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Biomedical subjects

H L Edmonds

Publications and source records attributed to H L Edmonds.

At least 19 recordsLinked to original sources
PubMed2001

Topiramate as a neuroprotectant in a rat model of global ischemia-induced neurodegeneration.

The neuroprotective properties of topiramate were evaluated in a rat model of stroke in which neurodegeneration was induced by temporary global ischemia. In this model, the ischemia resulted from 11 min of cardiac arrest during atraumatic chest compression. Resuscitated rats exhibit a characteristic neurological syndrome characterized by sound-induced convulsions, specific motor and behavioral deficits, and death of hippocampal CA1 pyramidal neurons. Topiramate, when administered i.v. 30 min after resuscitation, reduced the degree of motor impairment (P< 0.05 vs control at doses of 10 and 20 mg/kg) and seizure severity (P< 0.05 vs control at a dose of 10 mg/kg on the fifth recovery day). The highest dose of topiramate (20 mg/kg i.v.) eliminated nearly all histologic signs of hippocampal ischemic neuronal injury (P< 0.001). Phenytoin at 20 mg/kg i.v. exhibited neuroprotectant effects similar to those observed for topiramate at 20 mg/kg i.v.. In normal rats, neither topiramate nor phenytoin at 20 mg/kg i.v. induced any apparent neurological impairment; however, at 40 and 60 mg/kg i.v. both induced a mild impairment typical of most anticonvulsants. The results of this study support the concept that topiramate possesses neuroprotective properties.

Animals↗
PubMed2000

Tissue oximetry for the diagnosis of neurally mediated syncope.

This study examined the potential clinical contribution of noninvasive brain and skeletal muscle oximetry as a diagnostic aid in neurally mediated syncope. Tilt table testing was performed in 15 patients with a history of syncope and 9 healthy volunteers. Spatially resolved reflectance near-infrared spectroscopy was used to examine regional oxyhemoglobin saturation in the frontal cerebral cortex and pectoral muscle. During upright tilt, syncope occurred in four patients. Each episode was associated with bradycardia, hypotension, and brain oxygen desaturation of > 20% from the supine reference baseline, while the largest desaturation in nonsyncopal patients was 13%. In two syncopal patients, a sudden increase in pectoral oxygen saturation preceded cerebral oxygen desaturation and unconsciousness, suggesting a sudden loss of peripheral sympathetic tone. Simultaneous desaturation in both tissues in the other two patients appeared to be in response to a diminished cardiac output. The muscle and brain oxygen saturation ratio increased by 75% with apparent sympathetic dysfunction, but never changed by > 25% in the other patients, and varied by < 15% in the volunteers. These results suggest that during tilt table testing, simultaneous assessment of brain and skeletal muscle oxygenation may provide a simple, objective aid for the identification of contributory sympathetic dysfunction.

Adolescent↗
PubMed2000

A laryngoscope designed for intubation of the rat.

We successfully intubated 257 rats with a laryngoscope that we designed for this purpose. Orotracheal intubation with this laryngoscope can be performed quickly and without harm to the animal. This instrument provides direct visualization of the vocal cords, allowing rapid, safe intubation of the rat. Maintenance of an adequate airway with endotracheal intubation is superior to tracheostomy for repeated experiments, and therefore this laryngoscope makes such studies easier and safer to perform.

Animals↗
PubMed1999

Auditory brainstem evoked responses and temperature monitoring during pediatric cardiopulmonary bypass.

PURPOSE: To examine the effects of temperature on auditory brainstem responses (ABRs) in infants during hypothermic cardiopulmonary bypass for total circulatory arrest (TCA). The relationship between ABRs (as a surrogate measure of core-brain temperature) and body temperature as measured at several temperature monitoring sites was determined. METHODS: In a prospective, observational study, ABRs were recorded non-invasively at normothermia and at every 1 or 2 degrees C change in ear-canal temperature during cooling and rewarming in 15 infants (ages: 2 days to 14 months) that required TCA. The ABR latencies and amplitudes and the lowest temperatures at which an ABR was identified (the threshold) were measured during both cooling and rewarming. Temperatures from four standard temperature monitoring sites were simultaneously recorded. RESULTS: The latencies of ABRs increased and amplitudes decreased with cooling (P < 0.01), but rewarming reversed these effects. The ABR threshold temperature as related to each monitoring site (ear-canal, nasopharynx, esophagus and bladder) was respectively determined as 23 +/- 2.2 degrees C, 20.8 +/- 1.7 degrees C, 14.6 +/- 3.4 degrees C, and 21.5 +/- 3.8 degrees C during cooling and 21.8 +/- 1.6 degrees C, 22.4 +/- 2.0 degrees C, 27.6 +/- 3.6 degrees C, and 23.0 +/- 2.4 degrees C during rewarming. The rewarming latencies were shorter and Q10 latencies smaller than the corresponding cooling values (P < 0.01). Esophageal and bladder sites were more susceptible to temperature variations as compared with the ear-canal and nasopharynx. CONCLUSION: No temperature site reliably predicted an electrophysiological threshold. A faster latency recovery during rewarming suggests that body temperature monitoring underestimates the effects of rewarming in the core-brain. ABRs may be helpful to monitor the effects of cooling and rewarming on the core-brain during pediatric cardiopulmonary bypass.

