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Biomedical subjects

A M Borkon

Publications and source records attributed to A M Borkon.

At least 37 records · Page 2Linked to original sources
PubMed1988

Aortic valve selection in the elderly patient.

To determine the influence of valve selection on valve-related morbidity and mortality and patient survival, comparative long-term performance characteristics of mechanical (N = 68) and bioprosthetic (N = 73) heart valves were analyzed for 141 patients more than 70 years old who underwent isolated aortic valve replacement between 1970 and 1985. Cumulative patient follow-up was 491 patient-years (average, 4.3 years per patient). Hospital mortality was 18% and 19% for patients with mechanical valves and bioprosthetic valves, respectively. Survival at 5 years was 61 +/- 7% (+/- the standard error) and 67 +/- 10% for recipients of mechanical valves and bioprosthetic valves, respectively. Male sex (p = 0.014) and urgency of operation (p = 0.006) were independent risk factors for hospital mortality. Atrial fibrillation increased valve-related mortality (p = 0.01). No patient required reoperation or experienced structural valve failure. While anticoagulant-related hemorrhage was increased in recipients of mechanical valves (9.2 +/- 2.1%/patient-year) compared with recipients of bioprosthetic valves (2.3 +/- 1.1%/patient-year), it did not result in a death or lead to permanent disability. There was no difference in freedom from any valve-related complication at 5 years. However, when all morbid events are considered, recipients of bioprosthetic valves experienced fewer valve-related complications than patients receiving mechanical valves (10.7 +/- 2.3%/patient-year versus 17.6 +/- 2.5%/patient-year, respectively; p less than 0.05). The reduced incidence of anticoagulant-related hemorrhage and the infrequent need for warfarin sodium anticoagulation favor selection of a bioprosthetic heart valve in patients older than 70 years.

Aged↗
PubMed1988

Mitral and aortic blood flows during spontaneous respiration in dogs.

Left sided hemodynamic events during respiration remain a controversial subject. Left ventricular (LV) hemodynamic events were evaluated during obstructed and partially obstructed inspiration in anesthetized dogs acutely instrumented with mitral (Qm) and ascending aortic (Qa) flow probes. This allows classification of the inspiratory decrease in LV stroke volume as either a diastolic event (e.g., ventricular interdependence) in which case the LV inflow volume (integral of Qm) should decrease before the LV outflow volume (integral of Qa), or a systolic event (e.g., afterload or contractility) in which case outflow (integral of QA) should decrease before inflow (integral of Qm). During either unobstructed (n =8) or partially obstructed (n = 5 spontaneous ventilation, Qm reached both its inspiratory minimum and expiratory maximum prior to the associated minimum and maximum values for integral of in 80% or more of the respiratory cycles. Thus, a diastolic event dominates both in reducing the subsequent LV outflow during the expiratory increase in intrathoracic pressure. However, because a diastolic event did not occur first at all times, a systolic event must occur first at all times, a systolic event must also be present. If a rapid change in intrathoracic pressure occurred during diastole, integral of Qm invariably immediately increased. If a rapid in intrathoracic pressure occurred during systole, integral of Qa could change independently of the preceding integral of Qm. Both systolic and diastolic mechanisms contribute to the inspiratory fall in LV output. These mechanisms will not be clearly delineated without evaluating the effects of intrathoracic pressure within a single cardiac cycle.

Airway Obstruction↗
PubMed1988

Neurohumoral modulation of the pulmonary vasoconstrictor response in the autoperfused working heart-lung preparation during cardiopulmonary preservation.

Uncontrolled pulmonary hypertension during autoperfusion of the heart and lungs for preservation has been described, and it may result in extensive pulmonary injury and occasional early failure of the preparation. In order to investigate the neurohumoral mediators of the vasoconstrictor response in the pulmonary circulation of the autoperfused working heart-lung preparation, heart-lung organ blocks were harvested from calves, placed in a normothermic autoperfusion circuit, and studied. Effects of beta-adrenergic stimulation with isoproterenol, nonspecific vasodilatation with nitroglycerin, alpha-adrenergic blockade with phentolamine, phospholipase A2 inhibition with methylprednisolone, cyclooxygenase inhibition with indomethacin, and white blood cell depletion were independently evaluated. Untreated animals, pre- and postexplant, served as controls. Multipoint pulmonary vascular pressure-cardiac output plots were constructed for each animal. An index of pulmonary vascular resistance was obtained from the linear relation: mean pulmonary artery pressure minus pulmonary capillary wedge pressure divided by cardiac output. An intense flow-dependent pulmonary vasoconstrictor response was confirmed to exist in the denervated bovine autoperfused working heart-lung preparation. Isoproterenol afforded better protection against this response than the other agents studied. White blood cell depletion reduced postexplant pulmonary vasoconstriction, implying that circulating polymorphonuclear leukocytes mediate the response in the autoperfused working heart-lung preparation. White blood cell depletion and the administration of selected pharmacologic agents provide modalities for regulating the pulmonary vasoconstrictor response, and thus may enhance lung preservation in the autoperfusion model.

