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Biomedical subjects

L L Michaelis

Publications and source records attributed to L L Michaelis.

At least 73 records · Page 4Linked to original sources
PubMed1977

Evolution of regional ischemia distal to a proximal coronary stenosis: self-propagation of ischemia.

The temporal evolution of myocardial ischemia was studied in open chest dogs at constant preload, afterload and heart rate. In one group of animals, a variable circumflex arterial stenosis was used to maintain constant distal circumflex arterial hypotension (40 to 50 mm Hg). During a 3 hour period of stenosis, flow in the subendocardial fourth of the ischemic ventricular wall decreased from 0.22 to 0.09 ml/g per min (P less than 0.02), whereas subepicardial flow was not significantly changed. Local vascular resistance, therefore, doubled in the most ischemic area of myocardium. In a second group of animals in which proximal coronary stenosis was held constant and pressure varied, an ischemia-mediated increase in local vascular resistance was also demonstrated. In addition, a reciprocal relation was observed between changes in flow in the left anterior descending coronary region and changes in collateral flow to the region of the circumflex artery. A coronary steal mechanism and an ischemia-mediated resistance increase may be two means by which ischemia is self-propagating.

Animals↗
PubMed1977

The effects of isoproterenol and dopamine on regional myocardial blood flow after stenosis of circumflex coronary artery.

The effects of isoproterenol and dopamine on regional myocardial blood flow were studied in 10 open-chest dogs after acute stenosis of the proximal circumflex coronary artery. Blood flow was determined by the radioactive microsphere technique. Isoproterenol led to a homogenous increase in blood flow in the normal myocardium. In the myocardium with compromised coronary blood flow, isoproterenol led to a relative subendocardial ischemia. This occurred despite increased aortic flow and peak left ventricular dp/dt. Dopamine also increased aortic flow and peak left ventricular dp/dt, but it did not cause regional myocardial ischemia. The findings suggest that dopamine is the preferable inotropic agent in managing low cardiac output in patients with significant coronary artery disease.

Animals↗
PubMed1977

Effects of dipyridamol and methylprednisolone on intimal thickening in vein grafts.

Fibrous intimal proliferation severe enough to produce occlusion has been observed in vein segments used for aorta-coronary bypass grafts. In an attempt to improve graft patency and decrease intimal fibrous thickening, animals with vein grafts were treated with dipyridamole or methylprednisolone for 8 to 12 weeks. Femoral vein segments were used to bypass the femoral artery in 36 dogs. Thirty-four of these grafts were patent at 8 weeks, with no statistically significant differences between control and drug treatment groups. Intimal thickness measurements were taken at three different points along the graft: proximal (upstream end), middle,and distal (downstream end). Dogs treated with methylprednisolone had significantly less intimal thickening (214 versus 125 mu, p less than 0.05) than did control animals in the middle of the veins but there was no difference in thickness measurements at the proximal and distal ends. Dipyridamole-treated animals did not differ from control dogs. Although these data show decreasing intimal thickening in the middle of grafts with methylprednisolone therapy, the intimal thickness was still considerably greater than normal. The lack of response near the anastomotic sites suggests that clinical application of either agent to improve long-term patency is unwarranted.

Animals↗
PubMed1976

Mediastinoscopy: a diagnostic aid in metastatic carcinoma of the breast.

Six patients with metastatic carcinoma of the breast underwent mediastinoscopy to obtain tissue for estrogen receptor analysis and pathologic confirmation of metastatic tumor. The indication for mediastioxcopy was an abnormal mediastinal accumulation of gallium in five patients, only two of whom had an abnormality noted on tomography. All six patients had tumor recovered by mediastinoscopy as demonstrated by pathologic examination and/or estrogen receptor assay, Therefore, the diagnosis of mediastinal metastases in breast cancer may be suggested by either chest roentgenograms, mediastinal tomography, or gallium scintigraphy. Mediastinoscopy is a safe, effective procedure capable of establishing the diagnosis of metastatic carcinoma of the breast and of procuring sufficient tissue for estrogen receptor analysis in patients without more readily accessible sites of metastases.

Adult↗
PubMed1976

Pneumocystis pneumonia: the importance of early open lung biopsy.

Pulmonary infection due to Pneumocystis carinii is now recognized as the leading cause of death from infection in patients with a hematologic malignancy who are in remission. Effective treatment requires suspicion of the infection in susceptible patients and rapid identification of the organism. In most patients, open lung biopsy performed through a small anterior thoracotomy provides immediate identification or exclusion of the organism, thus allowing treatment of infected patients and avoidance of inappropriate therapy in patients without the disease. We feel that the use of early thoracotomy, in spite of the fact that it exposes these very ill patients to a major surgical procedure and general anesthesia, is ultimately the safest therapeutic course.

Adolescent↗
PubMed1976

Tricuspid regurgitation. A comparison of nonoperative management, tricuspid annuloplasty, and tricuspid valve replacement.

