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Biomedical subjects

R J Porter

Publications and source records attributed to R J Porter.

At least 91 records · Page 5Linked to original sources
PubMed1983

Nonsedative regimens in the treatment of epilepsy.

Trends in the diagnosis of epilepsy have continued to focus on the fundamental cause of the seizures, as well as the seizure type. It is the latter that determines symptomatic therapy. New drugs have improved the lives of many epileptic patients, and emphasis on nonsedative medications, both new and old, is now possible and desirable in most patients. Finally, new and better drugs are needed for the many severely affected epileptic patients who are not helped by the currently available antiepileptic drugs.

Carbamazepine↗
PubMed1983

Petit mal status.

Petit mal status is a heterogeneous clinical syndrome of nonconvulsive status epilepticus. The EEG accompaniment is likewise heterogeneous. Petit mal status occurs at all ages. The characteristics of this syndrome are quite nonspecific and consist of (a) behavioral changes, usually associated with lethargy, slowness, and decreased mental function, (b) abnormal generalized continuous or nearly continuous epileptiform EEG activity, and (c) absence of gross tonic-clonic activity or highly lateralized clonic activity. These criteria do not distinguish petit mal status from complex partial status. Clinical evidence for abruptness of recovery and EEG evidence for localization are required for this distinction, an important factor in therapeutic decisions.

Adolescent↗
PubMed1982

Psychogenic seizures. A study of 42 attacks in six patients, with intensive monitoring.

Intractable complex partial seizures and seizures of unknown type were studied in 78 patients, six of whom were found to have psychogenic seizures. Evaluation by intensive monitoring included simultaneous six-hour telemetered EEG and videotape recordings and daily determination of plasma antiepileptic drug levels. Diagnosis was determined by assessment of four major criteria: deviation of seizures from characteristics of known seizure types, absence of epileptiform activity in the ictal EEG, absence of slowing in the postictal EEG, and relation of seizure frequency to decreasing plasma concentrations of antiepileptic drugs. No single criterion is sufficient for an unequivocal diagnosis of psychogenic seizures.

Adult↗
PubMed1982

Phenytoin: an inhibitor and inducer of primidone metabolism in an epileptic patient.

The interaction between primidone and phenytoin was studied in an epileptic patient treated with primidone only and primidone plus phenytoin for 3 months. Plasma and urine levels of drugs and metabolites were monitored daily by GC and GC-MS. The addition of phenytoin to the regimen increased steady-state plasma levels of phenobarbitone and phenylethylmalonamide (PEMA), metabolites of primidone, and decreased levels of primidone and unconjugated p-hydroxyphenobarbitone (p-OHPB), a metabolite of phenobarbitone. After withdrawal of phenytoin, plasma phenobarbitone and primidone levels slowly returned to previous steady-state levels, PEMA rapidly decreased to lower levels than before, and p-OHPB levels rose rapidly. Urinary excretion of primidone and its metabolites paralleled the changes in their plasma levels after the addition of phenytoin but the percentage of unconjugated p-OHPB in urine was unchanged during the course of the study. In conclusion phenytoin initially induces the conversion of primidone to PEMA and phenobarbitone, although each to a different extent, but it appears to inhibit the hydroxylation of phenobarbitone. Thus, two apparently contradictory phenomena seem to be involved in the primidone-phenytoin interaction. The net effect is an enhanced increase in plasma phenobarbitone levels.

Adult↗
PubMed1981

Visual evoked potentials and eye dominance.

The amplitudes of pattern-reversal VEPs in 25 healthy volunteers were significantly higher from the dominant eye than the non-dominant eye in right eye dominant subjects. The difference was present over both hemispheres and over the midline. Handedness did not appear to influence the amplitude asymmetry. A similar trend was noted in left eye dominant subjects, but the difference was significantly only at O2. The mean latency of the P100 peak was significantly shorter with stimulation of the dominant eye. These amplitude and latency disparities between dominant and non-dominant eyes provide electrophysiological evidence of lateralization in the nervous system.

Analysis of Variance↗
PubMed1981

Mechanism of valproate-phenobarbital interaction in epileptic patients.

