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Biomedical subjects

R S Mitchell

Publications and source records attributed to R S Mitchell.

At least 109 records · Page 6Linked to original sources
PubMed1984

Independent determinants of operative mortality for patients with aortic dissections.

A 20 year (1963 to 1982) surgical experience including 175 consecutive patients with aortic dissections was analyzed by logistic discriminant analyses to identify predictors of high operative risk. The patient population had characteristics similar to those in large autopsy series. Sixty-nine percent had type A and 58% had acute dissections. The intimal tear was located in the ascending aorta in 60% of the patients, the descending aorta in 27%, and the transverse arch in 13%. The overall operative mortality rate was 23 +/- 3%. The operative mortality rates were substantially lower between 1977 and 1982: mortality in patients with acute type A dissections, 7 +/- 5%; in those with chronic type A, 11 +/- 7%; in those with acute type B, 13 +/- 12%; and in those with chronic type B, 11 +/- 11%. After preliminary univariate screening, the following factors were determined to be significant independent predictors of operative mortality (in rank order of declining predictive power): type A patients (n = 121), renal dysfunction, tamponade, renal/visceral ischemia, and operative date; type B patients (n = 54), rupture, renal/visceral ischemia, and age; all patients (n = 175), renal dysfunction, renal/visceral ischemia, site of tear (ascending less than descending less than arch), tamponade, operative date, and pulmonary disease. Interestingly, several variables had no important bearing on operative mortality, including type (acute vs chronic) of dissection, age, previous operation, rupture, stroke, paraplegia, Marfan's syndrome, concomitant aortic valve replacement and/or coronary artery bypass grafting, site of tear, and whether or not the tear was resected in type A patients; emergency operation, hypertension, previous cardiac symptoms, paraplegia, site of tear, and resection of tear in type B patients; and, when all patients were considered together, age, sex, cardiac symptoms, prior operation, stroke, paraplegia, acute myocardial infarction, acute aortic regurgitation, Marfan's syndrome, and tear resection. These data allow calculation of any individual patient's operative risk and document that the operative mortality rate today is relatively low for all patients with aortic dissections, irrespective of type or acuity. Earlier surgical referral of patients with acute type A or acute type B dissection before irreversible major end-organ ischemia and/or infarction is probably in part responsible for the substantially improved results since 1977.

Aortic Dissection↗
PubMed1984

Degenerative and atherosclerotic aneurysms of the thoracic aorta. Determinants of early and late surgical outcome.

To identify significant predictors of early and late mortality, multivariate discriminant analyses were applied to the clinical outcome of 175 consecutive patients with thoracic aortic aneurysms operated upon over a 20 year span. Only atherosclerotic and degenerative aneurysms were included; the patients were segregated into two groups according to location of the aneurysm. The ascending aortic aneurysm group consisted of 124 patients, 85% of whom required concomitant aortic valve replacement. There were 51 patients in the descending aortic aneurysm group. Mean follow-up was 4.9 years (maximum of 19 years), with a total of 860 patient-years of follow-up. Multivariate analyses revealed that surgical priority and advanced age were independent determinants of hospital mortality in the ascending group; for the descending group, surgical priority and the presence of congestive heart failure were the strongest predictors of hospital mortality. Late mortality in the ascending group correlated with advanced age. Hypertension and the presence of preoperative congestive heart failure were independent determinants of late mortality in the descending group. Several variables did not have any independent bearing on hospital or late mortality, including etiology and location of the aneurysm, previous myocardial infarction, chronic lung disease, and concomitant aortic valve replacement. High-risk subgroups of patients with thoracic aortic aneurysms can be identified by these variables. Aggressive medical plus surgical management and operation prior to aneurysm rupture is necessary to improve both early and long-term survival rates.

Adult↗
PubMed1984

Dobutamine and dopamine after cardiac surgery: greater augmentation of myocardial blood flow with dobutamine.

Left ventricular hemodynamics, dimensions and coronary sinus blood flows were measured simultaneously after infusions of dobutamine and dopamine. Ten patients were studied 6, 10 to 15, and 24 hr after cardiopulmonary bypass surgery. The dose of each drug was adjusted to increase cardiac output by 25%. Heart rate was held constant with atrial pacing. Dobutamine and dopamine increased peak left ventricular dP/dt from baseline values by 72% vs 58% during the early study, 77% vs 78% in the intermediate study, and 95% vs 79% in the late study (all NS, difference between drugs). Similarly, there were no significant differences in hemodynamic response or in cardiac dimensions after the two drugs in any period. Both drugs increased myocardial oxygen uptake during the intermediate and late studies (32% vs 33% and 34% vs 25%). With dobutamine this increase was matched by a similar increase in coronary blood flow; however, failure of the expected increase in coronary blood flow with dopamine suggested coronary constriction. Although dobutamine and dopamine have similar hemodynamic effects, dobutamine has the advantage of not limiting the increase in coronary blood flow associated with increased oxygen demand.

Catecholamines↗
PubMed1984

Performance characteristics of the Starr-Edwards Model 1260 aortic valve prosthesis beyond ten years.

