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Biomedical subjects

C B Shields

Publications and source records attributed to C B Shields.

At least 37 records · Page 2Linked to original sources
PubMed1998

Primary culture of adult mouse olfactory receptor neurons.

Olfactory receptor neurons (ORNs) are unique because they can be replaced by stem cells throughout life. Previous studies have demonstrated that adult mouse olfactory epithelium (OE) injured by exposure to ZnSO4 through nasal irrigation can stimulate stem cell mitotic activity in situ, which continues when placed in culture. We report on an improved ZnSO4 delivery method, mist inhalation, which produces more consistent and greater yields of OE cells. Cultures established following this method contained bipolar, nest, fusiform, and giant cells. The bipolar cells usually underwent asymmetric process development. Some bipolar cells reacted positively to neuron-specific antibodies and were immunonegative for keratin and glia-specific proteins, suggesting that they were ORNs. Those that were negative for the neuron-specific proteins may represent either neuron progenitors or olfactory ensheathing cells. The fusiform cells were relatively small and undifferentiated, exposure to brain-derived neurotrophic factor resulted in their decrease and an increase in bipolar cells. Therefore, they might be the stem cells. The nest cells had morphological characteristics of epithelia and bound keratin antibodies. The giant cells had the morphology of epithelial cells but were negative for keratin; they may represent a unique cell population induced by the ZnSO4. These results indicate that the major cell types of intact OE are present in our cultures, and each retains characteristics found in situ. The mist inhalation method provides an in vitro population of adult mitotically active neurons for study.

Administration, Inhalation↗
PubMed1995

An evaluation of motor-evoked potentials for detection of neurologic injury with correction of an experimental scoliosis.

STUDY DESIGN: Controlled correction of scoliosis in a rat model was used to assess the accuracy of intraoperative motor-evoked potential monitoring. OBJECTIVES: The purpose of this study was to develop a model in which motor-evoked potential changes could be compared with neurologic function after surgery, such that a threshold for responding to motor-evoked potential changes may be established. SUMMARY OF BACKGROUND DATA: Intraoperative motor-evoked potential monitoring has become technically feasible. Clinical application now depends on the development of useful interpretation parameters and correlation with neurologic sequelae. METHODS: Experimental scoliosis was produced in 30 rat pups. After growth, the rats underwent correction of their scoliosis by distraction. Changes in tcMMEP onset latency and amplitude were measured. Distraction was applied either until a 10% delay in tcMMEP onset latency (Group 1), until tcMMEP responses were ablated (Group 2), or for 10 minutes after the loss of transcranial magnetic stimulation response (Group 3). RESULTS: In Group 1 (n = 10), all animals had tcMMEP with normal onset latency and normal neurologic examinations 24 hours after surgery. In Group 2 (n = 10), tcMMEP were normal in four rats, markedly delayed in three rats, and absent in three rats 24 hours after surgery. neurologic examination was normal in the four rats with normal tcMMEP. Moderate deficit was noted in two of the three rats with prolonged onset latency 24 hours after surgery; the third was intact. Moderate neurologic injury was noted in two of three rats with absent tcMMEP 24 hours after surgery; the third rat was paralyzed. In Group 3 (n = 10), vertebral dislocation was noted on lateral radiographs in eight of 10 animals. Twenty-four hours after surgery, tcMMEP remained absent, and paralysis was noted in the eight rats with dislocation. The two rats without dislocation had delayed tcMMEP but some return of neurologic function. CONCLUSIONS: Comparison of the three groups shows a significant correlation between tcMMEP and endpoint neurologic outcome. None of the rats in Group 1 had a neurologic deficit after surgery as opposed to five of 10 rats in Group 2 and 10 of 10 rats in Group 3 with significant neurologic injury. These findings suggest that a 10% delay in onset latency would be an appropriate threshold for responsing to changes in tcMMEP.

Analysis of Variance↗
PubMed1995

A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation.

