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Biomedical subjects

L Bunegin

Publications and source records attributed to L Bunegin.

At least 55 records · Page 3Linked to original sources
PubMed1982

Mechanical and neurological response of cat spinal cord under static loading.

The force/deformation relationship of the exposed spinal cord of cats was studied when the force was gradually applied posteriorly at T10. A linear elastic behavior was identified for deformation less than 0.5 mm, but it was not observed when the static force was no longer supported by the dural sheath. Nonlinear force/deformation, along with a strong hysteresis during a cycle of compression and decompression. The mechanical behavior remained practically the same in a repeated loading if the deformation was less than 2 mm. The motor function of cats did not recover after the cord had been compressed to 4 mm. The associated static force was about 15% of the dynamic force producing the same deformation.

Animals↗
PubMed1982

High frequency ventilation in dogs with open chests.

This study evaluated and compared the physiological responses to high frequency percutaneous transtracheal ventilation in dogs before and after median sternotomy thoracotomy. Standard intermittent positive pressure ventilation (IPPV) was established before and after high frequency rates (100 and 300 breath/min) with the chest closed and then after thoracotomy. Gas exchange as judged by arterial and mixed venous blood gases, and cardiac performance as judged by pulmonary capillary wedge pressure, pulmonary and systemic arterial pressures, vascular resistances, and cardiac index all remained clinically acceptable. Physiologically, ventilation in the open chest condition was adequate but was associated with a slight decrease in PaCO2 and a decrease in PaO2. Peak and mean airway pressures were similar for IPPV and high frequency modes of ventilation.

Animals↗
PubMed1981

Positioning the right atrial catheter: a model for reappraisal.

A flexible Silastic casting of the human right atrium was developed to correspond to some in vivo human right atrium hemodynamic characteristics including chamber pressures, pulsatility, fluid output, and flow velocity. Using an infusion pump, air was introduced (10 ml in 30 s) into the superior vena cava of the model and aspirated via a catheter from different positions within the model atrial chamber. The tests were carried out at atrial inclinations of 60 degrees, 80 degrees, and 90 degrees from the horizontal and compared the aspiration efficiency of a single-orificed 16-gauge catheter to a 16-gauge multiorified (5 aperatures) catheter. Optimal air aspiration occurred with the multiorificed catheter tip positioned within the area 2.0 cm below the junction of the superior vena cava (SVC) and the atrial chamber at an inclination of 80 degrees. As much as 80 per cent of the incoming air could be aspirated under these conditions. At its optimal position the single-orificed catheter gave a maximal yield of 45 to 50 per cent aspiration when the tip was positioned 3.0 cm above the SVC and atrial chamber junction. Aspiration of air from mid right atrium (4.5 cm below the SVC-atrial junction) was poor regardless of the type of catheter used or atrial inclination. These data suggest a need for reappraisal of catheter design and placement.

Cardiac Catheterization↗
PubMed1980

Analysis and comparison of venous air embolism detection methods.

Changes in precordial ultrasonic Doppler patterns in dogs were compared with changes of end-tidal carbon dioxide (EtCO2) and pulmonary arterial pressure (PAP). Possible mechanisms of pulmonary arterial hypertension after air embolism in dogs are discussed. After the injection of air, an immediate change in the Doppler ultrasonic pattern was detected, including a shift of the base line. The duration of change of Doppler patterns varied depending upon the length of time that trapped air remained in the right heart. There was a delay of 15 to 30 seconds before the EtCO2 and PAP responded. In a group of dogs pretreated with 0.3 mg of propranolol per kg, there was a significant decrease in the PAP response due to induced air embolism compared to the control group (P < 0.05). We found that the Doppler ultrasonic device was the most sensitive for detecting venous air embolism at a level as low as 0.05 ml of air per kg compared to 0.25 ml/kg for the PAP and EtCO2 responses.

Animals↗
PubMed1979

The standardization of experimental impact injury to the spinal cord.

The biomechanical criteria for standardization of experimental impact injury to the spinal cord are derived. The theory is verified experimentally using cats. The undesirable effect due to heavy impounders is discussed. A falling mass of 20 gm and a small impounder 5 mm in diameter with a mass of 0.1 gm are recommended, leaving the momentum of the falling body to be controlled for different degrees of trauma.

Animals↗
PubMed1979

Cerebellar retraction: significance and sequelae.

Does cerebellar retraction during operations in the posterior fossa contribute to increased morbidity and mortality, and if so, what are the critical factors involved? In order to answer these questions, graded retractor pressures of 10, 20, and 30 mm Hg were applied for one hour to the cerebellar hemispheres of dogs in the sitting position. It was noted that the amount of mechanical pressure and the difference between systemic perfusion pressure and retractor pressure were important determinants of the outcome. The mechanism of damage from retractor pressure is discussed.

Animals↗
PubMed1975

Biomechanical responses to open experimental spinal cord injury.

