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Biomedical subjects

D K Swanson

Publications and source records attributed to D K Swanson.

35 records · Page 2Linked to original sources
PubMed1983

Videodensitometric quantitation of mean blood flow.

Standard angiography demonstrates the anatomy of arterial occlusive disease but does not define its physiological significance. However, measurement of flow in a compromised vessel at rest and following peripheral dilatation provides important physiological information. Using digital subtraction angiography, femoral arterial flows determined by the cross-correlation transit time technique were compared to measurements by electromagnetic flowmeter. Thirty-five femoral arterial flow measurements were obtained in nine dogs instrumented with an electromagnetic flow probe and balloon occluder. Renografin 76 (7 cc) was power-injected at 14 cc/sec into the distal abdominal aorta. Angiographic flow measurements correlated well with electromagnetic flowmeter measurements (r = 0.94, standard deviation of the difference (SDD) = 15 ml/min). Intravenous studies provided somewhat poorer correlation due to difficulties in defining dimensions (r = 0.72, SDD = 36). Paired contrast injections (2 injections in succession) in 11 studies increased flow from an average of 80 to 250 ml/min (a 210 +/- 100% increase), providing an estimate of a vessel's capacity to provide increased flow during peripheral dilatation. Thus, reliable angiographic flow determinations may be obtained by arterial and intravenous contrast injections, adding physiological information to anatomical definition.

Absorptiometry, Photon↗
PubMed1983

Work in progress: a correction for tissue iodine accumulation in videodensitometric measurements of left ventricular ejection fraction.

Left ventricular ejection fractions were determined following eight intravenous injections in three dogs using area/length and digital videodensitometric techniques. Ejection fractions were measured by both techniques for all beats during left ventricular opacification. Even after noniodinated background corrections, tissue iodine accumulation produced large errors in measured iodine content late in the contrast material curve. By using a model for tissue iodine accumulation, an algorithm was developed that appears to reduce these errors. The measured ejection fraction for ten beats following the peak of the contrast material curve declined an average of 1.8% following correction, compared with 14% prior to correction. Following correction for tissue iodine accumulation, correlation between area/length and video-densitometric ejection fractions was 0.94. By correcting for tissue iodine accumulation, much more of the contrast material curve provides usable data for estimating ejection fractions.

Absorptiometry, Photon↗
PubMed1983

Diagnosis and management of the hypothyroid patient with chest pain.

A retrospective analysis of 38 patients undergoing cardiac catheterization with the diagnoses of hypothyroidism and chest pain revealed 23 to be euthyroid while receiving replacement therapy and 15 to be hypothyroid. Cardiac index was significantly reduced (p less than 0.01) in hypothyroid and euthyroid patients with thyroxine values between 4 and 7 micrograms/dl (2.8 +/- 0.7 and 3.0 +/- 0.9 L/min/m2, respectively), compared to euthyroid patients with thyroxine values greater than 7 micrograms/dl with or without coronary artery disease (4.0 +/- 1.2 and 4.0 +/- 0.7 L/min/m2, respectively). Ten hypothyroid patients underwent coronary artery bypass. There were no deaths, and only one patient required prolonged postoperative intubation. With a mean follow-up of 36 months, there have been no myocardial infarctions and one late death, which occurred at 7 years secondary to stroke. We conclude that preoperative thyroid replacement therapy is theoretically dangerous and may not significantly improve hemodynamics until full replacement is achieved. Coronary bypass grafting can be performed safely despite hypothyroidism with excellent early results.

Adult↗
PubMed1983

Effect of reperfusion temperature and pressure on the functional and metabolic recovery of preserved hearts.

Reperfusion conditions significantly affect recovery following global myocardial ischemia. Using an isolated dog heart model, we investigated the effect of initial (first 10 minutes) reperfusion temperature and pressure on the metabolic and functional recovery of the preserved heart. Four groups of five or six dogs each underwent 2 hours of ischemic cardioplegic arrest at 15 degrees C following single-dose crystalloid cardioplegia. Hearts were initially reperfused at 37 degrees C (high temperature) or 28 degrees C (low temperature) and at 50 mm Hg (low pressure) or 80 mm Hg (high pressure), giving four groups: (1) high-temperature, high-pressure; (2) high-temperature, low-pressure; (3) low-temperature, high-pressure; and (4) low-temperature, low-pressure. Septal temperatures were continuously recorded. Ventricular function curves 1 and 2 hours following reperfusion were significantly depressed in the high-temperature, high-pressure group (70%, p less than 0.01, and 83%, p less than 0.02) and the low-temperature, high-pressure group (78%, p less than 0.03, and 85%, p less than 0.03) but were normal in the low-temperature, low-pressure and the high-temperature, low-pressure groups. All groups showed edema 1/2 hour after reperfusion as measured by water and sodium content in myocardial biopsy specimens but only the high-temperature, high-pressure and the low-temperature, high-pressure groups showed persistent edema at 3 hours (3.95 +/- 0.2 ml H2O/gm dry weight, p less than 0.03 and 3.99 +/- 0.16 ml/gm, p less than 0.02, respectively). Only low-temperature, high-pressure reperfusion resulted in statistically significant reductions in adenosine triphosphate (ATP) 1/2 hour and 2 hours following reperfusion (a 15% reduction from baseline). Maximum rewarming rates were measured for each group. High-temperature, high-pressure = 2 degrees C per second; low-temperature, high-pressure = 1 degree C per second; high-temperature, low-pressure = 0.75 degrees C per second; and low-temperature, low-pressure = 0.4 degrees C per second. High-pressure reperfusion following global myocardial ischemia results in rapid rewarming and is associated with prolonged myocardial edema, depressed ATP levels, and delayed functional recovery. Therefore, we employ 10 minutes of low-pressure reperfusion in our patients undergoing potassium cardioplegic arrest.