STUDY DESIGN: In a prospective study of 90 patients undergoing lumbar pedicle screw instrumentation, 512 screws were tested intraoperatively using electrical stimulation. The accuracy of this technique was verified after surgery by computed tomography. OBJECTIVES: Computed tomographic scans taken after surgery were used to evaluate the efficacy of intraoperative screw stimulation and electromyographic monitoring of pedicle screw placement. SUMMARY OF BACKGROUND DATA: Previous cadaveric and clinical studies showed the risk of pedicle screw malposition and the inadequate reliability of intraoperative radiographs to identify misplaced screws. METHODS: Screws (total, 512) in 90 patients were stimulated intraoperatively, and stimulation threshold was recorded. Computed tomographic scans were taken after surgery to document pedicle screw position. Electromyographic thresholds and computed tomographic data were evaluated independently and compared to assess the accuracy of the electromyographic screw stimulation technique. RESULTS: Intraoperative screw stimulation was extremely accurate in confirming the adequacy of screw position. A stimulation threshold greater than 15 mA provided a 98% confidence that the screw was within the pedicle. In eight of 90 patients (9%), electromyographic monitoring detected a screw malposition that was not identified on lateral radiograph. CONCLUSIONS: Screw stimulation monitoring is a valuable and efficacious adjunct to lumbar pedicle screw instrumentation. A stimulation threshold greater than 15 mA reliably indicates adequate screw position. A stimulation threshold between 10 and 15 mA was generally associated with adequate screw position, although exploration of the pedicle is recommended. A stimulation threshold less than 10 mA was associated with a significant cortical perforation in most instances.

Bone Screws↗
PubMed1995

The effects of propofol on rat transcranial magnetic motor evoked potentials.

INTRAOPERATIVE MONITORING OF motor evoked potentials (MEPs) may become a valuable test of spinal cord function during surgery. Unfortunately, MEP responses are affected by most common anesthetics. We studied the effect of intravenous propofol on transcranial magnetic MEPs (tcMMEPs) in the rat. Baseline tcMMEPs were recorded before administration of the drug. Each rat then received three induction doses of propofol, 10, 5, and 5 mg/kg (totaling 10, 15, and 20 mg/kg) and three successive 20-minute infusion doses at rates of 10, 20, and 40 mg/kg/h, respectively. An MEP intensity series was performed after each induction dose, during each infusion, and during a 20-minute recovery period. tcMMEPs recorded during the induction period demonstrated a significant, dose-dependent increase in onset latency and a marked decrease in amplitude. Infusion tcMMEPs displayed increased onset latencies but demonstrated a significant change in amplitudes only after the largest infusion dose. The MEPs approached baseline levels after discontinuation of the propofol. This study demonstrates that tcMMEPs can be successfully recorded from the rat during propofol anesthesia.

Anesthetics, Intravenous↗
PubMed1995

Transcranial magnetic motor-evoked potentials in scoliosis surgery.

Spinal cord monitoring using SSEPs is an accepted adjunct in the surgical correction of spinal deformities, but does not directly assess motor function. Motor-evoked potentials have been introduced in an effort to meet this important need. In this series of 18 patients, the feasibility of intraoperative monitoring using transcranial magnetic motor-evoked potentials is documented. The potential value of this neurophysiologic monitoring technique, as well as the pitfalls in interpretation, are reviewed.

Adolescent↗
PubMed1993

Anesthetic effects on motor evoked potentials in dogs.

The effects of the various anesthetic agents on the production of transcranial magnetic motor evoked potentials (tcMMEP) were studied in a canine model. Pre-anesthetic baseline tcMMEPs demonstrated consistency in onset latency measurements and variability in measurement of peak-to-peak amplitudes. Changes in tcMMEPs were evaluated following the individual administrations of sodium pentothal, etomidate, halothane, fentanyl, and ketamine. For induction of anesthesia, etomidate was compatible with tcMMEP production, whereas sodium pentothal resulted in loss of hindlimb potentials for a period of 45 minutes. For maintenance of anesthesia, halothane was incompatible with the measurement of tcMMEPs. Fentanyl administration was consistent with the recording of reliable tcMMEPs, with consistent onset latencies but widely variable peak-to-peak amplitudes. Ketamine was compatible with stable and reproducible tcMMEP production. The results of this study suggest that anesthetic agents have a predictable and consistent effect on tcMMEP responses.

Anesthetics↗
PubMed1993

Imaging of radiation dose for stereotactic radiosurgery.

