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Biomedical subjects

P Brown

Publications and source records attributed to P Brown.

At least 145 records · Page 8Linked to original sources
PubMed2000

Amino acid homologies between human biotinidase and bacterial aliphatic amidases: putative identification of the active site of biotinidase.

A search of protein databases revealed amino acid homologies among human biotinidase, bacterial aliphatic amidases, and bacterial and plant nitrilases. Amino acids YRK(210-212) of biotinidase are conserved among the enzyme families. This homology and naturally occurring mutations that cause biotinidase deficiency suggest that this region is essential for enzyme activity and is conserved from bacteria. Cys(245) is likely the cysteine in the active site of biotinidase.

Amidohydrolases↗
PubMed2000

Electron microsocopy of brain amyloid plaques from a patient with new variant Creutzfeldt-Jakob disease.

Cerebral cortex biopsy from a patient with new variant Creutzfeldt-Jakob disease (nvCJD) has been examined at the electron microscope level. Spongiform changes corresponded mostly to distended neurites scattered in the neuropil or surrounding amyloid plaques. These latter exhibited heterogeneous submicroscopic morphology including variable amount of loosely interwoven amyloid fibrils admixed in a cellular-rich environment constituted essentially by abnormal neuronal processes. By immunoelectron microscopy, fibrils and some membrane structures reacted with anti-prion protein (PrP) antibodies. One striking aspect was the presence of many small dystrophic neurites without paired helical filaments. Moreover, amyloid fibrils showed unexpected intimate association with abnormal membranes, suggesting a relationship between PrP fibrillogenesis and membrane alteration. These ultrastructural findings provide an additional criterion to distinguish nvCJD-from sporadic CJD-type plaques and reinforce the hypothesis that nvCJD brain is infected by a distinctive strain of the transmissible agent encephalopathy.

Adult↗
PubMed2000

Cortical drives to human muscle: the Piper and related rhythms.

During voluntary activity in humans, motor units are exposed to a number of descending drives that tend to synchronize motor unit activity at particular frequencies. In particular, the contralateral motor cortex drives muscle discharge in the beta (15-30 Hz) and Piper (30-60 Hz) bands. The cortical activity in these bands is task-specific, somatopicly distributed and generally precedes muscle discharge by an interval appropriate for conduction in fast pyramidal pathways. Coherence between cortex and muscle in the beta band is found during isometric contractions of weak to moderate strength. Thus oscillations within the beta band seem to coincide with a stable, relatively immutable state--a free running mode of the motor cortex that may maintain stable motor output with a minimum of computational effort. In contrast, coherence between cortex and muscle in the Piper band is most evident during strong isometric contractions or during movement. Demands on the motor cortex are likely to be greater and more mutable under these circumstances. Synchronisation in the gamma band may provide a means of binding together those particular, often spatially distributed, cortical elements involved in movement execution under conditions that vary from moment to moment and require some attention. Mechanisms both intrinsic and extrinsic to the cortex determine the pattern of rhythmic cortical activity. The basal ganglia have a pivotal role in this regard, and inadequate output from these nuclei leads to a disappearance of the beta and Piper drives to muscle. This may in turn contribute to slowness and weakness in Parkinson's disease.

Animals↗
PubMed2000

Phase relationships between cortical and muscle oscillations in cortical myoclonus: electrocorticographic assessment in a single case.

AIM: To compare voluntary- and sensory-induced myoclonic jerks using spectral analysis in a subject with cortical myoclonus. METHODS: The coherence, phase and cumulant density estimates were calculated between right electrocorticographic (ECoG) signals and distal left leg muscles in a patient with subdural electrodes inserted over the right sensorimotor cortex. RESULTS: Significant coherence between sensorimotor cortex and muscle was found up to 60 Hz during voluntary induced myoclonic jerks. Additional higher frequency coherence ( approximately 140 and 190 Hz) was found during sensory-induced myoclonic jerks. The cortical signals phase led muscle signals at frequencies >15 Hz by delays consistent with transmission along corticospinal pathways. Below 15 Hz the cortex phase lagged the muscle signals. Polarity reversal of the cumulant density estimate and the ECoG site demonstrating the highest coherence helped to localize the site of the abnormal oscillatory activity to the leg area of the motor cortex. CONCLUSIONS: Oscillations of different frequencies can co-exist at a given location and can both phase lead and lag contralateral muscle. This has implications for cortex-muscle latency measures calculated by back-averaging techniques.

Aged↗
PubMed2000

Contrast echocardiography is superior to tissue harmonics for assessment of left ventricular function in mechanically ventilated patients.