Animals↗
PubMed1982

Digital subtraction angiography as a method of screening for coronary artery disease during peripheral vascular angiography.

Since myocardial infarction is the major cause of perioperative and postoperative death following peripheral vascular surgery, an accurate method of screening for coronary artery disease in this group of patients is needed. Digital subtraction angiography (DSA) with the use of intra-arterial aortic root injection of contrast material was evaluated as a method of screening for coronary artery disease in patients undergoing angiography for peripheral vascular disease. The feasibility of this method was demonstrated in animal experiments. Fifteen milliliters of Renografin-76 was power injected into the aortic root of seven anesthetized 20 kg mongrel dogs. Normal coronary artery anatomy was clearly demonstrated with DSA, and a series of iatrogenically created stenoses and occlusions were accurately identified. Excellent definition of patent grafts to the left anterior descending and circumflex coronary arteries was obtained in two dogs that had undergone previous coronary artery bypass grafting. A balloon occluder on one graft was used to demonstrate partial and near-total obstruction of the bypass graft. We are currently studying the use of aortic root injections using DSA to determine coronary artery disease in patients having standard angiography for peripheral vascular disease. Adequate visualization of coronary arteries and bypass grafts with only 20 ml of contrast has been obtained. The potential ability of this technique to identify and allow treatment of life-threatening coronary artery lesions in patients prior to or simultaneously with peripheral vascular surgery may result in reduced mortality.

Angiography↗
PubMed1982

Computerized fluoroscopy: new technique for the noninvasive evaluation of the aorta, coronary artery bypass grafts, and left ventricular function.

A computerized fluoroscopy system has been developed on the basis of real-time digital processing of x-ray transmission data from traditional image-intensified fluoroscopy equipment. High-quality visualization of any part of the arterial system is obtained following intravenous injection of 0.5 to 0.75 ml/kg of iodinated contrast materials. This report describes the use of this technique to evaluate the aortic arch, left ventricular function, and coronary artery bypass graft patency. Fifty intravenous studies were performed in 25 patients. Among 20 patients with coronary artery bypass grafts, computerized fluoroscopy correctly identified 11 of 15 patent grafts and 11 of 11 occluded grafts as confirmed by standard coronary arteriography in 11 of these patients. Unlike computerized tomography, our technique gives a longitudinal view of the bypass graft much like direct coronary angiography. Aortic arch studies included demonstration of a right aortic arch with a small left subclavian artery, a coarctation, and a normal aortic arch in a trauma patient with a wide mediastinum. Segmental wall motion abnormalities were clearly identified by a modification of the technique which produces a negative outline on the ventriculogram in dyskinetic segments. Ejection fractions may be calculated by determining the amount of iodine in the ventricle in systole and diastole. This technique may also be used to evaluate carotid disease and peripheral vascular disease in patients undergoing coronary artery bypass procedures. Computerized fluoroscopy, therefore, allows evaluation of the entire cardiovascular system by the relatively noninvasive technique of intravenous angiography.

Angiography↗
PubMed1980

Improved myocardial preservation at 4 degrees C.

We tested the ability of various cardiac preservation techniques to preserve left ventricular function of isolated canine hearts using preservation temperatures of 4 degrees or 15 degrees C. The four techniques tested were: (1) topical hypothermia, and hypothermic arrest induced by (2) perfusion of 1 liter of a modified Collins solution, (3) perfusion of 1 liter of a modified extracellular solution (DKS), or (4) perfusion of 500 ml of blood cardioplegia. Following the cold ischemia period, the hearts were reperfused with blood in the working heart preparation and tested for their ability to recover left ventricular function. Hearts preserved 2 hours at 15 degrees C using hypothermia, modified Collins solution, or DKS solution achieved an average of 60, 73, and 95%, respectively, of baseline function. Hearts preserved 3 hours at 4 degrees C using topical hypothermia attained 70% of baseline function, while hearts stored 5 hours at 4 degrees C using modified Collins solution or DKS solution recovered 83 and 92%, respectively, of baseline function. Hearts preserved at 4 degrees C functioned at levels equal to or greater than that of hearts stored at 15 degrees C, even though the hearts preserved at 4 degrees C were stored for longer periods than those preserved at 15 degrees C. Hearts preserved with blood cardioplegia for 2 hours at either 4 degrees or 15 degrees C achieved functions statistically the same as baseline levels during the reperfusion period. These data show no advantage for preservation temperatures of 15 degrees C compared with 4 degrees C. Our data provide a firm experimental basis for the clinical use of myocardial preservation temperatures of 4 degrees C, especially when combined with cardioplegia.

