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Biomedical subjects

C Chua

Publications and source records attributed to C Chua.

18 recordsLinked to original sources
PubMed2004

Clinico-pathological findings in diarrhoea-negative haemolytic uraemic syndrome.

This is a retrospective, national clinico-pathological study of past and current patients with haemolytic uraemic syndrome not associated with diarrhoea (D- HUS). Thirty-four patients were analysed and notified by members of the British Association for Paediatric Nephrology in 1998-1999. There was a 2:1 excess of males. Ten presented in infancy. The aetiology included 5 patients with complement abnormalities, 2 patients with complications of pneumococcal infection, and 2 with malignancies. Parental consanguinity was noted in 6 patients. Five children died, 9 developed chronic renal failure, and 10 end-stage renal failure. Only 7 made full recoveries. With a single exception, the pathological findings were unlike the previously reported glomerular thrombosis that is characteristic of diarrhoea-associated HUS, or HUS complicating verocytotoxin-producing Escherichia coli infection. Early and late glomerulopathy could be distinguished. Arteriolar and arterial disease was observed in 8 and 7 patients, respectively. Arterial disease correlated with a poor outcome. The pathology of D- HUS is of prognostic value, but this study was not powered to identify specific aetiological/pathological correlations.

Arteries↗
PubMed2004

Comparison between standard Goldmann applanation prism and disposable applanation prism in tonometry.

BACKGROUND: Disposable devices are increasingly becoming the preferred choice where possible in contact medical equipment. AIM: To evaluate the accuracy of the disposable applanation tonometer head as a potential substitute to the standard Goldmann applanation head. METHODS: The study was prospective. The intraocular pressure recordings in 80 eyes of 42 patients were compared using the disposable and standard Goldmann applanator heads. The Bland and Altman method of assessing agreement between two methods of clinical measurement was used in the analysis. RESULTS: The difference in the readings between the two types of tonometer heads was highly variable (mean difference=0.78 mm Hg, range=-1 to 11 mm Hg). This was because of the distortions on the applanating surface of the disposable device. When the readings associated with the defective heads were excluded, very strong agreement was obtained (mean=0.07 mm Hg, range=-1 to 2 mm Hg). CONCLUSION: Good agreement with standard Goldmann applanation is achieved with the disposable heads except where surface distortions induce significant errors. Careful inspection to ensure well-structured disposable units is imperative in disposable applanation tonometry.

Adult↗
PubMed2004

Laser vs ultrasound biometry--a study of intra- and interobserver variability.

BACKGROUND: Accurate biometry is of vital importance in achieving predictable postoperative refraction following cataract surgery. AIM: To evaluate the accuracy and consistency in biometry, achieved by the new generation laser biometric system in comparison with the ultrasound biometric system. METHODS: The study was randomized and prospective. Biometry was performed in 68 eyes of 39 patients by three groups of biometrists (expert, intermediate user, novice). Expert and intermediate users are compared as group A, and expert and novice are compared in group B. Axial length, anterior chamber depth (ACD), and keratometry results are compared by t-test analysis. RESULTS: Axial length measurement variation between expert and non experts was 10 times less using laser than ultrasound (P<0.001). ACD measurement variation was also significantly less when using laser compared to ultrasound (P=0.003). Need for some level of user training is indicated in ACD measurement since group A achieved more consistent readings than group B. Keratometry measurements on the laser system were unreliable due to high range of results. Biometric failure was seen in 12% of eyes undergoing laser and 1% undergoing ultrasound biometry. CONCLUSION: Axial length determination by laser biometry is more accurate and consistent at all levels of biometrist expertise, compared to ultrasound biometry. ACD and keratometry measurements on the laser systems need some degree of user training in order to produce consistent results.

Adult↗
PubMed2003

What is true community-acquired urinary tract infection? Comparison of pathogens identified in urine from routine outpatient specimens and from community clinics in a prospective study.

In order to identify the true nature of community-acquired urinary tract infections, the uropathogens isolated from 100 patients with urinary tract infection included in a prospective study conducted in community clinics were compared to 244 isolates from outpatient urine specimens routinely submitted to the laboratory. Significant differences in both the spectrum of bacteria and their antibiograms were found between the two groups. Laboratory data analysis of uropathogens from outpatient urine specimens may not reflect the true bacteriology of urinary tract infections acquired in the community. Hence, surveys based on laboratory data alone may overestimate resistance rates, leading to misinformed choices being made when treatment is empirical.

Anti-Bacterial Agents↗
PubMed2003

Driving ability after pupillary dilatation.

