Biomedical subjects

M Green

Publications and source records attributed to M Green.

At least 1,027 records · Page 57Linked to original sources

PubMedDate not supplied

Parallel pathways, noise masking and glaucoma detection: behavioral and electrophysiological measures.

PURPOSE: We tested the hypothesis that because of their reduced neural efficiency, glaucoma patients should have increasingly impaired thresholds as external noise is added to a stimulus. METHOD: We compared the performance of 20 normals (mean age = 39 years) with that of 15 patients with early glaucoma or at very high risk for glaucoma (mean age 45 years). All patients had normal visual acuity. Contrast thresholds were measured on two sets of tasks: (1) behavioral and (2) sweep visually evoked potentials (VEPs). Two stimuli were used (a) 7.5 Hz reversing gratings of 0.69 cpd, and (b) 5.5 cpd gratings. Noise was binary and contrast varied from 0 to 80%. Psychophysical thresholds were determined using a staircase which employed a spatial four alternative forced choice procedure (4AFC) and converged on 50% correct. Sweep VEP thresholds were determined by extrapolation to zero volts as a function of log contrast. RESULTS: Differences between normal subjects and patients with early glaucoma were not significant without noise. Both the absolute size of the difference and its significance increased as noise level increased. For the behavioral thresholds these trends were clearer with the 5.5 cpd grating, while for the sweep VEPs they were more clear for the 0.69 cpd grating. CONCLUSION: The performance deficit of glaucoma patients which may be minimal under normal testing conditions is magnified when external noise is added to the stimulus. VEPs and psychophysical thresholds show interesting differences in their sensitivity to this effect. Implications for the early detection of glaucoma are discussed.

Adult↗

PubMedDate not supplied

Rapid motion aftereffect seen within uniform flickering test fields.

Prolonged viewing of a moving pattern selectively elevates the threshold for a pattern moving in the same direction and induces the classical motion aftereffect (MAE). The aftereffect is seen as a slow drift in the opposite direction, which is visible even with the eyes shut or while viewing a uniform field. However, as we report here, a strikingly different aftereffect is seen when the test field is uniform and sinusoidally flickered: the field is filled with rapid motion in the direction opposite the adapting motion. This flicker MAE has distinct properties: the adapting grating must be of low spatial frequency; the effect is promoted by high contrast and high temporal frequencies of both adapting and test stimuli; and the aftereffect does not transfer interocularly. In all these respects the flicker MAE differs from the traditional MAE. Motion detectors have been identified in human vision by the threshold detectability and discriminability of moving patterns and by selective adaptation. The flicker MAE selectively taps a class of transient motion mechanisms that are selective for rapid motion and low spatial frequency. Uniform flicker is an effective stimulus for these mechanisms. It thus appears that the human visual system contains at least two distinct classes of mechanisms for sensing motion.

Humans↗

PubMedDate not supplied

Elastin gene deletions in Williams syndrome patients result in altered deposition of elastic fibers in skin and a subclinical dermal phenotype.

Williams syndrome (WS) is a complex developmental disorder with multisystem involvement known to be the result of a microdeletion in the q11.23 region of chromosome 7. This deletion involves several genes, including the elastin gene. Although elastic fibers are important constituents of skin, little is known about the skin phenotype in WS patients. We have therefore studied the skin of four WS patients in which we've shown the deletion of one copy of the elastin gene. Physical examination and indirect immunofluorescent microscopy of elastin did not detect any major phenotypic or morphologic changes in the skin. We were able, however, to show subtle textural changes in skin and, by electron microscopy, that the amorphous component of elastic fibers in WS patients was consistently reduced when compared to normal controls. These findings indicate that deletion of one copy of the elastin gene results in reduced deposition of elastin in dermal elastic fibers, an altered elastic fiber ultrastructure, and a subclinical dermal phenotype in the children and young adult patients analyzed in this study.

Adult↗

PubMedDate not supplied

A comparison of the early growth of twins and singletons.