Animals↗
PubMed1988

Effects of changes in left ventricular loading and pleural pressure on mitral flow.

The cause of the fall in left ventricular (LV) stroke volume (SV) during a fall in pleural pressure (Pp1) has been in dispute for over a century. We have defined the changes in the temporal relationship between LV inflow (Qm) and outflow (Qa) in a canine preparation to test the mutually exclusive hypotheses that the fall in LVSV is caused only by changes during diastole (e.g., ventricular interdependence) or only by changes during systole (e.g., afterload). The ability of the experimental preparation to measure the results of acute changes in right heart volume or output and acute changes in LV afterload was validated in open-chest studies with and without pericardial constraint. In closed-chest studies, with a fall in Pp1 during a Mueller maneuver Qm reached both its inspiratory minimum and expiratory maximum before Qa in 80% of the Mueller maneuvers, invalidating both hypotheses, which each required that one flow lead the other in 100% of the Mueller maneuvers. Review of individual records suggested that if the rapid changes in Pp1 occurred during systole, Qa could vary in a manner independent of the preceding Qm. These studies suggest that both diastolic and systolic events may contribute to the fall in SV, while causing opposite changes in LV volumes.

Animals↗
PubMed1988

Immediate enhancement of left ventricular relaxation by coronary artery bypass grafting: intraoperative assessment.

We investigated the effect of coronary artery bypass grafting on the rate of left ventricular relaxation as defined by the time constant for isovolumetric relaxation, T, measured in milliseconds. Completeness of relaxation at rapid heart rates was determined by comparison of the relationship between left ventricular pressure and echocardiographic left ventricular cross-sectional cavity area during rapid ventricular pacing with that obtained after a prolonged diastole when the ventricle was maximally relaxed. Twelve patients with coronary artery disease had significantly higher T values (94.5 +/- 6.2) than six patients without coronary artery disease who were undergoing other open heart procedures (39.5 +/- 5.0, p less than .001). T was significantly reduced after coronary artery bypass grafting (68.2 +/- 5.1, p = .007), but was unchanged in the six control patients after cardiopulmonary bypass (37.8 +/- 4.5, p = .54). Similar changes were found during rapid pacing to 100, 120, and 140/min. Incomplete relaxation was detected in three of 10 (heart rate 120 beats/min) and nine of 11 (heart rate 140 beats/min) patients with coronary artery disease and this decreased to 0 of 10 (heart rate 120 beats/min) and six of 11 (heart rate 140 beats/min) patients after coronary artery bypass. Incomplete relaxation before bypass at a heart rate of 120 beats/min averaged 0.9 +/- 0.3 mm Hg. At a heart rate of 140 beats/min, incomplete relaxation averaged 5.6 +/- 1.6 mm Hg before and 1.4 +/- 0.5 mm Hg after bypass. Intake of beta-blockers or calcium-channel blockers, body temperature, and systolic blood pressure were not found to be related to these changes. We conclude that immediately after coronary artery bypass relaxation of left ventricular muscle is enhanced and incomplete relaxation at rapid heart rates is less likely. The most probable cause of this improvement in ventricular relaxation after coronary artery bypass grafting is relief of ischemia.

Blood Vessel Prosthesis↗
PubMed1988

31P nuclear magnetic resonance determination of changes in energy state in lung preservation.

The significance of dynamic changes in energy state during lung harvesting and preservation has not been extensively studied. Phosphorus 31 nuclear magnetic resonance spectra at 81 MHz were obtained from degassed rabbit lungs. Changes in the adenosine 5'-triphosphate-to-inorganic phosphate peak-intensity ratios were used to measure changes in energy state. Two groups of rabbit preparations were studied to evaluate the effect of hypothermia during the initial 120 minutes of harvesting (n = 8 at 36 degrees C and n = 5 at 4 degrees C). The significance of these changes was assessed in a second experiment in which lungs were reperfused in vitro at selected intervals of hypothermia (5, 12, and 24 hours) and assessed for injury. Hypothermic preservation sustained a significantly higher energy state. The depletion of energy state was correlated with injury, particularly as measured by lung edema (r2 = -0.715). Short periods of warm ischemia (30 minutes) result in a significant depletion of energy state, which may be a component of pulmonary injury during harvesting and preservation.