The best means of managing tricuspid regurgitation associated with mitral or mitral and aortic valve disease is still to be determined. During the period 1972 to 1974, we treated 76 patients who had tricuspid regurgitation along with associated valvular dysfunction. Patients with mold regurgitation were treated conservatively, those with moderate regurgation underwent annuloplasty, and those with severe regurgitation had tricuspid valve replacement. We found the results to be less satisfactory in the group treated by annuloplasty than in the other two groups. We still manage conservatively those patients with mild regurgitation, but we believe it appropriate to replace the valve in an increasing number of subjects who have tricuspid regurgitation of moderate severity.

Animals↗
PubMed1976

The contribution of atrial contraction to right heart function before and after right ventriculotomy. Experimental and clinical observations.

Effective atrial contraction was abolished by simultaneous atrial and ventricular (A-V) pacing in an acute canine preparation. At constant cardiac output, aortic pressure, and heart rate, only a small rise (1.4 mm. Hg) in mean right atrial pressure was observed before vertical right ventriculotomy, but a larger rise (9.5 mm Hg) occurred after ventriculotomy (p less than 0.01). Right heart failure with tricuspid regurgitation was induced after ventriculotomy by volume overload and A-V pacing. Restoration of atrial contraction (sequential A-V pacing) eliminated regurgitation and lowered average mean right atrial pressure from 22 to 4 mm. Hg (p less than 0.001). After right ventriculotomy, loss of atrial contraction at a constant right atrial pressure resulted in a 42 per cent reduction in cardiac output. In 8 patients who had had right ventriculotomies, abolition of effective atrial contraction by A-V pacing caused an average reduction in cardiac output of 22 per cent, whereas cardiac output fell only 5 per cent in 5 control patients (p less than 0.01).

Animals↗
PubMed1975

Coronary artery perfusion.

Perfusion of the coronary arteries with oxygenated blood during cardiopulmonary bypass should in theory offer perfect myocardial protection, but the difficulties sometimes encountered with direct cannulation and the hazards of prolonged fibrillation in spite of perfusion raise questions regarding its universal efficacy. Arguments for and against coronary artery perfusion are presented and the hazards of partial perfusion are stressed.

Heart Arrest, Induced↗
PubMed1975

Coronary collateral function in patients without occlusive coronary artery disease.

Little is known of the functional capacity of coronary collaterals in humans without occlusive coronary artery disease. We, therefore, measured peripheral coronary pressure (PCP) and retrograde flow (RF) from coronary arteries at aortic valve replacement in seven patients without occlusive coronary artery disease. Using a T-connection interposed in left (LCA) and right (RCA) coronary perfusion lines, data were obtained during brief proximal occlusion of each line. PCP was expressed as a fraction of perfusion pressure (PP), and collateral resistance (CR) was calculated as PP/RF. Median values were as follows: (a table was included). In contrast, previous studies of well-collateralized distal segments of diseased coronary arteries revealed mean RF 15.7, CR 5.1 and PCP/PP 0.50. Under the conditions of study, all vessels interconnecting the non-diseased RCA and LCA delivered flow and pressure less readily than collaterals to a single distal segment of a diseased coronary artery. Thus, collaterals in patients without diseased coronary arteries have an extremely limited capacity to transmit either flow or pressure. The absolute values of RF were small relative to the muscle mass perfused by each coronary artery, suggesting that perfusion of only one coronary artery in man during operation may not provide substantial perfusion for large portions of myocardium. Comparison of performance of collaterals supplying atherosclerotic and nonatherosclerotic coronary arteries indicates that proximal occlusion may be an important factor stimulating enhancement of collateral function. Moreover, the nitroglycerin-induced improvement in collateral function seen in patients with chronic occlusive coronary disease was not demonstrable in patients without coronary occlusion. Thus, coronary collaterals may acquire nitroglycerin responsiveness as a result of changes induced by chronic coronary occlusion.

Adult↗
PubMed1975

Measurement of mitral orifice area in patients with mitral valve disease by real-time, two-dimensional echocardiography.

A quantitative assessment of mitral valve orifice area can be achieved in patients with pure mitral stenosis by cardiac catheterization. In the presence of mitral regurgitation, however, accurate measurement often is impossible because total diastolic flow through the mitral valve frequently is unknow. Using a recently developed real-time, two-dimensional echocardiography system, we are able to obtain cross-sectional images of the mitral valve by scanning the heart perpendicular to its long axis at the level of the tip of the mitral leaflets. Twenty consecutive patients undergoing operation for mitral valve disease were studied during the week prior to operation. In 18 of 20 (90%) the mitral orifice was imaged successfully in early diastole by two-dimensional echocardiography so that mitral valve orifice area could be measured directly in square centimeters. In 14 patients (ten with associated mitral regurgitation), mitral orifice area was measured both by echocardiography and directly at time of operation. In 12 of 14 (86%) patients, mitral orifice area by two-dimensional echocardiography was within 0.3 square centimeters of that measured at operation (correlation coefficient for all 14 patients equals 0.92). We conclude that two-dimensional echocardiography is extremely useful in the evaluation of patients with mitral valve disease because it provides a noninvasive method for directly measuring the mitral valve orifice area that is accurate even in the presence of mitral regurgitation.

