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Biomedical subjects

W S Ring

Publications and source records attributed to W S Ring.

72 records · Page 4Linked to original sources
PubMed1981

The deformational characteristics of the left ventricle in the conscious dog.

We studied left ventricular minor and major axis diameters and equatorial wall thickness in eleven conscious dogs with chronically implanted pulse-transit ultrasonic dimension transducers. Left ventricular transmural pressure was measured with micromanometers. Left ventricular volume was varied by inflation of implanted vena caval or aortic occluders. The geometry of the left ventricle was represented as a three-dimensioal ellipsoidal shell. Left ventricular eccentricity was found to be a linear function of ventricular volume during both diastole and ejection. However, the relationship was not the same for diastole and ejection, and during diastole the left ventricle was mre spherical at large volumes and more elliptical at small volumes than during ejection. The rearrangements in geometry observed during isovolumic contraction appeared to be transitional stages from the diastolic to the ejection-phase relationship. Thus, during isovolumic contraction, the left ventricle became more elliptical at large volumes and more spherical at small volumes. These relationships were not altered significantly by increased afterload or inotropic interventions. We also observed that the diastolic deformation of the ventricular chamber occurred in a set and predictable manner that seemed to be determined by the three-dimensional mechanical properties of the myocardium. The geometric inter-relationships of the ventricular wall determined the relationship between diastolic transmural pressure and mural stress. These findings probably reflect basic structural characteristics of the myocardium and provide a convenient method for quantitatively representing the dynamic geometry of the left ventricle.

Animals↗
PubMed1981

Left ventricular dynamic geometry and diastolic mechanics in a model of chronic cyanosis and right ventricular pressure overload.

Left ventricular (LV) mechanics and dynamic geometry were studied in eight dogs 1 to 151 days after creation of a model of cyanosis and increased right ventricular (RV) pressure. In each dog, an 8 mm conduit was interposed between the main pulmonary artery and left atrium; the pulmonary artery was then banded distal to this shunt. Ultrasonic dimension transducers were subsequently implanted for the measurement of LV equatorial minor axis and wall thickness. Catheter-tipped micromanometers were used to measure LV and pleural pressures; RV pressure was measured with a fluid-filled catheter and an external transducer. Eight control animals were similarly instrumented. At the time of study, the cyanotic dogs had significantly decreased arterial oxygen saturations (66% +/- 7% versus controls: 96% +/- 5%), significantly elevated peak RV pressures, (55 +/- 7 mm Hg versus controls: 30 +/- 5 mm Hg) and significantly elevated ratios of RV to LV mass (0.52 +/- 0.05 versus controls: 0.36 +/- 0.05). Diastolic pressure-dimension curves were generated and time constant for LV relaxation were calculated for each animal. The diastolic curves obtained from the cyanotic dogs were not significantly different from those of the control animals, and LV relaxation was not prolonged in the cyanotic dogs. In the three dogs that were cyanotic for 4 months or longer, there was a profound abnormality in the geometric pattern of LV contraction, manifested by asynchronous shortening of the anteroposterior equatorial minor axis. In two of these three dogs, inotropic reserves were assessed by means of postextrasystolic potentiation and were found to be normal. The results of this study indicate that short-term mild cyanosis and RV pressure overload do not alter diastolic compliance nor prolong relaxation of the LV. LV dynamic geometry may become abnormal after 4 months, with preservation of global LV inotropic reserves.

Animals↗
PubMed1980

Effect of heart rate on myocardial blood flow in dogs with left ventricular hypertrophy.

Because of the previous suggestion that subendocardial perfusion may be inadequate in the hypertrophied heart, this study was carried out to examine the response of transmural myocardial blood flow to pacing induced tachycardia in dogs with chronic left ventricular hypertrophy. Myocardial hypertrophy, produced by banding the ascending aorta of puppies at 5-6 wk of age, resulted in an 87% average increase in relative left ventricular mass compared with the control dogs. Myocardial blood flow was examined during ventricular pacing at heart rates of 100, 200, and 250 beats/min using radionuclide-labeled microspheres. Mean blood flow per unit myocardial mass was similar in the two groups of dogs at a heart rate of 100 beats/min and increased regularly during pacing in both groups of animals. Increasing heart rates did not change the transmural pattern of myocardial blood flow in the normal dogs, but in the animals with left ventricular hypertrophy pacing at 250 beats/min resulted in a significant redistribution of perfusion away from the subendocardium, with the ratio of subendocardial/subepicardial blood flow falling from 1.03 +/- 0.08 at 100 beats/min to 0.83 +/0 0.06 at 250 beats/min (P < 0.01). This redistribution of blood flow away from the subendocardium was especially marked in the regions encompassing the papillary muscles and the intervening left ventricular lateral wall.

