Biomedical subjects

T A Brandon

Publications and source records attributed to T A Brandon.

9 recordsLinked to original sources

PubMed1991

Hemodynamic responses to 6 degree head-down rest in dogs: effect of aerobic conditioning.

The -6 degree head-down position is used in humans to produce fluid shifts that resemble those occurring in microgravity. Alternative animal models of microgravity may be helpful for extensive exploration of this unique condition. The dog may be a viable candidate. Sixteen dogs were assigned to one of three conditions: anesthetized open chest, anesthetized closed chest, and awake. Dogs in groups 1 (N = 6) and 2 (N = 6) were divided into an exercise or a sedentary treatment, and dogs in group 3 (N = 4) served as their own controls. Following instrumentation the dogs were put in the head-down position for 1 h. Measurements included right atrial pressure, heart rate, and mean arterial pressure for all groups, left ventricular pressure and LV dp/dt for group 1, and cardiac output and iliac flow for group 2. Right atrial pressure increased for all groups. Heart rate demonstrated non-significant changes over time or group. Significant differences were noted for mean arterial pressure, left ventricular pressure and LV dp/dt for exercise condition in response to HDR. It appears that -6 degrees of head-down rest produces similar cardiovascular responses in dogs as those observed in humans and that exercise has a minor effect on those responses.

Animals↗

PubMed1990

Thermoelectric enzyme sensor for measuring blood glucose.

A new calorimetric sensor has been developed which employs a thin-film thermopile in association with an immobilized enzyme. The thermopile detects the minute temperature rise that occurs when a specific chemical substrate is catalyzed by the enzyme. A prototype sensor is described which generates an equivalent proportional voltage response to glucose concentrations present in either buffer solution or blood. These sensors have remained useful for up to 18 days when operated intermittently for measuring glucose in buffer solutions, or for up to 4 days when operated continuously. When implanted inside cardiovascular shunts on anesthetized dogs, the sensors responded appropriately to changes in the blood glucose concentration.

Animals↗

PubMed1985

Influence of alpha-adrenergic blockade on platelet-mediated thrombosis in stenosed canine coronary arteries.

The functional significance of platelet alpha-adrenergic receptors in vivo is uncertain. The aim of this study was to elucidate their role in experimental coronary thrombosis. In 46 open-chest dogs with a critical coronary stenosis produced by plicating the coronary artery wall with a suture, blood flow showed cyclical reductions followed by an abrupt return to control levels. The flow reduction were previously shown to be caused by platelet aggregation. In the present study they were unaffected by heparin (1,000 U . kg-1 . h-1) at the start of the experiment but consistently abolished by aspirin (30 mg . kg-1) at the end of the protocol, further supporting platelet aggregation as the primary mechanism. After 1 h of observation, dogs were assigned to one of the following groups: control (no intervention, n = 9), phentolamine (a nonselective alpha-blocker) "low dose" (0.07 mg . kg-1 bolus followed by 0.1 mg . kg-1 . min-1, n = 4), phentolamine "high-dose" (3 mg . kg-1 bolus followed by 0.07 mg . kg-1 . min-1, n = 6), prazosin (an alpha 1-blocker, 2 mg . kg-1, n = 8), yohimbine (an alpha 2-blocker, 3 mg . kg-1, n = 11) or prazosin + yohimbine (same doses, n = 8). In controls, cyclical reductions in flow continued unchanged for another hour. Phentolamine effected a partial dose-related inhibition of flow reductions; however, prazosin and yohimbine, given separately or in combination, failed to produce any significant effect despite an alpha-blocking action equivalent to or greater than that of phentolamine (alpha-agonist dose-response studies).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗

PubMed1979

Cardiac lymph flow in conscious dogs.

The cardiac lymphatic duct was cannulated in dogs and the exteriorized cannula allowed chronic collection of lymph during the awake state for as long as 3 wk. The surgical methodology and inherent difficulties in the technique are describ:d. Cardiac lymph flow ranged from 0.45--5.6 ml/h in the control state in 14 dogs. An occluding device and flow probe were placed on the circumflex coronary artery (CFX); ultrasonic segment length crystals were placed in the left ventricular free wall in 4 dogs. Occlusion of the CFX in these conscious dogs caused lymph flow to fall as great as 46% below control during the 1st half-hour. Reperfusion of the occluded vessel caused an increase in lymph flow as great as 67% above control. The effect on cardiac lymph flow was demonstrated for a few select drugs that have known effects on the cardiovascular system. Cardiac lymph flow was altered from control as follows: isoproterenol, 42 +/- 11% increase; RO 2-2985, 118 +/- 8% increase; verapamil, 101 +/- 10% increase; propranolol caused no significant change. The conscious dog with cardiac lymph vessel cannulated should provide a model to further study the complexities of cardiac metabolism and physiology without interference of anesthesia and surgical stress.

Animals↗

PubMedDate not supplied

Total pericardial replacement. Design and preliminary evaluation in greyhounds.