Anesthesia↗
PubMed1998

Evidence for improved cerebral function after minimally invasive bypass surgery.

BACKGROUND: Neurological impairment is a major cause of morbidity after cardiac surgery and may be associated with occurrence of cerebral microemboli generated during cardiopulmonary bypass (CPB). This study evaluates cerebral dysfunction following coronary artery surgery on-pump and off-pump. METHODS: Neurological outcome was evaluated in 322 patients with a coronary artery bypass graft (CABG). Conventional CPB was used (on-pump) in 305 patients and in 17 patients no CPB was used (off-pump). Intraoperatively, a pulsed-wave transcranial Doppler with a 2-MHZ probe measured high-intensity transient signals (HITS) by ultrasonic insonnation of the middle cerebral artery indicating the presence of emboli within the vessel lumen. Transcranial near-infrared spectroscopy measured cerebral venous oxygen saturation for adequate perfusion. Postoperatively, all patients were subjected to the antisaccadic eye movement (ASEM) test, a sensitive indicator of neurocognitive deficits secondary to frontal lobe dysfunction. RESULTS: While there was no significant difference in O2 saturation, the number of microemboli HITS generated was significantly higher in the on-pump group than the off-pump group. In the off-pump group, 16 (94%) of 17 patients had perfect scores on the ASEM test, while only 108 (35.4%) of 305 patients achieved a perfect score in the on-pump group (p < 0.01). Furthermore, while all patients in the off-pump group achieved at least 90%, 28% (86/305) in the on-pump group scored "zero" on the ASEM test. CONCLUSION: Cerebral dysfunction as evidenced by ASEM errors is common following coronary bypass on-pump, but rare with off-pump bypass surgery. Cerebral microemboli generated during CPB may account for this difference.

Cardiopulmonary Bypass↗
PubMed1997

Benefit of neurophysiologic monitoring for pediatric cardiac surgery.

BACKGROUND: Pediatric patients undergoing repair of congenital cardiac abnormalities have a significant risk of an adverse neurologic event. Therefore this retrospective cohort study examined the potential benefit of interventions based on intraoperative neurophysiologic monitoring in decreasing both postoperative neurologic sequelae and length of hospital stay as a cost proxy. METHODS: With informed parental consent approved by the institutional review board, electroencephalography, transcranial Doppler ultrasonic measurement of middle cerebral artery blood flow velocity, and transcranial near-infrared cerebral oximetry were monitored in 250 patients. An interventional algorithm was used to detect and correct specific deficiencies in cerebral perfusion or oxygenation or to increase cerebral tolerance to ischemia or hypoxia. RESULTS: Noteworthy changes in brain perfusion or metabolism were observed in 176 of 250 (70%) patients. Intervention that altered patient management was initially deemed appropriate in 130 of 176 (74%) patients with neurophysiologic changes. Obvious neurologic sequelae (i.e., seizure, movement, vision or speech disorder) occurred in five of 74 (7%) patients without noteworthy change, seven of 130 (6%) patients with intervention, and 12 of 46 (26%) patients without intervention (p = 0.001). Survivors' median length of stay was 6 days in the no-change and intervention groups but 9 days in the no-intervention group. In addition, the percentage of patients in the no-intervention group discharged from the hospital within 1 week (32%) was significantly less than that in either the intervention (51%, p = 0.05) or no-change (58%, p = 0.01) groups. On the basis of an estimated hospital neurologic complication cost of $1500 per day, break-even analysis justified a hospital expenditure for neurophysiologic monitoring of $2142 per case. CONCLUSIONS: Interventions based on neurophysiologic monitoring appear to decrease the incidence of postoperative neurologic sequelae and reduce the length of stay. Inasmuch as the break-even cost for neurophysiologic monitoring is more than four times the actual average charge, both patients and hospital may profit from this service. Because this study was not a truly randomized clinical trial, unintentional statistical bias may have occurred and caution is urged in interpreting the magnitude of apparent intergroup outcome differences.

Algorithms↗
PubMed1997

Neurophysiologic monitoring to assure delivery of retrograde cerebral perfusion.