BACKGROUND: Assessment of left ventricular function by echocardiography is frequently challenging in mechanically ventilated patients. We evaluated the potential value of contrast-enhanced imaging and tissue harmonic imaging over standard fundamental imaging for endocardial border detection (EBD) in these patients. METHODS AND RESULTS: Fifty patients underwent standard transthoracic 2D echocardiography and were imaged in fundamental and tissue harmonic modes and subsequently with intravenous contrast (Optison). Two echocardiographers reviewed all studies for ease of visualization of endocardial border segments and scoring of wall motion. EBD for each wall segment was graded from 1 to 4 (1 = excellent EBD). Wall motion was scored by a standard 16-segment model and 1 to 5 scale. Studies were categorized as nondiagnostic if 4 of 6 segments in the apical 4-chamber view were either poorly seen or not seen (EBD score 3 or 4). Quantification of ejection fraction was independently performed offline. Visualization of 68% of all segments improved with contrast echocardiography versus 17% improvement with tissue harmonics compared with fundamental mode. Significant improvement (poor/not seen to good/excellent) occurred in 60% of segments with contrast echocardiography versus 18% with tissue harmonics. A total of 850 segments were deemed poor/not seen, 78% of which improved to good/excellent with contrast echocardiography versus 23% with tissue harmonics. Interobserver agreement on EBD was 64% to 70%. Conversion of nondiagnostic to diagnostic studies occurred in 85% of patients with contrast echocardiography versus 15% of patients with tissue harmonics. Scoring of wall motion with fundamental mode, tissue harmonics, and contrast echocardiography was possible in 61%, 74%, and 95% of individual segments, respectively (P <.001). Wall motion scoring was altered in 17% of segments with contrast echocardiography and in 8% with tissue harmonics. Interobserver agreement on wall motion scoring was 84% to 88%. Contrast echocardiography permitted measurement of ejection fraction 45% (P =.003) more often over fundamental mode versus a 27% (P =.09) increase with tissue harmonics. CONCLUSIONS: Contrast echocardiography is superior to tissue harmonic imaging for EBD, wall motion scoring, and quantification of ejection fraction in mechanically ventilated patients.

Adult↗
PubMed2000

Frequency analysis of EMG activity in patients with idiopathic torticollis.

The pathophysiology of idiopathic dystonic torticollis is unclear and there is no simple test that confirms the diagnosis and excludes a psychogenic or voluntary torticollis in individual patients. We recorded EMG activity in the sternocleidomastoid (SCM) and splenius capitis (SPL) muscles of eight patients with rotational torticollis and eight age-matched controls, and analysed the signals in the frequency and time domains. All control subjects but one showed a significant peak in the autospectrum of the SPL EMG at 10-12 Hz, which was absent in all patients with torticollis. Conversely, patients with torticollis had evidence of a 4-7 Hz drive to the SPL and SCM that was absent in coherence spectra from controls. The pooled cumulant density estimates revealed a peak in both groups, and within the patient group there was a second narrow subpeak with a width of 13 ms. The activity in the SCM and SPL was in phase in the patients but not in the controls. The lack of any phase difference and the suggestion of short-term synchronization between SCM and SPL are consistent with an abnormal corticoreticular and corticospinal drive in dystonic torticollis. Clinically, the pattern of SPL EMG autospectra and of SCM-SPL coherence may provide a sensitive and specific feature distinguishing dystonic from psychogenic torticollis.

Electromyography↗
PubMed2000

Coherence between cerebellar thalamus, cortex and muscle in man: cerebellar thalamus interactions.

Local field potentials (LFPs) were recorded in seven unanaesthetized patients between the four adjacent contacts of a macroelectrode stereotactically implanted for the treatment of tremor. The LFPs were presumed to arise predominantly from the nucleus ventralis intermedius (Vim) of the thalamus, the implantation target. They were recorded simultaneously with the ipsilateral EEG and contralateral EMG during an isometric contraction or at rest. The patients had a history of either isolated tremor (essential tremor, n = 2; benign tremulous Parkinson's disease, n = 1) or tremor with signs of a cerebellar syndrome (multiple sclerosis, n = 3; essential tremor and ataxia, n = 1), although clinical tremor was absent at the time of recording because of a temporary microthalamotomy effect in four patients. In patients with isolated tremor, oscillatory activity picked up by contacts in Vim (cerebellar thalamus) was invariably coherent with that in the sensorimotor cortex or contracting muscle in the 8-27 Hz range. Such coherence was absent in two of the four subjects with tremor associated with a cerebellar syndrome. Coherence between LFPs recorded from more caudally placed contacts and the sensorimotor cortex or contracting muscle was negligible in all patients. These caudally placed contacts demonstrated the highest sensory evoked potential in response to median nerve stimulation. Oscillatory activity in the cerebellar thalamus (Vim) lagged behind that in both cortex and muscle. Coherent activity between the cerebellar thalamus (Vim) and the cortex persisted at rest. It is suggested that rhythmicities in the 8-27 Hz range could provide the basis for a temporal framework that is widely distributed within the motor system.