Existing pericardial substitutes, used for the prevention of pericardial and pleural adhesions to the epicardium, are in the form of a patch. To improve on this concept, an elastic, anatomically correct, implantable sac has been developed for total pericardial replacement. Total pericardial substitutes fabricated from Silastic silicone rubber and Mitrathane polyetherurethane urea were implanted in greyhound dogs and harvested at 8 weeks. Pericardial adhesions were prevented by the substitutes that remained intact. Fibrous tissue formation had occurred on the epicardium underlying the substitutes, the extent being more severe in response to the Silastic compared with the Mitrathane. However, the Silastic was superior to the Mitrathane in retention of its tensile strength and elastic modulus over the implant period (p less than 0.05). Further development of total pericardial substitutes from different materials shows promise.

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PubMedDate not supplied

Performance of a hydrogel composite pericardial substitute after long-term implant studies.

A novel composite patch has been tested as a pericardial substitute to reduce adhesion formation after cardiac surgery. The patch consists of poly 2-hydroxyethyl methacrylate (pHEMA) hydrogel reinforced with a polyethylene terephthalate (PET) mesh. The hydrogel-PET composite pericardial patches were implanted in canines for 6, 9, and 12 months. Upon termination, adhesion formation and epicardial reaction to the implant were rated. No adhesions formed between the patch and the native pericardium or epicardium. A thin fibrous layer on the epicardium progressively developed where the patch contacted the heart. The coronary anatomy remained visible. Histologically, the response to the implant was fibrous in nature. No significant signs of cellular inflammation were found. The gross appearance of the retrieved patches was nearly identical to that of preimplant patches. Mechanical tests showed no significant changes (alpha = 0.05) in patch strength or stiffness. Hydrogel water content initially increased during implantation. The thickness of the patch did not change significantly (alpha = 0.05) throughout the study. Scanning electron microscopy (SEM) revealed unequal layers of hydrogel on either side of the PET mesh and cracks in the hydrogel surfaces of retrieved patches. Both SEM and light microscopic observation of the patches showed traces of calcification in patches in the 9 and 12 month studies.

Animals↗

PubMedDate not supplied

In vivo results of hydrogel composite pericardial substitutes.

In this study, two improved pericardial patches were developed and evaluated for their efficacy as pericardial substitutes. The patches are composites consisting of a hydrogel (PHEMA) that coats an underlying mesh (either ETFE or PET). Studies were conducted using subcutaneous implants in rats and pericardial patch implants in greyhound dogs. Adhesions between the substitute and pericardium and the epicardium were minimal. The ETFE composite patch caused an unacceptable epicardial reaction. The PET patch results were encouraging; the epicardium was largely unaffected by the patch.

Animals↗

PubMedDate not supplied

A hydrogel pericardial patch.

Patients undergoing repeat cardiac operations are higher operative risks than those undergoing an initial cardiac procedure because adhesion formation can occur if the native pericardium is not closed. A unique composite patch that may be used to augment the pericardial tissue when primary closure is not possible has been developed. The patch is made of a hydrogel, poly (2-hydroxyethyl methacrylate), reinforced with an ethylene tetrafluoroethylene (ETFE) mesh. The mesh provides the needed mechanical properties, whereas the patch's surface properties are comparable to the hydrogel. Two types of patches were fabricated: one with the mesh weave at a perpendicular orientation and one at 45 degrees to the principle loading direction. The patches were mechanically tested and compared with canine pericardium. Ultimate tensile strength of the patches is not significantly different from canine pericardium (p less than 0.05), are the patch suture strength is nearly twice that of canine pericardium. The perpendicular patch is stiffer than canine pericardium, whereas the 45 degree patch is not (p less than 0.05). The 45 degree patch shows considerable promise as a pericardial substitute because it closely matches the properties native canine pericardium.

Animals↗

PubMedDate not supplied

An efficient method for removing bilirubin.

Bilirubin is tightly bound to albumin, making hemoperfusion an ineffective treatment for hyperbilirubinemia. By adding a safe unbinding agent to the blood (solutizer), which itself is adsorbed, hemoperfusion can become efficient and practical. Canines were made hyperbilirubinemic with an intravenous infusion of a 5 mg/ml solution (with Na2CO3) for 1 hour. Peak concentrations of 14-22 mg/dl were reached in adult dogs (25-35 kg). Hemoperfusion was then initiated with or without (control) the solutizer (sodium benzoate). The bilirubin unbinding effect of sodium benzoate was rapid and effective. Because of the simultaneous adsorption of sodium benzoate, a small activated carbon section that was presaturated with the solutizer was located proximal to the main hemoperfusion column, in addition to continuous infusion to reach 20 mM in the blood. Comparison of the normalized bilirubin concentration for benzoate augmented hemoperfusion with the average for control dogs, shows that benzoate results in a threefold decrease in the normalized bilirubin concentration after 1.5 hr of hemoperfusion. Sodium benzoate may also have the advantage of protecting platelets during hemoperfusion.

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