Animals↗
PubMed1980

Heart and kidney transplantation using total lymphoid irradiation and donor bone marrow in mongrel dogs.

Heart and kideny allografts showed markedly prolonged survival in unrelated mongrel dogs following total lymphoid irradiation (TLI) and donor bone marrow without any other immunosuppression. In every animal the heart survived longer than the kidney; genetic disparity was ruled out, since the heart and kidney from the same donor were placed into one recipient. Placing the kidney allograft in the abdomen with the bone marrow given intraperitoneally doubled kidney survival over placement in the neck, but heart survival was equally prolonged in the abdomen or neck. Splenectomy before TLI or after TLI, but just before transplantation, almost completely eliminated the prolonged survival of both heart and kidney allografts. Thus there is suggestive evidence from the work of Slavin and his colleagues and from our study that TLI plus bone marrow from the donor may be valuable for transplantation in man, particularly heart transplantation.

Animals↗
PubMed1980

Left ventricular function after preserving the heart for 2 hours at 15 degrees C.

Hearts preserved for 2 hours at 15 degrees C were evaluated for maximum function with the use of an isolated working dog heart subjected to stress. We determined left ventricular function by controlling aortic flow resistance and flow into the left atrium. Groups studied were hypothermia alone (H), hypothermia with a modified extracellular solution (H + DKS), hypothermia with a modified Collins solution (H + C), six periods of 20 minutes of hypoxic hypothermia followed by 10 minutes of blood reperfusion (H20 + R10) and blood cardiplegia (BC). Hypothermia alone for 1 hour was also evaluated. Functions were studied for 2 1/2 hours following reperfusion by determining Starling's curves for each heart. Our data show that H alone gave adequate myocardial protection for only 1 hour but not for 2 hours. H20 + R10 was better than H, but function was depressed. Use of H + C provided protection equal to H20 + R10, but the hearts recovered function slowly. Only hearts preserved by H + DKS and BC for 2 hours had normal function. Hearts from all groups except H + DKS and BC became edematous. Excellent function was obtained with DKS or BC following 2 hours of ischemia at 15 degrees C. Initial clinical use of BC supported these laboratory findings.

Animals↗
PubMedDate not supplied

Improved heart preservation with UW preservation solution.

Despite the good clinical results obtained with the current heart preservation techniques, these methods need to be improved. The UW solution has provided excellent preservation for the pancreas, kidney, and liver after extended cold ischemic storage times. We have tested the ability of the UW solution to store hearts for 5 and 12 hours and compared the results with those obtained from hearts preserved by either Stanford or modified Collins' solutions. Three groups of five canine hearts each underwent 5 hours, and three groups of five canine hearts underwent 12 hours of ischemia at 4 degrees C. Then the hearts were reperfused in an isolated working canine heart preparation. Those hearts preserved for 5 hours had nearly normal ventricular function and adenosine triphosphate contents and were able to maintain normal tissue electrolyte concentration and water contents. After 12 hours of storage time only adenosine triphosphate contents were similar among the groups. Hearts preserved with the UW solution rapidly recovered, reaching nearly normal left ventricular function by 60 minutes of reperfusion; hearts preserved by the modified Collins' solution recovered more slowly, but function was good after 120 minutes of reperfusion. Hearts preserved by the Stanford solution never attained adequate function. The three groups of hearts preserved for 12 hours did not differ in their ability to utilize lactate or in their rates of oxygen utilization. Tissue water and sodium contents were considerably lower in the hearts preserved with the UW solution after 150 minutes of reperfusion compared with hearts stored in the modified Collins' or Stanford solutions. Hearts stored 12 hours in the UW solution under cold ischemic conditions recovered left ventricular function rapidly after reperfusion with normal blood, utilized lactate and oxygen at normal rates, and were able to regulate tissue water and sodium contents to nearly normal levels. Because of the superior preservation obtained by the UW solution, the solution deserves further evaluation for possible future use in clinical heart transplant programs.

Adenine Nucleotides↗
PubMedDate not supplied

Pump-induced hemolysis in a rabbit model of neonatal ECMO.

There is no significant difference in hemolysis between pediatric centrifugal pumps and roller pumps during ECMO of 8 hours duration in rabbits or in comparable 24 hour isolated pump circuits. There is also no significant difference in heat production by either pump. Reports of severe hemolysis using the centrifugal pump in neonatal ECMO are likely due to other factors. Proper cannula selection and positioning are important measures to reduce hemolysis by minimizing circuit pressure and maximizing venous return. Avoidance of inadvertently high rotor speed in the centrifugal pump is also recommended.

Adult↗