Leslie A. Geddes

Small intestinal submucosa as a large diameter vascular graft in the dog

Autogenous saphenous vein and synthetic materials, such as Dacron and expanded polytetrafluoroethylene, have been used extensively as vascular grafts with moderate success. Improved success rates for vascular graft surgery may be possible if superior graft material was available. We tested the use of autogenous small intestinal submucosa (SIS) as a large diameter (10 mm) vascular graft in the infrarenal aorta of 12 dogs. One dog died with graft thrombosis within 48 hr of surgery. Nine dogs were sacrificed at various times during a 52-week post-surgical period and showed patent grafts without infection, thrombosis, intimal hyperplasia, or adverse effects upon blood pressure. There was no ultrastructural evidence of endothelial cell growth on the luminal surface of the SIS graft which was composed of a dense, non-thrombogenic, organized collagenous connective tissue. The SIS material was approximately one order of magnitude less elastic than natural aorta and showed an immediate dilatation of approximately 18% after exposure to the systemic blood pressure. However, there was no progressive dilatation during the 52-week postsurgical period. Two dogs remain alive at 8 and 52 weeks post-surgery with patent grafts as determined by positive contrast radiography and Doppler studies. We conclude that autogenous small intestinal submucosa can be successfully used as a large diameter arterial graft in the dog and is worthy of further investigation.

Small Intestinal Submucosa as a Vascular Graft: A Review

Continuing investigations of vascular graft materials suggest that unacceptable graft complications continue and that the ideal graft material has not yet been found. We have developed and tested a biologic vascular graft material, small intestine submucosa (SIS), in normal dogs. This material, when used as an autograft, allograft, or xenograft has demonstrated biocompatibility and high patency rates in aorta, carotid and femoral arteries, and superior vena cava locations. The grafts are completely endothelialized at 28 days post-implantation. At 90 days, the grafts are histologically similar to normal arteries and veins and contain a smooth muscle media and a dense fibrous connective tissue adventitia. Follow-up periods of up to 5 years found no evidence of infection, intimal hyperplasia, or aneurysmal dilation. One infection-challenge study suggested that SIS may be infection resistant, possibly because of early capillary penetration of the SIS (2 to 4 days after implantation) and delivery of body defenses to the local site. We conclude that SIS is a suitable blood interface material and is worthy of continued investigation. It may serve as a structural framework for the application of tissue engineering technologies in the development of the elusive ideal vascular graft material.

Characterization of the Oscillometric Method for Measuring Indirect Blood Pressure

In this study, human subjects and dogs were used to determine the ability of the oscillometric method to indicate systolic and diastolic pressure. In the human studies, the auscultatory method was used as the reference. In the animal studies, directly recorded blood pressure was used as the reference. The ability of the sudden increase in cuff pressure oscillations during cuff deflation to indicate systolic pressure was examined and found to overestimate systolic pressure slightly in man, but more in animals. Systolic pressure was encountered when the cuff pressure oscillations were about one half of their maximum amplitude. However, in both man and animals the ratio was not constant; although the range was less in man than in animals. Diastolic pressure was encountered when cuff-pressure oscillation amplitude was about 0.8 of the maximal amplutide. This ratio for diastolic pressure was not constant over a range of diastolic pressure. The range of variability was less for man than for the dog.

Small Intestinal Submucosa as a Small-Diameter Arterial Graft in the Dog

Autogenous saphenous vein, human umbilical vein, modified bovine collagen, Dacron, and PTFE have been used as small-diameter arterial grafts with moderate success. We tested autogenous small intestine submucosa as a small-diameter arterial graft in both a carotid and femoral artery (mean ID 4.3 mm) of 18 dogs (total of 36 grafts). All dogs received aspirin and warfarin sodium for the first 8 weeks after surgery. Graft patency was evaluated by Doppler ultrasound techniques and angiography. Two grafts ruptured and 5 grafts occluded by 21 days after surgery. One graft became occluded at 14 weeks. Fifteen dogs were sacrificed at periodic intervals until 48 weeks after surgery. Patent grafts had no evidence of infection, propagating thrombus, or intimal hyperplasia. Graft aneurysmal dilation occurred in 4 grafts (11%). The grafts were composed of a dense organized collagenous connective tissue with no evidence of endothelial cell growth on the smooth luminal surface. Three dogs are alive at 76 to 82 weeks after surgery. Overall, graft patency was 75%. Graft patency after cessation of anticoagulation therapy was 92.3% (12 of 13 grafts). We conclude that autogenous small intestinal submucosa can be used as a small-diameter arterial graft in the dog and is worthy of further investigation.

Criteria for the selection of materials for implanted electrodes.

AbstractThere are four criteria that must be considered when choosing material for an implanted electrode: (1) tissue response, (2) allergic response, (3) electrode-tissue impedance, and (4) radiographic visibility. This paper discusses these four criteria and identifies the materials that are the best candidates for such electrodes. For electrodes that make ohmic contact with tissues: gold, platinum, platinum–iridium, tungsten, and tantalum are good candidates. The preferred insulating materials are polyimide and glass. The characteristics of stimulator output circuits and the importance of the bidirectional wave- form in relation to electrode decomposition are discussed. The paper concludes with an analysis, the design criteria, and the special properties and materials for capacitive recording and stimulating electrodes.

