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Biomedical subjects

J W Hammon

Publications and source records attributed to J W Hammon.

At least 91 records · Page 5Linked to original sources
PubMed1985

Tetralogy of Fallot: selective surgical management can minimize operative mortality.

Although tetralogy of Fallot can be completely corrected at any age, it appears that preliminary shunting may be of benefit in infancy. To better define the optimum age for shunting, the following patient data were reviewed. One hundred five patients with tetralogy of Fallot were treated between December, 1975, and July, 1984. Eight of 100 patients undergoing intracardiac repair died. Operative mortality was 14.3% (4 of 28 patients) when intracardiac repair was done before the patient was a year old, but only 5.6% (4 of 72 patients) after that age. Seven (13%) of 54 patients requiring transannular patch reconstruction of the right ventricular outflow tract died, whereas only 1 (2.2%) of 46 having repair without this type of reconstruction died (p less than 0.05). Twenty-one patients were initially palliated with systemic-pulmonary artery shunts, with 1 noncardiac death related to associated congenital neurological anomalies (4.8%). There was no statistically significant difference in mortality for primary versus secondary intracardiac repair. Left ventricular end-diastolic volume determination in 26 patients less than 2 years old demonstrated that 14 patients had small left ventricles and that 3 of them less than 1 year of age died at corrective operation. The remaining 12 had a left ventricle of normal size, and 1 of them died at operation. Palliative shunts can be performed safely in the very young child with no increased mortality at subsequent intracardiac repair. Diffuse hypoplasia of the right ventricular outflow tract and pulmonary arteries requiring transannular patch reconstruction, and age less than 1 year both alter operative mortality, their combined impact being additive.

Adolescent↗
PubMed1985

The results of valve replacement for mitral valve prolapse.

Between January, 1975, and December, 1982, 33 patients underwent mitral valve replacement for mitral valve prolapse secondary to myxomatous degeneration. The majority were in the seventh decade of life (median age, 62 years), and all were seen with symptoms of mitral regurgitation. Echocardiography was more accurate in making the diagnosis of mitral valve prolapse more often (75%) than angiography (66%). Thirty-eight percent of the patients who underwent cineangiography had concomitant coronary artery disease and had coronary artery bypass grafting as well as mitral valve replacement. There was 1 operative death, an operative mortality of 3%. There were 6 late deaths, a late mortality of 18%. Of the 26 long-term survivors, 23 (88%) were in New York Heart Association Functional Class I and 3 (12%) were in Class II. The average length of follow-up was 33.25 months, and the 5-year actuarial survival was 76%. There was only one incident of thromboembolism (3%). Short-term and long-term survival were not related to the severity of mitral regurgitation but to the status of the left ventricle and the overall condition of the patient. These data suggest that older patients with severe mitral regurgitation secondary to mitral valve prolapse can undergo valve replacement with low operative mortality and gratifying long-term results.

Actuarial Analysis↗
PubMed1985

Amelioration of the deleterious effects of platelets activated during cardiopulmonary bypass. Comparison of a thromboxane synthetase inhibitor and a prostacyclin analogue.

Thrombocytopenia and platelet dysfunction are commonly seen after cardiopulmonary bypass. In addition, the microvascular bed of ischemic myocardium is a potent stimulus for platelet deposition and microvascular plugging. Thus, it would appear theoretically advantageous to provide pharmacologic protection of platelets by inhibiting their response to activating agents and thereby preventing their loss into the extracorporeal circuit; this would further inhibit myocardial platelet deposition and the deleterious effects therein. Twenty-one mongrel dogs were placed on cardiopulmonary bypass with 30 minutes of normothermic global ischemia. They were randomly assigned to receive pretreatment with an infusion of saline (control, n = 8), a thromboxane synthetase inhibitor (RO-22-4679, n = 5), or a prostacyclin analogue that does not produce hypotension (ZK 36,374, n = 8). The platelet count in those animals treated with ZK 36,374 was significantly higher at the end of the experiment than in the control group (102.8 +/- 10.7 X 10(3) versus 69.7 +/- 10.6 X 10(3), p less than 0.01); the animals treated with RO-22-4679 had a platelet count between the other two groups (92.8 +/- 14.8 X 10(30)), which was not significantly different from either. Myocardial platelet deposition was measured with indium 111-labeled platelets. Those animals treated with ZK 36,374 had a much lower level of platelet deposition than the group of controls; again the RO-22-4679 group had values between the other two. Finally, myocardial blood flow after global ischemia and cardiopulmonary bypass, measured with radioactive microspheres, was significantly higher in the ZK 36,374 group than in the control group. We conclude that ZK 36,374 prevents platelet consumption during cardiopulmonary bypass over and above that seen with inhibition of thromboxane synthesis alone. It also prevents deposition of platelets into the myocardium after global ischemia and we presume by that mechanism increases myocardial blood flow.

