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Biomedical subjects

M S Albin

Publications and source records attributed to M S Albin.

At least 19 recordsLinked to original sources
PubMed1998

Physiologic, histologic, and neurologic responses to simultaneous bilateral cerebral vessel Doppler imaging at high beam intensity.

This study evaluates physiological fluid heating during continuous bilateral insonation at 530 mW/cm2 for 8 h in a bench simulation. It also examines the physiologic, histopathologic, and neurologic effects of bilateral Doppler imaging of middle cerebral artery (MCA) blood flow velocity using ultrasonic beams with 530 mW/cm2 intensity in a canine model immediately after and 2 weeks after insonation. In saline-filled containers, instrumented with opposing Doppler probes angled 10 degrees off axis, temperature was recorded at 15-min intervals for approximately 8 h at the intersection of the Doppler probe axes. Three conditions were tested: 1) an ambient control, 2) continuous bilateral insonation at 530 mW/cm2 per channel with the thermistor in position, and 3) intermittent thermistor insertion. In one group of canines, physiopathologic responses during continuous bilateral insonation of the MCAs for 8 h at 2 MHz and 530 mW/cm2 were studied. Brains were prepared for histologic examination immediately after insonation. Cerebral temperature; arterial, venous, pulmonary artery, and capillary wedge pressures; electrocardiogram; cardiac output; MCA velocity; and arterial blood gases were monitored. In a second group of canines, a neurologic evaluation was performed before and after insonation and again after 2 weeks. Brain tissue was evaluated histologically after the last neurologic examination. Light microscopic study was used for all histologic evaluations. In the bench experiments, a net temperature rise in the fluid of the simulation amounted to 0.0075 degrees C/h in the overlap region after correction for ambient temperature effects and artifact thermistor heating. In canines, brain temperature (after correction for core body temperature changes and artifact heating of the thermistor) rose a mean of 0.2 degrees C (p < 0.05) by the first hour, thereafter unchanging. No significant changes in the physiologic, neurologic, or histologic evaluations were observed in either of the experimental groups.

Animals↗
PubMed1996

The isolation and transplantation of the brain. An historical perspective emphasizing the surgical solutions to the design of these classical models.

Following an historical review of earlier attempts to develop separated head and brain preparations and their contributions to modern-day understanding of the neurophysiology and neurochemistry of the central nervous system, the experiments that eventually led to the first successful total isolation of the mammalian brain are presented. The operative strategies emphasizing the anatomical and physiological problems requiring solution that resulted in vascular and neurogenic separation from the parent body and cephalon are described. The innovative engineering concepts that were utilized in the design of miniaturized equipment to maintain the isolated brain in a living state under conditions of cross circulation, extracorporeal artificial perfusion and transplantation are elaborated. Investigations employing isolated brain and cephalic preparation documenting tissue substrate requirements, metabolic and rheological conditions prevailing at various low temperatures and the immunologically privileged state of the separated organ are briefly presented. The unique opportunities these isolated brain models offer for study are emphasized as well as the complexity of their surgical preparation, which, to date, has limited their universal applications.

Animals↗
PubMed1994

Detection and volume estimation of embolic air in the middle cerebral artery using transcranial Doppler sonography.

BACKGROUND AND PURPOSE: Cerebral embolism has been implicated in the development of cognitive and neurological deficits following bypass surgery. This study proposes methodology for estimating cerebral air embolus volume using transcranial Doppler sonography. METHODS: Transcranial Doppler audio signals of air bubbles in the middle cerebral artery obtained from in vivo experiments were subjected to a fast-Fourier transform analysis. Audio segments when no air was present as well as artifact resulting from electrocautery and sensor movement were also subjected to fast-Fourier transform analysis. Spectra were compared, and frequency and power differences were noted and used for development of audio band-pass filters for isolation of frequencies associated with air emboli. In a bench model of the middle cerebral artery circulation, repetitive injections of various air volumes between 0.5 and 500 microL were made. Transcranial Doppler audio output was band-pass filtered, acquired digitally, then subjected to a fast-Fourier transform power spectrum analysis and power spectrum integration. A linear least-squares correlation was performed on the data. RESULTS: Fast-Fourier transform analysis of audio segments indicated that frequencies between 250 and 500 Hz are consistently dominant in the spectrum when air emboli are present. Background frequencies appear to be below 240 Hz, and artifact resulting from sensor movement and electrocautery appears to be below 300 Hz. Data from the middle cerebral artery model filtered through a 307- to 450-Hz band-pass filter yielded a linear relation between emboli volume and the integrated value of the power spectrum near 40 microL. Detection of emboli less than 0.5 microL was inconsistent, and embolus volumes greater than 40 microL were indistinguishable from one another. CONCLUSIONS: The preliminary technique described in this study may represent a starting point from which automated detection and volume estimation of cerebral emboli might be approached.

