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Biomedical subjects

P A Hamilton

Publications and source records attributed to P A Hamilton.

At least 37 records · Page 2Linked to original sources
PubMed1992

Ultrastructural changes of human trabecular meshwork after photocoagulation with a diode laser.

A diode laser, which emitted infrared radiation at a wavelength of 810 nm, was used to perform trabecular photocoagulation in a human eye due for enucleation for malignant melanoma. For comparison, burns were applied with an argon blue-green laser (488-514.5 nm). With each laser, the treatment spot size was 100 microns and the pulse duration was 0.20 sec. Visible lesions were produced with a power of between 750 mW and 1.2 W with the diode laser, and 500-900 mW with the argon laser. The pattern of damage produced by both modalities was similar and essentially consisted of contraction or expansion of trabecular beams, with trabecular destruction occurring only in relation to high power exposures. These findings confirm that trabecular photocoagulation is not a process that depends upon the wavelength of the incident energy at the two spectral extremes of 488 nm and 810 nm.

Aged↗
PubMed1990

Electroejaculation in goats.

A comparison was made of a sine-wave and a pulse-wave electroejaculator for the collection of semen from male goats. Six animals were ejaculated once, using one or other instrument and 8 were ejaculated with each device with an intervening rest period. Comparing the sine-wave with the pulse-wave equipment, the mean total number of sperm collected was 5.3 x 10(9) and 2.1 x 10(9) cells respectively, in the first experiment and 4.0 x 10(9) and 1.0 x 10(9) cells, respectively, in the second experiment. In the latter experiment, a significant difference (p less than 0.05) was found in the sperm concentration, which was higher with the sine-wave generator. This instrument, with controlled output, was considered less stressful to the animal.

Animals↗
PubMed1990

Diode laser trabeculoplasty (DLT) for primary open-angle glaucoma and ocular hypertension.

A pilot study has been carried out to examine the efficacy of diode laser trabeculoplasty in the treatment of primary open-angle glaucoma and ocular hypertension. The device used was portable and could be attached to a standard slit-lamp microscope. Powers of 0.8-1.2 W were used, with a spot size of 100 microns and a pulse of 0.20 second. Laser trabeculoplasty carried out on 20 eyes for glaucoma resulted in a mean ocular hypotensive effect of 10.2 mmHG at two weeks after treatment and of 9.55 mmHg at 6 months. It is concluded that diode laser trabeculoplasty is an effective mode of treatment for eyes with open-angle glaucoma or with ocular hypertension.

Aged↗
PubMed1990

Mediastinal Castleman's disease: demonstration with computed tomography and angiography.

The authors report a case of Castleman's disease in the mediastinum that was discovered in a young woman receiving high-dose steroids for oral pemphigus vulgaris. Computed tomography demonstrated that the mass was calcified and was markedly enhanced after intravenous injection of contrast material, a manifestation of the hyaline-vascular histologic variant. Arteriography proved invaluable in planning the surgical approach to this highly vascular mass. Because Castleman's disease is rare most radiologists are not familiar with the radiographic features and are unaware that profuse hemorrhage may complicate biopsy and surgery.

Adult↗
PubMed1989

Relationship between neurodevelopmental status of very preterm infants at one and four years.

The neurodevelopmental status of 171 very preterm infants was assessed at one and four years of age. At one year 17 had major impairments and 14 had minor ones. At four years the numbers had increased to 25 with major and 25 with minor impairments. Infants with no impairments at one year had a 4 per cent probability of a major impairment at four years, whereas infants with a major impairment had a 94 per cent probability. Infants who later proved to have major neuromotor impairments had been accurately identified at one year, as had infants with sensorineural hearing-loss. Infants with minor impairments of tone and reflexes at one year did not develop cerebral movement disorder, but as a group their scores on tests of cognitive functioning were low. An additional group of infants with cognitive impairments was identified who were unimpaired at one year. The emergence of cognitive deficits largely accounted for the increase in impairments between one and four years.

Child, Preschool↗
PubMed1989

Phosphorus metabolites and intracellular pH in the brains of normal and small for gestational age infants investigated by magnetic resonance spectroscopy.