BACKGROUND: The Royal College of Ophthalmologists' guidelines and Driver and Vehicle Licensing Agency (DVLA) recommend that a patient should not drive with dilated pupils based on the rationale that vision may be compromised in acuity and ability to tolerate glare. Arguments exist against these recommendations suggesting that pupillary dilatation does not have any real bearings on driving ability. Aim To determine the effects of pupillary dilatation on the ability to drive. METHODS: The study was randomised and prospective. A total of 28 patients had their visual parameters (distance vision, near vision, licence plate reading at 20 m or shorter, and glare) measured and analysed pre- and post-tropicamide 1% dilatation. Paired two-tailed Student's t-test and chi(2)-test were used in the analysis. RESULTS: At 20 min, following instillation of one drop of tropicamide 1% there is a significant reduction in visual acuity (VA), for distance Snellen and near. There is a significant reduction in the number of people who could read the licence plate at 20 m. Subjective glare assessment changed from 'none' (average score) in the undilated state to 'mild' in the dilated states. The overall patient feedback indicated that a significant 14% believed they would find it difficult to drive postdilatation. CONCLUSION: This study demonstrates the rationale behind disallowing driving following pupillary dilatation. The risks to safe driving are proved significant as a result of significant reduction in visual quality and quantity after dilatation.

Adult↗
PubMed2001

Sex differences and opposite effects of stress on dendritic spine density in the male versus female hippocampus.

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Despite much information about their structure, their functional significance remains unknown. It has been reported that females in proestrus, when estrogen levels are elevated, have a greater density of apical dendritic spines on pyramidal neurons in area CA1 of the hippocampus than females in other stages of estrous (Woolley et al., 1990). Here we replicate these findings and in addition, show that females in proestrus have a greater density of spines in area CA1 of the hippocampus than males. Moreover, this sex difference in spine density is affected in opposite directions by stressful experience. In response to one acute stressful event of intermittent tailshocks, spine density was enhanced in the male hippocampus but reduced in the female hippocampus. The decrease in the female was observed for those that were stressed during diestrus 2 and perfused 24 hr later during proestrus. The opposing effects of stress were not evident immediately after the stressor but rather occurred within 24 hr and were evident on apical and to a lesser extent on basal dendrites of pyramidal cells in area CA1. Neither sex nor stress affected spine density on pyramidal neurons in somatosensory cortex. Sex differences in hippocampal spine density correlated with sex hormones, estradiol and testosterone, whereas stress effects on spine density were not directly associated with differences in the stress hormones, glucocorticoids. In summary, males and females have different levels of dendritic spine density in the hippocampus under unstressed conditions, and their neuronal anatomy can respond in opposite directions to the same stressful event.

Animals↗
PubMed1997

Risks for fetal abnormalities after very and moderately elevated AF-AFPs.

In the 2 years between 1993 and 1995, we assayed alpha-fetoprotein (AFP) in 48,412 amniotic fluids (AFs). One thousand and eighty-six (2.2 per cent) measured > or = 2.0 MOM and these were subdivided into three groups; mildly (2.0-4.9 MOM), moderately (5.0-9.9 MOM), and very elevated (> or = 10.0 MOM). Abnormalities occurred in 25 per cent of the mildly elevated compared with 88 per cent of the moderately and 98 per cent of the very elevated cases. Forty-five per cent of the neural tube defects (NTDs) had AF-AFPs in the 5.0-9.9 and 36 per cent in the > or = 10.0 MOM range. After a positive acetylcholinesterase (AChE) test, both the moderately and the very elevated groups had abnormalities in > or = 95 per cent of cases, compared with 85 per cent in the mildly elevated group. After a negative AChE test, abnormalities occurred in 79, 52 and 18 per cent in the very elevated, moderately, and mildly elevated groups, respectively. Excluding chromosome abnormalities, an abnormal twin, and bloody samples, the risk of a fetal abnormality after a normal ultrasound was less than 1 per cent if the AChE was positive in both the moderately and the very elevated groups. If the AChE was negative, the risk was 18 per cent for the moderately and 55 per cent for the very elevated groups, of which congenital nephrosis accounted for 75 per cent; AFP levels usually increased in a later AF sample. Repeat amniocentesis may be offered to women with AF-AFPs > or = 5.0 MOM if no abnormality is seen with high-resolution ultrasound.

Acetylcholinesterase↗
PubMed1995

Detecting neural tube defects by amniocentesis between 11 and 15 weeks' gestation.

Forty-two open neural tube defects (NTDs) were identified in our series of 7440 amniocenteses tested between 11 and 15 weeks of gestation. Using a cut-off of > or = 2.0 MOM, the detection rate for open NTDs was 95 per cent; 100 per cent each for anencephaly and spina bifida; and 78 per cent for encephalocele. Two encephaloceles had AFP levels less than 2.0 MOM and negative AChEs. Thirty-four (81 per cent) of these NTDs were tested between 13 and 15 weeks and 8 (19 per cent) before 13 weeks. There were 0.6 per cent false positives by AFP (excluding serious abnormalities and fetal death) and 0.1 per cent after AChE. The likelihood of an open NTD after an elevated AFP (> or = 2.0 MOM) was 24 and 77 per cent for any serious abnormality. These results, when combined with an earlier study, indicate that amniotic fluid AFP appears to be as sensitive a test for open NTDs between 13 and 15 weeks as between 16 and 20 weeks. Additional experience is necessary to determine this before 13 weeks.