Animals↗
PubMed1994

The effect of anesthetics on neurologic outcome during the recovery period of spinal cord injury in rats.

We evaluated the effects of anesthetics on neurologic outcome in a model of recoverable experimental spinal cord injury (SCI). Adult rats were implanted with various sizes of hygroscopic plastic material at the T12 spinal level to determine the dimensions that would produce a progressive neurologic deficit from which recovery could occur. Neurologic evaluation was conducted on an inclined plane, noting the maximum angle at which an animal was able to maintain orientation perpendicular to the longitudinal midline. Scores were statistically modeled for each group to develop profiles of neurologic deficits. Rats were subjected to a 4-h exposure to isoflurane, fentanyl/nitrous oxide, or ketamine 7 or 8 days postimplantation. Neurologic outcomes were compared to a SCI reference group which received no postimplant anesthesia. An animal weight/desiccated implant volume (Wa/Vi) ratio of 53 to 73 g/mm3 produced postimplant neurologic deficits which deteriorated to near maximum within 3 days, followed by a gradual improvement beginning at Day 8 and returning to near normal between 21 and 25 days. Final outcome was based on modeled ramp scores for each group and reported in degrees +/- SD: reference, 71.2 +/- 1.1; fentanyl/N2O, 70.4 +/- 0.3; isoflurane, 72.6 +/- 1.1; and ketamine, 64.9 +/- 0.6. The fentanyl group attained maximum recovery first (P > 0.05) but did not recover to a level different on the average from the reference group. The ketamine group demonstrated a poorer (P > 0.05) recovery level relative to the other anesthetic protocols.

Anesthetics↗
PubMed1993

Canine tracheal blood flow after endotracheal tube cuff inflation during normotension and hypotension.

Tracheal tissue damage associated with endotracheal intubation may be a direct result of high mucosal contact pressure (MCP) generated by the endotracheal tube cuff. Tracheal blood flow (TBF) was measured at MCPs in the normotensive and hypotensive (mean arterial blood pressure, 50 mm Hg) canine model. Control TBFs through the individual rings in contact with the endotracheal tube cuff ranged between 26.6 +/- 2.7 and 44.5 +/- 5.0 with a mean of 35.0 +/- 2.5 mL.min-1 x 100 g-1 during normotension, and 15.0 +/- 4.9 and 22.5 +/- 5.0 with a mean of 18.9 +/- 0.9 mL.min-1 x 100 g-1 during hypotension. TBF was reduced significantly at all elevated MCPs in both groups. TBF also was measured during normotension and hypotension after cuff inflation to 15 mm Hg MCP at 1-h intervals for 3 h. TBF was reduced significantly from control to 14.9 +/- 1.5 mL.min-1 x 100 g-1 after 1 h during normotension, and continued to decline to 6.1 +/- 0.9 mL.min-1 x 100 g-1 after 3 h. During hypotension, TBF decreased significantly from control to 6.1 +/- 0.6 mL.min-1 x 100 g-1 at 1 h and remained unchanged at 3 h. These findings suggest that even at 20 mm Hg MCP, significant reductions in TBF may occur. For prolonged endotracheal intubation, especially during hypotension, significant reductions in TBF may occur at even lower MCP.

Animals↗
PubMed1992

Anatomy of a defective barrier: sequential glove leak detection in a surgical and dental environment.

