Biomedical subjects
Publications and source records attributed to J N Ross.
Conventional adulticidal therapy may cause acute death due to embolism in major pulmonary arteries resulting in severe infarction of the lung. To avoid this problem removing a significant number of worms with flexible alligator forceps prior to adulticidal therapy is recommended. Before surgery, an accurate diagnosis and critical evaluation of the patient is mandated for proper choice and sequence of treatment.
In a series of 3 studies, indirect blood pressure measurements were obtained to define normal variance, identify hypertension, and estimate the prevalence of hypertension in apparently healthy dogs. In part 1, we measured values in 5 clinically normal dogs twice weekly for 5 weeks in a home setting. Mean +/- SD systolic arterial pressure (SAP) and diastolic arterial pressure (DAP) was 150 +/- 16 and 86 +/- 13 mm of Hg, respectively. The DAP significantly (P less than 0.01) decreased with repeated measurements over the 5-week period. In part 2, we assessed the variation between blood pressures measured in a clinic vs those measured in the home. Within a 2-week period, measurements were obtained from 10 clinically normal dogs in a private veterinary clinic and again in their home. Significant differences were not observed between clinic and home measurements of SAP and DAP; however, heart rate was significantly (P less than 0.05) higher in the clinic. In part 3, SD about the SAP and DAP mean values were determined in 102 clinically normal dogs. Canine hypertensive status was determined, using statistical methods and data from 102 clinically normal dogs. Values of SAP greater than 202 mm of Hg and DAP greater than 116 mm of Hg were determined to be 2 SD beyond the mean and, therefore, were interpreted to be hypertensive. Approximately 10% of the 102 apparently healthy dogs measured in this study were considered hypertensive on the basis of these criteria. In addition, a border zone of suspected hypertension was estimated, using the mean + 1.282 SD. The SAP border zone was between 183 and 202 mm of Hg, whereas the DAP border zone was between 102 and 113 mm of Hg. Of the 102 dogs, 12 had values within these zones of suspected hypertension.
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M-mode echocardiograms were recorded from 21 adult sheep (20 ewes, 1 whether). Fifteen echocardiographic measurements were taken and compared with body weights or heart rates, using linear regression equations. Significant correlations (P less than 0.05) were found when body weight was compared with left ventricular internal dimensions in systole (Yo = 0.187 Xo + 18.60, P less than 0.05) and diastole (Yo = 0.346 Xo + 26.69, P less than 0.02), septal thickness in systole (Yo = 0.0876 Xo + 7.64, P less than 0.05) and diastole (Yo = 0.0673 Xo + 4.45, P less than 0.05), aortic root dimension (Yo = 0.129 Xo + 23.40, P less than 0.05), and left atrial dimension (Yo = 0.194 Xo + 15.95, P less than 0.005). Heart rate was significantly correlated (P less than 0.05) with body weight (Yo = -0.245 X 96.71, P less than 0.05), ejection time (Yo = -0.0013 Xo + 0.376, P less than 0.001), velocity of circumferential fiber shortening (Yo = 0.0061 Xo + 0.928, P less than 0.05), mean velocity of mitral valve middiastolic closure (Yo = -0.184 Xo + 1.65, P less than 0.02), and left atrial dimension (Yo = -0.109 + 40.55, P less than 0.005). Fractional shortening of the left ventricle was (mean) 37.2 +/- 5.7% and the left atrial to aortic root ratio was (mean) 0.92 +/- 0.10.
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Protruding intimal lesions in canine pulmonary trunk induced by naturally occurring heartworm disease were further characterized at light and electron microscopic levels. The pulmonary trunk was dissected free, fixed and subdivided into many specimens which were routinely prepared for scanning electron microscopy (SEM). After SEM observation, selected samples were embedded in Epon-Araldite and sectioned for correlated light (LM) and transmission electron microscopic (TEM) observation. SEM observation revealed protruding lesions of various sizes and shapes on the luminal surface. These ranged from papillae to complex lamellar projections extending far into the lumen. This suggests a progressive growth pattern. A layer of cells covered most of the lesion surface and between the lesions. These cells had a rounded conformation and no uniform orientation on the luminal surface. Other areas of the lesion surface appeared fibrous and devoid of cells. LM and TEM sections of the SEM specimens revealed three types of surfaces on the protruding fibro-muscular lesion. The lesion was primarily covered by cells which were (1) endothelial or (2) non-endothelial in nature. The non-endothelial surface cells were separated from each other and did not have the typical characteristics of endothelial cells. The third region was acellular and had the fibrous appearance of extracellular matrix. The acellular and non-endothelial portions formed a significant amount of the lesion surface. Previous reports have indicated these lesions were covered by typical endothelium. This report indicates that further characterization and quantitation of the cells covering the lesion surfaces is necessary.
Scanning electron microscopy (SEM) was used to study the arrangement of elastic fibers in the canine saphenous vein as the basis for further studies of veins used in by-pass grafting operations. The elastic fiber arrangement in distended and non-distended veins was examined in both immersion-fixed and perfusion-fixed vessels. Transmission electron microscope (TEM) observation of the SEM samples confirmed the identity of these fibrillar structures as elastic fibers. In addition, specific stains for elastic fibers (Verhoeff's iron hematoxylin and orcein) were used. The elastic fibers forming the internal elastic lamina were arranged in a fishnet-like pattern. Large-diameter fibers, running longitudinally along the vascular wall, were interconnected by smaller oblique fibers. Together the fibers formed an elastic cylindrical network between the endothelium and the smooth muscle cells. The thicker longitudinal fibers were the same diameter in distended and non-distended veins. By contrast, the oblique fibers were thinner and more complexly branched in distended veins. The architecture of the elastic fiber network contributes to vascular flexibility and allows circumferential distension. The interconnecting oblique fibers presumably serve to distribute internal pressure equally around the venous wall.