Animals↗
PubMed1980

The diastolic mechanical properties of the intact left ventricle.

Recent studies have improved our understanding of the diastolic mechnical properties of intact myocardium. In order to obtain meaningful data, pressures external to the heart should be measured, forces and dimensions should be properly normalized, and measurements should be obtained over a wide range of ventricular volumes. Diastolic filling appears to be a passive phenomenon and is not affected significantly by systolic relaxation or mural inertia. Thus, the relationship between diastolic myocardial force and length is determined primarily by the elastic properties of the muscle and by viscous properties during dynamic filling. In the absence of ischemia, the diastolic mechanics of intact myocardium are not altered significantly by acute physiological interventions. Chronic changes in diastolic properties do occur, however, and are fundamentally important to the regulation of cardiac function. Myocardial creep induced by chronically elevated diastolic presssure produces ventricular dilatation, thereby altering chamber geometry, systolic loading, and overall global function. Thus, a detailed analysis of diastolic mechanical properties is essential to the assessment of the performance characteristics of the intact heart.

Animals↗
PubMedDate not supplied

Echocardiographic diagnosis of discontinuous left pulmonary artery as an isolated lesion.

The diagnosis of a discontinuous left pulmonary artery arising from a left ductus arteriosus was made by two-dimensional and Doppler echocardiography in an infant with recurrent pneumonia. The diagnosis was later confirmed at cardiac catheterization and surgery. The suprasternal notch views were especially useful for the identification of the left pulmonary artery. In this patient with a right aortic arch, the left pulmonary artery was supplied by a left ductus arteriosus that arose from the innominate artery. This case report describes the echocardiographic diagnosis of discontinuous left pulmonary artery as an isolated lesion, an unusual lesion that can easily be missed. It emphasizes the necessity of a careful and complete examination with particular emphasis on pulmonary artery continuity in patients suspected of having congenital heart disease or respiratory compromise as a result of a cardiovascular cause.

Echocardiography↗
PubMedDate not supplied

Cardiac beta-adrenergic responsiveness is well preserved in moderate protein calorie malnutrition from semistarvation.

Twenty-one dogs underwent instrumentation of the left ventricle with ultrasonic dimension to study the effects of acute protein-calorie malnutrition on the adrenergic responsiveness of the heart. This study allowed a chronic and dynamic measurement of the major cardiac axes and the ventricular wall thickness, which in turn can be used to derive sophisticated measurements of global and intrinsic left ventricular function. Of the 21 dogs, 11 received a protein- and calorie-deficient diet designed to achieve a mean weight loss from a baseline of 20-25% over a 4-week period. The other 10 dogs received a normal diet. Dogs were also randomized to receive either acute propranolol beta-receptor blockade (n = 9) or acute isoproterenol beta-receptor stimulation (n = 12) during their baseline studies. Of the nine dogs given propranolol, five were subsequently malnourished and four served as controls. Of the 12 given isoproterenol, six were rendered malnourished and six were controls. All dogs were studied at both baseline and 4 weeks and received drugs in an identical fashion during both studies. The significant changes with malnutrition consisted of decreases in heart rate, cardiac mass, and left ventricular wall thickness. The degree of change in stroke volume, ejection fraction, cardiac output, dp/dt, and Emax (index of left ventricular contractility), with the administration of propranolol or isoproterenol was unaltered by malnutrition. These data support the contention that moderate protein-calorie malnutrition is well tolerated in instrumented, unstessed dogs and that the left ventricle's capacity to respond to beta-stimulation and to tolerate beta-blockade is largely unimpaired.