BACKGROUND: It is well known that the birth weight of twins is less than that of singletons, but there is less information about how birth lengths compare and how twins grow in the postnatal and early childhood period. The implications of the shorter duration of gestation of twins in comparing their postnatal progress with that of singletons are seldom taken into consideration. AIMS: The study aimed to compare the growth of healthy twins and singletons over the first 4 years of life. SUBJECTS AND METHODS: Birth length data on English twins born between 1990 and 1997 were used to produce reference values for gestational ages from 33 to 40 weeks. Follow-up data of weights and lengths up to the equivalent of 40 weeks' gestation are reported on some of these infants who were born pre-term. On the basis of questionnaires, the growth of twins in terms of weight, length/height and head circumference has been followed up to 4 years of age. RESULTS: Mean birth length of twins showed a fall-off when compared with singletons at comparable gestational ages, which was more marked in boys than girls and evident earlier. Extrauterine growth of twins born pre-term was comparable to that of adequately nourished twins remaining in utero until term. Much of the smallness of twins at birth was because of their shorter gestation. Subsequently singletons gained weight faster. Lengths/heights showed no deficit compared with singletons. Head circumferences of twins were, however, smaller than singletons throughout. CONCLUSIONS: The early growth of normal twins differs markedly from that of singletons. It is important to recognize that singleton reference values do not correctly reflect the growth of twins.

Age Factors↗

PubMedDate not supplied

Aspergillosis of the CNS in a pediatric liver transplant recipient: case report and review.

A 2-month-old infant who had undergone orthotopic liver transplantation at the age of 2 weeks for carbamoyl phosphate synthetase deficiency developed infection of the CNS due to Aspergillus fumigatus. The patient was successfully treated with administration of a combination of antifungal agents (including intraventricular amphotericin B), drainage of the parietal lobe abscess, and cessation of immunosuppression. An intraventricular catheter was used both to obtain ventricular fluid for microbiologic testing and to deliver amphotericin B during nearly 4 months of treatment. We review literature on aspergillosis in solid-organ transplant recipients, especially those in whom the disease involves the CNS, and discuss in particular clinical presentation, diagnosis, treatment, and outcome.

Antifungal Agents↗

PubMedDate not supplied

Morphine and etorphine: XIV. Detection by ELISA in equine urine.

We have raised antibodies to morphine and etorphine and developed one-step enzyme-linked immunosorbent assays (ELISA) for these drugs as part of a panel of post race tests for drugs in racing horses. These tests are simple, can be completed in 2 h, and can be read by visual inspection. The morphine ELISA has an I50 for morphine of about 1.5 ng/mL, while the etorphine ELISA has an I50 for etorphine of 250 pg/mL. Cross-reactivity studies show that the antimorphine antibody cross-reacts well with levorphanol, hydromorphone, and oxycodone, while the anti-etorphine antibody showed no cross-reactivity with buprenorphine, diprenorphine, oxymorphone, morphine, or thebaine. The morphine test readily detected parent morphine or its metabolites in equine urine for at least 8 h after administration of 50 mg/horse, while a 0.1 micrograms/kg dose of etorphine was detectable for up to 48 h post dosing. For each test the background activity in post-race urines was equal to or less than the I50 for the standard curves, making them useful equine forensic tests. Each of these tests has detected "positives" in post race urine samples and as such these tests are capable of substantially improving the speed and efficacy of both pre-race and post-race testing for morphine, etorphine, and their congeners in racing horses.

Animals↗

PubMedDate not supplied

Effects of body surface thermal injury on apparent renal and cutaneous blood flow in goats.

The etiology of postburn circulatory impairment ("burn shock") is multifactorial and incompletely understood. However, systemic vasoconstriction is a consistent observation during this period and occurs in spite of aggressive fluid resuscitation therapy. We studied the degree and time course of systemic vasoconstriction in goats for 24 hours following burns of two sizes (20% and 35% TBSA), in which fluid resuscitation was performed according to a common clinical crystalloid regimen. Cardiac index and urine output (reflecting renal perfusion) fell dramatically at two hours after burn, but returned slowly to preburn levels by 24 hours. The degree of fall and rate of recovery were dependent on burn size. Dermal perfusion was assessed by laser Doppler flowmetry in both burned and unburned skin. Dermal perfusion was negligible in burned skin. Unburned skin blood flow fell with increasing burn size, progressively recovered to preburn levels after the small burn, but at 24 hours remained significantly depressed after the larger burn. The stimulus for this persistent skin vasoconstriction is unclear.