Calcinosis↗
PubMed1975

Delayed coronary artery dissection after angiography. A case description with successful operative treatment.

A patient is described in whom right coronary artery dissection occurred 48 hours after coronary angiography. Successful operative treatment consisted of immediate saphenous vein bypass grafting and ligation of the proximal coronary artery. Several aspects of the case are characteristic of this pathological entity as reported in the literature and suggest principles of surgical management.

Adult↗
PubMed1975

Long-term morphologic and hemodynamic evaluation of the left ventricle after cardiopulmonary bypass. A comparison of normothermic anoxic arrest, coronary artery perfusion, and profound topical cardiac hypothermia.

In order to assess the long-term effects of cardiopulmonary bypass (CPB) in combination with pupular methods of myocardial protection, 37 dogs were placed on CPB for 100 minutes with the use of a bubble oxygenator without hemodilution. A separate group (I) of eight normal dogs served as a control for assessment of hemodynamic changes. The operative groups were as follows: II, continuous coronary perfusion with an empty, beating heart for 60 minutes at 35 degrees C.; III, hypothermic anoxic arrest (aortic occlusion) for 60 minutes with topical cold saline lavage (4 degrees C.); IV, anoxic arrest for 60 minutes at 35 degrees C. Subgroups of Groups III and IV received intracoronary perfusion with Ringer's lactate or Sacks' solution during aortic occlusion and were compared with those animals receiving no perfusion. Survival in Groups II and III was significantly better than in Group IV (82 and 92 per cent vs. 45 per cent). Coronary perfusion with Ringer's lactate or Sack's solution did not influence survival. The 23 survivors from all groups underwent left heart catheterization and LV cineangiography 5 months after operation. All three operative groups had significant elevation of LVEDP and depression of maximum developed dp/dt when compared with normal dogs. Ejection fraction was significantly depressed in Groups III and IV, and there was evidence of left ventricular hypokinesia and/or akinesia in all three operative groups. Differences in function between Groups II, III, and IV were not significant. The use of intracoronary solutions during anoxic arrest did not significantly influence these functional alterations. Evidence of subendocardial fibrosis was found in each of the operative groups, with the most marked changes found in the normothermic arrest group. Moderate fibrosis was present, however, in some survivors in both the continuous coronary perfusion and topical hypothermic arrest groups. These data indicate that although survival is greatly enhanced when coronary artery perfusion or topical hypothermia is used, neither method prevents chronic deterioration in ventricular function nor the development of subendocardial fibrosis.

Animals↗
PubMed1975

Experimental coronary artery fistula.

Despite numerous clinical reports of coronary artery fistulas, there have been no laboratory models. A circumflex coronary-pulmonary artery fistula was constructed with a vein graft in 11 adult foxhounds. A temporary intravascular shunt obviated the need for cardiopulmonary bypass. Measurements of aortic flow, arterial pressure, left ventricular pressure and its derivative, heart rate, and flow in the proximal coronary, distal coronary, and fistula were made with the fistula open and closed in 9 animals. Mean fistula flow was 89 c.c. per minute, representing a 1.1:1 left-to-right shunt. Mean proximal coronary flow increased 211 per cent, and there was a relative steal of 26 per cent of distal coronary flow with the fistula functioning. Phasic flow patterns showed continuous systolic and diastolic flow in the proximal coronary artery and fistula. Despite the striking changes in coronary flow patterns, there was no significant effect on measured left ventricular function. Futher uses for this model and variations of it aresuggested.

Animals↗
PubMed1975

Atrioventricular valve replacement with the Hancock porcine xenograft: a five year clinical experience.

Since July, 1970, 111 patients have undergone mitral and/or tricuspid valve replacement with a glutaraldehyde-fixed porcine xenograft mounted on a flexible stent; 41 of these patients also had aortic valve replacement with a Starr-Edwards or Bjork-Shiley valve, and 85 patients presently are alive. Cumulative follow-up totals 2,060 months, with 16 patients followed more than 4 years. Anticoagulants have not been administered postoperatively, and one patient has had a systemic embolus. Postoperative hemodynamic assessments have been carried out in 54 patients, and in either the mitral or tricuspid position the valve was shown to have good hydraulic function. Significant mitral regurgitation, secondary to prosthetic dysfunction, occurred in one patient 56 months following implantation. Progressive prosthetic stenosis has not occurred, and hemolysis or anemia of clinical significance has not been observed as a consequence of the use of the use of the xenograft. To date, these clinical and hemodynamic data indicate that the glutaraldehyde-fixed xenograft, mounted on a flexible stent, is the prosthesis of choice for mitral and tricuspid valve replacement.

Aortic Valve↗