Valproate effects on phenobarbital biodisposition were examined in a search for the mechanisms of the valproate-induced elevation of plasma phenobarbital during antiepileptic therapy. The study involved patients who were treated with phenobarbital alone and phenobarbital plus valproate. Several kinetic parameters were determined after a pulse dose of stable isotope-labeled phenobarbital, with plasma phenobarbital levels at a steady state. Plasma elimination of labeled phenobarbital was studied by selected ion monitoring. The addition of valproate to the phenobarbital regimen resulted in elevation of plasma phenobarbital and increase in urinary output of unchanged phenobarbital. There was no effect on urinary pH. The rise in plasma phenobarbital was paralleled by lengthening of phenobarbital elimination half-life while the decrease of plasma phenobarbital clearance paralleled the decrease in phenobarbital elimination rate constant. These findings suggest that inhibition of phenobarbital metabolism by valproate is the mechanism for this clinically important drug-drug interaction.

Adolescent↗
PubMed1981

The hospital experience and seizure control.

We studied 30 patients who were admitted to the hospital because of intractable seizures. Twenty-three had fewer seizures during one or both of the first 2 hospital weeks than before admission, although medication was not changed. The role of environment in seizure control is difficult to measure, but hospital admission itself is a form of environmental manipulation. When seizure control is achieved in the hospital, the hospital experience itself must be considered in addition to other therapeutic interventions.

Anticonvulsants↗
PubMed1980

Epileptiform ocular movements with methylmalonic aciduria and homocystinuria.

A 7 1/2-year-old girl with a rare defect in cobalamin (vitamin B12) metabolism ("cobalamin C" type) developed epileptiform ocular and eyelid movements as the major clinical manifestation of the disease. One of three other patients who have been described with congenital syndrome was similarly noted to have "fluttering" of the eyelids interpreted as epileptic discharges. The metabolic abnormality produced a defect in synthesis of cobalamin coenzymes. It is characterized biochemically by the excreation of methylmalonic acid and homocystine in the urine.

Child↗
PubMed1980

Speech-production measures of speech perception: rapid shadowing of VCV syllables.

Five listeners rapidly repeated ("shadowed") a random presentation of the vowel-consonant vowels (VCV's)/aba, apa, ama, aka, aga/. Initial vowel duration was varied to eliminate it as a temporal cue to the occurrence of the consonant. These shadowing, choice reaction times (RT's) were compared to simple RT's obtained when listeners always produced /aba/ or /ba/ to the same syllables. Both /aba/ and shadowing reactions were extremely fast (170 to 240 ms). Latency differences between the two tasks were attributable to differences in the point at which cues sufficient for responding were present. These results suggest that speech-perception decisions in shadowing are directly available to, and are perhaps made to occur at a point comparable to the consonantal release seen for the simple /aba/ responses. This result suggests that the motor organization required for a /ba/ response includes an implicit time interval appropriate for a consonantal closure.

Female↗
PubMed1980

Dichotic and monotic masking of CV's by CV second formants with different transition starting values.

Listeners were asked to identify ambiguous and unambiguous stop-vowel targets placed in monotic and dichotic competition with second formants (bleats) from voiced consonant-vowel (CV) syllables lying along a place-of-articulation continuum. Target performance varied with bleat-continuum position as well as bleat intensities. In cases where target errors occurred, either dichotically or monotically, they reflected predominantly the place cue of the bleat. This result, like that of previous studies, suggests the dominance of target or bleat reflects the relative "salience" of the two signals' cues. Differences were seen between monotic and dichotic conditions in the rate of change in performance with bleat intensity and continuum position. The rate of monotic performance change was a more precipitous (higher slope) function of these variables than was dichotic performance. This difference was interpreted as suggesting that monotic interference includes a peripheral masking component which is sensitive to the relative spectral energies of target and bleat. Dichotic effects, in contrast, seem to primarily reflect the operation of (central) processes which grant different perceptual weights to signals' cues depending on their intensity-dependent saliences. The observation that ambiguity, per se, of the targets (or the CV's from which the bleats were extracted) played little role in predicting results, was interpreted as reflecting a primarily prephonetic (i.e., auditory) locus for both monotic and dichotic interactions.

Humans↗
PubMed1980

The "Linguameter": a device for investigating tongue-muscle control.

A device we call a Linguameter is described. It allows measurement of subjects' abilities to position their tongues at points in the horizontal plane. Results with a prototype are reported for three tasks. All subjects could reproduce, bisect, and transpose arbitrary intervals with a very high degree of accuracy. This highly accurate normal performance, coupled with the sensitivity of the device, may make it of interest in studies of the oral or other sensory-motor system's normal functioning, as well as in investigations of sensory-motor pathology.

Humans↗