The distributions of radiation dose for stereotactic radiosurgery, using a modified linear accelerator (Philips SL-25 and SRS-200), have been studied by using three different dosimeters: (1) ferrous-agarose-xylenol orange (FAX) gels, (2) TLD, and (3) thick-emulsion GafChromic dye film. These dosimeters were loaded into a small volume of defect in a phantom head. A regular linac stereotactic radiosurgery treatment was then given to the phantom head for each type of dosimeter. The measured radiation dose and its distributions were found to be in good agreement with those calculated by the treatment planning computer.

Humans↗
PubMed1993

Correlation of motor-evoked potentials, somatosensory-evoked potentials, and the wake-up test in a case of kyphoscoliosis.

The ability to monitor the descending motor pathways of the spinal cord during surgery is an important goal in neurophysiologic monitoring of spinal deformities. This report describes a case of a severe spinal deformity for which instrumentation and reduction carried a significant risk of neurologic complications. During the procedure, changes in neurologic status were monitored simultaneously using both SSEPs and tcMMEPs. The reliability of these two complimentary modalities was then verified by concurrent wake-up tests. This case provides documentation of the reliability of tcMMEP responses when an accurate assessment of motor function was necessary.

Adult↗
PubMed1993

Radioneurosurgery using the LINAC scalpel: technique, indications, and literature review.

Two available commercial units for radiosurgery are the modified linear accelerator (LINAC scalpel) and the gamma knife. Advantages of the LINAC scalpel over the gamma knife are its greater accuracy, the availability of a wide range of collimator sizes that allow for a more homogeneous field of radiation for large lesions, state-of-the-art computer software programs, and lower expense. Radiosurgery does not require an incision, is painless, and can be performed on an outpatient basis. It is ideally suited for the treatment of inaccessible, deep intracranial lesions that are radioresistant to conventional forms of radiotherapy, such as arteriovenous malformations, meningiomas, vestibular schwannomas, selected primary brain tumors, and cerebral metastases. Radiosurgery is an attractive treatment alternative to conventional neurosurgery for several intracranial lesions.

Brain Diseases↗
PubMed1992

Quantitative electroencephalographic monitoring during myocardial revascularization predicts postoperative disorientation and improves outcome.

We evaluated computerized quantitative electroencephalography for the intraoperative detection of cerebral dysfunction. The quantitative electroencephalogram was recorded continuously during 96 myocardial revascularizations involving hypothermic cardiopulmonary bypass using Cerebrovascular Intraoperative MONitor (CIMON) software. CIMON relies on an adaptive statistical approach to detect subtle, but clinically relevant, changes in electroencephalographic activity indicative of cerebrocortical dysfunction. Relative (percent of total) low-frequency (1.5 to 3.5 Hz) power was chosen as the single quantitative electroencephalographic descriptor because it is an established hallmark of cortical dysfunction and is surprisingly insensitive to moderate changes in body temperature and level of opioid anesthesia. Reference values for this measure were established for each patient after anesthetic induction before sternotomy. The large sample variance often seen in low-frequency power was dramatically decreased by using log-transformed data and allowing each patient to serve as his own control. Quantitative electroencephalographic changes in standard deviation units or z-scores were determined from the individualized reference self-norm. Prolonged (greater than 5 minutes) and statistically significant (greater than 3 standard deviation) focal increases in relative low-frequency power were temperature-corrected to determine a standardized cerebrocortical dysfunction time at 37 degrees C. (CDT37). In phase I (n = 48), this objective quantitative electroencephalogram-based numeric descriptor was used to predict neuropsychologic outcome. These CDT37 greater than 5-minute episodes occurred 38 times in 19 patients. The quantitative electroencephalogram-based descriptor predicted the occurrence of such disorientation (n = 14 or 29%) with a 68% false positive rate but only an 8% false negative rate. Since these intraoperative quantitative electroencephalographic episodes were often (19/38) associated with low (less than 50 mm Hg) pump pressures, phase II (n = 48) sought to correct the quantitative electroencephalographic abnormality and prevent postoperative disorientation by appropriate increases in cerebral perfusion. Although the number of episodes of quantitative electroencephalographic abnormality was similar (n = 31) in phase II, these ischemic events disappeared after prompt elevation of perfusion pressure. The phase II disorientation rate fell significantly (p less than 0.002) to 4%. Thus statistically significant increases in low-frequency electroencephalographic relative power persisting for a temperature-corrected duration of 5 minutes or more are a reliable means of alerting the surgical/anesthesia team to the presence of cerebrocortical dysfunction and provide a rational and objective basis for corrective intervention. This form of electroencephalographic monitoring appears to offer an opportunity for the timely correction of perfusion abnormalities or the administration of cerebroprotectant compounds.