BACKGROUND: Patients undergoing complex aortic procedures performed with deep hypothermia and circulatory arrest have a significant risk of an adverse neurologic event when the arrest period is prolonged. Retrograde cerebral perfusion appears to improve cerebral protection, although collapsed cortical veins or functional jugular venous valves may restrict flow at the frequently recommended maximum pressure of 25 mm Hg. Therefore, the purpose of this study was to demonstrate the benefit of multimodality neurophysiologic monitoring in assuring delivery of retrograde cerebral perfusion. METHODS: Electroencephalography, cerebral blood flow velocity, and regional cerebral venous oxygen saturation were used to quantify the intraoperative neurophysiologic changes accompanying retrograde cerebral perfusion. The magnitude of changes was compared with those previously observed during arrest without retrograde cerebral perfusion. RESULTS: Thirty patients underwent complex aortic procedures necessitating circulatory arrest, 22 with retrograde cerebral perfusion. The mean retrograde perfusion pressure of 40 mm Hg (30 to 49 mm Hg, 95% confidence interval) and flow rate of 1.2 L/min (0.9 to 1.6 L/min) necessary to achieve documented retrograde cerebral perfusion was much higher than previously recommended. During both retrograde cerebral perfusion and rewarming, cerebral oximetric monitoring guided adjustments in perfusion parameters to limit the rate of desaturation to 0.4% per minute (0.3% to 0.6%). With retrograde cerebral perfusion there was a rapid (1) recovery of electroencephalographic activity during rewarming (21 minutes [range 16 to 26 minutes]) and (2) return of consciousness after the operation (81% [58% to 95%, 95% confidence interval] awake by 12 hours). There was no transcranial Doppler evidence of cerebral edema with retrograde cerebral perfusion. Two neurologic complications occurred in the 22 patients managed with retrograde cerebral perfusion and one in the eight patients managed with arrest only. CONCLUSIONS: Multimodality neurologic monitoring assured optimal brain cooling and bihemispheric delivery of retrograde cerebral perfusion. Necessary retrograde pressure and flow were often higher than values previously reported. Avoidance of profound cerebral venous oxygen desaturation during retrograde cerebral perfusion and rewarming was associated with rapid recovery of neurologic function.

Adult↗
PubMed1997

Outcome effects of different protective hypothermia levels during cardiac arrest in rats.

BACKGROUND: Although hypothermia is widely used to protect the brain during cardiac and neurologic surgery, the optimal level of cooling has not been established. This study examined the protective effect of graded levels of surface cooling on cerebral function in rats after complete global cerebral ischemia. METHODS: Groups of ketamine-anesthetized rats (13 animals in each group) were cooled to cranial temperatures of 34, 30, 27, 24, or 22 degrees C before circulatory arrest. Also a normothermic (37 degrees C) group was tested. After cooling, an 11-min circulatory arrest was produced by atraumatic chest compression. Circulatory arrest was followed by cardiopulmonary resuscitation and rewarming without postischemic intensive care. On the fifth postinsult day, neurologic outcome was scored on a 50-point neurodeficit scale (NDS 0 = normal). The percent of ischemic pyramidal neurons in the CA1 hippocampal region was also determined. RESULTS: There were no survivors in the normothermic group. Neurologic recovery was enhanced with 30 degrees C cranial temperature, as compared to outcome in the 34 degrees C group. Further cooling did not change outcome. The neurodeficit scales were significantly lower in all other groups compared to the 34 degrees C group on the fifth postinsult day. The percent of ischemic neurons did not change significantly as a function of cooling, but the lowest count appeared at 27 degrees C. CONCLUSION: In this model, moderate (30 degrees C) cooling improved neurologic outcome. There was no additional benefit from more extreme hypothermia.

Animals↗
PubMed1996

Spinal cord and nerve root monitoring in spine surgery and related procedures.

Intensive research in the field of intraoperative neurophysiologic monitoring has been performed directed at finding reliable stimulating and recording techniques and adequate anesthetic regimes applicable to spinal procedures. The aim is a comprehensive monitoring not only of afferent and efferent spinal cord pathways but also of sensory and motor nerve roots and cauda equina fibers. Conventional somatosensory evoked potentials (SEPs) are complemented by motor evoked potentials, dermatomal sensory evoked potentials, spinal cord evoked potentials, evoked electromyography, sensory and motor fiber mapping of the cauda equina, bulbocavernosus reflex testing, and neurogenic evoked potentials. Apart from describing the essentials of these techniques and their indications and limitations, this article deals with the influence of anesthetic management on the production and interpretation of evoked potentials.