The Starr-Edwards non-cloth-covered silicone ball (Model 1260) aortic valve prosthesis has been widely used for over 15 years and remains a standard against which newer values are compared. To define more completely the performance characteristics of this prosthesis, this study (including 449 patients) analyzed the long-term function of this specific valve over a cumulative total of 2,896 patient-years (pt-yrs) of follow-up which extended beyond 13 years. Expressed in both actuarial (% [+/- standard error of the mean] free at 10 years) and linearized (%/pt-yr) terms, respectively, valve-related complications occurred at the following rates: thromboembolism, 76 +/- 3 and 2.7; anticoagulant-related hemorrhage, 74 +/- 3 and 3.1; prosthetic valve endocarditis, 92 +/- 2 and 0.9; reoperation, 90 +/- 2 and 1.1; valve failure, 82 +/- 2 and 2.2; all valve-related morbidity and mortality, 51 +/- 3 and 6.0; and valve-related death, 88 +/- 2 and 1.3. Thirteen percent of hospital and 18% of late deaths were due to valve-related causes. No case of structural failure was documented. This prosthesis has an admirable structural durability record out to 13 years, and its long-term performance is satisfactory, albeit not optimal. Despite the indestructable design and construction of this mechanical valve substitute, 12% +/- 2% of patients had died of valve-related complications by 10 years, and fully 49% +/- 3% had had some form of serious valve-related complication. The long-term data reported herein can be used for analytical comparison when follow-up of patients with newer mechanical prostheses and tissue bioprostheses reaches 10 years to elucidate whether or not these newer valves truly represent improvements and which type of valve substitute proffers the most possible net benefit to the patient.

Actuarial Analysis↗
PubMed1983

Discriminant analysis of the changing risks of coronary artery operations: 1971-1979.

The risk of perioperative myocardial infarction (PMI) and operative mortality (OM) associated with coronary artery bypass grafting (CABG) has declined since the introduction of this procedure 15 years ago. Rigorous scientific investigation of the reasons for this trend has been hindered by the complex interactions between changing indications for operation, criteria for patient selection, and management methods. Using univariate and multivariate logistic regression analyses, we investigated the effects of 42 variables on PMI and OM for two cohorts undergoing CABG between 1971 and 1975 (Group A) and 1977 and 1979 (Group B). According to previously identified risk factors, Group B patients were at higher potential risk than those in Group A. Nevertheless, the PMI and OM rates declined from 8.7% +/- 0.9% to 4.6% +/- 0.7% (p = 0.005) and from 2.4% +/- 0.5% to 1.2% +/- 0.4% (p = 0.07), respectively. In calendar year 1979 (N = 438), the PMI and OM rates were 2.8% +/- 0.8% and 0.7% +/- 0.4%. More importantly, the independent determinants of PMI and OM for the two time intervals were distinctly different. Factors which affected the PMI rate in Group A were no longer determinants of PMI in Group B; with the exception of emergency operation and, to a modest extent, congestive heart failure (CHF), predictors of OM in Group A were not determinants of OM in Group B. Thus the adverse impact of multiple patient-related and disease-related determinants of PMI and OM has been neutralized over this decade by the real improvements in patient management. The specific factors and management concepts responsible for these superior results in sicker patients remain uncharacterized; however, in general terms, more sophisticated medical, anesthetic, and nursing management and more refined surgical expertise have essentially nullified the concept of high-risk candidates. Furthermore, the more propitious early results being attained currently may translate directly into parallel long-term improvements in functional benefit and survival.

Coronary Artery Bypass↗
PubMed1983

Aneurysm of the diverticulum of the ductus arteriosus in the adult. Successful surgical treatment in five patients and review of the literature.

Sixteen aneurysms of the diverticulum of the ductus arteriosus in adults have been previously reported. Ten patients died of rupture of the aneurysm or died at surgical exploration. Only one previous patient underwent successful aneurysmectomy. Five new cases of aneurysm of the adult ductal diverticulum, all diagnosed preoperatively and successfully repaired, are presented. All five patients are alive 6 to 33 months postoperatively. Our experience with these patients suggests several important features of these aneurysms: (1) Diagnosis may be difficult and may require multiple-view aortography or computed tomographic (CT) scanning to differentiate from tumor. (2) The operative approach, either left thoracotomy or median sternotomy, may be determined by the necessity for concomitant procedures. (3) Unlike true atherosclerotic aneurysms of the aortic arch, these aneurysms can be repaired effectively by aneurysmorrhaphy. (4) Because of their critical location and the high incidence of complications in reported cases, aneurysms greater than 3 cm in diameter, those producing symptoms, or those showing progressive enlargement should be surgically resected.

Aged↗
PubMed1982

Diagnosis of arterial prosthetic graft infection by indium-111 oxine white blood cell scans.

Early and accurate diagnosis of infected prosthetic arterial grafts is difficult, despite the application of diverse diagnostic modalities. Delay in making the diagnosis is largely responsible for the high amputation and mortality rates associated with this complication. In nine patients with suspected graft infections, indium-111 white blood cell scanning was useful and accurate. Graft infection was proved in five cases and ruled out in three. One false-positive scan was due to a sigmoid diverticular abscess overlying the graft. Indium-111 white blood cell scans may improve the accuracy of diagnosing infected prosthetic grafts, which may result in better limb and patient salvage rates.