Historical evolution of circuit models for the electrode-electrolyte interface

Electrodes are widely used to measure bioelectric events and to stimulate excitable tissues. In one form or another, electrodes have been around for nearly two centuries; yet our ability to predict their properties is extremely limited, despite considerable research, especially during the last century. This paper chronicles the accumulation of knowledge about the electrode-electrolyte interface as a circuit element. Our understanding of this interface starts with the Helmholtz double layer of charge and progresses through the Warburg and Fricke lowcurrent-density models, which demonstrated that the resistive and capacitive components are polarization elements, the values of which depend on frequency. The discovery by Schwan, showing that the components of the Warburg-Fricke model are current-density dependent, is recounted, along with the discovery of the rectifying properties of the electrode-electrolyte interface and how it was put to practical use. The very high current-density operation of the interface is discussed in terms of gas evolution, arcing, and shock-wave production. Finally the evolution of recording electrodes is traced. Because electrodes can be operated over a very wide range of current density, it is unlikely that a single model can be created for the electrode-electrolyte interface, although over a restricted current-density range such a model may be possible.

Comparison of the resistance to infection of intestinal submucosa arterial autografts versus polytetrafluoroethylene arterial prostheses in a dog model

PURPOSE Prosthetic graft infection represents a most challenging complication to the vascular surgeon. Although expanded polytetrafluoroethylene (ePTFE) grafts have an acceptable patency rate, especially in the large-diameter arterial location, bacterial contamination of this material usually requires surgical removal of the graft. METHODS We compared the resistance of large-diameter ePTFE grafts and grafts constructed of small intestinal submucosa (SIS) to deliberate infection with Staphylococcus aureus. Eighteen dogs were divided into two equal groups, and the infrarenal aorta was replaced with either ePTFE or SIS graft material. One hundred million S. aureus organisms were deposited directly on the graft at the time of surgery, and the dogs were observed for 30 days. RESULTS One dog with an ePTFE graft died of hemorrhage from anastomosis site at 21 days. Of the remaining eight dogs with ePTFE grafts, four had positive culture results from the removed graft material, and all had histologic evidence for persistent infection. These dogs also had chronic fever, and the average white blood cell count at day 30 was 15,600/mm3. All nine dogs with SIS grafts had patent grafts, were afebrile after the first week, had an average white blood cell count of 11,500/mm3 at 30 days (p value = NS), had negative culture results, and had the histologic appearance of graft remodeling with collagen that was free of active inflammation. CONCLUSIONS We conclude that large-diameter arterial SIS grafts are more resistant to persistent infection with S. aureus than ePTFE grafts in this dog model of deliberate bacterial inoculation.

Small intestinal submucosa as a superior vena cava graft in the dog.

Autogenous spiral vein grafts and ePTFE have been used for reconstruction of the superior vena cava with moderate success. We tested autogenous small intestine submucosa as a superior vena cava interpositional graft in nine dogs. All dogs received aspirin and warfarin sodium for the first 8 weeks after surgery. Graft patency was evaluated by serial venography. One dog died from excessive anticoagulation. Eight dogs were sacrificed at periodic intervals until 72 weeks after surgery. Patent grafts had no evidence of thrombosis, aneurysm, or stenosis. The grafts consisted of dense, organized collagenous connective tissue with a complete endothelial cell layer on the luminal surface. Two dogs are alive at 28 and 34 months after surgery. Graft patency was 89% (eight of nine grafts). We conclude that autogenous small intestine submucosa can be used as a superior vena cava graft in the dog and is worthy of further investigations.

Relationship of blood pressure and flow during CPR to chest compression amplitude: Evidence for an effective compression threshold

This study was conducted to investigate the importance of the depth of chest compression in producing effective cardiopulmonary resuscitation (CPR) in animals, as indicated by cardiac output and mean arterial blood pressure. Cardiac output was measured by a modified indicator dilution technique in 8 anesthetized dogs, 6 to 12 kg body weight, during repeated 2-minute episodes of electrically induced ventricular fibrillation and CPR provided by a mechanical chest compressor and ventilator (Thumper). Chest compression exceeding a threshold value (xo) between 1.5 and 3.0 cm was required in each animal to produce measurable cardiac output. In particular, cardiac output (CO) was linearly related to chest compression depth (x) by an expression of the form CO = a(x-xo) for x greater than xo. The mean value of xo was 2.3 cm. A similar threshold for measurable blood pressure was observed in 7 of the 8 dogs, with a mean value of 1.8 cm. For chest compression of 2.5 cm or greater, relatively modest increases in chest compression depth caused relatively large changes in cardiac output.

The Exercise-Responsive Cardiac Pacemaker

The heart has two properties: rhythmicity and contractility. Rhythmic contractions are initiated by the hearts pacemaker, the sinoatrial node, which lies in the right atrium. If the sino-atrial node fails, or if its electrical excitations are not propagated to the ventricles (the main pumping chambers), they wil still contract rhythmically but at a rate that is sometimes too slow to provide enough cardiac output to sustain consciousness. It is for this reason that rhythmic electrical stimuli are delivered to the ventricles in order to increase cardiac output to a level adequate to permit the subject to perform routine daily tasks. The technique of applying rhythmic electrical stimuli to the ventricles is called cardiac pacemaking; it can be achieved in several interesting ways, as this paper will describe.