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Biomedical subjects

D H York

Publications and source records attributed to D H York.

At least 37 records · Page 2Linked to original sources
PubMed1983

Routine, direct measurement of aortic pressure in the conscious rabbit.

A method for preparation and application of an indwelling catheter for measurement of aortic pressure in conscious rabbits is described. The catheter is generally reliable for periods longer than one month and requires little interference with the normal circulation. The system utilizes coiled polyethylene tubing which has a tapered tip covered with silicone rubber tubing and, at its exterior end, a Velcro matrix for skin healing. The catheter tip is pulled into the abdominal aorta with a trocar, directed caudally. The exterior end is run subcutaneously to the nape of the neck. In 19 rabbits prepared by this method, mean pressure was determined to be 68 +/- 2 mm Hg and pulse pressure was 29 +/- 1 mm Hg two weeks after implantation. The catheters remained patent in 17 rabbits at the time of sacrifice, 12 to 120 days later. In an in vitro sweep-frequency test, maximal resonance of the catheter system was found to lie between 12-14 Hz, at which point the measured pressure amplitude exceeded control by 12.5%.

Animals↗
PubMed1983

Evoked potentials from the motor tracts in humans.

Spinal cord monitoring during operation is of increasing importance in the prevention of injury. However, there is no direct monitor of the motor tracts available. We have reported a system using direct stimulation of the area overlying the motor tract between the intermediolateral sulcus and the dentate ligament in cats. This produces a 100-m/second signal with later components, which is abolished by section of the motor area, but not by section of the dorsal columns or the anterior quadrant of the spinal cord. Such stimulation also produces motor movement when the correct frequency is used. We now report the first application of this technique in humans, in whom we found the same 100-m/second signal, as well as slower components. We were able to elicit distal limb motor movement with stimulation of the motor tract area, but not with stimulation of the dorsal column area. This technique can be used either in open surgical cases or percutaneously and should provide an additional valuable technique for assessing spinal cord function.

Adult↗
PubMed1982

Involvement of both adrenergic and cholinergic receptors in the cardiovascular effects of naloxone during hemorrhagic hypotension in the conscious rabbit.

Opiate receptor blockade with naloxone reverses the hypotension associated with severe hemorrhage in a variety of animal models. In the present study, we examined the mechanisms of naloxone's actions in conscious rabbits made hypotensive by hemorrhage. This was accomplished through pharmacological blockade of the efferent limbs of the sympathetic or parasympathetic nervous systems prior to naloxone injection. In addition, we examined the effects of naltrexone in the same model. Naloxone treatment in hypotensive-hypovolemic, conscious rabbits results in an increase in mean arterial blood pressure (BP) and a decrease in heart rate (HR). The bradycardia appears to be due to a reduction in beta-adrenergic and an increase in muscarinic-cholinergic activity. The pressor effect is apparently due to increased alpha-adrenergic receptor activation, and is accompanied by an increase in cardiac output, stroke volume, and total peripheral resistance. Naltrexone did not significantly affect BP but it did reduce HR. The results from the present study suggest that naloxone's effects are mediated by an integrated response of the sympathetic and parasympathetic nervous systems. The actions of naloxone may be mediated through antagonism of endogenous opiates.

Adrenergic Fibers↗
PubMed1981

The reversal of hemorrhagic hypotension by naloxone in conscious rabbits.

The effects of naloxone on blood pressure and heart rate were studied in conscious, chronically prepared rabbits. In addition, the effects of barbiturate anesthesia on the response to naloxone were investigated. Initial surgery to implant arterial and venous catheters was performed under halothane anesthesia. Experiments were begun 10 days to 2 weeks later. The rabbits were divided into two groups: a normotensive group and a group made hypotensive by hemorrhage. In the normotensive rabbits, naloxone (2 mg/kg i.v.) did not alter mean arterial blood pressure (BP), pulse pressure, (PP), or heart rate (HR). However, a 5 mg/kg dose increased BP and PP, and decreased HR. In the hypotensive group, naloxone in a dose of 2, 3, or 5 mg/kg i.v. significantly increased BP and PP while decreasing HR in a dose-related manner. A dose of 0.2 mg/kg did not significantly alter any of the measured parameters. Pentobarbital anesthesia significantly reduced the effects of the 3 mg/kg naloxone dose in the hypotensive group. These actions of naloxone may be mediated through antagonism of endogenous opiates.

Animals↗
PubMed1981

Relationship between visual evoked potentials and intracranial pressure.

The relationship between intracranial pressure (ICP) and latency of visual evoked potentials (VEP) was investigated in hydrocephalic patients with severe head trauma. A positive correlation of increase in latency of wave N2 (normal latency 71 +/- 9.2 msec) of the VEP with elevations in ICP was observed. A potential role for VEP in both the assessment of shunt function and the monitoring of patients with severe head injury is suggested by these findings.

Adolescent↗
PubMed1979

Effects of chronic intraventricular administration of angiotensin II on drinking behavior and blood pressure.

Angiotensin II was continuously infused into the lateral cerebral ventricle of rats, and the effects on daily food and water consumption, urine volume, and aortic blood pressure were studied. All was infused at a rate of 10 ng/hr for seven days, using subcutaneously implanted osmotic minipumps. An intraventricular (IVT) control group was infused with only the saline vehicle, while a third group received AII subcutaneously. IVT AII rats showed a four-fold increase in water consumption, to a mean of 171 ml/day during Days 2-4 of infusion, whereas water intake of the other groups did not change from preinfusion levels. Urine volume showed a similar pattern to water intake, increasing five-fold in the IVT AII group during Days 2-4. These measures declined during the final three days of AII infusion, but significant tolerance was not observed. Food intake decreased markedly in both saline and IVT AII groups after implantation of the pumps, but the latter resumed normal food intake more slowly than the former, and body weight remained below preinfusion levels throughout the AII period. Aortic blood pressure of the IVT AII rats showed a slight, but progressive, rise during the infusion period, but it did not significantly exceed that of the saline rats. These results indicate that continuous, low-level, intraventricular infusion of AII may markedly increase water intake without significantly increasing fluid retention or blood pressure.

Angiotensin II↗
PubMed1975

The effect of synthetic TRH on transmembrane potential and membrane resistance of adenohypophysial cells.

An evaluation of the stimulus-secretion coupling hypothesis was undertaken by the intracarotid administration of synthetic thyroid releasing hormone (TRH) while recording the transmembrane potential (Vm) and membrane resistance (Rm) of cells in the adenohypophysis of propylthiouracil pretreated male rats. Of those 75 cells which responded to TRH administration with a change in membrane parameters, the most predominant effect was a depolarization with a decrease in Rm observed in 21 cells, or no change in Vm but an increase in Rm observed in 23 cells. These results are discussed in terms of the thyrotrophs and other cells comprising the adenohypophysis.

Animals↗