using 2D US, biplanar 2D US, and 3D US for guidance. Surgeon-controlled US imaging was also tested. The evaluation tasks were (1) bead-in-hole navigation; (2) bead-to-bead navigation; and (3) clip fixation. Performance measures included completion time, tool tip trajectory, and error rates, with endoscope-guided performance serving as a gold-standard reference measure for each subject. RESULTS: Compared to 2D US guidance, completion times decreased significantly with 3D US for both bead-in-hole navigation (50%, p = 0.046) and bead-to-bead navigation (77%, p = 0.009). Furthermore, tool-tip tracking for bead-to-bead navigation demonstrated improved navigational accuracy using 3D US versus 2D US (46%, p = 0.040). Biplanar 2D imaging and surgeon-controlled 2D US did not significantly improve performance as compared to conventional 2D US. In real-time 3D mode, surgeon-controlled imaging and changes in 3D image presentation made by adjusting the perspective of the 3D image did not diminish performance. For clip fixation, completion times proved excessive with 2D US guidance (> 240 s). However, with real-time 3D US imaging, completion times and error rates were comparable to endoscope-guided performance. CONCLUSIONS: Real-time 3D US can guide basic surgical tasks more efficiently and accurately than 2D US imaging. Real-time 3D US can also guide more complex surgical tasks which may prove useful for procedures where optical imaging is suboptimal, as in fetal surgery or intracardiac interventions.

Humans↗