Biomedical subjects
Publications and source records attributed to B R Wilcox.
We present a method of pacemaker implantation in neonates using a subxyphoid epicardial lead and subrectus placement of the pulse generator. This method is simple and safe and carries minimal morbidity.
A 26-year-old woman with end-stage lung disease due to eosinophilic granulomatosis had single right lung transplantation with an excellent function result that persists beyond 9 months of follow-up. Single lung transplantation offers excellent palliation to selected patients with end-stage lung disease.
There is still no consensus as to how best to categorize and describe interventricular communications. In a series of three reviews, a system will be described showing how the anatomical criteria chosen for categorization will also serve as a guide for surgeons as to the location of the axis responsible for atrioventricular conduction tissue. In this first review, the defects described are not complicated by overriding of arterial or atrioventricular valves and are present in hearts that have basically normal segmental connections, or have some discordant connections (complete transposition or congenitally corrected transposition). The rims of the defect categorize the boundaries to which a surgeon may place a patch. Variations in these rims produce three classes of defect: perimembranous; muscular; and doubly committed and juxtaarterial (subarterial). The second part of the classification recognizes the further variation existing with respect to the component of the morphologically right ventricle into which the defect predominantly empties. Deficient atrioventricular septation can also lead to interventricular shunting in isolation, but the morphology is then quite different from hearts with simple deficiencies of the ventricular septum. We emphasize the abnormal location of the atrioventricular node in hearts with atrioventricular, as opposed to ventricular, septal defects.
Current preservation techniques for lung transplantation limit ischemic time to 6 hours. The purpose of this study was to evaluate the ability of dimethylthiourea, a low molecular weight free radical scavenger, to prolong this interval. An in vivo canine transplantation model was used to assess lung function. At harvest and after circulatory arrest, the donor lung was flushed with modified Euro-Collins solution (50 mL/kg). In a blinded fashion, dimethylthiourea (5 g) or saline solution was added to the flush solution at harvest and also infused (20 g over 2 hours) at reimplantation. Harvested lungs were stored for 12 hours at 4 degrees C. Allotransplantation was performed in recipient dogs ventilated with 40% O2. After 1 hour, the contralateral pulmonary artery was ligated, forcing the dog to be dependent on the transplanted lung. Twelve dogs were studied, with 6 randomly assigned to each treatment group in a blinded fashion. Measurements were recorded for 8 hours, keeping the inspired oxygen fraction constant at 0.40. All dimethylthiourea-treated dogs survived the observation period, whereas one third of the dogs that received saline solution died. Dimethylthiourea-treated dogs had significantly greater arterial oxygen tension and significantly less pulmonary vascular resistance compared with control animals. These results suggest that treatment of the lung with a free radical scavenger (dimethylthiourea) improves pulmonary function after reimplantation in a canine model after 12-hour hypothermic storage.
A shortage of suitable donors is a serious obstacle to the widespread application of isolated lung transplantation for end-stage lung disease. We hypothesized that lung tissue likely remains viable for a sufficient period of time to allow for safe postmortem retrieval of lungs for transplantation. Studies were conducted in a nonsurvival model of canine lung allotransplantation. Donor animals were sacrificed, and subsequent lung harvest was delayed for 1 hour, 2 hours, or 4 hours. Pulmonary retrieval was then performed in a standard fashion, flushing the lung block with modified Euro-Collins solution. Lungs were then stored for 4 hours before single allotransplantation. Recipient animals were maintained anesthetized, and followed up for 8 hours. By occlusion of the pulmonary artery and bronchus to the native lung, recipient animals were forced to survive solely on the transplanted lung, with a constant inspired oxygen fraction of 0.40. All 5 recipient animals of 1-hour cadaver lungs survived the 8-hour observation period with excellent hemodynamics and gas exchange. Two of 5 recipients of 2-hour cadaver lungs survived the observation period, whereas a third animal survived for 5 hours with excellent gas exchange. One of 4 animals transplanted with a 4-hour cadaver lung survived the observation period. Retrieval of lungs from cadavers whose hearts are not beating may prove to be a safe and effective method to increase the pulmonary donor pool.
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The coronary sinus is an important landmark for the position of the atrial component of the atrioventricular conduction axis and, thus, assumes special relevance to the surgeon in the operating room. We describe here 2 patients with atrioventricular septal defect characterized by an unusual termination of the coronary sinus within the left atrium. We discuss the potential importance of this finding to the disposition and surgical avoidance of the conduction tissues.
An in vivo canine model was used to assess the ability of an oxygen free radical scavenger to decrease reperfusion injury in lung transplantation. In 12 dogs, the left lungs were transplanted after they had been preserved for 24 hours at 4 degrees C after pulmonary artery flushing with modified Eurocollins solution. In 6 dogs, dimethylthiourea, a potent oxygen free radical scavenger, was added to the flush solution and was also given to the recipients just before reperfusion. In all animals, the contralateral pulmonary artery and bronchus were ligated and lung function was assessed for 12 hours or until death. Three dogs died prematurely in the control group, whereas only 1 dog died prematurely in the dimethylthiourea group. This resulted in a statistically significant difference in the average length of survival (p less than 0.05). Pulmonary artery and right atrial pressures were significantly lower in the dimethylthiourea group during the first 6 hours (p less than 0.05). Treatment with dimethylthiourea resulted in a significantly higher arterial oxygen tension at 4 hours, and intrapulmonary shunt tended to be lower. Thus, it would appear that dimethylthiourea has a protective effect on lungs preserved for 24 hours before transplantation in dogs.
