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Biomedical subjects

J K Brown

Publications and source records attributed to J K Brown.

At least 73 records · Page 4Linked to original sources
PubMed1994

Low birthweight: a 10-year outcome study of the continuum of reproductive casualty.

Disability rates among low-birthweight infants, particularly those related to congenital abnormality and cerebral palsy, are high. Both prenatal and perinatal factors are likely to be involved in the aetiology of most types of disability. IQ tends to be lower among low-birthweight infants, but does not appear to be closely related to birthweight alone. The confounding effect of social class should be considered when assessing aetiology and outcome. The long-term outcome for the increasing number of low-birthweight infants who survive and receive intensive neonatal care requires to be continually assessed; however, studies should not be confined to the very- and extremely-low-birthweight infant requiring prolonged intensive care, but should include abortions, stillbirths and neonatal deaths. As disability in survivors can relate to preterm birth but not perinatal complications, all low-birthweight infants require to be studied if selective bias is to be solved.

Case-Control Studies↗
PubMed1994

Assessment of spasticity in hemiplegic cerebral palsy. I. Proximal lower-limb reflex excitability.

The quadriceps and hamstring muscles of 13 children with hemiplegic cerebral palsy were studied using ramp and sinusoidal stretches at three different muscle lengths. Overall, the hamstring muscles showed greater velocity sensitivity than the quadriceps, with the hamstrings having the lowest reflex velocity and frequency thresholds close to maximum knee extension. At this position, the hemiparetic hamstrings alone showed a weakly significant reduced reflex frequency threshold compared with non-paretic muscles. For all other muscle lengths, non-paretic and hemiparetic muscles displayed similar reflex thresholds when subjected to sudden, discontinuous or repetitive rhythmical, sinusoidal stretches. The number of muscles for which a reflex threshold could be established declined progressively as the angle at the knee joint approached 90 degrees of flexion. Muscles for which no reflex threshold could be demonstrated had similar velocities and frequencies of stretch as those in which a reflex was obtained.

Biomechanical Phenomena↗
PubMed1994

Assessment of spasticity in hemiplegic cerebral palsy. II: Distal lower-limb reflex excitability and function.

A clinical method for measuring the stretch reflex threshold and gain of muscles acting across the ankle joint in children with congenital hemiplegia is described. The stretch reflexes of all limbs were velocity-dependent. Hemiparetic limbs were not necessarily spastic compared with non-paretic limbs, suggesting that the term 'spastic hemiplegia' should be used more selectively and emphasis be placed on the heterogeneity of the hemisyndromes of childhood. Abnormal motor control, planning and dexterity, the hemipostures and plastic (non-electrical) muscle changes may be more important measures of impairment than reflex excitability. A general scheme for assessing reflex excitability and available treatments applicable to all types of cerebral palsy is proposed.

Ankle Joint↗
PubMed1994

The use of therapeutic electrical stimulation in the treatment of hemiplegic cerebral palsy.

The effect of electrical stimulation of the anterior tibial muscles of children with hemiplegic cerebral palsy was studied. 10 children received electrical stimulation, applied by their parents daily for an hour for 35 days; they were compared with 10 matched controls. Active and passive ranges of movement of the ankle, and knee and ankle motion during walking were measured before and after therapy using electrogoniometers. The results showed a significant increase in passive range of movement among children receiving electrical stimulation. Gait analysis of knee and ankle motion showed little change.

Cerebral Palsy↗
PubMed1994

Alpha thalassaemia mental retardation (ATR-X): an atypical family.

A novel form of severe, X linked mental retardation associated with alpha thalassaemia (ATR-X syndrome) has recently been described. Two affected cousins are described, one of whom has an unusually mild haematological phenotype. HbH inclusions, which are the hallmark of this disease, were only detected in the peripheral red blood cells after repeated observations.

Adolescent↗
PubMed1994

Alpha-adrenergic and muscarinic cholinergic inhibition of ACh release in guinea pig trachea: role of neuronal K+ channels.

