Biomedical subjects
G J Wilson
Publications and source records attributed to G J Wilson.
Intramyocardial pH as an index of myocardial metabolism during cardiac surgery.
At present, a practical method for continuous monitoring of the state of tissue metabolism in the individual patient's heart during cardiac operations is not available. We have explored the use of miniature electrode measurements of myocardial interstitial pH to provide this monitoring capability, making comparisons with intracellular pH in left ventricular biopsy specimens and with tissue PCO2 measured by mass spectrometry. The electrode system consisted of a hydrogen ion-sensitive glass miniature electrode, housed in the beveled end of a 21 gauge (0.8 mm diameter) hypodermic needle, and a 2 mm diameter reference electrode, with an internal silver-silver chloride electrode coupled to tissue through a saline bridge (150 mM/L sodium chloride) saturated with silver chloride. Accuracy in blood at 37 degrees C was compared with conventional instrumentation (Radiometer BMS-3 MK-2 Blood Micro System) over a pH range of 7.4 to 6.4 with linear regression analysis (n = 26) revealing a high correlation (r = 0.997) and a mean difference in paired observations of only 0.01 +/- 0.004 (mean +/- SEM) pH units. In two groups of dogs on cardiopulmonary bypass, the pH needle and reference electrodes were inserted into the anterior wall of the left ventricle. Ischemic arrest of the heart at 37 degrees C was used to vary myocardial pH. In Group 1 (n = 8), intracellular pH was estimated from left ventricular biopsy specimens (400 mg each) taken over a microelectrode pH range of 7.37 to 6.37, snap frozen, and homogenized. In Group II (n = 6), tissue PCO2 in the anterior wall of the left ventricle was determined by mass spectrometry (sampling catheter 1.3 mm diameter). Miniaturized electrode (interstitial) pH exceeded biopsy (intracellular) pH under control conditions by 0.28 +/- 0.025 pH units (p less than 0.001), but below an electrode pH of 6.8 the results of the two techniques did not differ significantly. The tissue PCO2 rose from 69 +/- 2 mm Hg to a final plateau of 419 +/- 25 mm Hg, which was similar to the predicted value of 427 +/- 28 mm Hg calculated from the pH change (7.37 +/- 0.01 to 6.01 +/- 0.07), providing a further independent check on the pH electrode technique. These data indicate that our intramyocardial pH measurements do reflect intracellular metabolism during elective arrest of the heart and may have potential for clinical use.
The porous-surfaced electrode: a new concept in pacemaker lead design.
Three major problems which may be encountered with endocardial pacemaker electrodes are a lack of stable position, a chronic increase in stimulation threshold, and a diminishing magnitude of the sensed endocardial signal. These problems are particularly manifest in the atrium. Having previously shown that porous metal surfaces can support stable tissue ingrowth in both bloodstream and soft tissue environments, we set out todetermine the performance of porous-surfaced endocardial pacing electrodes in the atrial position. In two groups of six dogs each, J-shaped atrial leads with Elgiloy electrode tips (2.3 mm. in diameter, 2.3 mm. in length), having either conventional smooth surfaces (control) or porous surfaces (20 to 50 micron particle size) produced by powder metallurgy techniques, were positioned in the right atrial a-pendage. Stimulation thresholds and P-wave amplitude were repeatedly measured until the dogs were put to death 30 w-eks following implantation. The presence or absence of electrode fixation was observed and the atrial tissue reaction was examined grossly and by both light and scanning electron microscopy (SEM). The porous-surfaced electrodes demonstrated superior long-term stimulation thresholds which, at 30 weeks, averaged less then one third of those in the control group. In addition, the porous group showed a small but significant improvement in the amplitude of the sensed P wave. None of the smooth-surfaced electrodes showed fixation, and the tissue reaction consisted of a thick layer of granulation and fibrous tissue on the underlying endocardium, widely separating the electrode from the myocardium. In contrast, all of the porous-surfaced electrodes were fexed to the endocardium by fibrous tissue ingrowth into the surface pores. This tissue fixation of the electrode tip in close proximity to underlying myocytes explains their superior performance.