The brains of 30 normal preterm and term infants whose birth wt were appropriate for gestational age and 13 who were small for gestational age but healthy were studied by phosphorus magnetic resonance spectroscopy to determine values for metabolite concentration ratios and intracellular pH. In the AGA infants, phosphocreatine/inorganic orthophosphate increased between 28 and 42 wk of gestational plus postnatal age, suggesting a rise in the phosphorylation potential of brain tissue. At the same time, the concentration of phosphomonoester (mainly phosphoethanolamine) fell and that of phosphodiester (including phosphatidylethanolamine and phosphatidylcholine) increased. These changes reflected myelination and proliferation of membranes. Intracellular pH was approximately 7.1 and did not change with brain maturation. No differences were detected in these variables between the infants who were small for gestational age and those who were appropriate for gestational age.

Body Fluids↗
PubMed1989

Prognosis of newborn infants with hypoxic-ischemic brain injury assessed by phosphorus magnetic resonance spectroscopy.

To investigate the prognostic significance of abnormalities of oxidative phosphorylation, the brains of 61 newborn infants born at 27-42 wk of gestation and suspected of hypoxic-ischemic brain injury were examined by surface-coil phosphorus magnetic resonance spectroscopy. Of these infants, 23 died, and the neurodevelopmental status of the 38 survivors was assessed at 1 y of age. Of the 28 infants whose phosphocreatine/inorganic orthophosphate (PCr/Pi) ratios fell below 95% confidence limits for normal infants, 19 died, and of the nine survivors, seven had serious multiple impairments (sensitivity 74%, specificity 92%, positive predictive value for unfavorable outcome 93%). Of the 12 infants with ATP/total phosphorus ratios below 95% confidence limits 11 died (sensitivity 47%, specificity 97%, positive predictive value 91%). Among the 46 infants with increased cerebral echodensities, PCr/Pi was more likely to be low, and prognosis poor, in infants whose echodensities were diffuse or indicated intraparenchymal hemorrhage than in infants whose echodensities were consistent with periventricular leukomalacia. We conclude that when reduced values for PCr/Pi indicating severely impaired oxidative phosphorylation are found in the brains of infants suspected of hypoxic-ischemic injury, the prognosis for survival without serious multiple impairments is very poor, and that when ATP/total phosphorus is reduced, death is almost inevitable.

Asphyxia Neonatorum↗
PubMed1989

Prolonged rupture of the fetal membranes and neonatal outcome.

In order to establish the incidence of neonatal infection following prolonged (greater than 24 hours) rupture of the fetal membranes (PROM) and assess outcome of two year retrospective study was undertaken. The names of all babies born following PROM were obtained from the computerised obstetric record and the bacteriological results and outcome reviewed. Of 208 babies born following PROM only three had blood cultures containing pathogens--all of whom were of less than 1500 g birthweight and all of whom died. This represents a fivefold increased frequency of infection for premature babies but no increased risk for full term babies. The overall incidence of infection was much lower than in previous series and this may be due to performing amniocentesis as soon as possible following rupture and inducing labour where there was evidence of incipient chorioamnionitis. Meningitis was not associated with prolonged rupture of the membranes. The mortality for these babies was higher than those of babies without PROM in the 28-31 week gestation group. This was strongly associated with early onset of membrane rupture and none of the babies born following membrane rupture prior to 20 weeks gestation survived. Non-infective pulmonary disease was the main cause of increased mortality.

Bacterial Infections↗
PubMed1988

Precision of ultrasound diagnosis of pathologically verified lesions in the brains of very preterm infants.

Abnormalities detected by a mechanical sector scanner were compared 'blind' with autopsy findings in the brains of 56 infants born at less than 33 weeks gestation. Intraventricular haemorrhage was found in 53 of 112 hemispheres and had been accurately diagnosed by ultrasound (sensitivity 91 per cent; specificity 81 per cent). Isolated germinal layer haemorrhage was less successfully identified (sensitivity 61 per cent; specificity 78 per cent); false-positive diagnoses were partly due to difficulty in distinguishing haemorrhage from the normal choroid plexus in extremely preterm infants. Haemorrhagic parenchymal lesions were correctly identified in nine infants (sensitivity 82 per cent; specificity 97 per cent). Only 11 of 39 hemispheres with histological evidence of hypoxic-ischaemic injury, without marked bleeding, were correctly identified by ultrasound (sensitivity 28 per cent), mainly because of failure to detect small areas of periventricular leucomalacia and diffuse gliosis. 10 hemispheres with periventricular echodensities thought to represent leucomalacia showed no histological evidence of hypoxic-ischaemic injury (specificity 86 per cent). Ventricular dilatation in seven infants was always associated with evidence of hypoxic-ischaemic injury at autopsy.

Brain↗
PubMed1988

Prediction of neurodevelopmental impairment at four years from brain ultrasound appearance of very preterm infants.