Animals↗
PubMed1985

Pathophysiology of chronic cyanosis in a canine model. Functional and metabolic response to global ischemia.

To investigate the pathophysiology of chronic cyanosis, we subjected 14 adult mongrel dogs to diversion of the inferior vena cava to the right inferior pulmonary vein. This produced a mean oxygen tension of 42 +/- 2 mm Hg and a calculated right-to-left shunt of 52.0% +/- 3.9%. These animals (Group C) and 15 normal dogs (Group N) were subjected to cardiopulmonary bypass with 20 minutes of normothermic global ischemia. Functional indices studied were rate of rise of left ventricular pressure and the end-systolic pressure/volume ratio. Metabolic status was assessed by obtaining transmural myocardial biopsy specimens for measurement of adenosine triphosphate content. Myocardial blood flow was measured with radiolabeled microspheres. There were no significant differences between Group C and Group N in either functional index or blood flow measurement prior to global ischemia. At 45 minutes after ischemia, Group N animals had a significantly greater rate of rise of left ventricular pressure (at a left ventricular end-diastolic pressure of 0, 5, 10, and 15 mm Hg, p less than 0.025 to 0.05) and subendocarial perfusion (endocardial/epicardial flow ratio 0.961 +/- 0.037 versus 0.815 +/- 0.021, p less than 0.01). At 90 minutes after ischemia, Group N animals exhibited a significantly higher end-systolic pressure/volume ratio (4.9 +/- 0.7 versus 3.0 +/- 0.4 mm Hg/ml, p less than 0.05), rate of rise of left ventricular pressure (at an end-diastolic pressure of 0 to 20 mm Hg, p less than 0.005 to 0.05), and endocardial/epicardial flow ratio (1.065 +/- 0.046 versus 0.829 +/- 0.059, p less than 0.01). No differences in adenosine triphosphate content were found at any sampling period. The Group C left ventricles exhibited no hypertrophy but were significantly dilated compared to Group N (38.8 +/- 0.3 versus 30.1 +/- 0.2 mm, p less than 0.05). Inferior vena cava to pulmonary vein diversion produces cyanosis with left ventricular dilatation but without hypertrophy. It is proposed that abnormal loading characteristics of the left ventricle are responsible for the functional derangements that result from global ischemia.

Adenosine Triphosphate↗
PubMed1985

Improved right ventricular function after intra-atrial repair of transposition of the great arteries.

Current interest in the arterial switch operation for simple transposition of the great arteries (TGA) has led us to evaluate our latest patients who have undergone intra-atrial repair. Right ventricular function and overall results were compared in 32 patients who had undergone the Senning procedure between 1978 and 1983 and 26 patients who had undergone Mustard repair between 1971 and 1978). Deep hypothermia and circulatory arrest were used in all Senning operations and in 18 of 26 Mustard procedures. Cardiac catheterization was performed an average of 1 year after surgery in all patients. Postoperative right ventricular ejection fraction (EF) was below normal (less than 0.49) in 16 of 32 patients who underwent the Senning procedure and averaged 0.48 +/- 0.09. In the patients in this group with abnormal right ventricular EFs after repair there was a fall in the value after surgery (0.51 to 0.40, p less than .001), while in those with normal right ventricular EFs after repair there was no change (0.57 to 0.55, NS). All 32 patients who underwent the Senning procedure were compared with 26 patients who underwent the Mustard operation (13 treated between 1971 and 1974 and 13 treated between 1975 and 1978). An older age at surgery (12 +/- 7 vs 6 +/- 8 months, p less than .006) and a lower preoperative right ventricular EF (0.46 +/- 0.09 vs 0.54 +/- 0.08, p less than .007) characterized the Mustard vs the Senning group.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1984

Perioperative beta blockade with propranolol: reduction in myocardial oxygen demands and incidence of atrial and ventricular arrhythmias.

