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Biomedical subjects

G Novak

Publications and source records attributed to G Novak.

At least 19 recordsLinked to original sources
PubMed1998

Effects of clozapine on auditory event-related potentials in schizophrenia.

BACKGROUND: Schizophrenia is associated with cognitive deficits that are an intrinsic component of the disorder. Clozapine is an atypical antipsychotic that is superior to typical agents in the treatment of positive symptoms. The degree to which clozapine ameliorates cognitive deficits, however, is still controversial. Mismatch negativity (MMN), N200 (N2), and P300 (P3) are cognitive event-related potentials (ERPs) that index preattentive (MMN) and attention-dependent information processing (N2, P3) and provide a measure of cognitive deficits associated with schizophrenia. In schizophrenic patients deficient generation of MMN, N2, and P3 has been observed, suggesting impairments of discrete stages of information processing. METHODS: This study investigates the effects of clozapine treatment on MMN, N2, and P3 generation. Patients were recruited from a haloperidol-controlled, double-blind treatment study of clozapine in chronic schizophrenia. ERPs were obtained at the beginning of the study and after 9 weeks (4 patients) and 16 weeks (13 patients) of treatment. RESULTS: Clozapine treatment was associated with a significant increase of P3 amplitude, which was not observed in the haloperidol group; however, clozapine treatment did not affect deficits in MMN and N2. CONCLUSIONS: These findings suggest that clozapine--in contrast to conventional antipsychotics--improves electrophysiological measures of attention-dependent information processing, but does not ameliorate preattentive deficits.

Adult↗
PubMed1997

Risk factors for status epilepticus in children with symptomatic epilepsy.

The purpose of this study was to determine risk factors for status epilepticus (SE) in children with symptomatic epilepsy through a retrospective case-control study. Patients (44 children with a prior diagnosis of symptomatic epilepsy experiencing one or more episodes of SE between January 1, 1991, and June 1, 1995) were matched for age at follow-up to controls (88 children with symptomatic epilepsy without SE during that interval) and medical records were reviewed. Patients and controls did not differ in etiology or in age at epilepsy onset (1 year 5 months [SD, 2 years 3 months] versus 1 year 3 months [SD, 1 year 5 months]). Univariate analysis revealed significant associations between SE and several factors, including history of a first seizure as SE, partial epilepsy, partial seizures with secondary generalization, focal paroxysmal abnormalities and focal background abnormalities on EEG, and generalized abnormalities on neuroimaging. Groups did not differ in the proportion of patients on polypharmacy or with subtherapeutic serum antiepileptic drug levels, but there was a trend for greater use of phenobarbital in patients (57% versus 38%, odds ratio (OR) = 2.6, p = 0.057). With multiple logistic regression, four factors emerged as independent predictors of SE risk: focal background EEG abnormalities (OR = 6.51, p = 0.0005), partial seizures with secondary generalization (OR = 4.61, p = 0.0021), first seizure as SE (OR = 3.99, p = 0.034), and generalized abnormalities on neuroimaging (OR = 2.85, p = 0.034). These four factors are indicators of a higher risk of SE in children with symptomatic epilepsy.

Case-Control Studies↗
PubMed1996

Status epilepticus in children with epilepsy: the role of antiepileptic drug levels in prevention.

OBJECTIVES: To determine the association between subtherapeutic antiepileptic drug (AED) levels or AED withdrawal and status epilepticus (SE) in children with epilepsy. METHODS: We studied the AED levels at the time of SE in 51 consecutive children with epilepsy. Information about prior AED levels, possible etiology of seizures, and acute precipitants was extracted from medical records. RESULTS: The mean age at the time of SE was 5.7 years (range, 3 months through 18 years). Forty-three patients had history of remote insult, five had history of progressive encephalopathy, and three patients were classified as idiopathic. At the time of SE all AED levels were therapeutic in 34 (66%) patients and at least one level was therapeutic in 42 (82%) patients. All levels were subtherapeutic in 9 (18%) patients. Four patients had their AED reduced or discontinued less than 1 week before SE. Twelve patients with therapeutic AED levels on their most recent clinic visit had at least one subtherapeutic level at the time of SE. Eight (16%) patients were febrile and one was hyponatremic. Of the 51 patients, 31 (61%) had no obvious explanation for the development of SE, as all known AEDs were therapeutic and there were no known acute insults. CONCLUSIONS: Neurologically abnormal children with preexisting epilepsy are at high risk for development of SE despite having therapeutic AED levels at that time. Acute precipitants of SE, such as fever or AED withdrawal, may play a role in inducing SE only in a minority of patients.

Adolescent↗
PubMed1995

Isoperistaltic jejunal interposition for intractable postgastrectomy alkaline reflux gastritis.

BACKGROUND: The Roux-en-Y gastrojejunostomy is a popular method in the operative treatment of alkaline reflux gastritis and other postgastrectomy sequelae, but is associated with a high incidence of the so-called "Roux stasis syndrome." The Henley jejunal interposition has been used occasionally, albeit not widely, as an alternative to the Roux-en-Y reconstruction. STUDY DESIGN: Six patients underwent Henley gastrojejunoduodenostomy to treat severe (Visick grade IV) symptoms following Billroth I and II procedures for peptic ulcer disease. All interposed jejunal segments were 40 cm in length and isoperistaltic in orientation. All patients had follow-up examination and telephone interview (mean 4.3 years, range 2.2 to 7.8 years). RESULTS: All patients noted dramatic improvement after remedial surgery in the first year of follow-up. After the first postoperative year, all patients remained virtually symptom-free (Visick grade I and II) with no complaints of gastrojejunal stasis or bile acid reflux. CONCLUSIONS: This experience suggests that the Henley jejunal interposition is our effective method of treating reflux gastritis and is not associated with the poor emptying frequently associated with the Roux-en-Y reconstruction.