Animals↗

PubMedDate not supplied

Laser Doppler monitoring of microcirculatory changes in acute burn wounds.

Because burns are dynamic wounds that can change in apparent depth during the first 72 hours, we asked whether measuring changes in cutaneous blood flow might help predict the ultimate fate of burns that were not obviously shallow or deep. A laser Doppler flowmeter was used to study cutaneous perfusion for at least 72 hours in partial-thickness wounds on patients with burns of less than 15% TBSA and in experimental wounds of similar size on rats. Clinical wounds that healed without grafting consistently showed elevated perfusion levels which increased further within 72 hours, whereas wounds eventually requiring grafting experienced lower perfusion levels with no obvious pattern of increase. Differences between average flow levels for healing and nonhealing burns were statistically significant throughout the study period. Perfusion levels in experimental wounds were stratified according to burn severity, with shallower wounds showing a pattern of increase similar to the clinical wounds.

Adult↗

PubMedDate not supplied

Use of amphotericin B colloidal dispersion in children.

PURPOSE: To describe the experience with a new lipid-based amphotericin product (amphotericin B colloidal dispersion or ABCD) in children with fever and neutropenia who are at high risk for fungal infection. PATIENTS AND METHODS: Forty-nine children with febrile neutropenia were treated in a prospective, randomized trial comparing ABCD with amphotericin B. An additional 70 children with presumed or proven fungal infection were treated with 5 different open-label studies of ABCD. Patients were registered into these studies for reasons of: 1) failure to respond to amphotericin B; 2) development of nephrotoxicity or preexisting renal impairment; or 3) willingness to participate in a dose-escalation study. Extensive data detailing response and toxicity were collected from each patient. RESULTS: In the randomized trial, there was significantly less renal toxicity in the children receiving ABCD than in those receiving amphotericin B (12.0% vs. 52.4% [P = 0.003]). Other adverse symptoms were not significantly different. In the additional open-label studies, although 80% of patients receiving ABCD reported some adverse symptom, the majority of these were infusion related, and nephrotoxicity was reported in only 12% of these patients. CONCLUSIONS: ABCD was well-tolerated at doses up to 5 times greater then those usually tolerated with amphotericin B. Renal toxicity was markedly less than expected, and there were no other unexpected severe toxicities. Further randomized studies are needed to further define the role of this and other liposomal products in children.

Adolescent↗

PubMedDate not supplied

The effect of sinus node depression on heart rate variability in humans using zatebradine, a selective bradycardic agent.

Zatebradine is a bradycardic agent with a selective effect on the pacemaker current in the sinus node. The effect of such drugs on heart rate variability is not known. Thirty-six patients without structural heart disease were randomly assigned to receive 10 mg of zatebradine i.v. (n = 24) or isotonic saline (n = 12). Heart rate variability (HRV) was recorded as power in the very low frequency (VLF, 0.003-0.040 Hz), low frequency (LF, 0.040-0.150 Hz), and high frequency (HF, 0.150-0.400 Hz) spectral bands as well as total power (TP, 0.003-0.400 Hz) during 5-min ECG acquisitions at baseline, 30, and 60 min following the start of the infusion. No change in heart rate variability was detected in the control group. Zatebradine significantly reduced heart rate variability at 60 min in all frequency bands: VLF (-12+/-4%, p<0.001), LF (-19+/-4%, p<0.001), and HF (-26+/-5%, p<0.001). The reduction in HRV following zatebradine is due to depression of sinus node response to all external stimuli and underscores the need for documentation of normal sinus node function in HRV research.

Adult↗

PubMedDate not supplied