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Biomedical subjects

M Pollay

Publications and source records attributed to M Pollay.

At least 19 recordsLinked to original sources
PubMed2001

The importance of valve alignment in determining the pressure/flow characteristics of differential pressure shunt valves with anti-gravity devices.

OBJECT: The proper functioning of shunt valves in vivo is dependent on many factors, including the valve itself, the anti-siphon device or ASD (if included), patency of inlet and outlet tubing, and location of the valve. One important, but sometimes overlooked, consideration in valve function is the valve location relative to the tip of the ventricular inlet catheter. As with any pressure measurement, the zero or reference position is an important concept. In the case of shunt valves, the position of the proximal inlet catheter tip is fixed and therefore serves as the reference point for all pressure measurements. This study was conducted to document the importance of this relationship for the pressure/flow characteristics of the shunt valve. METHODS: We bench-tested differential pressure valves (with integral anti-gravity devices; AGDs) from three manufacturers. Valves were connected to an "infinite" reservoir, and the starting head pressure for each was determined from product inserts. The inlet catheter tip was fixed at this position, and the valve body was moved in relation to the inlet catheter tip. Outflow rates were determined gravimetrically for positions varying between 4 cm above and 8 cm below the inlet catheter tip. CONCLUSIONS: All differential pressure valves utilized in this study that contained AGDs showed significant increases in outflow rate as the valve body was moved incrementally below the level of the inlet catheter tip. To allow functioning as a zero-hydrostatic pressure differential pressure valve, the AGD and the inlet catheter tip should be aligned at the same horizontal level.

Cerebrospinal Fluid Pressure↗
PubMed1999

The importance of shunt valve position in flow characteristics of the Medtronic PS Medical Delta valve.

This study was conducted to document the extent to which flow depends on valve position in relation to head-pressure reference. Medtronic PS Medical Delta valves (contour model, performance levels 0.5, 1.0, 1.5, and 2.0) were studied in a bench test designed to evaluate flow rates with respect to valve position in relation to the head-pressure reference postion. The valves were connected to an "infinite" reservoir by the standard inlet catheter. An initial head (proximal) pressure was selected for each valve based on package insert data. The position of the inlet catheter tip was fixed at this starting head pressure, thus making the inlet catheter tip position the reference for relative head pressures on the valve assembly. When the valve body is positioned above this level, the effective head pressure is lowered, and when the valve body is positioned below this level, the effective head pressure is raised. Flow was established with the siphon control portion of the valve body located on the same horizontal level as the inlet catheter tip (the reference head pressure or "0" position). A standard silastic catheter was attached to the outlet of the valve, and its length was fixed at 50 cm for all valves (-50 cm H(2)0). The distal end of the outlet catheter was connected to a fraction collector, and 1-minute samples (five replicates) were collected for gravimetric determination of flow rate. The valve assembly was then moved in 1-cm increments through the range of 4 cm above to 8 cm below the head-pressure reference position. Samples were collected from each position (4 cm to -8 cm) relative to the inlet catheter tip. Flow rate, in milliliters/hour, was plotted against both relative position (4 cm to -8 cm) and absolute head pressure (in centimeters of water). Each of the valves tested was shown to have a linear relationship between flow and position relative to the inlet catheter tip (or absolute head pressure). The average increase in flow per centimeter of displacement of valve from catheter tip was 16.5 ml/hr/cm (range 14.4-17.6 ml/hr/cm). Once the inlet catheter tip is fixed in position, it serves as a pressure reference. Movement of the valve above this level results in a net decrease in effective head pressure, and movement below this position results in a net increase in effective head pressure. Thus, the positioning of shunt valves in locations different from this pressure reference position should be performed only with the knowledge that significant increases in outflow rate may occur when the valve body is positioned lower than the inlet catheter tip. This increase in outflow rate is not the result of siphoning or a defect in the antisiphon device but instead the result of a net increase in effective head pressure.

Journal Article↗
PubMed1994

Pediatric syringomyelia.