This study evaluates the dynamic biomechanical responses of the cat spinal cord during experimental impact injury. Temporal deformations of the laminectomized spinal cord were recorded by a high speed camera (1500-3000 frames/sec). The cinematograph revealed large deformations, the cord being compressed to half its posterior-anterior diameter 7 msec after the onset of the impact. Peak impact force produced by a 20 gm mass falling from 15 cm height (300 GCF) averaged about 1.2 pounds, and the corresponding stress acting on the dural surface reached 42 pounds per square inch (or 2200 mm Hg). Both positive and negative pressure waves were found to be propagated in the cerebrospinal fluid.

Animals↗
PubMedDate not supplied

Autoregulation of spinal cord blood flow: is the cord a microcosm of the brain?

The autoregulatory capability of regional areas of the brain and spinal cord was demonstrated in 18 rats anesthetized with a continuous infusion of intravenous pentothal. Blood flow was measured by the injection of radioactive microspheres (Co57, Sn113, Ru103, Sc46). Blood flow measurements were made at varying levels of mean arterial pressure (MAP) which was altered by neosynephrine to raise MAP or trimethaphan to lower MAP. Autoregulation of the spinal cord mirrored that of the brain, with an autoregulatory range of 60 to 120 mm Hg for both tissues. Within this range, cerebral blood flow (CBF) was 59.2 +/- 3.2 ml/100 g/min (SEM) and spinal cord blood flow (SCBF) was 61.1 +/- 3.6. There was no significant difference in CBF and SCBF in the autoregulatory range. Autoregulation was also demonstrated regionally in the left cortex, right cortex, brainstem, thalamus, cerebellum, hippocampus and cervical, thoracic and lumbar cord. This data provides a coherent reference point in establishing autoregulatory curves under barbiturate anesthesia. Further investigation of the effects of other anesthetic agents on autoregulation of the spinal cord is needed. It is possible that intraspinal cord compliance, like intracranial compliance, might be adversely affected by the effects of anesthetics on autoregulation.

Anesthesia, Intravenous↗
PubMedDate not supplied

Evoked potential changes during brain retraction in dogs.

Brain retraction and induced hypotension are surgical adjuncts capable of compromising cerebral blood flow. To evaluate their effects upon brain function, cortical evoked potentials, neurological status and cortical histological changes were determined as a function of graded levels of brain retractor and systemic perfusion pressure in the dog. Somatosensory evoked potentials recorded from the site of application of brain retraction showed a decrement as a function of both the amount of retraction pressure and the systemic perfusion pressure. An electrode distant from the retractor site showed similar, though reduced and more variable changes in amplitude. For higher levels of brain retractor pressure, induced hypotension to 50 mm Hg systemic perfusion pressure produced greater reductions in evoked potentials than in normotensive subjects. It was demonstrated that a reduction of 50% of the evoked potential amplitude after sixty minutes brain retraction signaled, with high probability, the occurrence of postoperative sensory and/or motor deficits and cortical histopathology. It was concluded that cortical evoked potentials represent a reliable indicator of the functional effects produced by applied cortical retraction pressure at several levels of systemic perfusion pressure. It was suggested that the recording of evoked potentials would prove most useful during neurosurgical procedures employing induced hypotension and brain retraction.

Animals↗
PubMedDate not supplied

A rat model of neurobehavioral sensitization to toluene.

Some individuals report that, following either a single high-level or repeated lower-level exposures to chemicals (initiation), subsequent exposure to very low concentrations of chemicals (triggering) produces a variety of adverse effects, including disruption of cognitive processes. Our objective was to model this two-step process in a laboratory animal. Two groups of 16 rats, eight male and eight female, received whole-body inhalation exposure to toluene, either at 80 ppm for 6 h/day for 4 weeks (Repeat group) or to 1600 ppm for 6 h/day on one day only (Acute group). Two other groups (Trigger group and Clean group) of 16 were sham-exposed. After 17 days without toluene exposure, the Acute, Repeat and Trigger groups began a series of daily toluene 'trigger' exposures (10 ppm for 1 h) followed immediately by testing on an operant repeated-acquisitions task requiring learning within and across sessions. The Clean group was sham-exposed prior to operant testing. Trigger or sham exposures and operant testing continued 5 days/week for 17 sessions. Analysis of variance revealed a variety of statistically significant (P < 0.05) differences between treatment groups. Furthermore, the patterns of differences between groups differed (P < 0.05) for female and male rats. For example, male rats of the Trigger group made the most responses, and female rats of the Repeat group responded most slowly. The observation of important changes in the operant behavior of female and male rats previously exposed to toluene, at relatively low concentrations (80 or 1600 ppm) and then later re-exposed at very low concentrations (10 ppm), is consistent with the experiences of humans reporting cognitive difficulties following acute or chronic exposures to chemicals.

Administration, Inhalation↗