Our goals were to establish that an alpha 2-adrenergic agonist (clonidine) inhibits ACh release from airway nerve endings and to test effects of iberiotoxin (IBTX), an inhibitor of fast-conductance, Ca(2+)-activated K+ channels on alpha 2-adrenergic and muscarinic attenuation of ACh release. Guinea pig tracheas were mounted between electrodes in buffer containing indomethacin and neostigmine, and high-performance liquid chromatography with electrochemical detection was used to measure ACh release during electrical field stimulation. Clonidine inhibited ACh release in a concentration-dependent fashion [maximum reduction: 48 +/- 3%; 50% inhibitory constant (IC50): 0.1 microM], and idazoxan, alpha 2-adrenergic antagonist, reversed the effect. However, IBTX failed to alter clonidine-induced attenuation of ACh release. In contrast, IBTX did cause an increase in tracheal tension. In addition, IBTX failed to reverse any of the potent autoinhibitory effects of endogenous ACh. Our results confirm the presence of inhibitory alpha 2-adrenergic receptors. However, activation of IBTX-sensitive K+ channels does not appear necessary for either alpha 2-adrenergic or muscarinic cholinergic inhibition of ACh release.

Acetylcholine↗
PubMed1993

Heterogeneity of neurological syndromes in survivors of grade 3 and 4 periventricular haemorrhage.

To evaluate the topographical neurological distribution, patterns of abnormal tone and related functional neuromotor impairment after grade 3 and grade 4 intraventricular/periventricular haemorrhage (IPVH), 33 children with previous grade 3 or 4 IPVH of mean gestational age 30.9 weeks (range 25-40 weeks) and mean birth weight 1743 g (range 866-3600 g) were examined neurologically at 4.7 years (range 0.75-10.8 years). Neurological signs were absent in 10/33 cases which were equally distributed between the grade 3 and grade 4 IPVH groups. The largest single topographical neurological distribution was hemiparesis in 8/23, followed jointly by diplegia (cerebral paraplegia) in 6/23 and triplegia in 6/23 cases and finally quadriplegia in 3/23 cases. Grade 4 IPVH tended to result in asymmetrical syndromes, accounting for 7/8 cases of hemiparesis and 5/6 cases of triplegia, whereas all 3/3 cases of quadriplegia followed grade 3 IPVH. The 6/23 cases of diplegia were shared between the grade 3 and grade 4 IPVH groups. Tone was normal in 7/8 of the hemiparetic subjects. Dystonia was the commonest tone abnormality, affecting 8/23 children with neurological disturbance, followed by ataxia/hypotonia in 4/23 and mixed dystonia/hypotonia in 3/23. Only 1/23 cases had signs of spasticity. Spasticity is rare following severe IPVH. Diplegic children had a better functional neuromotor grade than hemiparetic children, who in turn did better than triplegic children. Ataxia hypotonia resulted in better functional outcome than dystronia, which in turn was more favourable than mixed tone patterns. Cranial imaging by ultrasound (US) or computed tomographic (CT) scanning proved an unreliable prognostic indicator except in the case of hemiparesis, for which US scans correctly predicted the affected side in 5/7 cases. The neurological syndromes following severe IPVH differ from the classical encephalopathy of prematurity, and this should lead to a re-appraisal of the trends in the prevalence of cerebral palsy. Caution should be exercised in the interpretation of cranial imaging with regard to pessimistic prognoses in the presence of changes or undue optimism in their absence.

Brain Damage, Chronic↗
PubMed1993

Quantitative, noninvasive assessment of antidiarrheal actions of codeine using an experimental model of diarrhea in man.

Enteric coating of a capsule has been used to deliver a bolus of radioisotope to the ileocecal region. This has allowed quantitative assessment of regional colonic transit in a group of healthy subjects whose proximal colonic transit was accelerated by lactulose 20 ml thrice daily. In this experimental model of diarrhea, codeine delayed transit from mouth to terminal ileum and also delayed transit through the ascending colon from 5.3 +/- 2.5 hr to 7.4 +/- 2.5 hr, N = 11, P < 0.05. Furthermore, codeine delayed whole colon transit, as assessed by geometric center analysis, which showed the delay to be most marked in the right colon with little effect noted in the left colon. In addition, codeine significantly reduced the number of retrograde movements observed and reduced the colonic response to eating. The antidiarrheal effect of codeine appears to be due to a combination of delayed mouth-cecum transit plus an additional delay in the ascending colon. This colonic delay may be partially explained by a reduction in postprandial propulsive movements that were seen in this model of diarrhea.

