摘要:

IN ONE STRATEGY for the treatment of unilateral vestibular schwannomas measuring up to 3 cm in diameter, decision analysis shows that gamma knife radiosurgery has probabilistic dominance over microsurgical resection. That is, radiosurgery produces better results for any value assigned to treatment outcomes (ranked from best to worst) of the following: no complications, hearing loss only, residual/recurrent tumor, facial paralysis, major disability, or death. This little-known principle of decision analysis will be explained. It implies that when patients prefer the preservation of facial nerve function, even if that requires leaving a tumor remnant, then gamma knife radiosurgery is a better treatment strategy than microsurgical resection.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

CHANGES IN VENTILATORY rate affect arterial blood pH and PCO2within seconds to minutes, but the corresponding acute changes for cerebrospinal fluid (CSF) pH and PCO2have not been as well documented. Using our previously-described swine model of brain retraction ischemia, we examined changes in arterial and CSF pH and PCO2with acute changes in ventilation in four animals. Newly developed fluorescent dye technology permitted near-instantaneous recording of CSF pH and PCO2during acute hyperventilation (end-tidal PCO2of 20 mm Hg) and acute hypoventilation (end-tidal PCO2of 50 mm Hg). The Puritan-Bennett 3300 Intra-Arterial Blood Gas Monitor (PB3300) was used with the sensor placed in the CSF in the interhemispheric fissure posterior to the corpus callosum. The following data were gathered at 5, 15, 30, and 60 minutes after the ventilatory change: arterial pH and PCO2, end-tidal CO2, laser-Doppler cerebral blood flow, and CSF pH and PCO2. The baseline (normoventilation) values for arterial and CSF pH and PCO2in swine were comparable to those in humans: arterial pH 7.44 and PCO243 mm Hg; CSF pH 7.31 and PCO255 mm Hg. Changes in pH and PCO2with hyperventilation and hypoventilation occurred rapidly in both arterial blood and CSF. Steady-state values were reached within 15 minutes for hypoventilation, and 30 minutes for hyperventilation. The correlation between arterial and CSF values for both pH and PCO2at 5, 15, 30, and 60 minutes were all very highly significant (P< 0.001) except for arterial and CSF PCO2at 5 minutes (P< 0.01). CSF pH and PCO2follow arterial blood gas pH and PCO2rapidly with acute changes in ventilation. These results are consistent with previous research, and indicate the PB3300 may be useful in monitoring CSF pH and PCO2.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

THE PURPOSE OF this experiment was to characterize the longitudinal field gradients from exogenously applied electrical stimulation in the normal and injured rodent spinal cord. In addition, we compared the field gradients arising from stimulation with two different types of stimulating electrodes. Twenty normal rats underwent the surgical implantation of either extradural disc (n = 10) or cuff (n = 10) electrodes in the lower cervical and upper thoracic spinal cord. Sine waves of 1.5 to 50 μA and 0.5 to 50 Hz were used for stimulation. Field gradients were measured differentially from two extracellular glass microelectrodes, positioned stereotactically in the spinal cord at different locations between the stimulating electrodes. The effect of acute spinal cord injury on local field strength was studied in five animals from each group. The field gradients from stimulation with disc electrodes were greatest in close proximity to the discs and decreased markedly toward the point equidistant between the electrodes. In contrast, the gradients produced by cuff electrodes were much more evenly distributed along the spinal cord, increasing only slightly in proximity to the electrodes. These fields were also more evenly distributed throughout the spinal cord in cross-section but were generally weaker than those arising from disc electrodes. Acute spinal cord injury significantly increased the field gradients arising from both disc and cuff electrodes. However, the observed gradients remained substantially lower than those reported to enhance neurite growth in vitro. We conclude that the position and design of stimulating electrodes has a profound effect on longitudinal field gradients within the mammalian spinal cord, as does the presence of an acute spinal cord injury.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