Aged↗
PubMed1992

The role of stereotactic technology in the management of intracerebral hemorrhage.

Stereotactic techniques have been utilized for more than 40 years in clinical neurosurgical practice. There has been considerable experience with stereotactic techniques in the drainage of intracerebral hemorrhages, although its effectiveness remains controversial. Stereotactic craniotomy, often incorporating advanced computer guidance, is increasingly applied to effect complete resection of small, deep brain lesions. Radiosurgery has become a viable alternative for the treatment of arteriovenous malformations that, in most cases, are untreatable by other means. Currently, stereotaxis is a valuable part of the therapeutic armamentarium available to cerebrovascular neurosurgeons.

Cerebral Hemorrhage↗
PubMed1991

Is defibrillation testing safe?

Determination of defibrillation thresholds (DFTs) and implantable cardioverter defibrillator (ICD) testing requires repeated inductions of ventricular fibrillation (VF) and defibrillation attempts using known energy outputs. Little is known about the individual and cumulative effects of repetitive brief episodes of VF and hypoperfusion on cerebral function. The potential clinical utility of quantitative electroencephalographic (QEEG) monitoring during intraoperative ICD testing, by using processed 19-channel EEG (0.5-35 Hz bandwidth), was examined in ten anesthetized patients, five males and five females (mean age 62 +/- 10 years), who underwent ICD implantation and testing. Ischemic QEEG patterns were defined as those with a 3 standard deviation increase (P less than 0.01) in absolute delta (1.5-3.5 Hz) power persisting for greater than or equal to 2.5 minutes. The majority (80%) of the VF episodes (70) were accompanied by QEEG "slowing" (doubling of the pre-VF low frequency delta waves amplitude). All the patients (5/5) experiencing greater than 6 VF episodes showed a statistically significant increase in the low frequency amplitude. In contrast, this EEG abnormality was apparent in only one of five patients experiencing less than 6 VF episodes. These results suggest a cumulative QEEG depression associated with ICD testing. QEEG may provide an objective means for establishing an individualized upper safe limit of DFT testing and the total number of induced VF episodes.

Electric Countershock↗
PubMed1989

Leadership in neurosurgery.

These are challenging times for neurosurgery. Although no one can predict our future, great changes are in the wind--many of which we are powerless to prevent. We must all take on added social responsibility, above and beyond that of patient care. The leadership of your organization can only act with the support of active and concerned neurosurgeons who are willing to participate in many programs available to our profession. The individual must personally embrace the leadership standards of Sir William Osler and Harvey Cushing. One of the privileges of giving a presidential address is to pay public homage to those who have been supportive and instrumental in my long professional journey. During my residency, Dr. Dwight Parkinson was my mentor and teacher and set a wonderful standard for the ideal practice of neurosurgery. Decisions were black or white, never gray, with Dr. Parkinson, who left little doubt as to the correct way to handle clinical problems. He was, and continues to be, one of the most incisive, imaginative, innovative scientific minds in neurosurgery, and I owe him a great debt of gratitude. Two other men influenced my neurosurgical development. They are Dr. William Horsey, formerly neurosurgeon at the St. Michael's Hospital in Toronto, and Dr. Peardon Donaghy, with whom I spent a most enjoyable and productive year in Burlington at his microvascular neurosurgical laboratory. These two men demonstrated the humility, warmth, and kindness to patients that cannot be learned by formal study, but comes from observing the example of people who manifest those qualities in their own personality.(ABSTRACT TRUNCATED AT 250 WORDS)

History, 20th Century↗
PubMed1989

Isolated injection injury to the posterior femoral cutaneous nerve.

The sciatic nerve is by far the most common nerve accidentally injured during intramuscular injection. Despite its close proximity to the sciatic nerve, however, injury to the posterior femoral cutaneous nerve is apparently quite rare. In this report, clinical features of a patient with isolated injection injury to the posterior femoral cutaneous nerve are described.

Humans↗