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A quantitative method for the analysis of 201thallium myocardial scintigrams, developed in an experimental infarcted dog heart model, has been compared with two nonquantitative methods for interpretation of stress myocardial scintigrams in two groups of patients studied with coronary angiography: 11 with normal coronary arteries and 14 with coronary artery disease. Three independent observers interpreted scintigrams which were 1) not computer processed; 2) corrected for background activity in lungs and chest wall; and 3) processed by a computer method which uses a uniform threshold of counts determined from the dog model to define perfusion defects. Interobserver variability as well as sensitivity and specificity of detecting coronary disease were examined. In patients with coronary artery disease interobserver variability was improved by using the computer technique: observers agreed as to the existence of a perfusion defect in 93% of the scintigrams as compared to 55% and 81% for the unprocessed and background-subtracted images respectively. No false positive indications of coronary disease were obtained by any of the three techniques. Use of the computer method did not improve the sensitivity of detecting coronary disease, however--71% compared to 64% for unprocessed images and 79% for background-substracted images. The advantages of this quantitative computer method are increased consistency of interpretation and lack of false positive diagnoses of coronary disease. An improved sensitivity of detection may be gained by varying thallium count thresholds according to anatomic location in the heart.
A method has been developed for measurement of myocardial infarct size from thallium-201 scintigrams that depends on computer measurement of levels of radioactivity in the myocardium. In 16 dogs, thallium-201 scintigrams were obtained in the left lateral and left anterior oblique projections 48 hours after ligation of the left anterior descending coronary artery. Scintigraphic results were obtained by two independent observers and were compared with tissue measurements of infarct volume calculated from thallium autoradiograms and nitro-blue tetrazolium (NBT)-stained tissue slices. Infarct volumes derived from tissue measurements were used to develop criteria for the computer scintigraphic technique. There was no significant difference in the scintigraphic measurements made by the two observers. Scintigraphic infarct size in the left lateral and left anterior oblique projections correlated with tissue infarct size with r values of 0.88 and 0.75, respectively, for thallium autoradiography and 0.71 and 0.70, respectively, for NBT tissue staining. The range of infarct volume was 3.3 to 14.8 percent of the left ventricular mass. Results of this study suggest that scintigraphic quantitation of infarct size is feasible in this dog model.
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Polyacrylonitrile fabric (Orlon) may by oxidized by heating in air, when it becomes black and carbonized. During the heat treatment, the fibers shrink; this shrinkage allows components such as diaphrams to be shaped around molds. Oxidation reduces the tensile strength by about 25% and also reduces the stiffness of the material. The oxidized Orlons was screened in tissue culture for possible cytotoxic effects. Finding none, patches of the material were sutured into the right atrium of dogs and examined after 48 hr. Because of encouraging results, 10 atrial patches, consisting of Dacron velour and oxidized Orlon side-by-side, were implanted into the right atrium of dogs. Five patches were backed with Silastic to render them impervious, and five with segmented polyurethane. The atrial patches were examined after 48 hr, and in all instances the oxidized Orlon part of the patch was coated with a thinner and smoother fibrin layer than was the Dacron velour half. a left ventricular bypass pump was fabricated from oxidized Orlon and spray-coated on the nonblood surface with segmented polyurethane. After 48 hr implantation in the chest cavity of a calf, pumping without systemic anticoagulation, the pump was found covered by a thin, smooth, firmly attached layer of fibrin.
This report describes the measurement of systolic time intervals in a nine year old female domestic pony which was found at necropsy to show coarctation of the aorta and bilateral ventricular hypertrophy. Electrocardiogram, phonocardiogram and direct arterial blood pressure were recorded from the pony in a standing unmedicated state and systolic time intervals were measured from the resulting tracings. A prolongation of left ventricular ejection time and shortening of the pre-ejection period were observed in comparison to a group of normal ponies similarly examined. Such changes are consistent with outflow tract obstruction. The pony was also hypotensive and this condition was interpreted as a long-term compensation for the obstructive lesion. It is likely that the changes in systolic time intervals were at this stage predominantly affected by the hypotension. The report notes that the existence of such a case of spontaneous cardiovascular disease in the pony population might suggest the utility of the animal as a resource in comparative cardiovascular physiology and medicine.
Clinical use of profound hypothermia and total circulatory arrest has been accompanied by occasional postoperative neurological abnormalities. In a series of infant baboons, surface cooling to 32 degrees C (brain) followed by perfusion cooling by cardiopulmonary bypass with a membrane oxygenator and heat exchanger to 18 degrees C was carried out, after which the circulation was stopped for 30 minutes. The animal was rewarmed to 35 degrees C. Marked alterations in the regional cerebral circulation were observed during perfusion cooling and rewarming. Regional cerebral ischemia was negatively correlated with jugular outflow (total cerebral blood flow) during rewarming, while regional hyperemia showed positive correlation both following perfusion cooling and after rewarming. A higher degree of ischemia in brain ischemic samples was found during rewarming than during cooling. These alterations in regional cerebral perfusion were associated with lactacidosis and hyperglycemia after rewarming, and may be considered potentially responsible for posthypothermic cerebral dysfunction.
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