Humans↗
PubMed1996

Anticonvulsant activity of topiramate and phenytoin in a rat model of ischemia-induced epilepsy.

Topiramate, a structurally novel anticonvulsant, and phenytoin were evaluated in a rat model of ischemia-induced epilepsy. In this model a transient global cerebral ischemia is induced by cardiac compression. By precisely controlling the experimental conditions the procedure causes reproducible neurological deficits that include audiogenic epileptic seizures. The seizures can be broadly separated into three types reflecting the degree of severity: wild running, clonic seizures, and tonic extension seizures of the forelimbs and hindlimbs. Topiramate and phenytoin blocked all three types of seizures. Calculated ED50 values for topiramate 1 hr after oral administration were 8.2, 13.0 and 36.1 mg/kg for blockade of tonic extension seizures, clonic seizures and wild running, respectively. Corresponding ED50 values for phenytoin were 5.0, 10.8 and 20.7 mg/kg. These results support the concept that the anticonvulsant activity of these drugs is due primarily to an ability to block the spread of seizures.

Acoustic Stimulation↗
PubMed1996

The role of neuromonitoring in cardiovascular surgery.

This review describes the techniques currently used for quantitative neurophysiologic measurement during cardiac surgery and their potential impact on clinical outcome. Electroencephalography (EEG) characterizes cerebrocortical neuronal electrical activity and was part of some of the earliest cardiopulmonary bypass procedures, yet today it is not widespread use. Each of the common misunderstandings regarding a supposed limitation of this technology is explained. Its major genuine shortcoming, a lack of selectivity, may now be overcome with the combined use of additional monitoring modalities. The influence of intracranial hemodynamics on observed EEG changes may be determined continuously and noninvasively with transcranial Doppler (TCD) ultrasound. TCD provides an indication of sudden change in either blood flow or vascular resistance as well as the detection of emboli. In addition, the metabolic status of cortical neurons can be monitored by regional cerebral venous oxygen saturation (rCVOS) using noninvasive transcranial near-infrared spectroscopy. The % rCVOS tends to remain remarkably stable over a wide range of temperatures, perfusion pressures, and anesthetic states. Marked change in either direction signifies a serious imbalance between oxygen delivery and consumption. Measurement of rCVOS does not require blood flow, pulsatile or otherwise, so that it offers the only means of monitoring during circulatory arrest. By characterizing the dynamic interplay among cerebral hemodynamics, metabolism, and electrogenesis, these technologies permit the rapid detection and correction of potentially hazardous conditions.

Brain↗
PubMed1995

Auditory evoked responses in children during hypothermic cardiopulmonary bypass: report of cases.

Variations in core temperature and cerebral blood flow during open heart surgery may affect auditory brainstem responses (ABRs) and middle latency responses (MLRs) in both adults and children. We documented the changes in ABRs of two infants (ages 3 and 11 weeks, respectively) with variations in core temperature during hypothermic cardiopulmonary bypass and total circulatory arrest and compared them with those of a 19-year-old adult. Changes in MLRs that occurred in association with reductions in cerebral blood flow as monitored by transcranial Doppler are also reported in a 6-year-old child. With the reductions in temperature in both infants and the young adult, ABR latencies increased and amplitudes decreased. Effects of hypothermia on ABR latencies were completely reversed by rewarming. MLR amplitudes were transiently reduced during periods of normothermic hypoperfusion. Hypothermia partially prevented these changes, and normoperfusion after rewarming recovered MLRs. Monitoring ABRs and MLRs may be a useful technique for assessment of brain function during hypothermic cardiopulmonary bypass in children and infants.

Adult↗
PubMed1994

Auditory steady-state response, upper facial EMG, EEG and heart rate as predictors of movement during isoflurane-nitrous oxide anaesthesia.

We have studied the relationship between patient movement and changes in the auditory steady-state evoked potential, upper facial muscle electromyogram (FEMG), electroencephalographic-zero crossing frequency (EEG-ZCF) and heart rate during emergence from anaesthesia. Twelve healthy patients underwent surgery during stable isoflurane-nitrous oxide-oxygen anaesthesia without neuromuscular block. After skin closure, anaesthesia was discontinued abruptly while mechanical ventilation was continued until the patient moved. The magnitude of change in each physiological signal was evaluated in decibels (dB). Both the auditory steady state evoked potential and FEMG showed significant increases in amplitude during the last 5-min period before movement (6.1 and 10.7 dB, respectively). EEG-ZCF increased rapidly after anaesthesia was discontinued (2.5 dB) but there was no further increase in activity before movement. Heart rate did not change before movement. The use of the decibel transformation offers a promising method of displaying and interpreting changes in physiological variables during anaesthesia.

Adult↗