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Biomedical subjects

A Aschoff

Publications and source records attributed to A Aschoff.

At least 55 records · Page 3Linked to original sources
PubMed1995

Overdrainage and shunt technology. A critical comparison of programmable, hydrostatic and variable-resistance valves and flow-reducing devices.

When vertical body position is simulated, conventional differential pressure valves show an absolutely unphysiological flow, which is 2-170 times the normal liquor production rate. Although this is compensated in part by the resistance of the silicon tubes, which may produce up to 94% of the resistance of the complete shunt system, a negative intracranial pressure (ICP) of up to 30-44 cmH2O is an unavoidable consequence, which can be followed by subdural hematomas, slit ventricles, and other well-known complications. Modern shunt technology offers programmable, hydrostatic, and "flow-controlled" valves and anti-siphon devices; we have tested 13 different designs from 7 manufacturers (56 specimens), using the "Heidelberg Valve Test Inventory" with 16 subtests. "Programmable" valves reduce, but cannot exclude, unphysiological flow rates: even in the highest position and in combination with a standard catheter typical programmable Medos-Hakim valves allow a flow of 93-232 ml/h, Sophy SU-8-valves 86-168 ml/h with 30 cmH2O. The effect of hydrostatic valves (Hakim-Lumbar, Chhabra) can be inactivated by movements of daily life. The weight of the metal balls in most valves was too low for adequate flow reduction. Antisiphon devices are highly dependent on external, i.e. subcutaneous, pressure which has unpredictable influences on shunt function, and clinically is sometimes followed by shunt insufficiency. Two new Orbis-Sigma valves showed relatively physiological flow rates even when the vertical position (30 cmH2O) was simulated. One showed an insufficient flow (5.7 ml/h), and one was primarily obstructed. These have by far the smallest outlet of all valves. Additionally, the ruby pin tends to stick. Therefore, a high susceptibility to obliterations and blockade is unavoidable. Encouraging results obtained in pediatric patients contrast with disappointing experiences in some German and Swedish hospitals, which suggests that our laboratory findings are confirmed by clinical results. The concept of strict flow limitation seems to be inadaequate for adult patients, who need a relatively high flow during (nocturnal) ICP crises. The problem of shunt overdrainage remains unsolved.

Adult↗
PubMed1995

In vitro and in vivo efficacy of a rifampin-loaded silicone catheter for the prevention of CSF shunt infections.

Infection of cerebrospinal fluid (CSF) shunts is one of the major complications associated with their use and is usually managed by shunt removal, temporary insertion of an external drainage and implantation of a new shunt system. We have evaluated the efficacy of a rifampin-loaded silicone ventricular catheter to prevent bacterial colonization and infection in vitro and in an animal model. On the basis of an incorporation process a rifampin-loaded catheter was developed which is capable of releasing rifampin in bacteriocidal concentrations for 60 days and more. In a stationary bacterial adherence assay using S. epidermidis as test strain, the colonization resistance of the device was demonstrated. To assess the capability of the catheter to prevent CSF shunt infections, a rabbit model was developed which allowed the establishment of a reliable and reproducible CSF infection by implantation of silicone catheters into the ventricle and inoculating S. epidermidis (minimal dose 10(6) cfu) or S. aureus (minimal dose 10(3) cfu). Rifampin-loaded catheters (12 animals inoculated with S. epidermidis, 8 animals inoculated with S. aureus) were compared with non-loaded (14 animals inoculated with S. epidermidis, 19 animals inoculated with S. aureus) control catheters, and infection was documented by clinical, microbiological and histological methods. In contrast to the control group, none of the animals with rifampin-loaded catheters showed clinical signs of infection. Furthermore, in none of the materials obtained after sacrifice of the animals (catheter, brain tissue, CSF, blood) could the infecting bacteria be cultured, whereas in materials from animals with the unloaded catheter the infecting strains could always be cultured from the catheter and from surrounding brain tissue. The histological examination of catheter-adjacent tissue supported these findings. We conclude that a rifampin-loaded silicone ventricular catheter is capable of completely preventing bacterial colonization and infection by staphylococci as the main causative organisms in CSF shunt infections and should be further evaluated in clinical trials.

Animals↗
PubMed1995

Combined microneurosurgical and endovascular "trapping-evacuation" technique for clipping proximal paraclinoidal aneurysms.

A method is described in which a combined endovascular and microneurosurgical approach is used for clipping aneurysms of the proximal paraclinoidal segment of the internal carotid artery. By temporary occlusion of the cervical carotid artery and continuously retrograde sucking of blood from the distal vessel via a double lumen ballon catheter, clip application to large and critically located aneurysms is facilitated applying decompression to the trapped arterial segment under intraoperative somatosensory-evoked potential (SEP) monitoring.

Journal Article↗
PubMed1995

Decompressive surgery in space-occupying hemispheric infarction: results of an open, prospective trial.