To determine the effect of beta blockade with propranolol on myocardial oxygen demands and postoperative arrhythmias in patients having coronary bypass operations, 50 patients with chronic stable angina undergoing operation were randomized in a double-blind fashion to receive either propranolol (60 mg every 6 hours) or a placebo. Drug administration began 24 to 48 hours prior to operation and continued through the operative period and for one month after operation. There were no deaths. Two perioperative myocardial infarctions occurred, both in patients receiving a placebo. Myocardial oxygen demand as measured by the rate-pressure product (heart rate X mean arterial pressure) was significantly reduced during induction of anesthesia (7,658 +/- 451 versus 5,786 +/- 340; p less than 0.002) and during sternotomy (8,400 +/- 550 versus 6,756 +/- 384; p less than 0.02) in propranolol-treated patients. In the first two postoperative days, nitroprusside was required for control of hypertension of 10 patients in the placebo group but in only 3 patients given propranolol (p less than 0.05). Postoperatively, 15 of the 26 patients who received a placebo had 45 episodes of arrhythmia. Seven of the 24 propranolol-treated patients had 17 episodes (p less than 0.04). We conclude that propranolol given perioperatively in doses large enough to induce beta blockade significantly reduces myocardial oxygen demands in the vulnerable period during induction of anesthesia and sternotomy, reduces the need for antihypertensive therapy in the immediate postoperative period, and causes a marked reduction in the incidence and frequency of both supraventricular and ventricular arrhythmias in the postoperative period.

Angina Pectoris↗
PubMed1984

Global ischemia in the immature canine ventricle. Enhanced protective effect of verapamil and potassium.

The efficacy of the addition of verapamil to a cardioplegic solution was evaluated in immature canine hearts subjected to normothermic global ischemia. Two groups of mongrel puppies less than 10 weeks old were subjected to 30 minutes of global myocardial ischemia while on cardiopulmonary bypass. One group (Group K) was arrested with cardioplegic solution containing 20 mEq/L of KCl; the other group (Group K + V) was arrested with the same solution containing 0.2 mg/kg of verapamil. Ultrasonic crystals were placed for measurement of left ventricular dimensions, and micromanometers measured left ventricular pressures. Functional measurements included left ventricular strain, first derivative of left ventricular pressure (dP/dt), and the end-systolic pressure/volume ratio (Emax). Metabolic recovery was assessed by measuring myocardial adenosine triphosphate (ATP) content. Ninety minutes following ischemia, Group K + V exhibited greater minor axis strain at a left ventricular end-diastolic pressure of 15 and 20 mm Hg (p less than 0.05), greater dP/dt (p less than 0.05 to 0.001), and greater Emax (p less than 0.05) than Group K. ATP content in Group K + V was greater at 60 minutes (Group K + V: 12.74 +/- 1.60 mumol/gm; Group K: 8.39 +/- 1.30, p less than 0.05) and 90 minutes (Group K + V: 10.34 +/- 0.46; Group K: 7.55 +/- 1.42, p less than 0.05) after ischemia. The addition of verapamil to a cardioplegic solution containing potassium enhances the recovery of function and high-energy phosphate stores in the immature myocardium following normothermic global ischemia.

Animals↗
PubMed1983

A reproducible model of chronic hypoxemia.

This report presents our experience with producing a stable chronic hypoxemia preparation in the dog without the disadvantages of prosthetic graft insertion or sacrifice of pulmonary tissue. In 28 adult dogs, the intrapericardial inferior vena cava and the area of junction of the right and left inferior pulmonary veins were exposed through a right thoracotomy. The cava was clamped at the diaphragm and at the right atrium, divided at the atrial clamp, and quickly anastomosed to the inferior pulmonary veins. The mean arterial O2 tension (PaO2) decreased from 83.2 +/- 1.6 mmHg preoperatively in mechanically ventilated (room air) animals to 35.3 +/- 1.5 mmHg postoperatively in awake animals spontaneously breathing room air (P less than 0.001). There was persistent depression of the PaO2 (49.1 +/- 1.8 mmHg) and elevation of the hematocrit (64.8 +/- 2.0%) in six animals tested at 18.5 mo postoperatively. Shunt patency without significant stenosis was confirmed in each animal at autopsy. This method attains predictable and persistent hypoxemia and polycythemia and is simple to perform. It may be useful in studying various aspects of ventricular function and ventricular histological and biochemical changes with chronic cyanosis.