Adenosine Triphosphate↗
PubMed1988

Predictors of perioperative mortality in patients with unstable postinfarction angina.

Factors associated with increased operative mortality in patients with postinfarction angina have not been defined. Two hundred twenty-five patients underwent urgent coronary artery bypass grafting from 1982 through 1986. One hundred sixty-two men and 63 women averaged 62 years of age (range, 35-87 years). Operative mortality was 5.3%. To assess the predictors of perioperative mortality, 16 variables were evaluated by univariate and multivariate analyses. Significant independent predictors of perioperative mortality were the presence of a transmural anterior myocardial infarction (p less than 0.0005) and the need for preoperative intra-aortic balloon pumping for angina or congestive heart failure (p = 0.009). All perioperative mortalities (12 patients) occurred in this subset (anterior myocardial infarction, intra-aortic balloon pumping, or both) that included 101 patients. The mean follow-up period was 27.8 months (range, 1-69 months). There were 11 late deaths, resulting in an actuarial survival of 92 +/- 2%, 91 +/- 2%, 88 +/- 2.6%, and 88 +/- 4% at 1,2,3, and 4 years, respectively. Ninety-six percent of survivors were assigned to New York Heart Association Class I or II for congestive heart failure, and 96% were assigned to Class I or II for angina. Urgent coronary artery bypass grafting can be performed in patients with unstable postinfarction angina with acceptable mortality, although a significant increase in risk exists for patients with preoperative transmural anterior myocardial infarction, intra-aortic balloon pumping, or both.

Adult↗
PubMed1987

Assessment of myocardial blood flow by real-time infrared imaging.

In order to evaluate the applicability of infrared imaging for the assessment of myocardial perfusion, 10 open-chested dogs were studied by a real-time infrared imaging system. The left anterior descending coronary artery was occluded for 90 min followed by 210 min of reperfusion. During the experiment, myocardial surface temperature was mapped by an infrared imaging system with a thermal resolution power of 0.1 degree C and correlated with regional myocardial blood flow measured using radiolabeled microspheres. Following the experiment, acute myocardial injury was evaluated using triphenyltetrazolium chloride staining. After 90 min of ischemia, there was a significant correlation between myocardial blood flow and myocardial surface temperature (R = 0.694, P less than 0.001). After reperfusion, temperature did not correlate with blood flow, but there was a significant correlation between temperature and ischemic myocardial injury (R = 0.551, P less than 0.05). Temperature changes during acute regional ischemia and reperfusion may be regulated by the changes in myocardial blood flow and myocardial metabolism. Temperature analysis using real-time infrared imaging may be a useful means for the evaluation of myocardial blood flow and myocardial injury during ischemia and reperfusion.

Animals↗
PubMed1987

Ten-year analysis of the Björk-Shiley standard aortic valve.

Long-term performance characteristics of the Björk-Shiley standard aortic valve were determined by analyzing the follow-up of 514 patients undergoing operation between 1971 and 1981. Cumulative follow-up was 2,601 patient-years (average, 5.3 +/- 3.8 years); 53% (238/452) of hospital survivors have been followed more than 5 years. Valve-related complications expressed as both actuarial event-free percents (+/- standard error at 10 years) and first-event linearized determinations (percent per patient-year) occurred at the following rates: thromboembolism, 82 +/- 3 and 2.3 +/- 0.3, respectively; anticoagulant-related hemorrhage, 60 +/- 4 and 5.6 +/- 0.5; prosthetic valve endocarditis, 94 +/- 2 and 0.8 +/- 0.2; valve thrombosis, 97 +/- 1 and 0.4 +/- 0.1; reoperation, 94 +/- 2 and 0.6 +/- 0.2; valve failure, 82 +/- 4 and 1.6 +/- 0.2; and composite valve-related morbidity and mortality, 46 +/- 4 and 8.8 +/- 0.2. Overall survival was 72 +/- 2% at 5 years and 55 +/- 3% at 10 years; valve-related complications accounted for 22% of the late deaths. Although no instance of structural valve failure could be identified, 25% of valve-related complications resulted from valve failure, of which 67% were fatal. By 10 years, 54% of patients had experienced at least one form of major valve-related complication, 16% of which proved fatal. The Björk-Shiley standard aortic valve has late valve-related complications similar to other existing mechanical prostheses that have been subjected to long-term analysis.