OBJECTIVE: Space-occupying hemispheric infarctions, requiring neurocritical care treatment, demonstrate high mortality and morbidity rates. This study was performed to determine the beneficial effects of decompressive craniotomy on mortality and morbidity rates. DESIGN: Open, nonrandomized, control trial. Outcome was rated at discharge from the hospital (Glasgow Outcome Scale) and at follow-up (Barthel Index, Oxford Handicap Scale). SETTING: Patient recruitment from the Department of Neurology, University of Heidelberg (primary care center) over 65 months. PATIENTS: Thirty-two patients were prospectively selected for surgical treatment; 21 patients were treated conservatively. INTERVENTIONS: Extended craniotomy and dura patch enlargement were performed in all surgically treated patients. MEASUREMENTS AND MAIN RESULTS: At discharge, the outcome of six (18.8%) of 32 surgically treated patients was good compared with 0 (0%) of 21 conservatively treated patients. Fifteen (46.9%) of 32 surgically treated patients were moderately to severely disabled compared with five (23.8%) of 21 conservatively treated patients, and 11 (34.4%) of 32 surgically treated patients died compared with 16 (76.2%) of 21 conservatively treated patients. At follow-up in surgically treated patients, the Barthel Index (mean 62.6) showed an excellent level of daily activity in one patient, minimal assistance (Barthel Index of > or = 60) in 15 patients, and dependency in five patients. The Oxford Handicap Scale indicated no handicap in one patient, moderate handicaps in 15 patients, and moderately severe handicaps in five patients. In the control group, all five surviving patients needed assistance and all but one patient demonstrated a moderately severe handicap. CONCLUSIONS: Hemicraniotomy may improve survival in massive hemispheric stroke victims, decreasing mortality rates to < 35%. The disability rate remains high (24%), although some patients seem to benefit significantly.

Adolescent↗
PubMed1995

[Craniectomy in space-occupying middle cerebral artery infarcts].

Space occupying supratentorial ischemic stroke has a high mortality. The benefit of decompressive surgery in these patients is still matter of debate. In a prospective study we performed craniectomy in 37 patients with acute middle cerebral artery infarction and progressive deterioration under conservative antiedematous therapy. Twenty-one patients treated conservatively during the same period served as control group. All survivors were reexamined between one to two years after surgical decompression. In addition, neuropsychological tests were performed, including an Aachener Aphasie Test (AAT) in those patients with infarction of speech-dominant hemisphere. Clinical evaluation was graded using the Barthel index (BI). Mortality rate in the operated group was 37%. Twenty-three patients survived acute stroke and were reexamined. Despite complete hemispheric infarction, no patient suffered from complete hemiplegia or was permanently wheel chair bound. In speech dominant hemispheric infarction (n = 8) only mild to moderate aphasia could be detected. Mean BI was 64. Mortality rate in the conservatively treated group was 76%. The clinical outcome following craniectomy for the treatment of severe ischemic hemispheric infarction is unexpectedly good. Therefore, decompressive surgery should be considered in cases of space-occupying hemispheric infarctions and conservatively uncontrollable intracranial pressure.

Adolescent↗
PubMed1994

Risks of using siphon-reducing devices.

Reducing the cerebrospinal flow is the task of siphon-reducing devices (SRD). This paper shows test results with SRD, with special reference to the aspect of dysfunction of shunt valves in combination with anti-siphon. The local influences acting on the anti-siphon at the place of implantation and the dependence of the pressure range were examined as possible causes of dysfunction.

Cerebral Ventricles↗
PubMed1993

Clipping of proximal paraclinoid aneurysms with support of the balloon-catheter "trapping-evacuation" technique. Technical note.

A method is described in which we use a combined endovascular balloon-catheter technique and open microneurosurgical approach for clipping aneurysms of the proximal paraclinoidal intracranial segment of the internal carotid artery. By temporary occlusion of the cervical carotid artery and continuously retrograde sucking of blood from the distal vessel via a double-lumen balloon-catheter, clip application to large and critically located aneurysms is facilitated applying evacuation-decompression to the trapped arterial segment under intra-operative SEP-monitoring.

Adult↗
PubMed1993

Prognostic and clinical relevance of pupillary responses, intracranial pressure monitoring, and brainstem auditory evoked potentials in comatose patients with acute supratentorial mass lesions.