Animals↗
PubMed1983

Kinetics and imaging of indium-11-labeled autologous platelets in experimental myocardial infarction.

The kinetics of accumulation and the external imaging patterns of indium-111-labeled platelets infused in a dog model of left anterior descending coronary artery occlusion with reperfusion were studied. The effects of infarct age and regional residual myocardial blood flow upon platelet accumulation were quantified, and the capacity of indium-111 platelets to image the experimental infarction was evaluated qualitatively. The endocardial accumulation of indium-111 platelets occurred primarily in infarct zones with residual blood flow less than 0.6 times normal and was maximal (24.98 +/- 2.76 times normal) in the lowest blood flow zone (less than 0.1 times normal). Indium-111 platelet accumulation in the epicardium occurred in the regions with blood flow less than 0.6 times normal and was maximal (17.83 +/- 1.20 times normal) in the lowest blood flow zone (less than 0.1 times normal). The maximal endocardial and epicardial platelet accumulation occurred 24 hours after reperfusion and was significantly decreased at 48 hours. In vivo cardiac images revealed discrete areas of increased myocardial radioactivity uptake in the anterior wall of dogs 24 hours after reperfusion. All images 48 hours after reperfusion were negative. Thus, in the experimental setting, indium-111 platelets allow quantification of platelet accumulation after myocardial infarction at a tissue level and provide a noninvasive means of in vivo imaging of reperfused infarcted myocardium.

Animals↗
PubMed1982

Functional and metabolic preservation of the immature myocardium with verapamil following global ischemia.

This study investigated the effects of the calcium antagonist verapamil on the functional and biochemical recovery of the immature heart following 30 minutes of normothermic ischemia. Verapamil (0.2 mg per kilogram of body weight) was infused into the aortic root in 5 puppies (8 to 10 weeks of age) prior to cardiopulmonary bypass. Five additional puppies received saline solution as a control. Left ventricular developed pressure, rate of rise of left ventricular pressure (dP/dt), left ventricular endsystolic pressure-diameter relationship (emax), compliance, and water content were assessed before and after bypass. Serial myocardial biopsies for adenosine triphosphate (ATP) and creatine phosphate were obtained. Puppies pretreated with verapamil recovered more than 80% of the preischemic left ventricular developed pressure, dP/dt, and emax in contrast to 50% recovery in the controls (p less than 0.05). The ATP content declined 40% during the interval of ischemia in the control puppies, versus 14.6% in the verapamil-treated puppies (p less than 0.05). Myocardial compliance was preserved in the verapamil-treated puppies and was associated with significantly less myocardial water content (78% versus 80.1% in the controls)(p less than 0.01). This study demonstrates the protective effects of verapamil on the immature heart during ischemic arrest. These results suggest that verapamil may be a useful adjunct to current methods of protecting the infant heart during cardiopulmonary bypass.

Adenosine Triphosphate↗
PubMed1982

Thiopental modification of ischemic spinal cord injury in the dog.

Spinal cord ischemia was produced in male mongrel dogs by permanent occlusion of the infrarenal aorta. All animals were anesthetized with a mixture of nitrous oxide and 1.5% halothane. Group 1 animals were the controls. Group 2 animals were pretreated, 30 minutes prior to aortic occlusion, with sodium thiopental, 20 mg per kilogram of body weight, over 5 minutes, followed by an infusion of 10 mg/kg/hr for 2 1/2 hours. Groups 3 animals received the identical dose of sodium thiopental and, in addition, received mannitol, 1 gm/kg, and methylprednisolone 1 mg/kg. There were no differences in hemodynamic data or arterial blood gases among the groups, except that the thiopental bolus caused a transient reduction in mean arterial pressure. Ninety percent of Group 1 animals were paraplegic, while only 30% of Group 2 and 40% of Group 2 animals were paraplegic. The difference in the incidence of paraplegia in Groups 2 and 3 compared with Group 1 was statistically significant (p less than 0.05). Therefore, thiopental significantly decreased the incidence of paraplegia, while methylprednisolone and mannitol did not enhance its protective effect.

Animals↗
PubMed1982

Cardiovascular effects of ventilation with positive expiratory airway pressure.