The neurodevelopmental status of 171 very preterm infants whose brains had been scanned prospectively with ultrasound was assessed blind at four years using a wide range of tests, including tests of cognitive function. Highly significant correlations were found between the ultrasound appearance of the brain and outcome. The probability of a major neurodevelopmental impairment among the 137 children who had a normal ultrasound scan or uncomplicated periventricular haemorrhage at discharge from the unit was 7 per cent; and for any neurodevelopmental impairment (major plus minor) it was 22 per cent. The probabilities for major, or any, neurodevelopmental impairment among the 18 children who had ventricular dilatation were 33 and 50 per cent, respectively; and for the 16 with hydrocephalus and/or cerebral atrophy (loss of brain-tissue from any cause) the probabilities were 56 and 69 per cent. Impairments predicted from lesions detected by ultrasound were largely neurological. There was no evidence that cognitive impairments could be predicted among infants free of neurological impairments.

Atrophy↗
PubMed1987

Probability of neurodevelopmental disorders estimated from ultrasound appearance of brains of very preterm infants.

The neurodevelopmental status of 342 very preterm infants who had undergone prospective ultrasound brainscans was assessed at a median corrected age of 52 weeks. The probabilities for neurodevelopmental disorders were calculated according to the ultrasound findings. The results showed that the probability of a major or minor disorder was low for infants whose scans did not show periventricular haemorrhage or markedly increased parenchymal echodensities in the first week of life, and for those whose scans at discharge gave no evidence of ventricular dilatation, hydrocephalus or cerebral atrophy. By contrast, the probability of a disorder was very high for infants with markedly increased parenchymal echodensities in the first week, and for infants with evidence of cerebral atrophy at discharge. The majority of the infants could be assigned, on the basis of the ultrasound scan at discharge, either to a large group who were at low risk of neurodevelopmental disorders or to a small group who were at high risk; the remainder were at intermediate risk. These findings may be used as a guide to the prognosis for other infants whose ultrasound scans show similar appearances.

Atrophy↗
PubMed1987

Cerebral monitoring in newborn infants by magnetic resonance and near infrared spectroscopy.

Phosphorus magnetic resonance spectroscopy (MRS) and near infrared spectroscopy (NIRS) have been used to study the brains of normal newborn infants and infants with cerebral disorders admitted to a neonatal intensive care unit. MRS, which involves transporting the infant to the spectrometer, allows measurement of mobile phosphorus compounds such as adenosine triphosphate and phosphocreatine in brain tissue, and has been performed on over 160 babies. NIRS gives cotside information about cerebral oxygenation and haemodynamics and has recently been introduced. These techniques, especially when used together, show promise of providing important information about the mechanisms and prognostic significance of hypoxic-ischaemic damage to the brain--the most important cause of permanent neurodevelopmental disabilities in infants who require intensive care.

Brain↗
PubMed1986

Impaired energy metabolism in brains of newborn infants with increased cerebral echodensities.

Intracellular energy metabolism was studied by phosphorus magnetic resonance spectroscopy in the brains of 27 preterm and term infants with increased echodensities consistent with hypoxic-ischaemic injury and 18 comparable normal infants. In the normal infants the phosphocreatine (PCr)/inorganic orthophosphate (Pi) ratio increased significantly from 0.77 +/- 0.24 (95% confidence limits) at a gestational plus postnatal age of 28 weeks to 1.09 +/- 0.24 at 42 weeks. 9 of the 15 infants with increased echodensities whose PCr/Pi ratios fell below the normal range died; in all 6 survivors cerebral atrophy developed (cysts in brain tissue or microcephaly). In contrast, all 12 infants with increased echodensities whose PCr/Pi ratios remained within the normal range survived, although cerebral atrophy developed in 3 with ratios towards the lower limit of normal.

Age Factors↗
PubMed1985

Underestimation of arterial oxygen tension by transcutaneous electrode with increasing age in infants.

To investigate the effect of increasing gestational and postnatal age on the relation between transcutaneous oxygen tension (tcPO2) and arterial oxygen tension (PaO2) 160 simultaneous measurements of tcPO2 and PaO2 tensions were made on 42 infants born at 24-41 weeks' gestation and aged 0-32 weeks from birth. Irrespective of gestational age a progressive fall in the tcPO2:PaO2 ratio with increasing postnatal age was found. At all postnatal ages tcPO2:PaO2 tended to be lower in the more mature infants.

Aging↗