Adult↗
PubMed1992

Mismatch detection and the latency of temporal judgements.

Event-related potentials were recorded in two auditory tasks involving the discrimination of pitch or duration of binaurally presented tones. Frequently-presented nontarget tones, when compared to the same tones in a simple reaction time task, elicited two negative peaks, NA1 and NA2, followed by a positive peak, nontarget positivity. Infrequently-presented target tones, when compared to the nontargets, elicited mismatch negativity (MMN), followed by N2 and P3b. The peak latencies of NA1 and NA2 did not differ between the pitch and duration tasks, but the duration of NA1 and the peak latencies of mismatch negativity, N2, and P3b, as well as reaction time, increased in parallel for the duration task. It is proposed that the NA1-nontarget positivity sequence reflects the initiation, maintenance, and termination of an attention-modulated process, which is required for the performance of an auditory discrimination task, and that the MMN-N2-P3b sequence reflects a process elicited by infrequently-presented targets, which is the main determinant of reaction time under these testing conditions.

Adult↗
PubMed1992

The chronometry of attention-modulated processing and automatic mismatch detection.

Event-related potentials were recorded from normal subjects in an auditory selective attention task. Targets were rare longer (170-ms) tones of a designated pitch, embedded in a sequence of 100-ms standard tones. The effects of attention-modulated processing were evident in the event-related potentials elicited by the standards. Those to relevant standards were similar for easy (1000 Hz vs. 2000 Hz) and hard (1000 Hz vs. 1030 Hz) pitch separations, and were more negative frontocentrally than those to irrelevant standards. Difference waveforms (attended minus unattended standards) revealed Nd, a negative deflection that was earlier in latency for the easy task (onset, 120 ms; peak, 250 ms) than for the hard task (onset, 250 ms; peak, 350 ms). The speed of detection of the deviant longer tones was insensitive to the attention-modulated processes indexed by Nd. Median reaction time did not differ between tasks, although there were more misses and false alarms in the hard task (and nearly all of the latter were to the irrelevant longer tones). Neither direction of attention nor task difficulty affected the latency of mismatch negativity, N2, or P3 (as identified in difference waveforms: attended or unattended longer tones minus their respective standards). The data suggest that performance was guided by two independent but converging processes, automatic mismatch detection of the longer tone and attention-modulated processing of pitch, followed by selection of response.

Adult↗
PubMed1981

A comparison of carbon-fiber and aluminum front plates in rapid film changers.

The radiation transmission characteristics of 2-mm-thick aluminum front plates and 2-mm-thick carbon-fiber-reinforced plastic front plates for rapid film changers were compared. While the carbon-fiber plates were found to be intrinsically more radiolucent than the aluminum plates, the decrease in patient exposure with the carbon-fiber plates was only approximately 25%. No measurable differences in image quality were observed in carefully controlled experiments on the two types of front plates.

Aluminum↗
PubMed1979

Plasmacytoma of the stomach.

A case of gastric plasmacytoma is presented. A detailed study including a selective angiogram described this unusual gastric neoplasm. Pathological examination by both light and electron microscopy confirmed the diagnosis of primary gastric plasmacytoma. The diagnosis and treatment of primary gastric plasmacytoma is discussed and pertinent literature is reviewed.

Aged↗
PubMed1978

Morphologic sequelae to contrast medium deposits in the kidney. An experimental investigation in the rabbit.

Various doses of Pantopaque and Vascoray were injected percutaneously into the kidneys in 17 rabbits. Histologic examination of the kidneys at different time intervals following the injection demonstrated only slight injury to the renal parenchyma which could be related to the contrast media. Therefore, it seems reasonable to assume that the risk of causing renal damage by using Pantopaque in connection with renal cyst puncture is small.

Animals↗
PubMed1977

The production of cerebrospinal fluid in experimental communicating hydrocephalus.

Utilizing an atraumatic model to produce chronic hydrocephalus, CSF production was measured during and after development of communicatin hydrocephalus. CSF volume production was significantly lower in animals with increased pressure. Animals with chronic hydrocephalus and normal pressures had abnormal CSF production. Diminished CSF production appears to offer a potential compensatory mechanism when CSF absorption is altered.

Animals↗
PubMed1977

Evaluation of cerebrospinal fluid production in the development of communicating hydrocephalus.

Diminished absorption of cerebrospinal fluid (CSF) is the most common cause of communicating hydrocephalus. Soon after the absorptive capacity is decreased, the CSF pressure increases, producing ventricular enlargement if the process is not halted. CSF production was measured by ventriculo-cisternal perfusion during and after the production of communicating hydrocephalus, using an atraumatic animal model. Animals with chronic hydrocephalus and normal pressure had normal CSF production. CSF production tended to be lower in animals with increased pressure. When CSF absorption is compromised, decreased CSF production does not appear to be a significant compensatory mechanism.

Acute Disease↗
PubMed1976

The use of diagnostic ultrasound in evaluation of the abdomen in primates with emphasis on the rhesus monkey (Macaca mulatta).

To characterize the sonographic appearance of the abdominal organs in primates, a program of routine imaging and diagnostic evaluation was undertaken. Compound B-mode methodology with bistable and grey scale machines was employed utilizing a 2.25- to 3.5-MHZ transducer focused at 7 cm. Visualization of the liver, gallbladder, spleen, kidney and of intraabdominal pathology are described. The stage, position, and condition of a pregnancy can be determined by this methodology.

Abdomen↗