The broad clinical application of positive and expiratory pressure (PEEP) in the treatment of a variety of respiratory disorders has led to the observation that positive airway pressure can result in cardiac dysfunction. Recent attempts to integrate and extend the results of past research have led to diverse explanations of the overall cardiopulmonary effects of PEEP. This review summarizes previous work in the field and attempts to explain the basis of the divergent conclusions of previous investigators. Data are presented from several experimental models, as well as studies in postoperative patients to formulate an overall analysis of the influence of airway pressure on the central circulation. It appears that the effects of PEEP are primarily mechanical and are mediated through a combination of right ventricular preload limitation and outflow obstruction. Both effects are additive in limiting left ventricular preload and can be ameliorated by volume loading in the absence of significant right ventricular or pulmonary vascular disease. Neural, humoral and ventricular interactive forces appear to be insignificant under most circumstances. The clinical implications of these advances in the current understanding of PEEP are reviewed.

Animals↗
PubMed1982

The effects of airway pressure on cardiac function in intact dogs and man.

Ventilation with positive end-expiratory pressure (PEEP) is associated with reduced cardiac output, but the mechanisms involved are controversial. Possible explanations include increased intrathoracic pressure, reflex changes in myocardial inotropism, pulmonary vascular obstruction and abnormal ventricular interaction. Three types of conscious canine preparations were developed to examine simultaneously each of these factors during ventilation with PEEP. In addition, similar measurements were obtained in patients after cardiac surgical procedures and compared with the results of animal experiments. The primary cause of reduced cardiac output during PEEP appeared to be a diminished end-diastolic volume of the left ventricle, and this appeared to be the result of elevated intrathoracic pressure and increased impedance to blood flow through the lungs. Abnormal interventricular septal shifting and reflex autonomic alterations did not appear to be significant in the normal cardiovascular system. These data provide insight into the cardiac effects of PEEP and emphasize the importance of simultaneous quantification of biventricular performance when assessing cardiopulmonary function.

Animals↗
PubMed1982

Repair of atrioventricular canal malformation in the first year of life.

Disappointing results with pulmonary artery banding and subsequent correction led to the decision in 1977 that all infants presenting to our hospital with atrioventricular (AV) canal and evidence of severe heart failure, lack of growth, or pulmonary hypertension should have early operative correction. Since that time 24 consecutive infants have undergone repair. All had refractory heart failure. Average age at operation was 18 weeks (3 to 38) and average weight was 4.3 kg (2.3 to 6.4). Only four patients were older than 6 months of age at operation. Preoperative peak pulmonary artery pressure was 81 +/- 3.3 mm Hg, which was equal to systemic arterial pressure in all cases. Mean pulmonary-to-systemic resistance ratio was 0.28 +/- 0.05. five patients had moderate mitral regurgitation and five had a ductus arteriosus. Three had significant associated malformations. Profound hypothermia and circulatory arrest were utilized in all patients. Common AV valve tissue was divided and valvular integrity was ensured by resuspension to a single Dacron patch which closed both the atrial and ventricular defects. Operative death occurred in two patients (8%) both with associated defects (one with total anomalous pulmonary venous connection and the other with coarctation). One late death occurred in a patient with associated partial anomalous pulmonary venous connection, and one patient has had a pacemaker implanted. Survivors have been followed for 7 to 60 months. All patients are growing at an increased rate postoperatively. All cardiac medications have been discontinued in 16 of 21 patients. Operative repair of complete atrioventricular canal can be performed in infancy with low operative and late death rates and will relieve signs and symptoms of heart failure and allow more normal growth and development. On the basis of this experience, it appears unnecessary to delay operative correction with the known increased risk of the development of pulmonary hypertension.

Blood Pressure↗
PubMed1981

Comparative right and left ventricular volumes and pump function in the newborn lamb.

A quantitative cineangiographic method is presented for studying neonatal lamb ventricular volumes and pump function without thoracotomy or surgical instrumentation of the heart. When this method was employed in lambs with a mean age of 24.4 hours it was found that the right and left ventricular end-diastolic volumes, ejection fractions and systolic outputs did not differ significantly at this early postnatal time. Restudy of these lambs at a mean age of 15.6 days showed that right and left ventricular end-diastolic volumes, normalized for body weight, and ejection fractions had not changed significantly. Although systolic outputs decreased, the difference was not significant. Thus there is early postnatal equalization of left and right heart volumes, and deviations from this relation should suggest abnormal hemodynamic function.

Animals↗