Improved thromboresistance of mechanical heart valves with endothelialization of porous metal surfaces.
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Computer-assisted reporting system for the follow-up of patients with prosthetic heart valves.
The implantation of large numbers of prosthetic heart valves carries with it the responsibility for continual reassessment of all aspects of patient management. Experience with more than 2,000 prosthetic valve operations since 1963 led to the development of a comprehensive computer-assisted data collection, management and reporting system. Over a 5 year period, data forms were developed for the detailed documentation of preoperative, intraoperative and postoperative information. These were designed in the form of checklists suitable for direct computer entry with use of mark-sense document readers. Special emphasis was placed on preoperative assessment of ventricular function, valve selection, intraoperative myocardial preservation, postoperative rehabilitation and prosthetic valve-related complications. This system makes possible rapid computer generation of a variety of reports to the referring physician regarding the individual patient and to the clinical investigator in relation to patient group statistics. Also, questionnaires to patients of physicians, or both, to update patient data can be produced by the computer at appropriate intervals after valve surgery. Experience indicated that a computer-assisted methodology is the only practical way to provide adequate follow-up of large groups of patients. Additionally direct access to relevant information helps to create an environment in which essential research can be carried out in the face of a demanding clinical practice.
The pathology of wear in the Beall model 104 heart valve prosthesis.
We examined 13 Beall model 104 prostheses recovered at surgery or autopsy 10 to 84 1/2 months after insertion and observed the pattern of prosthesis wear. We defined wear as "mild" when the disc was notched but neither the metal of the struts was exposed not the cloth seat torn. In "moderate" wear the disc was notched, the Teflon coating of the struts was worn away exposing the underlying metal but the cloth of the set was not torn. The cloth seat was torn in "severe" wear, exposing the metal seat and causing a different pattern of disc erosion. In one case this allowed the disc to tilt into the valve lumen and, later, to escape from its cage. Most of the prostheses studied showed "moderate" or "severe" wear. We believe that some degree of wear is inevitable. Clinical signs and symptoms were not specific but a rough correlation existed between the severity of hemolysis, as indicated by serum LDH levels, and the degree of prosthesis wear. When wear was "severe", the results of cardiac catheterization studies usually mirrored the change, but there were a few exceptions. All patients with the Beall model 104 prosthesis may eventually develop "severe" wear, and we recommend regular reassessment with a view toward prosthesis replacement.
Aortocoronary bypass graft in dogs: late histological changes.
Late histological changes occurring in aortocoronary bypass vein grafts were studied by lignt and electron microscopy in three dogs killed one, two and three years after grafting. The changes consisted of intimal thickening due to a proliferation of modified smooth muscle cells (myointimal hyperplasia) and replacement of most of the medial smooth muscle by fibrocytes. Serial angiography in the dogs did not reveal progression of the intimal thickening after one month.
Porous metal surfaces: a radical new concept in prosthetic heart valve design.
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Continuous measurement of left ventricular volume using a single dimensional transducer: a comparison of two techniques in open chested dogs.
A comparison has been made of the continuous measurement of left ventricular volume in open chested dogs by two simple dimensional transducer systems: a mercury-in-rubber strain gauge measuring epicardial arc length at the ventricular equator and a pair of electromagnetically coupled coils placed on opposite sides of the left ventricle to measure its diameter. The single dimensional measurements were converted to volume measurements after death by filling an intraventricular ballon with known volumes of liquid. The strain gauge proved clearly superior to the coupled coils because it was not possible in practice to position the coils precisely facing each other and they did not remain tangential to the epicardial surface throughout the cardiac cycle. A single epicardial strain gauge can provide sufficiently accurate measurements of left ventricular volume to warrant its use in physiological studies of cardiac function. Although considerable attention to detail is required this technique has the advantages of being inexpensive and producing a continuous record which is easily interpreted.
Ischemic contracture of the left ventricle. Production and prevention.