Adult↗
PubMed1987

Present expectations in cardiac transplantation.

The clinical introduction of cyclosporine has resulted in increased enthusiasm for cardiac transplantation. Since July, 1983, 61 patients (50 male and 11 female) have undergone orthotopic cardiac transplantation for cardiomyopathy (48 patients), ischemic heart disease (11), or congenital heart disease (2). Mean age was 39 years (range, 1.5 to 57 years). Median hospital stay was 26 days (range, 4 to 60 days). Maintenance immunosuppression consisted primarily of prednisone and cyclosporine; it was modified in 9 patients because of a pre-existing clinical condition. The incidence of rejection was 0.44 episode/patient-month within 3 months of cardiac transplantation and 0.10 episode/patient-month subsequently. The incidence of infection was 0.05 episode/patient-month. Major side effects of cyclosporine included renal dysfunction (63%) and hypertension (61%). No recipient required dialysis for renal dysfunction. Ten patients died (rejection, 4; infection, 3; carcinoma, 1; lymphoma, 1; and pulmonary hemorrhage, 1); actuarial survival at 1 and 2 years was 84 +/- 6% and 76 +/- 8%, respectively. Patient follow-up (cumulative, 719 patient-months) revealed that 96% of recipients were rehabilitated and 50% had returned to work. With increasing understanding of cyclosporine immunosuppression, recipients can continue to look forward to an extended life with nearly complete rehabilitation.

Adolescent↗
PubMed1987

Histologic predictors of acute cardiac rejection in human endomyocardial biopsies: a multivariate analysis.

To identify specific histologic abnormalities that could predict early cardiac rejection before the development of myocyte necrosis, 167 consecutive endomyocardial biopsy samples from 18 cardiac transplant recipients were retrospectively analyzed and 17 histologic variables were semiquantitatively graded from 0 to 3. Forty-five biopsy samples contained foci of myocyte necrosis and were labeled Rejectors. The two samples immediately preceding Rejector biopsies were labeled Predictors (n = 44). All remaining samples were labeled Others (n = 78). Endocardial and interstitial infiltrates, interstitial mononuclear cells, pyroninophilic mononuclear cells, polymorphonuclear leukocytes and other cells (eosinophils and plasma cells) were significantly increased in graded severity in Rejector biopsy samples as compared with Predictors or Others (p less than 0.001, ANOVA testing). These variables cannot distinguish Predictor biopsy specimens from Others. On the other hand, interstitial edema, perivascular karyorrhexis and perivascular infiltrate with intermyocyte extension are histologic abnormalities that can distinguish Predictor biopsy samples from Others (p less than 0.001, ANOVA testing). Multiple logistic regression analysis indicates that the relative risk of developing myocyte necrosis when a biopsy sample contains interstitial edema is 8.1. With perivascular infiltrate with intermyocyte extension in addition, the relative risk is 41.4. In summary, three histologic abnormalities have been identified that help predict the future development of myocyte necrosis within the next two endomyocardial biopsies. Biopsy specimens with these abnormalities probably represent early cardiac rejection before the development of myocyte necrosis.

Biopsy↗
PubMed1987

Immediate mitral valve replacement following gunshot wound to the heart.

Controversy exists in management of cardiac trauma as to whether or not injuries of the cardiac valves or septum should be repaired at initial operation. A patient is presented who required immediate mitral valve replacement for acute disruption of the mitral valve apparatus following a transventricular gunshot injury. The need to consider early repair or replacement of injured cardiac valves when they appear to have hemodynamic significance is emphasized.

Adult↗
PubMed1987

Successful extended cardiopulmonary preservation in the autoperfused working heart-lung preparation.