Animals↗
PubMedDate not supplied

Low incidence of neoplasia in heart and heart-lung transplant recipients receiving triple-drug immunosuppression.

The risk of neoplasias developing after solid organ transplantation is markedly increased by immunosuppressive therapy. Lymphoma has been reported to develop in 13% of heart and in 33% of heart-lung transplant recipients treated with cyclosporine, and the incidence of skin carcinoma ranges between 6% and 16%. The incidence of posttransplant neoplasias with the use of lower loading and maintenance doses of cyclosporine as used in triple-drug immunosuppression is unknown. From December 1983 through August 1988, 134 heart and seven heart-lung transplants were performed at the University of Minnesota. All patients received a combination of cyclosporine, azathioprine, and prednisone. Survival was 94% at 1 and 90% at 3 years in heart recipients. Probability of acute rejection was 9% at 3 months and 12% at 1 and 3 years. B-cell lymphoma developed after heart transplant in only two patients for an incidence of 1.5%. Episodes of acute rejection and mean cyclosporine blood level did not predict the occurrence of posttransplant lymphoma. The incidence of skin carcinoma was 6.4%. No neoplasia occurred in heart-lung transplant recipients. All neoplasias were observed in patients older than 50 years. Our data indicate that the risk for developing lymphoproliferative disorders, but not for basal cell carcinoma, is reduced in heart and heart-lung transplant recipients receiving triple-drug immunosuppression. Older recipients may be at increased risk, suggesting that lower doses of immunosuppressive therapy should be considered in this group.

Azathioprine↗
PubMedDate not supplied

Arterial hypertension in heart transplant recipients treated with triple-drug immunosuppressive therapy.

Arterial hypertension occurs in the majority of heart transplant recipients treated with high dosages of cyclosporine. The incidence of hypertension with lower loading and maintenance dosages of cyclosporine, as used with triple-drug immunosuppressive therapy is unknown. Fifty-six patients who had transplantation at the University of Minnesota, Minneapolis, from December 1983 through December 1986, received low loading (6 to 10 mg/kg) and maintenance dosages of cyclosporine in addition to azathioprine (2 to 2.5 mg/kg/day) and prednisone. Two weeks after transplantation 68% of the patients were hypertensive (blood pressure greater than 140/90 mm Hg) despite normal serum creatinine levels (1.14 +/- 0.33 mg/dl). The number of patients requiring treatment for hypertension increased progressively, with 92% of the patients being hypertensive by 6 months. No correlation was found between blood pressure values, serum creatinine levels, and cyclosporine levels in the blood. Systemic vascular resistances were elevated 1 year after transplantation, whereas cardiac output and ventricular filling pressures were normal. Circulating norepinephrine levels, abnormally elevated before transplantation, normalized after operation. In 13 heart recipients in whom sequential measurements were obtained, plasma norepinephrine levels decreased within 2 weeks after transplantation. These data indicated that hypertension develops in almost all patients after heart transplantation despite the lower dosage of cyclosporine used with the triple-drug immunosuppressive therapy and the absence of significant renal impairment with this regimen, and probably it is not the result of activation of the sympathetic nervous system.

Adult↗
PubMedDate not supplied

Serial myocardial T2 relaxation time measurements in normal subjects and heart transplant recipients.

Myocardial proton T2 relaxation measurements were performed on five normal subjects over 4 weeks (20 measurements) and on nine heart transplant recipients (35 measurements). All magnetic resonance measurements were performed with a 1 T system. All patients had endomyocardial biopsy the same day as magnetic resonance imaging. Results of biopsies were normal on 32 occasions and abnormal three times (two cases of acute rejection and one case of myocardial edema). T2 values for normal subjects were 46.6 +/- 8.1 and 46.9 +/- 4.9 msec (septum and left ventricular free wall, respectively). T2 values for transplant recipients with normal results of biopsies were 44.5 +/- 7.8 and 43.1 +/- 7.5 msec. T2 values in three patients with abnormal results from biopsies were elevated (69 +/- 7.6 msec, range 59.7 to 77.6 msec). The results show similar values in normal subjects and transplant recipients with normal results from biopsies. Increased T2 values in three patients with abnormal results from biopsies indicate that relaxation time measurements may be of value to identify patients at risk of rejection.