Ischemic contracture of the left ventricle ("stone heart") is a recognized complication of prolonged periods of interruption of the coronary circulation during open-heart surgery. We have examined the effects of moderate hypothermia (28 degrees C.) and preoperative beta-adrenergic blockade (propranolol, 0.5 mg. per kilogram; 1.0 mg. per kilogram) on contracture development during ischemic arrest of the heart. Four groups of 8 dogs each were placed on total cardiopulmonary bypass, and ischemic arrest of the heart was produced by cross-clamping the ascending aorta and venting the left ventricle. Intramyocardial carbon dioxide tension was continuously monitored by mass spectrometry. When anaerobic energy production ceased, as indicated by a final plateau in the intramyocardial carbon dioxide accumulation curve, the ischemic arrest was terminated and the contractile state of the heart observed. These results are given in the text. We conclude that beta-adrenergic blockade delays, but does not prevent, the onset of ischemic contracture of the left ventricle under normothermic conditions. Moderate hypothermia appears to prevent this complication completely.
Intramyocardial carbon dioxide tension. A guide to the safe period of anoxic arrest of the heart.
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Mass spectrometry for measuring changes in intramyocardial pO2 and pCO2.
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Rheolytic thrombectomy with use of the AngioJet-F105 catheter: preclinical evaluation of safety.
PURPOSE: A preclinical evaluation of the safety of the AngioJet-F105 rheolytic thrombectomy catheter. MATERIALS AND METHODS: The AngioJet-F105 catheter uses multiple retrograde high-speed fluid jets impinging on a primary aspiration lumen to create a hydrodynamic recirculation vortex that traps and fragments adjacent thrombus, with simultaneous evacuation of the resulting debris through the aspiration lumen. The effect of the AngioJet on treated vessels was evaluated in 10 canines. Vascular integrity on histopathologic examination and endothelial coverage on scanning electron microscopic study were examined in 15 vessel segments treated with the AngioJet-F105 catheter, compared with four vessel segments subjected to the Fogarty balloon maneuver, and 10 untreated vessel segments. The size distribution of particulate debris, upstream and downstream, after thrombectomy was determined in a flow-circuit model simulating the superficial femoral artery. Aliquots from the downstream effluent were then injected into the renal arteries of two healthy canines. RESULTS: The device caused only minimal focal endothelial denudation and no significant deep injury. No significant difference in endothelial coverage occurred in AngioJet-treated vessel segments compared to untreated control vessels (mean +/- standard deviation: 88.0% +/- 7.9% vs 89.7% +/- 11.6%, P = .77). Vessels treated with the Fogarty balloon pullback maneuver had significantly less residual endothelial coverage (58.0% +/- 8.0%, P < .03). Particulate microemboli in the effluent of the flow model accounted for 12% of the initial thrombus volume (0% > 100 microm, 99.83% < or = 10 microm). Histopathologic evaluation of the four renal beds injected with the resulting debris demonstrated no signs of necrosis. A moderate transient increase in plasma-free hemoglobin occurred, with a mild corresponding decrease in hematocrit. CONCLUSIONS: The AngioJet-F105 catheter resulted in only mild and focal injury to the treated vessels. The vast majority of resulting particulate debris consist of microscopic particles, without significant ischemic effect.
A self-expanding bifurcated endovascular graft for abdominal aortic aneurysm repair. An initial study in a canine model.
Approximately 50,000 abdominal aortic aneurysms (AAAs) are surgically repaired annually in the United States. Endovascular grafts (EVGs) combine a stent and a vascular graft offering great potential for reduced morbidity, mortality, and hospital stay because of minimally invasive endoluminal placement through catheters. Because most AAAs extend into one or both iliac arteries, a bifurcated EVG (bEVG) was developed, consisting of a proximal aortic trunk divided into two distinct lumens or sockets to receive two smaller diameter leg (iliac) components. All components were composed of Didcott self-expanding braided wire stents integrally attached to porous spun polycarbonate urethane liners. Successful placement of the bEVGs (trunks 10-12 mm and legs 5-6 mm diameter) by a 10 Fr introducer through the femoral arteries into the infrarenal aorta and external iliac arteries of 9 of 11 dogs was achieved. Subsequently, 11 of 12 bEVGs were successfully placed to exclude a saccular aneurysm exceeding three aortic diameters created by a fascia lata pouch extending from the aorta into the left external iliac artery, of which 7 were patent at 1 to 4 months. These findings establish design feasibility of the bEVG as well as the utility of the canine experimental model.
