Biomedical subjects

A G Denenberg

Publications and source records attributed to A G Denenberg.

4 recordsLinked to original sources

PubMed1991

Oxygenated cardioplegia: the metabolic and functional effects of glucose and insulin.

Reports differ as to the efficacy of glucose and insulin as cardioplegic additives. Although deliberate oxygenation of crystalloid cardioplegic solutions improves myocardial protection, little is known about the protection afforded by glucose and insulin in such oxygenated solutions. In the isolated working rat heart, we studied the addition of oxygen, glucose, and insulin, separately and together, to a cardioplegic solution. The solution was equilibrated with O2 or N2, with glucose added as a substrate or sucrose as a nonmetabolizable osmotic control, with or without insulin. Hearts were arrested for 2 hours at 8 degrees C by multidose infusions. Oxygenation decreased lactate production and improved high-energy phosphate and glycogen preservation during arrest, prevented ischemic contracture, and improved functional recovery. The addition of glucose to the oxygenated solution increased the level of adenosine triphosphate at end-arrest from 10.5 +/- 0.5 to 13.9 +/- 0.6 nmol/mg dry weight and glycogen stores from 18.7 +/- 2.5 to 35.7 +/- 5.5 nmol/mg dry weight. The further addition of insulin did not better preserve these metabolites. Improvements in functional recovery due to glucose or insulin in the oxygenated solution attained statistical significance when both additives were included. Glucose increased lactate production significantly only when the solution was nitrogenated. Insulin added to the nitrogenated glucose-containing solution increased adenosine triphosphate and glycogen levels after 1 hour of arrest; and, although insulin did not prevent ischemic contracture from developing during the latter part of arrest with profound depletion of these metabolites, functional recovery was improved. The mechanism of improved functional recovery by insulin is not clear.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗

PubMed1991

Protection of the hypertrophied myocardium by crystalloid cardioplegia.

Patients with left ventricular hypertrophy (LVH) have a worse outcome after cardiac surgery than those without hypertrophy. We studied protection of hearts with LVH in an isolated rat heart model using multidose, cold, oxygenated cardioplegia. LVH was produced by banding the abdominal aorta in young rats. Six weeks after banding, this produced a 31% increase in the left ventricular dry weight/body weight ratio compared to two age-matched control groups comprising sham-operated and nonoperated animals. The recovery of cardiac output after arrest was higher in LVH (82 +/- 4% of prearrest) than in sham-operated (69 +/- 4%) or nonoperated (66 +/- 3%) control groups. The improved functional recovery in LVH occurred although there were no differences among the groups in myocardial adenosine triphosphate (ATP) and phosphocreatine (PCr) prior to arrest, at the end of arrest, or after reperfusion. Glycogen levels were also similar among the three groups prior to arrest and after reperfusion but were highest in LVH after arrest. Myocardial oxygen consumption (MVO2) and efficiency, expressed as cardiac output/MVO2, were similar among the groups prior to arrest. Myocardial efficiency after reperfusion declined in all groups but was best preserved in LVH. We also compared the sensitivity of hypertrophied and control hearts to the deleterious effects of calcium in cardioplegia. Calcium in the cardioplegia increased myocardial lactate production during arrest in a dose-related fashion and depressed myocardial levels of ATP, PCr, and glycogen at end arrest in all groups. Cardiac output recovery was also depressed by calcium but was still best in LVH. We conclude that the hypertrophied myocardium is well protected by standard cardioplegia and that calcium in cardioplegia does not preferentially depress recovery in LVH.

Animals↗

PubMed1987

Maximal oxygenation of dilute blood cardioplegic solution.

The content of dissolved O2 (the major source of O2 for the myocardium) of dilute blood cardioplegic solution (dBCS) varied widely when oxygenated at 4 degrees C by surface flow of O2 in a Bentley BCR-3500 cardiotomy reservoir. We have modified the system to consistently deliver maximally oxygenated dBCS to the heart. Laboratory studies indicated that bubbling O2 through a 16-gauge intravenous catheter in a central Luer-Lok port of the cardiotomy reservoir provided contents of dissolved O2 that were consistently near maximal. We then studied 17 patients in the operating room. The first 6 patients received dBCS oxygenated with 100% O2 with a high dissolved O2 content of 3.2 +/- 0.2 ml/dl. However, the pH of the dBCS became highly alkaline (7.83 +/- 0.11 at 37 degrees C). Therefore, in the remaining 11 patients, 2% CO2 was added to the O2. The dissolved O2 content remained high (3.3 +/- 0.1 ml/dl), and the pH was in a more physiological range (7.35 +/- 0.09 at 37 degrees C). We conclude that consistently maximal oxygenation of a dBCS at a more physiological pH can be achieved by this method.

Blood↗

PubMed1987

Microsphere reference flow samples during systemic flow adjustment.

Regional myocardial blood flow measurements in the right heart bypass preparation can be particularly valuable, since this preparation provides control of the main hemodynamic determinants of coronary blood flow. We examined the validity of aortic reference flow samples in relation to coronary samples during continuous systemic flow adjustment for aortic pressure control in six dogs on right heart bypass, anesthetized with chloralose and urethan. Microsphere concentrations were compared in paired reference flow samples drawn from the aortic arch and from a coronary artery for 119 left atrial microsphere injections. During left subclavian artery infusion and during femoral artery infusion at rates above 2,000 ml/min, there were high percentage errors in microsphere concentration between paired samples, consistent with aortic sample dilution by systemically infused blood. In 52 injections during withdrawal or femoral infusion below 2,000 ml/min, at cardiac outputs of 390-4,800 ml/min, the percentage error was 0.001 +/- 1.18% (SE); the absolute value of this error was below 20% in 96%, and below 10% in 77% of these injections. Linear regression related these coronary to aortic microsphere concentrations by the equation Y = 1.005X - 1.64, r = 0.997, Sy.x = 13.2 (5.9%). (Sy.x represents the standard deviation from regression.) These data indicate that valid aortic reference flow samples can be obtained within specific hemodynamic conditions during systemic flow adjustment in the right heart bypass preparation.

Animals↗