Myocardial and pulmonary preservation can be prolonged in the autoperfused working heart-lung (AWHL) preparation by metabolic substrate enhancement. However, uncontrolled pulmonary hypertension following denervation may result in extensive lung injury and occasional early failure of the preparation. To determine whether cardiopulmonary preservation could be reliably extended without development of pulmonary hypertension, six heart-lung blocks were harvested from calves, placed in a normothermic AWHL circuit, and studied. Continuous infusions of isoproterenol and dextrose/insulin were administered for the duration of the preparation. Thirteen heart-lung preparations received neither isoproterenol nor metabolic substrate and served as controls. Myocardial function was assessed by sonomicrometric techniques and pulmonary preservation was evaluated by extravascular lung water, arterial oxygenation on 100% inspired oxygen, static lung compliance, and pulmonary vascular resistance. Pulmonary hypertension developed in the control group and these animals did not survive beyond 7.5 hours. The addition of isoproterenol and metabolic substrate increased organ survival from 4.8 +/- 0.4 to 18.0 +/- 1.4 hours (p = 0.0001) and significantly reduced postexplant pulmonary vasoconstriction (p less than 0.05). Addition of isoproterenol and metabolic substrate to the AWHL model prolonged support of cardiorespiratory function and provided a reliable method for distant procurement in heart-lung transplantation.

Animals↗
PubMed1987

The effects of age on outcome after coronary bypass surgery.

To study the effects of increasing age on outcome after coronary artery bypass grafting (CABG), 684 patients who underwent CABG from 1980 to 1985 were entered into a noncurrent prospective study. Patients were matched by date of operation and placed into three groups according to age: (1) 70 and older, (2) 55 to 69, or (3) less than 55. In addition to intraoperative and postoperative data collected on all patients, follow-up was obtained on 97% of the patients at a mean of 30 +/- 16 months. Older patients were more often female (p less than .002), and white (p less than .001) and had more preexisting cerebrovascular disease (p less than .0001), peripheral vascular disease (p less than .001), unstable angina (p less than .0001), and longer mean bypass pump times (p less than .001). Older patients had a higher hospital mortality (9.3% vs 2.2%), suffered more complications, including stroke, wound infection, reoperation for bleeding, need for intropic drug support, and prolonged ventilation, and had longer mean postoperative hospital stays (14 vs 9 days, p less than .0001). After discharge, mortality rates were similar in all groups, as was recurrence of symptoms and degree of rehabilitation. While patient age at operation significantly influenced hospital mortality and morbidity, this appeared to be a consequence of the greater frequency of risk factors in patients over 70 years of age. In addition, late follow-up failed to demonstrate any significant differences based on age alone in survival or functional status among patients undergoing CABG.

Activities of Daily Living↗
PubMed1987

Comparative analysis of mechanical and bioprosthetic valves after aortic valve replacement.

Comparative long-term performance characteristics of Björk-Shiley mechanical and bioprosthetic valves were analyzed for patients undergoing aortic valve replacement between 1976 and 1981. A total of 419 patients received either a standard Björk-Shiley (n = 266) or bioprosthetic (porcine, n = 126, or pericardial, n = 27) aortic valve. Cumulative patient follow-up was 1,705 patient-years; the average patient follow-up was 4.1 +/- 2.7 years. Survival data were obtained for all but 11 patients (97% complete follow-up) up to 9 years after operation. Survival at 5 years was 81% +/- 4% (+/- standard error) for Björk-Shiley and for bioprosthetic valve recipients. Valve failure in the Björk-Shiley group was predominantly due to valve-related mortality and did not result from structural failure. Patients with bioprosthetic valves experienced valve failure as a result of prosthetic valve endocarditis and intrinsic valve degeneration. Although patients with bioprostheses experienced a lower incidence of valve-related morbidity than Björk-Shiley valve recipients (p less than 0.03), no difference could be demonstrated in the incidence of valve-related mortality or valve failure at 5 years between bioprosthetic and Björk-Shiley valves. Mortality rate from valve failure was higher for Björk-Shiley (86%, 12/14) than bioprosthetic valves (36%, 5/14) (p less than 0.01).

Actuarial Analysis↗
PubMed1987

Extensive thrombus formation with heparin resistance during extracorporeal circulation. A new presentation of familial antithrombin III deficiency.

Extensive thrombus formation during extracorporeal circulation despite the administration of heparin sodium prompted investigation of a 15-year-old boy with a calcified right ventricular thrombus and a history of subacute bacterial endocarditis. In vitro studies confirmed the failure of heparin in standard doses to have an anticoagulant effect. Antithrombin III concentrations were low. The patient's mother, who had no history of thromboembolic disease, was also antithrombin III deficient. Resistance to heparin is a theoretical, but inconsistently documented, feature of antithrombin III deficiency. This deficiency state should be considered whenever heparin resistance is encountered, even in the absence of a personal and family history of thromboses.

Adolescent↗