The measurement of myocardial tissue gas tensions by mass spectrometry.
The mass spectrometer is a well established tool for the measurement of the partial pressures of gases in respiratory gas mixtures and in flowing blood. Only recently has mass spectrometry been applied to the measurement of gas tensions in tissue. Both blood and tissue gas tension measurements by mass spectrometry were made possible by the development of a special sampling catheter surrounded at its tip by a gas--but not liquid--permeable membrane. The partial pressure of each gas at the external surface of the membrane determines the flow of that gas across the membrane which, in turn, is measured by the mass spectrometer. The use of a Teflon membrane permits tissue measurements because its low permeability to gases reduces the sampling rate of gas molecules with the result that the depletion of gas molecules in the tissue surrounding the membrane is minimal. Mass spectrometry is the only technique whereby it is possible to measure regional tissue pO2 and pCO2 and other gas tensions simultaneously and continuously. One application of mass spectrometric tissue gas tension measurements is the monitoring of myocardial ischemia through measurements of myocardial tissue pO2 and pCO2. We have reviewed the work of others and ourselves in this field.
Mitral valve replacement in dogs. Surgical technique and postoperative management.
Although techniques for the perioperative management of patients undergoing mitral valve replacement have been well established in humans, the use of these techniques has not been widely accepted in veterinary practice. The purpose of this study is to demonstrate that low morbidity and mortality could be achieved in the dog undergoing mitral valve replacement. Nine mongrel dogs (25-45 kg body weight) were subject to left thoracotomy and mitral valve replacement using cardiopulmonary bypass (CPB). The average time on CPB was 1 hour with an aortic cross-clamping time of 40 minutes using chemically induced cardiac arrest. CPB was performed under conditions of moderate systemic hypothermia (28-30 degrees C) and hemodilution (hematocrit, 25-35%). Operative mortality was 22% (2/9) with one death from excessive bleeding and the other from cerebral air embolism. All other animals recovered and were clinically normal 3 weeks after surgery. The authors conclude that successful mitral valve replacement is possible in the large dog.
Temperature changes in dental pulp associated with use of power grinding equipment on equine teeth.
OBJECTIVE: To quantify the temperature changes in the dental pulp associated with equine dental procedures using power grinding equipment. DESIGN: A matrix experimental design with replication on the same sample was followed to allow the following independent variables to be assessed: horse age (young or old), tooth type (premolar or molar), powered grinding instrument (rotating disc or die grinder), grinding time (15 or 20 seconds) and the presence or absence of water coolant. PROCEDURE: Sound premolar and molar teeth from a 6-year-old horse and a 15-year-old horse, which had been removed postmortem, were sectioned parallel to the occlusal plane to allow placement of a miniature thermocouple at the level of the dental pulp. The maximum temperature increase, the time taken to reach this maximum and the cooling time were measured (n=10 in each study). The teeth were placed in a vice and the instrument used on the tooth as per clinical situation. RESULTS: Significant differences were recorded for horse age (P < 0.001), instrument type (P < 0.001), grinding time (P < 0.001) and presence or absence of coolant (P < 0.001). There was no significant difference for tooth type. CONCLUSION: Thermal insult to the dental pulp from the use of power instruments poses a significant risk to the tooth. This risk can be reduced or eliminated by appropriate selection of treatment time and by the use of water irrigation as a coolant. The increased dentine thickness in older horses appears to mitigate against thermal injury from frictional heat.
Facilitation of endothelial cell growth on hydroxylated ePTFE vascular grafts.
The authors have modified ePTFE by hydroxylating the surface using aluminum deposition and removal with sodium hydroxide. This process has no effect on the microfibrillar structure, but reduces the hydrophobicity of ePTFE. There were significantly greater numbers of rat aortic endothelial cells on the surface of modified as compared to control ePTFE after 14 days (469 +/- 44 vs. 4 +/- 3 cells/mm2, p less than 0.01, paired t-test). This simple chemical modification facilitates endothelialization, without using thrombogenic cell adhesives.