Syringomyelia was first recognized as a disease process some 400 years ago. The process of cystic dilation of the spinal cord is unpredictable and may result in a delay of many decades before the symptoms and signs of neurologic and orthopedic changes become apparent and commensurate with the observed cystic changes within the spinal cord. The syringomyelic process is usually associated with trauma, tumor, or congenital abnormalities at the craniocervical junction or along the spinal neuraxis. Several theories have been proposed as to processes involved in the development of spinal cyst formation, although none are completely compatible with the observed clinical pathology of syrinx development. Magnetic resonance imaging has markedly improved our ability to study the anatomy and natural history of syrinx formation, but to date, our understanding of the process remains imprecise. In view of the limited understanding of the pathophysiology of this disease process, it is not surprising that a variety of treatment regimens have been proposed and their efficacy remains difficult to fully evaluate.

Brain Diseases↗
PubMed1993

Cranial hemophilic pseudotumor. Case report.

Hemophilic pseudotumor is a rare complication of hemophilia occurring in 1% to 2% of individuals with a severe factor VIII or IX deficiency. This pseudotumor has been defined as a progressive cystic swelling involving muscle that is produced by recurrent hemorrhage and may be accompanied by roentgenographic evidence of bone involvement. The case is presented of a 12-month-old child with mild factor VIII deficiency (10% of normal factor VIII activity), who developed a pseudotumor of the skull.

Bone Diseases↗
PubMed1991

The effect of apnea on brain compliance and intracranial pressure.

The effect of 2 minutes of apnea during endotracheal intubation on intracranial pressure (ICP), compliance, and cerebral blood volume (CBV) was studied in 19 adult dogs during normo-, hypo-, and hypercapnia. The compliance was measured from the cisterna magna in response to an intrathecal bolus injection (pressure-volume index). CBV was monitored by radiolabeled red blood cell activity. These measurements were made before and after 2 minutes of apnea. At normocapnia (pCO2 of 35-40 mm Hg), a period of apnea resulted in an increase in ICP from 9.6 to 26.3 mm Hg, a decrease in compliance from 0.051 to 0.020 ml/mm Hg (60%), and an increase in CBV of 0.26 ml (9.6%). When the animals were hypocapnic (pCO2 of 24-28 mm Hg), ICP increased from 12.8 to 19.6 mm Hg, compliance fell from 0.041 to 0.029 ml/mm Hg(29%), and CBV increased 0.07 ml (3.1%). Hypercapnia (pCO2 of 50-58 mm Hg) before apnea resulted in an increase in ICP from 21.5 to 47.1 mm Hg, a decrease in compliance from 0.032 to 0.015 ml/mm Hg (52%), and an increase in CBV of 0.41 ml (13.4%). These results suggest that hyperventilation (hypocapnia) before intubation limits the adverse decrease in brain compliance and increase in ICP by reducing changes in cerebral blood volume.

Animals↗
PubMed1990

Cystic optic glioma.

A pilocytic astrocytoma of the optic nerve, chiasm, hypothalamus, or third ventricle is a relatively common tumor of childhood. This case report illustrates such a tumor, originating from this location, which is unusual because of the association with two very large cystic extensions into the middle cranial fossa and into the third ventricle. The massive size and extent of this tumor and cysts was demonstrated on a magnetic resonance imaging (MRI) scan, with gadolinium enhancement. This case illustrates a novel macroscopic appearance for a pilocytic glioma of the anterior third ventricle. The purpose of this report is to alert clinicians to the varied morphology this tumor may present as we apply increasingly our improved radiological, operative, and histopathological techniques.

Astrocytoma↗
PubMed1990

Shunt-related brain abscess and ascending shunt infection.

We report the fifth case of shunt-related brain abscess. Two prior cases have been associated with colonic perforation and infection with gram-negative enteric organisms. These cases strongly suggest that ascending shunt infection is possible despite bulk cerebrospinal fluid flow in the opposite direction and add to our understanding of shunt infections.