Adult↗
PubMed1993

Noise propagation in SPECT images reconstructed using an iterative maximum-likelihood algorithm.

The effects of photon noise in the emission projection data and uncertainty in the attenuation map on the image noise in attenuation-corrected SPECT images reconstructed using a maximum-likelihood expectation-maximization algorithm were investigated. Emission projection data of a physical Hoffman brain phantom and a thorax-like phantom were acquired from a prototype emission-transmission computed tomography (ETCT) scanner being developed at UCSF. Computer-simulated emission projection data from a head-like phantom and a thorax-like phantom were also obtained using a fan-beam geometry consistent with the ETCT system. The simulation assumed a 99Tcm source, included collimator blurring but ignored photon scatter. For each phantom, a region of interest (ROI) at the centre of the reconstructed image was chosen for the purpose of noise analysis. In all cases, the mean value (m) in the ROI approached a constant value after approximately 20 iterations. The standard deviation (sigma) generally increased with the number of iterations. The ratio (sigma/m) was found to be inversely proportional to the square root of the total detected counts and proportional to the relative uncertainty in the attenuation maps. These two noise components contributed independently towards the noise in the reconstructed image. In the ETCT system employing an x-ray tube for attenuation map acquisition, the uncertainty in the reconstructed radionuclide distribution is limited mainly by photon noise in the emission projection data. Our results are expected to be generally applicable to other emission-transmission systems, including those using external radionuclide sources for the acquisition of attenuation maps.

Algorithms↗
PubMed1993

N-type, omega-conotoxin-sensitive Ca2+ channels mediate electrically evoked release of ACh in guinea pig trachea.

To determine whether N- or L-type Ca2+ channels mediate acetylcholine (ACh) release from airway parasympathetic nerve endings, we compared the effects of omega-conotoxin (N-type inhibitor) and nifedipine (L-type inhibitor) on electrically evoked release of ACh in guinea pig trachea. Reconnected segments of guinea pig trachea were mounted in organ baths containing Krebs-Henseleit buffer, indomethacin (10 microM) to inhibit cyclooxygenase, neostigmine (1 microM) to inhibit acetylcholinesterase, and atropine (0.3 microM) to inhibit muscarinic autoreceptors, as well as phentolamine and propranolol to inhibit adrenergic receptors. After electrical field stimulation (EFS), aliquots of buffer were removed, and ACh was measured directly by high-performance liquid chromatography with electrochemical detection. Tracheas were stimulated for 10-min periods at a frequency of 5 Hz, and ACh release was measured for five separate periods (S1-S5) after treatment with increasing concentrations of omega-conotoxin or vehicle alone (acetic acid). Thirty minutes was allowed between stimulation periods. We found that EFS-evoked release of ACh was inhibited by omega-conotoxin in a concentration-dependent manner [mean effective concentration (EC50) approximately 8 nM] but was unaffected by vehicle treatment. In other experiments, ACh release was measured for two separate periods (S1 and S2), and between periods tracheas were treated with omega-conotoxin (1 microM), nifedipine (10-100 microM), tetrodotoxin (TTX), or buffer containing low (0.8 mM) Ca2+. ACh release was 12 +/- 2 (mean +/- SE) and 3 +/- 0.3 pmol.mg protein-1.min-1 before and during omega-conotoxin (n = 5, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

Gender, age, usual weight, and tobacco use as predictors of weight loss in patients with lung cancer.