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The left lower lobes of 28 canine lungs were isolated, preserved, and then reperfused for 150 minutes. Five groups of lobes were studied: group 1, control (n = 5); group 2, one hour of warm ischemia (n = 5); group 3, one hour of warm ischemia + oxygen free radical scavengers (n = 5); group 4, 24 hours of cold ischemia (n = 8); and group 5, 24 hours of cold ischemia + oxygen free radical scavengers (n = 5). Oxygen free radical scavengers consisted of superoxide dismutase and catalase (100 micrograms/mL) given at the moment of reflow. Extravascular lung water (grams per gram of blood-free dry lobe weight) after reperfusion was 2.75 +/- 0.19, 5.46 +/- 0.60, 4.08 +/- 0.37, 9.43 +/- 0.98, and 6.91 +/- 0.95 for groups 1 through 5, respectively (p less than 0.05, groups 2 through 5 versus group 1; p less than 0.05, group 2 versus group 3 and group 4 versus group 5). Lung tissue lipid peroxidation, measured as thiobarbituric acid reactive material, was 117 +/- 14, 314 +/- 19, and 163 +/- 25 nmol/g dry lobe weight for groups 1, 4, and 5, respectively (p less than 0.05, group 4 versus group 1 and group 4 versus group 5). The data suggest that oxygen free radical scavengers attenuate reperfusion injury after long-term hypothermic lung preservation.
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The purpose of this study was to evaluate the ability of dimethylthiourea (DMTU), a low molecular weight hydroxyl free radical scavenger, to improve preservation of the lung for transplantation. Following preservation, 15 isolated canine left lower lobes were reperfused for 90 min with autologous blood. Five group I lobes served as controls and were not subjected to ischemia prior to reperfusion. Five group II lobes were flushed and submerged in a cold Euro-Collins solution and stored for 4 hr at 4 degrees C prior to reperfusion. Group III lobes were flushed with a 20 mM DMTU-enhanced Euro-Collins solution, stored for 4 hr, and then reperfused. The isogravimetric method was utilized to determine the capillary permeability coefficient (Kfc) for the reperfused lobes. The Kfc values were 0.10 +/- 0.01, 0.17 +/- 0.01, and 0.10 +/- 0.008 ml/min/mm Hg/100 g lung for groups I, II, and III, respectively (P less than 0.01 II vs I, III). Extravascular lung water values in the reperfused lobe were 4.44 +/- 0.45, 6.57 +/- 0.38, and 5.23 +/- 0.22 ml/g blood free dry lung weight for groups I, II, and III (P less than .05, II vs. I, III). Lung lipid peroxidation, measured as thiobarbituric acid-reactive material, was higher in group II, 146 +/- 6 nmole/g, than in either group I, 90 +/- 5 nmole/g, or group III, 91 +/- 4 nmole/g (P less than 0.01). The results indicate that the addition of DMTU improves hypothermic lung preservation by reducing lipid peroxidation and edema formation upon reperfusion.
Clinical investigations focused on finding characteristics of noninvasively obtained measurements of pulmonary blood velocity that can be used to quantitate pulmonary blood flow and/or pulmonary pressure have often yielded results whose imprecision has been attributed to flow pattern variability. To determine flow pattern variability in an in vivo animal model in varying hemodynamic states, main pulmonary artery blood velocity waveforms were recorded in 17 dogs at 2-mm intervals along an anterior to posterior wall-oriented axis using a 20-MHz pulsed Doppler needle probe. Control data were obtained before the animals were subjected to altered flow (atrial level shunts) and pressure (10% O2 inhalation) states. Instantaneous velocity profiles were computed throughout the cardiac cycle. Estimates of pulmonary blood flow were obtained assuming an elliptical model of the pulmonary artery which allowed computation of velocity at all points in the cross section, based on the measured values along the axis. Model-based estimates were compared to measured values and estimates obtained in the traditional fashion, i.e., the product of centerline velocity and cross-sectional area. Results clearly showed marked interanimal variability, even in control states. Reverse flow in the posterior half of the vessel, which tended to become more pronounced with increased pulmonary artery pressure, was observed during late systole and early diastole. Elevated pulmonary blood flow tended to increase the maximum velocities along the anterior wall relative to midline velocities. Neither estimate of cardiac output yielded consistently accurate results (r = 0.77 for model-based method, r = 0.80 for area times central velocity method). Findings of this study, which highlight the dependency of waveform characteristics on sampling site, the large degree of intersubject variability, and the need for large or multiple sample volumes for pulmonary blood flow determination, help clarify inconsistencies observed by clinicians and suggest that future work with animal models will facilitate a greater understanding of the determinants of human pulmonary velocity waveforms.
A fistula between the trachea and the innominate artery, a potentially fatal complication of tracheostomy, can be managed successfully. We have derived several guidelines from our experience with one such case and from a review of the 36 cases reported in the literature over the last decade. Diagnosis must be established before exsanguination occurs. Bronchoscopy and angiography are often nondiagnostic. Control of hemorrhage and a patent airway are the initial goals of treatment. Interruption of the innominate artery is the definitive treatment, with a low rebleeding rate (7%, 1/14 cases) and good long-term survival (64%, 9/14 cases). Maintenance of continuity of the innominate artery is contraindicated, because of a high rebleeding rate (60%, 6/10 cases) and poor long-term survival (10%, 1/10 cases). There is no convincing evidence that interruption of the innominate artery causes significant neurologic or vascular compromise.
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