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Biomedical subjects

R F Ghaly

Publications and source records attributed to R F Ghaly.

26 records · Page 2Linked to original sources
PubMed1990

The effect of nitrous oxide on transcranial magnetic-induced electromyographic responses in the monkey.

Transcranial magnetic stimulation (TMS) to produce motor evoked potentials (MEPs) is a newly developed intraoperative modality to monitor functional integrity of the motor pathways. The present study was designed to examine the reliability of magnetic MEP recording under nitrous oxide (N2O) inhalation. Following ketamine injection (10 mg/kg i.m.) and endotracheal intubation, 16 monkeys were exposed to N2O:O2 mixture ratios 1:3, 1:1, and 3:1. Electromyographic (EMG) responses, evoked by pulsed magnetic fields applied extracranially to the scalp zone overlying motor cortex, were recorded from the contralateral fore- and hind limb flexor muscles. The scalp topography zone for contralateral muscle excitation was markedly reduced by 75 vol% N2O. Significant stimulation threshold elevation, latency prolongation, and amplitude depression were noted after inhalation of 75 vol% N2O (p <0.05) compared with </=50 vol% N2O inhalation. The mean range of brain stimulation rise was 1%, 7-8%, and 13-20%, and MEP latency delay was 3%, 3-6%, and 7-11% on exposure to 25%, 50%, and 75 vol% N2O, respectively. The mean amplitude response first increased by 20% and 7% with 25% and 50% N2O, respectively, and then reduced by 60% with 75 vol%. We conclude that, in a primate model, while magnetic MEPs could reliably be recorded under 25-75% N2O, the evoked motor responses were least affected by </=50 vol% inhalation. Knowledge of N2O-induced MEP alteration is essential when interpreting the response change while using this agent.

Journal Article↗
PubMed1990

Transtentorial brain herniation in the monkey: analysis of brain stem auditory and somatosensory evoked potentials.

A monkey model of transtentorial brain herniation (TBH) was created to simulate the clinically encountered situation of a gradually expanding intracranial lesion. TBH was produced by extradural balloon inflation over a 4-hour period and documented by the appearance of the pupils as dilated or fixed at midposition. Intracranial pressure (ICP), brain stem auditory evoked potentials (BAEP), and short-latency somatosensory evoked potentials (SSEP) were recorded before, during, and after TBH. Statistical significance from baseline values to TBH was found for diminution of the BAEP amplitude, rise of the ICP, and diminution of the SSEP amplitude. An ICP rise to twice the baseline value and a 25% decrease in Wave V amplitude was found 1 hour before TBH. Changes in BAEP and SSEP took several minutes after deflation to return to baseline values. Analysis of Wave V of the BAEP was as sensitive as ICP in warning of TBH. Discussion centers upon previous animal studies of brain herniation and ICP elevation, and findings reported in humans deteriorating as a result of intracranial mass lesions. BAEP and SSEP monitoring may be used as noninvasive tests for brain stem compression in the setting of primate TBH, and in the future may be used to guide the effectiveness of therapy.

Animals↗
PubMed1988

Electroencephalography in acute head injury.

The established uses of standard and computerized EEG in acute head injury are outlined. Emphasis is placed on EEG correlation with level of consciousness, rostrocaudal deterioration, brainstem lesions, and prognosis. The utility of the standard EEG in seizures and toxic metabolic states accompanying severe head injury is also discussed.

Brain↗
PubMed1988

Evoked potentials in head injury and states of increased intracranial pressure.

Recent clinical studies have addressed the utility of sensory evoked potentials (auditory, somatosensory, and visual) in head injury. The clinical significance of evoked potentials in head trauma, states of increased intracranial pressure, and post-traumatic syndrome is discussed. Emphasis is placed on up-to-date studies discussing evoked potential correlation with clinical findings, lesion localization, intracranial pressure, brain herniation, and prognosis.

Brain↗
PubMed1987

Modified auditory brainstem responses (MABR): Part I--Rationale and normative study.

Binaural, rapid rate, ABR stimulation at four intensity levels (MABR) as well as ABR at two intensity levels were carried out in 35 normal subjects. Latency and amplitude relationship with stimulus intensity of wave V of the MABR was extensively studied in these subjects. MABR recording is a rapid, sensitive, non-invasive screening method readily done at the intensive care bedside. Less than 10 minutes is required in addition to the ABR examination time. Normality of the MABR potentials implies a high degree of peripheral auditory and brainstem functional integrity, augmenting information gained with standard ABR technique. Only clinical trials can decide if MABR sensitivity will exceed that of the ABR and prove helpful to diagnosis and patient care.

Acoustic Stimulation↗
PubMedDate not supplied

A comparative analysis of enflurane anesthesia on primate motor and somatosensory evoked potentials.

The effect of increasing enflurane concentration on magnetic-induced myogenic cranial (Cr) and peripheral (Pr) motor evoked potentials (MEPs), and electrically induced median (MN) and posterior tibial (PTN) somatosensory evoked potentials (SEPs) was studied in 10 monkeys. MEP, recorded from abductor pollicis brevis and abductor hallucis muscles, and SEP (short- and long-latency scalp recorded potentials) variables were examined at 0.25, 0.5, 0.75, 1.0 MAC enflurane concentrations. Cr-MEPs progressively attenuated (P less than 0.01) with 0.25 MAC and were abolished (greater than or equal to 0.75 MAC) by graded enflurane concentration. Stimulation threshold for Cr-MEP was progressively elevated (P less than 0.01), and eventually reliable responses were lost (greater than or equal to 0.75 MAC). Marked scalp zone reduction to obtain Cr-MEP responses was noted with increasing enflurane concentration. Pr-MEPs and most SEP peaks maintained good replicability but showed significant amplitude reduction (P less than 0.01). MEP and SEP latency values were not significantly delayed as long as the wave form remained identifiable. We conclude that enflurane has a differential influence on Cr-MEPs and SEPs. Administration of enflurane should be discouraged while monitoring myogenic Cr-MEPs since even a subanesthetic concentration is profoundly detrimental.

Analysis of Variance↗