Adolescent↗
PubMedDate not supplied

Heart transplantation in elderly patients.

During 1985 to 1986, 57 orthotopic heart transplantations have been performed at the University of Minnesota, Minneapolis. All patients received triple-drug immunosuppressive therapy of cyclosporine, azathioprine, and prednisone. Twenty-three patients were aged 55 years or older (mean age 58.0 +/- 2.6 years); 34 patients were under the age of 55 years (mean age 39.1 +/- 13.2 years). The initial in-hospital stay averaged 13 +/- 4 days in the older group and 16 +/- 13 days in the younger group. Perioperative mortality was similar in the two groups. The incidence of cerebrovascular accident was similarly low in the two groups, whereas incidence of steroid-induced diabetes (17% versus 9%) and significant osteoporosis (13% versus 3%) was significantly higher in older patients. The probability of survival and the actuarial freedom from rejection were identical in the two groups with 1-year survival of 96% and 94% of patients free of rejection at 12 months. Although the incidence of infection was not significantly higher in older patients (0.82 episode per patient) than in younger patients (0.78 episode per patient), life-threatening infections (Cryptococcus meningitidis, disseminated herpes simplex) were observed only in older patients. These data suggest that (1) heart transplantation is a valid therapeutic option even in elderly patients with end-stage heart failure, (2) it can be performed in selected patients at no increased operative risk with excellent long-term survival, (3) however, older patients are at higher risk for serious infections and for developing steroid-related complications.

Coronary Disease↗
PubMedDate not supplied

Reduction of infectious complications following heart transplantation with triple-drug immunotherapy.

Infection remains the major cause of mortality and is a significant source of morbidity following heart transplantation. Between March 1978 and March 1986, 62 orthotopic heart transplants were performed at the University of Minnesota. There were 56 clinically significant infectious episodes in 31 of the 58 patients surviving the perioperative period. The era I (1978-1982) experience with antilymphocyte globulin, prednisone, and azathioprine and the era II (1982-1983) experience with high-dose cyclosporine and prednisone were associated with a high incidence of cytomegalovirus and fungal infections. The conversion to low-dose triple-drug immunosuppression with cyclosporine, prednisone, and azathioprine in 1983 (era III) has markedly reduced infectious deaths and altered the spectrum of clinical infection by decreasing serious fungal and cytomegalovirus infections. This protocol has also significantly reduced the incidence of rejection. The reduction of infection and rejection complications with triple-drug immunosuppression has led to improved patient survival of 94% at 1 year and 87% at 2 years.

Adolescent↗
PubMedDate not supplied

Triple-drug immunosuppression with steroid discontinuation by six months after heart transplantation.

BACKGROUND: Triple-drug immunosuppression with cyclosporine, azathioprine, and prednisone is associated with complications which might be reduced by steroid withdrawal. METHODS: In two groups of heart transplant recipients maintained on an identical regimen of cyclosporine and azathioprine, prednisone was withdrawn in group I patients (n = 35) by 6 months after transplantation, whereas in group II patients (n = 49) prednisone was never discontinued. RESULTS: Survival was similar in the two groups. The incidence of acute graft rejection was significantly higher in group I (54%) than in group II (12%), whereas infective complications were significantly lower in group I than in group II (0.63 versus 1.02 episode/patient). The degree of posttransplantation weight gain, lipid abnormalities, and incidence of hypertension were not modified by the fast tapering of prednisone, whereas the incidence of cataract and compression fracture and the degree of bone loss were significantly reduced in group I. Graft function and incidence of coronary artery disease were similar in the two groups. CONCLUSIONS: The present data suggest that prednisone can be safely withdrawn in heart transplant recipients without jeopardizing survival and graft function. Longer follow-up is needed to assess the full impact of early withdrawal of steroids from triple-drug immunosuppression, especially on long-term graft function and incidence of coronary artery disease. Benefits of early steroid withdrawal included a reduction in bone loss, which might ultimately have a major positive impact on the extent of long-term rehabilitation and exercise tolerance after heart transplantation.

Azathioprine↗