OBJECTIVE: To test the hypothesis that the clinical condition and outcome in patients with acute supratentorial mass lesions can be assessed by determination of pupillary abnormalities, measurement of intracranial pressure, and results of brainstem auditory evoked potentials. DESIGN: Prospective case series of 55 patients presenting with supratentorial mass lesions. SETTING: Neurologic and neurosurgical intensive care unit of a tertiary care center. PATIENTS: Fifty-five comatose patients (26 female/29 male; 9 to 70 yrs of age [mean 44]). INTERVENTIONS: Pupillary abnormalities were rated "normal," "unilaterally enlarged," "unilaterally fixed," and "bilaterally abnormal." The outcome was rated using the Glasgow Outcome Scale. Intracranial pressure values were graded into five categories. Brainstem auditory evoked potentials were rated "bilaterally normal," "unilaterally abnormal," or "bilaterally abnormal," according to normative data. Statistical evaluation was performed by frequency analysis (Fisher's exact test, two-tailed) and calculation of contingency coefficients. MEASUREMENTS AND MAIN RESULTS: Outcome was poor in 24 patients, good in eight patients, and 23 patients were severely disabled. Statistical analysis showed prognostic significance of both pupillary abnormalities (p = .0000542; contingency coefficient = .589) and increased intracranial pressure (p = .0084; contingency coefficient = .352). Brainstem auditory evoked potential categories correlated significantly with pupillary abnormalities (p = .000276; contingency coefficient = .505) and increased intracranial pressure (p = .0301; contingency coefficient = .502) but did not predict outcome (p = .645; contingency coefficient = .321). CONCLUSIONS: Pupillary abnormalities may serve as a reliable parameter, which may even be superior to brainstem auditory evoked potential testing and intracranial pressure monitoring for prediction of outcome in comatose individuals with supratentorial mass lesions. Brainstem auditory evoked potentials can be used to support the clinical relevance of abnormal pupillary status and increased intracranial pressure but are of no prognostic value. Increased intracranial pressure is associated with abnormalities in pupillary status and brainstem auditory evoked potentials. Examination for pupillary abnormalities in combination with intracranial pressure monitoring and brainstem auditory evoked potential testing seems to be a useful strategy in managing patients with supratentorial mass lesions in critical care units.

Acute Disease↗
PubMed1993

Functional recovery and morphological changes after injury to the optic nerve.

Physiological and morphological parameters of optic nerve lesions followed by functional recovery are discussed in detail. To study functional and/or morphological recovery processes, a recently developed model of the 'graded optic nerve crush' is compared with other models of lesioning. It is concluded that the optic nerve crush model is a valuable tool when studying brain repair mechanisms. First results show that functional recovery depends on the initial preservation of a sufficiently large population of ganglion cells in the retina. It takes place despite the progressive loss of retinal ganglion cells during the recovery period.

Animals↗
PubMed1992

Effect of direct, reflex and exercise-provoked increases in sympathetic tone on idiopathic ventricular tachycardia.

Exercise treadmill testing and direct enhancement of sympathetic influence with agents such as isoproterenol are often used to reproduce ventricular tachycardia (VT). The cardiac effects of, and arrhythmia responses to, graded exercise, isoproterenol infusion and lower body negative pressure (the latter 2 with and without atrial and ventricular stimulation) were studied in 11 patients with idiopathic VT. During maximal exercise, substantial increases in heart rate and blood pressure occurred, but only 2 of 9 exercised patients had VT (during recovery in both). During programmed stimulation alone, VT was initiated in 6 patients. During maximum levels of lower body negative pressure (-60 cm of water in most), mean systolic blood pressure decreased by 10 mm Hg, heart rate increased by 15 beats/min, and ventricular refractory period decreased by 10 ms. In 4 patients VT occurred spontaneously during lower body negative pressure; in 2, lower body negative pressure was the only intervention producing VT. During isoproterenol infusion VT occurred spontaneously in 2 patients; both had VT initiated during other interventions. Lower body negative pressure and isoproterenol increased VT rate, but did not prolong it. It is concluded that there is significant variability in arrhythmia responses to sympathetic augmentation, suggesting that additional covariables such as parasympathetic input and ventricular volume may also have a role in arrhythmia occurrence.

Adult↗
PubMed1991

Topography of projections from the auditory cortex to the inferior colliculus in the rat.

We examined the organization of descending projections from auditory and adjacent cortical areas to the inferior colliculus (IC) in the rat by using the retrograde and anterograde transport of wheat germ agglutinin-horseradish peroxidase. Small tracer injections were placed into cytologically defined subnuclei of the IC. On the basis of the resulting pattern of retrogradely labeled neurons in the cortex, different cortical areas and fields were defined. Two secondary areas located ventrocaudally (Te2) and ventrally (Te3) to the primary auditory area (Te1) were delineated. The primary auditory area was subdivided into a posterior (Te1.p), a medial (Te1.m), and an anterior (Te1.a) auditory field. In addition, we outlined an area located rostrally to the auditory areas comprising a part of the secondary somatosensory cortex, as well as a dorsal belt surrounding dorsally the auditory areas. The following basic patterns of corticocollicular projections are revealed: 1) layers 2 and 3 of the dorsal cortex of the IC (DC2, DC3) are differentially innervated by the primary auditory fields (Te1.p and Te1.a project bilaterally to DC2, while Te1.m projects bilaterally and in topographical order to DC3); cells in Te1.m, arranged in caudal to rostral sequence, project to corresponding loci in DC3 arranged from dorsolateral to ventromedial; 2) the fibrocellular capsule of the IC, comprising layer 1 of the dorsal and external cortex of the IC, receives input from the secondary auditory area Te2; 3) layers 2 and 3 of the external cortex of the IC are only weakly innervated by the primary and secondary auditory cortex; 4) the intercollicular zone receives its major input from the secondary auditory area Te3, the secondary somatosensory cortex, and the dorsal belt; and 5) finally, the central nucleus of the IC receives no input from the temporal cortex at all. Our results demonstrate that the corticocollicular projections are highly organized. These pathways may modulate auditory processing in different functional circuits of the inferior colliculus.

Animals↗