Brain Abscess↗
PubMed1990

Benzodiazepine receptors and cerebrospinal fluid formation.

There is autoradiographic evidence that peripheral-type benzodiazepine ligands bind with high affinity to the membranes of choroid plexus tissue. In this study, the binding of a 4'-chloro analog of diazepam (Ro 5-4864) to rabbit choroid plexus and cerebral cortex was accomplished utilizing an in vitro radioactive assay method. A kinetic analysis of this binding revealed a relatively high affinity of this ligand (KD) for peripheral binding sites in plexus tissue (KD = 16.1 nM/mg protein). There was a 4.6-fold greater density of binding sites (total receptor density (Bmax) = 2.3 pmol/mg) in choroidal membrane as compared to cortical tissue (Bmax = 0.5 pmol/mg). In 40 rabbits in which a ventricular perfusion system was used, the rate of cerebrospinal fluid (CSF) formation was observed to decrease some 48% in the presence of 10(-4) M Ro 5-4864, although some inhibition of secretory activity was still noted at a CSF concentration of 10(-8) M. The choroid plexus tissue levels of adenosine 3',5'cyclic monophosphate (cAMP) and adenosine triphosphatase (ATPase) were not affected by 10(-4) M Ro 5-4864. The results of this study support the notion that the specific benzodiazepine peripheral binding sites in choroid plexus serve to modulate CSF formation. The mechanism of action is poorly understood but does not involve the transport ATPase system or the second messenger cAMP.

Adenosine Triphosphatases↗
PubMed1990

Fluid flow performance of a new siphon-control device for ventricular shunts.

Most available cerebrospinal fluid diversion systems utilize differential-pressure valves that often induce overshunting, resulting in complications due to the siphoning of fluid from the ventricular system when the patient is in the erect position. A new siphon-control device (SCD) was tested alone and in combination with four types of differential-pressure valves with low, medium, and high opening pressures (namely PS Medical, Heyer-Schulte, Cordis-Hakim, and Codman valves). The valve inlet and outlet pressures were measured at several fluid inflow rates between 2.0 and 50.0 ml/hr. Inlet pressure and valve resistance were determined when the outlet pressures of the differential-pressure valve or SCD were varied between 0 and -60 cm H2O. Of the differential-pressures valves tested, none provided protection against siphoning without the distal connection of the SCD. The SCD allowed all differential-pressure valves tested to maintain atmospheric pressure regardless of the outlet pressure. The SCD performs in a manner similar to the older anti-siphon device, but with some improvements in design and construction. The results of this investigation suggest that the increased resistance due to the inline SCD is not functionally significant when added to the conventional valve systems with low opening pressure.

Cerebrospinal Fluid Shunts↗
PubMed1989

Spina bifida occulta: early clinical and radiographic diagnosis.

Tethered cord syndrome (TCS) is produced by traction of the lumbosacral spinal cord. Clinically, patients with tethered cord syndrome present with various combinations of neurologic, orthopedic, and cutaneous abnormalities. These abnormalities are often subtle. Early diagnosis, and treatment when indicated, is essential to prevent progressive and frequently irreversible neurological deterioration. Early diagnosis is aided by a high degree of clinical suspicion. Plain spine films are useful in the preliminary evaluation of suspected dysraphism. When plain film abnormalities are present, magnetic resonance imaging (MRI) has been found to be the single most effective procedure for both initial diagnosis and pre-operative evaluation of patients with myelodysplasia.

Diagnosis, Differential↗
PubMed1987

Effect on intracranial pressure of furosemide combined with varying doses and administration rates of mannitol.