OBJECTIVES: a) To determine the frequency of perforations in latex surgical gloves before, during, and after surgical and dental procedures; b) to evaluate the topographical distribution of perforations in latex surgical gloves after surgical and dental procedures; and c) to validate methods of testing for latex surgical glove patency. DESIGN: Multitrial tests under in vitro conditions and a prospective sequential patient study using consecutive testing. SETTING: An outpatient dental clinic at a university dental school, the operating suite in a medical school affiliated with the Veteran's Hospital, and a biomechanics laboratory. PERSONNEL: Surgeons, scrub nurses, and dental technicians participating in 50 surgical and 50 dental procedures. METHODS: We collected 679 latex surgical gloves after surgical procedures and tested them for patency by using a water pressure test. We also employed an electronic glove leak detector before donning, after sequential time intervals, and upon termination of 47 surgical (sequential surgical), 50 dental (sequential dental), and in three orthopedic cases where double gloving was used. The electronic glove leak detector was validated by using electronic point-by-point surface probing, fluorescein dye diffusion, as well as detecting glove punctures made with a 27-gauge needle. RESULTS: The random study indicated a leak rate of 33.0% (224 out of 679) in latex surgical gloves; the sequential surgical study demonstrated patency in 203 out of 347 gloves (58.5%); the sequential dental study showed 34 leaks in the 106 gloves used (32.1%); and with double gloving, the leak rate decreased to 25.0% (13 of 52 gloves tested). While the allowable FDA defect rate for unused latex surgical gloves is 1.5%, we noted defect rates in unused gloves of 5.5% in the sequential surgical, 1.9% in the sequential dental, and 4.0% in our electronic glove leak detector validating study. In the sequential surgical study, 52% of the leaks had occurred by 75 mins, and in the sequential dental study, 75% of the leaks developed by 30 mins. In terms of the anatomical localization, the thumb and forefinger accounted for more than 60% of the defects. There were no differences in the frequency of glove leaks between the left and right hand. Leak rates were highest for the surgeon (52%), followed by the first assistant (29%) and the scrub nurse (25%). No false negatives were noted using the electronic glove leak detector; one false positive was seen out of 225 gloves tested (0.44%), as noted in our validation studies. CONCLUSIONS: Significantly high glove leak rates were noted after surgical and dental procedures, indicating that the present day latex surgical gloves can become an incompetent barrier once they are used. Unused latex surgical gloves demonstrated a higher rate of defects than allowed by the Food and Drug Administration standards, indicating substantial noncompliance of quality control standards by manufacturers as well as inadequate governmental oversight. Double gloving, or the use of thicker latex surgical gloves, would probably reduce the frequency of glove leaks. Latex surgical gloves should be tested for patency before use and during surgical and dental procedures.

Dentistry↗
PubMed1990

Intracranial and spinal cord hemodynamics in the sitting position in dogs in the presence and absence of increased intracranial pressure.

The effect of the sitting position on cerebral blood flow (CBF), spinal cord blood flow (SCBF), and cerebral metabolic rate for oxygen (CMRo2) was studied in anesthetized dogs with and without increased intracranial pressure. Blood flow measurements were made at four time periods: (a) initial supine; (b) after 5 min in the sitting position; (c) after 60 min in the sitting position; and (d) 15 min after resuming the supine position. Six dogs (group 1) served as a control group with a normal intracranial pressure (ICP). In five dogs (group 2) ICP was elevated with a parietal epidural balloon 1 h before the first measurements of blood flows were made. Saline was injected incrementally into the balloon so as to reach a steady-state ICP of 30 mm Hg for 1 h. Elevation of ICP in group 2 resulted in significantly lower CBF, SCBF, and CMRo2 compared with group 1. Postural changes in group 1 did not result in any significant change in blood flow measurements whereas in group 2, after 1 h in the sitting position, there were significant decreases in CBF and SCBF compared with the initial supine measurements. There was, however, no corresponding decrease in CMRo2 in group 2 with change in position. These data suggest that both the brain and spinal cord may be at risk for ischemia during sitting position procedures under general anesthesia in the presence of elevated ICP.

Animals↗