Adult↗
PubMed1979

Health effects of urban air pollution. Special consideration of areas at 1,500 m and above.

Urban air pollution, when sufficiently severe, can cause death in humans; these deaths occur preponderantly among those with increased susceptibility. Pollution--carbon monoxide and oxidants in particular--is capable of aggravating preexisting chronic heart and lung diseases. Pollution and tobacco (especially cigarette) smoke act synergistically in a causative role in chronic bronchitis and in an aggravating role in emphysema. Susceptibility to the effects of urban air pollution varies widely, with the most susceptible being fetuses, the newborn, the elderly, the infirm, those with chronic heart and lung diseases, and those who smoke. The carbon monoxide standards for sea level are probably too lenient for an altitude of 1,500 m and above. Using a broad definition of health, which takes into account concepts such as quality of life and social and mental well-being, few metropolitan residents would deny that their health is compromised by air that is malodorous, that irritates mucous membranes, and that obscures beautiful scenery.

Adult↗
PubMed1979

Proliferation of Rous sarcoma virus-infected, but not of normal, chicken fibroblasts in a medium of reduced calcium and magnesium concentration.

Both normal and Rous sarcoma virus-infected chicken fibroblasts proliferate actively in a culture medium containing physiological concentrations of calcium (1.2 mM) and magnesium (0.7 mM). In the presence of a physiological concentration of magnesium, reduction of the calcium concentration to 0.125 mM resulted in a significant decrease in the proliferation of the normal, but not of the neoplastic, fibroblasts. Reduction of the magnesium concentration to 0.05 mM in the presence of a physiological concentration of calcium had a similar effect. In a culture medium containing reduced concentrations of both calcium (0.20 mM) and magnesium (0.05 mM), the normal fibroblasts were maintained without proliferation, whereas the Rous sarcoma virus-infected fibroblasts continued to proliferate actively. The cytosol concentrations of ionized calcium and magnesium are known to be regulated by a balance between net passive influx and active extrusion and sequestration. On the basis of this consideration and the findings described above it can be hypothesized that: (i) Fibroblast replication is initiated when cytosolic concentrations of calcium, magnesium, or both rise above a critical level. (ii) Autonomous initiation of replication of neoplastic fibroblasts is a result of failure of cytoplasmic divalent cation homeostasis; alternatively, sarcoma virus infection may endow cells with a divalent cation-independent mechanism that bypasses an initiation mechanism that is, normally, divalent cation-dependent. (iii) Proliferation of normal fibroblasts is controlled by extracellular matrix components that interact with cell surfaces in a manner that limits the permeability of plasma membranes to divalent cations or otherwise functions to lower cytosol divalent cation concentrations.

Avian Sarcoma Viruses↗
PubMed1979

Thymidine and hypoxanthine requirements for the proliferation of normal and Rous sarcoma virus-infected chicken fibroblasts in the presence of methotrexate.

Cultured normal and Rous sarcoma virus-infected chicken fibroblasts do not differ in the concentrations of thymidine or of hypoxanthine that they require to proliferate in the presence of a methotrexate block. For maximal proliferation, thymidine is required at 10(-6) M, while hypoxanthine is required at 10(-5) M. The normal and Rous-infected fibroblasts show very similar, if not identical, decreases in proliferation rates at suboptimal concentrations of thymidine or hypoxanthine. These results suggest that conversion of fibroblasts to the neoplastic state does not alter their capacity to salvage thymidine or purines from the extracellular fluid or to metabolize these compounds.

Animals↗
PubMed1978

5-Methyltetrahydrofolic acid, 5-formyltetrahydrofolic acid (folinic acid), and folic acid requirements of normal and Rous sarcoma virus-infected chicken fibroblasts.

Normal and Rous sarcoma virus-infected chicken fibroblasts proliferate maximally in a culture medium containing a physiological (10 ng/ml) concentration of 5-methyltetrahydrofolic acid or folinic acid (5-formyltetrahydrofolic acid), while their maximal proliferation requires a hyperphysiological (1000 ng/ml) concentration of folic acid. The normal and Rous-infected fibroblasts do not differ in their requirements for 5-methyltetrahydrofolate, folinic acid, or folic acid.

Animals↗
PubMed1976

Proliferation of Rous sarcoma virus-infected, but not of normal, chicken fibroblasts in oxygen-enriched environment: preliminary report.

Both normal and Rous sarcoma virus-infected chicken fibroblasts proliferate in an incubator containing 95% air, 5% CO2. In an incubator atmosphere enriched with oxygen, however, the normal fibroblasts are maintained without proliferation, while the Rous sarcoma virus-infected fibroblasts continue to proliferate. This suggests that a respiratory function may be involved in the regulation of proliferation of normal cells, and that neoplastic cells may proliferate autonomously because of a deficiency in this regulatory function.

Atmosphere↗