Aged↗
PubMed2000

Prevalence of celiac disease in Down syndrome in the United States.

BACKGROUND: Numerous studies in Europe have documented a high prevalence of celiac disease in Down syndrome. This study was undertaken to estimate the prevalence of celiac disease in Down syndrome in the southeastern United States. METHODS: Seventy-five patients with Down syndrome were screened using immunoglobulin (Ig)A-anti antiendomysium antibodies, IgA-antigliadin antibodies, and total IgA level. When either antiendomysium or antigliadin antibodies produced positive findings, patients were referred to a pediatric gastroenterologist for consideration of a duodenal biopsy. RESULTS: Thirteen percent (10/75) were positive for antiendomysium antibodies. Half of these patients were also positive for antigliadin antibodies. Six of 10 patients positive for antiendomysium antibodies underwent intestinal biopsy. Changes consistent with celiac disease were documented in five. Histologic findings ranged from focal to total villous atrophy. None had IgA deficiency. CONCLUSIONS: There was a high prevalence of positivity to antiendomysium antibody in Down syndrome. Antiendomysium antibody was a more sensitive screening test than antigliadin antibody. The prevalence of celiac disease in Down syndrome in the southeastern United States was 1 in 14 cases. Screening with antiendomysium antibody and IgA for all children with Down syndrome is recommended, even if there are no gastrointestinal symptoms.

Adolescent↗
PubMed2000

Medical management of gastroesophageal reflux.

Gastroesophageal reflux (GER) is a common problem which can manifest as vomiting, failure to thrive, recurrent pneumonias, asthma, sinusitus, or subglottic stenosis. The medical management plan should be individualized. A "happy spitter" who has no complications of GER may respond well to conservative management, including positioning and thickening of feedings. A child with complications may require treatment with H-2 antagonists or proton pump inhibitors in conjunction with prokinetic agents. Children with gastrointestinal symptoms suggestive of GER who do not respond to antireflux management may need to be treated for eosinophilic esophagitis. Recent studies that assess the effect of medications on recognized complications of GER are reviewed.

Anti-Ulcer Agents↗
PubMed2000

An ambulatory dyskinesia monitor.

OBJECTIVES: New treatments are now becoming available for the management of levodopa induced dyskinesias in Parkinsons's disease. However, assessment of their efficacy is limited by the inadequacies of current methods of dyskinesia measurement. The objective was to develop and validate a portable device capable of objectively measuring dyskinesias during normal daily activities. METHODS: A portable device was developed based on a triaxial accelerometer, worn on the shoulder, and a data recorder that can record levodopa induced dyskinesias. A computer program plots raw acceleration and acceleration over 0.5 Hz frequency bands against time. The acceleration in the different bands can then be compared with the raw acceleration trace, enabling identification and exclusion of confounding activities such as tremor and walking, which have a characteristic appearance on the trace. The validity of this device was assessed on 12 patients and eight age matched controls by comparing accelerations in the 1-3 Hz frequency band with established clinical dyskinesia rating scales. While wearing the monitor, subjects were videorecorded sitting and during dyskinesia provocation tasks, including mental activation tasks, eating, drinking, writing, putting on a coat, and walking. The dyskinesias were graded with both modified abnormal involuntary movement (AIM) and Goetz scales. The clinical ratings were then compared with the mean acceleration scores. RESULTS: Acceleration in the 1-3 Hz frequency band correlated well against both scales, during all individual tasks. Acceleration produced by normal voluntary activity (with the exception of walking, which produced large accelerations, even in controls) was small compared with dyskinetic activity. With walking excluded, the mean acceleration over the rest of the recording time correlated strongly with both the modified AIM (Spearman's rank (r=0.972, p<0.001) and Goetz (r=0.951, p<0.001) scales. CONCLUSIONS: This method provides an accurate, objective means for dyskinesia assessment, and compares favourably with established methods currently used.

Adult↗