THE MECHANISMS UNDERLYING the beneficial effect of electrical stimulation of the posterior surface of the spinal cord in chronic pain states are unknown. The prolonged pain relief following a short stimulation period is believed to imply the activation of long-lasting neurochemical processes, mainly in the spinal cord, but possibly also involving other parts of the central nervous system. Previous studies have demonstrated that substance P and serotonin are released in the cat dorsal horn during spinal cord stimulation (SCS) with electrical parameters similar to those used in the clinic. However, gamma-aminobutyric acid (GABA) has also been hypothesized to play a role in the effect of SCS, but there have been no studies of the possible effects of SCS on GABA release. The authors applied SCS to anesthetized rats and monitored the extracellular concentration of GABA in the lumbar dorsal horns by microdialysis and a sensitive reverse-phase high-performance liquid chromatography technique. After 30 minutes of SCS, the GABA level increased significantly (by almost 270%) in comparison with the basal level recorded before stimulation, from 3.6 ± 1.0 nmol/L to 13.1 ± 2.2 nmol/L (mean ± the standard error of the mean;P< 0.05). The peak release was delayed and appeared in the 30-minute fraction collected after stimulation. Also, perfusion of the dialysis probes with potassium (100 mmol/L) induced an increase of the GABA level. In control experiments without electrical stimulation, slowly decreasing GABA levels were observed throughout the experiments. The present results may suggest an involvement of GABA in the mechanism for SCS-induced pain relief. A hypothetical role for GABA in the effect of SCS on the activity of wide dynamic range neurons and on symptoms of neuropathy is discussed on the basis of these observations and other recent experimental findings.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

MAGNETIC MOTOR EVOKED potentials (MMEPs) were recorded from the right cranial tibial muscle after magnetic stimulation of the left motor cortex in six dogs sedated with oxymorphone. Anesthesia was induced with an intravenous bolus of 5.5 mg/kg of methohexital and maintained with a methohexital infusion. The dogs inspired 100% oxygen during anesthesia. Blood pressure, heart rate, respiratory rate, esophageal temperature, and end-tidal carbon dioxide tension were recorded. The depth of anesthesia was increased until the amplitude of the MMEP was less than 5% of the control value, and the dogs were then allowed to recover. Every 5 minutes during anesthesia, a blood sample was taken for methohexital assay and at the same time, four replicate MMEPs were recorded. Plasma methohexital levels were significantly (P< 0.05) correlated with heart rate (ρ = 0.38) and end-tidal carbon dioxide tension (ρ = 0.49) and negatively correlated with respiratory rate (ρ = −0.74). There was no significant correlation between blood pressure and methohexital levels. The dogs regained consciousness at a plasma methohexital level of 10.4 ± 3.8 μg/ml (mean ± SD). The amplitude of the MMEP decreased significantly with increasing methohexital levels. In four dogs, the relationship was reasonably linear. The MMEP disappeared at a plasma methohexital level of 23 ± 6.6 μg/ml. The latency of onset of the MMEP increased significantly from its control value of 14.7 ± 1.0 ms to 17.5 ± 1.3 ms at the highest methohexital levels at which MMEPs were recordable. This study demonstrated that MMEPs can be reliably recorded under methohexital anesthesia.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

IN ORDER TO study the role of the Ca2+/calmodulin/myosin light chain kinase system in the development of chronic vasospasm caused by subarachnoid hemorrhage, the cytosolic Ca2+level ([Ca2+]i), measured with fura-2, a fluorescent Ca2+indicator, and contractile tension were measured simultaneously, and their quantitive correlation was examined in basilar arterial tissue obtained from the canine “two-hemorrhage” model. Sixteen adult mongrel dogs were divided into two groups, control (n = 8) and vasospasm (n = 8), and were killed 7 days after the first experimental subarachnoid hemorrhage. In basilar arterial tissue loaded with fura-2, 1) [Ca2+]iin the resting condition was not significantly different between the two groups; 2) the increment in [Ca2+]iinduced by 40 mmol/L K+stimulation was significantly smaller in vasospastic tissue (P< 0.01); and 3) 40 mmol/L K+-induced tension development per cross-sectional area for a fixed increment in [Ca2+]iwas significantly greater in vasospastic tissue (P< 0.01). In tissue not loaded with fura-2, active myogenic tone, which was tentatively represented by the ratio of tonus relaxed with 10−4mol/L papaverine to initial resting tone, was significantly greater in vasospastic tissue (P< 0.05). These findings, coupled with recent reports concerning the ratio of phosphorylated myosin light chain, indicate the following about vasospastic arterial tissue in vitro: 1) in the resting condition, augmented myogenic tone, which is not accompanied by [Ca2+]ielevation, is probably not attributable to the Ca2+/calmodulin/myosin light chain kinase system, and by contrast, 2) at a higher level of [Ca2+]i, a stronger contraction for a fixed increment in [Ca2+]iis induced by Ca2+sensitization mechanisms of the calmodulin/myosin light chain kinase system.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