Acetylcholinesterase↗
PubMed1983

Microcomputer evaluation of cerebral blood flow velocity studies in the neonate.

A semi-automated system for evaluation of Doppler cerebral blood flow studies obtained from newborn infants is described. A low cost digitizer is used to convert the graphic data from the flow tracing to digital data. A small business computer is used to analyze the data and produce a chartable report. The reliability of the digitizer is also evaluated.

Blood Flow Velocity↗
PubMed1982

The fontanelle tonometer: a noninvasive method for measurement of intracranial pressure.

The use of a modified pneumotonometer as a noninvasive method to measure intracranial pressure through the fontanel was evaluated in the animal laboratory and in the clinical setting. Pressure measured with the tonometer from a surgically created fontanel in an adult mongrel dog demonstrated good correlation with pressure measured from an epidural balloon catheter. Pressure recorded with the tonometer was compared with direct measurements in a single infant. There were 20 paired measurements with a correlation coefficient of 0.91. Fontanel pressure was measured in 72 healthy infants. The mean pressure was 7.0 mm Hg with a standard deviation of 1.75. This result compares favorably with previous reports utilizing other methods. The machine is safe and simple to use.

Animals↗
PubMed1982

Cross validation of serum to saliva relationships of caffeine, theophylline and total methylxanthines in neonates.

We have previously described the relationships of serum and saliva concentrations of caffeine, theophylline and total methylxanthines in premature infants. We have now extended the previous studies in order to validate the previously derived relationships with new data. The new serum to saliva relationships, derived using regression and ratio models, are cross validated against the relationships from the previous data, and vice versa. A good cross validation was observed for caffeine and total methylxanthine concentrations in infants treated with caffeine. In the theophylline treatment group, theophylline concentrations did not cross validate well, whereas the total methylxanthine concentrations did. Since in vivo conversion of theophylline to caffeine and vice versa may affect the individual methylxanthine relationships, the total methylxanthine equations are recommended for predicting serum concentrations from salivary concentrations.

Apnea↗
PubMed1980

Inhibitors of complement derived from the erythrocyte membrane in paroxysmal nocturnal hemoglobinuria.

Extracts of the membranes of normal red cells and red cells from all subpopulations of paroxysmal nocturnal (PNH) red cells inhibited antibody-mediated complement activation. These extracts were shown to accelerate decay of the complement complex. C42, and the relative amount of inhibitory activity was similar in normal and PNH membranes. Inhibitors derived from normal red cells markedly decreased lysis of both PNH and normal cells when antibody was present in excess and complement was limiting. These same inhibitors decreased PNH cell lysis to a much lesser degree when complement was activated with cobra venom or acidified serum. The susceptibility of the PNH cell to complement lysis because of an increased fixation of C3 to its membrane is not due to a difference in membrane-associated accelerator of the decay of the C42 complex.

Animals↗
PubMed1979

Noninvasive diagnosis of neonatal asphyxia and intraventricular hemorrhage by Doppler ultrasound.

The cerebrovascular hemodynamic alterations in asphyxia and intracerebral-intraventricular hemorrhage were determined by monitoring the pulsatile flow changes in the anterior cerebral arteries using Doppler ultrasound. The pulsatility index measurements, which were calculated from the recorded changes in Doppler frequency shifts, were obtained in four groups of newborn infants with the following diagnoses: Group I--normal term (n=21); Group II--asphyxia (n=12); Group III--IC-IVH (n=14); and Group IV--asymptomatic preterm (n=11). There was no significant difference between PI values of Groups I and IV. Compared to normal term infants, those diagnosed as having asphyxia had significantly lower PI measurements and those with IC-IVH had significantly higher PI values than the asymptomatic pretern infants. Serial Doppler studies were also performed in 22 preterm infants with respiratory distress. One-half of these infants subsequently developed IC-IVH. Prior to hemorrhage, their PI measurements were significantly lower than those who did not eventually have the complication. The low PI values in asphyxia and prior to the onset of IC-IVH indicate vasodilation and decreased resistance to blood flow. In IC-IVH, the high PI measurements denote the opposite. In infants with respiratory distress in the presence of significant vasodilation and lowered vascular resistance, CBF may increase to excessive levels, resulting in IC-IVH.

Asphyxia Neonatorum↗