The purpose of this study was to examine the relationships of gender, age, usual weight, and tobacco use with cancer-related weight loss, food intake, and resting energy expenditure. Data were collected from medical records, interviews, self-report diet records, indirect calorimetry, and 40K counting. A convenience sample consisted of 60 subjects with non-small cell lung cancer who were at least one month postradiotherapy. Mean weight loss was 2 kg at diagnosis and 6 kg at six weeks postradiotherapy. Partial correlations, controlling for stage of disease, indicated that gender, age, and current smoking correlate significantly with cancer-related weight loss and decreased food intake. Gender, age, and current smoking accounted for 21% of the variance of weight loss postradiotherapy over and above stage of disease. Potential practice implications focus on enhanced nutritional assessment and early intervention for men, the elderly, and current smokers, who are at higher risk for weight loss.

Activities of Daily Living↗
PubMed1993

Induction of micronuclei in peripheral blood lymphocytes of patients treated for rheumatoid or osteo-arthritis of the knee with dysprosium-165 hydroxide macroaggregates or yttrium-90 silicate.

The advantages of radiation synovectomy, using preparations containing dysprosium-165 (Dy-165), over conventional materials based on yttrium-90 (Y-90) include a more ideal spectrum of decay energies, and a much shorter half-life permitting quicker and more efficient treatment. A new therapeutic agent, Dy-165 hydroxide macroaggregates, has been developed for the treatment of arthritis making use of these advantages. As part of a clinical trial of this material 42 patients were examined for micronucleus frequency in their peripheral blood lymphocytes prior to, and 2 weeks after, radiation synovectomy using Dy-165 hydroxide macroaggregates or Y-90 silicate. In the majority of patients from each treatment group no significant increase in micronucleus frequency was observed. This indicates that in these cases leakage of material from the site of treatment was not resulting in detectable irradiation of circulating cells irrespective of the choice of radiopharmaceutical. The maximum increase in micronucleus frequency observed corresponded to a radiation dose to circulating cells of approximately 0.3 Gray.

Adult↗
PubMed1992

Neurological outcome following neonatal post-haemorrhagic hydrocephalus: the effects of maximum raised intracranial pressure and ventriculo-peritoneal shunting.

UNLABELLED: The neuromotor outcome of 33 survivors of grade 3 or 4 neonatal post-haemorrhagic hydrocephalus born between 1975 and 1988 was assessed at a mean age of 4.7 years (9 months to 13 years). Two outcomes were determined: 12 patients were either normal (10 or had neurological signs without functional impairments (2), while 21/33 were moderately (16), severely (2), or profoundly impaired (3). Intracranial pressure (ICP) was measured in 26/33 patients (4-40 mm Hg): 2 had normal pressures (< 5.6 mm Hg) and were normal. Raised ICP was not significantly different between outcome groups. Twenty-seven children were shunted; 10/27 had five or more operations (up to 14) and all of these had abnormal neurological outcomes, whereas the number of children with 1-4 shunt procedures was equal in both outcome groups. The rise in morbidity after the fourth shunt procedure may be associated with the ventriculitis suffered by 9 of the 10 patients with more than four shunts (P < 0.01): this compares with 4/14 cases of ventriculitis in the children with 2-4 shunts and no cases of infection in the 3/27 who were shunted once. Outcome was independent of antenatal and perinatal factors including the age at or mode of presentation, and was unrelated to grade of intraventricular haemorrhage or parenchymal changes on ultrasound or CT scanning. CONCLUSION: for these small numbers, adverse outcome is statistically related to more than four shunt procedures and ventriculitis but independent of maximum ICP or other perinatal factors.

Birth Weight↗
PubMed1992

Peripheral and central mechanisms of hindfoot equinus in childhood hemiplegia.

A detailed clinical examination of 24 hemiplegic children at a mean age of 9.9 years showed that nine had an obligate toe-strike when walking at a self-selected speed and this was maintained throughout stance. None of the 24 children had a fixed equinus. No association could be found between this pattern of gait equinus and lower-limb atrophy, reduced ankle-joint range, muscle extensibilite, power of dorsiflexors and plantarflexors or actual muscle imbalance at the ankle joint. Gait equinus was independent of reduced compliance of the calf muscles, of a clinical diagnosis of tonic spasticity, of fine-motor dexterity of the toes, and of the side of the hemiplegia. Gait equinus cannot be explained merely in terms of a central paralytic foot-drop. A developmental model of equinus is advanced.

Ankle Joint↗