LITTLE IS KNOWN about how intravenous fluids influence peritumoral edema formation. This experiment was designed to determine, in a rat glioma model, whether changes in plasma osmolality alter water content, as assessed by specific gravity (SpGr), in normal and neoplastic cerebral tissue. Cells cultured from an ethylnitrosourea-induced rat glioma were stereotactically implanted into the right striatum of Fischer 344 rats. A tumor growth interval of 21 days was allowed. In a second experiment, rats underwent a 60-second cortical freeze injury followed by 24 hours' recovery. In both experiments, rats were assigned to one of three groups: hypotonic (100 ml/kg of 0.2 mol/L NaCl in H2O, intraperitoneally; resultant plasma osmolality ≈ 268 mOsm/kg); isotonic (no treatment; plasma osmolality ≈ 298 mOsm/kg); or hypertonic (10 ml/kg of 1.0 mol/L NaCl in H2O, intraperitoneally; plasma osmolality ≈ 342 mOsm/kg). Thirty minutes after fluid injection, regional SpGr was determined using a kerosene-bromobenzene gradient. In subsets of rats, the tissue morphology and blood-brain barrier permeability of Evans blue dye were assessed. Tissue within the freeze lesion was stained by Evans blue dye with sharp demarcation. Evans blue dye did not stain gliomatous tissue, and central necrosis was not histologically evident. In isotonic rats, glioma SpGr was reduced (1.0411 ± 0.0012 g/ml) relative to the contralateral striatum (1.0437 ± 0.0008 g/ml;P< 0.001). Despite this, a strong linear relation was observed for SpGr and plasma osmolality in both neoplastic and normal tissue. Within the freeze lesion in isotonic rats, SpGr was severely reduced (1.0335 ± 0.0008 g/ml;P< 0.0001) compared with contralateral frontal cortex. SpGr within the freeze lesion did not change in response to changing plasma osmolality. In tissue impermeable to Evans blue dye, SpGr varied directly with plasma osmolality. Results from this model indicate that plasma osmolality remains a critical determinant of peritumoral edema formation when the blood-brain barrier is impermeable to macromolecules. Knowledge of plasma osmotic effects of available intravenous solutions would seem essential in defining fluid therapy for patients with intracranial neoplastic processes.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

CURRENT MANEUVERS TO diagnose the piriformis syndrome are less than ideal. Freiberg's maneuver of forceful internal rotation of the extended thigh elicits buttock pain by stretching the piriformis muscle, and Pace's maneuver elicits pain by having the patient abduct the legs in the seated position, which causes a contraction of the piriformis muscle. This report describes a maneuver performed by the patient lying with the painful side up, the painful leg flexed, and the knee resting on the table. Buttock pain is produced when the patient lifts and holds the knee several inches off the table. The maneuver produced deep buttock pain in three patients with piriformis syndrome. In 100 consecutive patients with surgically documented herniated lumbar discs, the maneuver often produced lumbar and leg pain but not deep buttock pain. In 27 patients with primary hip abnormalities, pain was often produced in the trochanteric area but not in the buttock. The maneuver described in this report was helpful in diagnosing the piriformis syndrome. It relies on contraction of the muscle, rather than stretching, which the author believes better reproduces the actual syndrome.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

EIGHT PATIENTS UNDERWENT microsurgical excision of small, deep-seated cavernous angiomas (maximum diameter, 0.9 to 2 cm; distance from cortical surface, 3.5 to 6.5 cm) by the stereotactic implantation of a guide catheter. In all cases, the lesion was quickly localized and completely removed. None of the patients had postoperative neurological deficits. Once the guide catheter has been implanted, the stereotactic headframe can be removed, allowing the unobstructed use of the operating microscope with frames not suitable for open surgery. Target localization is not affected by brain movement, which is inevitable during open surgery. The procedure described here is simple to perform and relatively inexpensive. It requires no specially designed equipment, only a standard stereotactic apparatus, an operating microscope, and the usual microsurgical instruments.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

FIVE INTRAMEDULLARY CAVERNOUS angiomas were surgically removed after being localized by intraoperative ultrasound imaging. Two patients were men, and three were women; in three patients, the symptoms had an acute onset, whereas in the other two, it was gradual. The vascular malformation was localized in the dorsal tract in three patients and in the cervical tract in two. Intraoperative ultrasound imaging visualized the lesion, which appeared hyperechogenous in all cases, and showed its relationship with the surrounding anatomical structures. Surgical removal was always total and was confirmed by both intraoperative echography and postoperative magnetic resonance imaging. In our experience, intraoperative ultrasound imaging was useful for localizing intramedullary cavernous angiomas, especially in cases where the lesion did not appear on the posterior surface of the spinal cord. In this way, it was possible to limit posterior myelotomy and confirm radical tumor removal intraoperatively.

ISSN:0148-396X    

出版商:OVID    

年代:1994

数据来源: OVID