The first part of this study investigated the combined use of furosemide and mannitol in the treatment of elevated intracranial pressure (ICP). Two groups of dogs were studied to determine if renal excretion of mannitol was altered in the presence of furosemide. No significant difference in excretion was noted between the two groups. Fifteen animals were used in other studies to identify the most advantageous sequence of administration of furosemide and mannitol. Infusion of mannitol followed by furosemide 15 minutes later resulted in the most profound and sustained ICP reduction. The effect on ICP reduction of varying the mannitol dose was observed in studies using single doses of 0.5 gm/kg, 0.75 gm/kg, and 1 gm/kg. The larger mannitol dose, resulting in a greater blood-brain osmotic gradient, proved to be the most efficacious in ICP reduction. A further 15 animals were used in investigations to determine whether changing the rate of delivery of the most effective mannitol dose (1 gm/kg) influenced resultant ICP reduction. The results indicated that rapid administration (2 ml/kg/min) produced higher peak serum concentrations of mannitol and more profound lowering of ICP than the same dose delivered at slower rates.

Animals↗
PubMed1986

Safety and efficacy of epidural analgesia in spine surgery.

Over the last 4 years, the authors have had experience with epidural analgesia for a variety of spinal operations in 24 patients. It has proved to be safe, reliable, and effective. No patient has had a new neurological deficit as a result of the epidural technique, and 18 of 22 patients with neurological deficit improved. Thus, epidural analgesia should not be excluded from the anesthesiologist's consideration simply because of the presence of spine disease or neurological deficit.

Adult↗
PubMed1985

Ocular motility, visual acuity and dysfunction of neuropsychological impairment in children with shunted uncomplicated hydrocephalus.

Children with shunted, uncomplicated, communicating hydrocephalus were tested to determine (1) the persistence of neuropsychological impairment and (2) the relationship between neuropsychological functioning, ocular motility, and acuity abnormalities. Eighteen hydrocephalic and 18 individually age- and sex-matched controls were given a neuropsychological battery, repeated after an interval of 1 year. Hydrocephalic children were also tested at the beginning of the second year for strabismus, amblyopia and visual acuity. Their medical records were reviewed for history of ocular motility and/or acuity abnormalities. Hydrocephalic children with normal range IQ were found to have lower verbal IQ, memory, and fine motor skills compared to controls. A history of ocular motility and acuity abnormalities was associated with impaired visuospatial and verbal problem-solving skills.

Achievement↗
PubMed1985

In vitro evaluation of CSF shunt function by radionuclides.

An in vitro study of clearance of a radiolabeled marker was conducted on nine commonly used shunting devices. Clearance of 0.5 ml of 113mIn-diethylenetriamine-pentaacetic acid (DTPA) injected into the chamber, by water infused through the system at constant rate (0.034-0.46 ml/min), was measured by monitoring activity over the chamber and accumulating counts at 5-s intervals on a multichannel analyzer. Each flow rate was triplicated, and a graph of log value of counts versus time made. A mean t1/2 was computed for each flow rate and a new graph constructed. A best-fit curve constructed for the graph of each shunt system allows determination of flow rate for a known half time of isotope clearance.

Cerebrospinal Fluid Shunts↗
PubMed1985

Choroid plexus Na+/K+-activated adenosine triphosphatase and cerebrospinal fluid formation.

The quantitative relationship between intraventricular fluid formation and choroid plexus Na+/K+-activated (transport) adenosine triphosphatase (ATPase) was studied in rabbit and dog by perfusing the ventricular system with a solution containing ouabain (10(-8) to 10(-3) M). The effect of ouabain in the same range of concentrations on ATPase activity was also measured by the release of inorganic orthophosphate from in vitro choroid plexus tissue. Normally, about 20 to 25% of ATPase activity in lateral ventricle plexus is Na+/K+-activated, and this component is almost completely inhibited by ouabain in a concentration of 10(-4) M. At this concentration, the rate of intraventricular cerebrospinal fluid (CSF) formation is decreased some 70 to 80% in dog and rabbit. The results of this study suggest that a portion of the intraventricular fluid formation is insensitive to cardiac glycoside inhibition and that either there are two different mechanisms responsible for choroid plexus fluid formation or there is a significant non-ATPase dependent extrachoroidal source of CSF.

Animals↗