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Biomedical subjects

V Chan

Publications and source records attributed to V Chan.

At least 109 records · Page 6Linked to original sources
PubMed1993

Detection of immunoglobulin gene rearrangement in lymphoid malignancies of B-cell lineage by seminested polymerase chain reaction gene amplification.

Seminested polymerase chain reaction (PCR) was used to amplify the DNA fragments of the complementarity-determining region 3 of the immunoglobulin (Ig) gene heavy chain from the malignant cell specimens of patients with leukemias and lymphomas of B-cell lineage. Two different pairs of primers were used sequentially. Twenty of the 27 (74%) acute lymphoblastic leukemia (ALL) patients, 14 of 19 (74%) chronic lymphocytic leukemia (CLL) patients and eight of 20 (40%) non-Hodgkin's lymphoma (NHL) patients, who had rearrangement of the Ig gene heavy chain by Southern analysis, were positive by the seminested PCR. False-negative results appeared to occur more commonly in cases of lymphoma. The PCR analysis was also less likely to be positive if one-stage PCR studies with either pair of primers were both negative. The seminested PCR technique was found to have a high sensitivity of detecting malignant cells at the level of 0.02%. The clinical application of this assay needs to be investigated further.

Base Sequence↗
PubMed1993

False non-paternity in a family for prenatal diagnosis of beta-thalassaemia.

Initial screening for the common beta-thalassaemia mutations with allele-specific oligonucleotide probes in an at-risk family suggested non-paternity. Subsequent DNA fingerprinting of the members proved otherwise. The mother had a codon 41/42 frameshift mutation and the father's defect, determined by direct sequencing of PCR-amplified beta gene, was a codon 43 nonsense mutation. In the affected children, the close proximity of these two defects resulted in the absence of a hybridization signal to the normal probe in that region and a wrong assumption of homozygosity for the codon 41/42 mutation. The non-reactivity of the father's amplified DNA to the codon 41/42 thalassaemic probe accounted for the initial wrong conclusion of non-paternity. Since prior screening for beta-thalassaemia mutations is done in all prenatal diagnosis programmes and concomitant inheritance of these two defects is relatively common in the Chinese, this 'artefact' of false non-paternity is worth noting.

Adult↗
PubMed1993

The effect of frequency and mean airway pressure on volume delivery during high-frequency oscillation.

The performance of a commercially available oscillator (SensorMedics 3100) at different frequencies was assessed. A frequency response curve of a pneumotachograph system was constructed and this was used to measure the volume delivered by the oscillator to a lung model. The volume delivered by a constant diaphragm displacement was demonstrated to be inversely proportional to the frequency, but unaffected by increasing mean airway pressure from 15 to 25 cm H2O. The volume delivered during high frequency oscillation (HFO) was then assessed in 8 infants, median gestational age 29 weeks. The infants were studied at two frequencies, 10 and 15 Hz, both of which were used at two levels of mean airway pressure (MAP): 2 and 5 cm H2O above the MAP level previously used during conventional ventilation. The delivered volume was not significantly different at the two MAP levels, but was significantly greater at 10 than 15 Hz at both MAP levels (P < 0.03); at MAP +2 cm H2O above baseline the reduction in delivered volume was from a median of 1.54 mL/kg (range, 0.88-3.12) at 10 Hz to 1.18 mL/kg (range, 0.65-4.5) at 15 Hz. These results suggest that higher frequencies would require an increase in the oscillator displacement if effective gas exchange is to be maintained.

Blood Gas Analysis↗
PubMed1993

Comparison of helium dilution and nitrogen washout measurements of functional residual capacity in premature infants.

Comparison has been made of measurements of functional residue capacity (FRC) by a helium gas dilution (He) and a nitrogen washout (N2) technique. Twenty infants (median gestational age, 29.5 weeks) were studied at a median postnatal age of 25 days. No infant was oxygen dependent. The coefficient of repeatability of FRC (He) was 6.4 mL/kg and of FRC (N2), 6.3 mL/kg. The coefficient of repeatability of the two methods combined was 13.8 mL/kg. In 10 infants the results of two techniques differed by more than 20% of the mean FRC; those infants were born at a significantly earlier gestation than the rest of the cohort (P < 0.01). We conclude that, except in very immature infants, techniques for measuring FRC (He) and FRC (N2) yield reproducible and comparable results in convalescent premature infants.

Female↗
PubMed1993

Determinants of oxygenation during high frequency oscillation.

Two studies are reported in which the aim was to assess whether oxygenation on transfer to or during high frequency oscillation (HFO) was influenced by the mean airway pressure (MAP) level. Sixteen infants, median gestational age 28 weeks, were recruited into the first study and 14 with a median gestational age of 29 weeks into the second. In the initial study, blood gases were measured immediately before and 30 min after transfer to HFO and comparison made of those infants in whom oxygenation did or did not improve. In the second study the infants were studied at two MAP levels, 2 and 5 cmH2O, above that used during conventional ventilation (baseline MAP) and at two frequencies (10 and 15 Hz), arterial blood gases were measured after 20 min on each setting. In the initial study, on transfer to HFO, oxygenation improved by a median of 21 mmHg in eight infants, but was either unchanged or deteriorated (n = 7) in the other eight infants, the median impairment in oxygenation was by 17 mmHg. The infants in whom oxygenation improved had required a significantly higher MAP during conventional ventilation than the rest of the study group. In the second study, increasing the MAP from 2 to 5 cmH2O above baseline resulted in a significant increase in oxygenation, which was significantly greater at 10 rather than 15Hz. Infants whose MAP remained below 13 cmH2O had impaired oxygenation during HFO compared to that experienced during conventional ventilation. The results of these two studies demonstrate that the MAP level during HFO is an important determinant of oxygenation.

Blood Pressure↗
PubMed1993

Randomised controlled trial of weaning by patient triggered ventilation or conventional ventilation.

A group of preterm infants (n = 40) were entered into a randomised controlled trial to compare the duration and efficacy of weaning by patient triggered ventilation (PTV) or conventional ventilation. Once recovery from respiratory distress had begun, enabling the ventilator rate to be reduced to 40 breaths/min, infants were randomised to either regime. Infants randomised to PTV were weaned by reduction in ventilator pressure only, whereas infants randomised to conventional ventilation were weaned by reduction in ventilator rate only. Only one infant required re-ventilation within 24 h of extubation; this infant had been weaned by conventional ventilation. Three infants, all of less than 28 weeks gestation, did not tolerate weaning by PTV and were subsequently weaned conventionally. The duration of weaning was analysed according to the original randomisation allocation and was significantly shorter in the PTV group, being a median of 30 h (mean 39, range 3-186) compared to a median of 61 h (mean 65, range 15-262) in the conventional group, P < 0.02. We conclude PTV is the more advantageous form of weaning in preterm infants of greater than 27 weeks gestational age.

Gestational Age↗
PubMed1993

Prenatal quantitation of number of X-chromosomes by slot blot hybridization and autoradiography.

OBJECTIVE: To study the use of slot blot hybridization as a method of prenatal quantification of the number of X-chromosomes in chorionic villi samples. METHOD: DNA of chorionic villi from fetuses with karyotypes of 46,XY; 45,XO; 47,XXX; 69,XXX and 48,XXXX were extracted, slot blotted and hybridized to the following radioactive probes: beta 0.9, FVIII, pY3.4 and pBLUR. DNA of chorionic villi from five other fetuses with unknown karyotypes were similarly blotted and hybridized. Autoradiography with pre-exposed films was carried out and the density of each of the hybridized bands was scanned by a laser densitometer. RESULTS: It was found that with increasing amounts of DNA in the samples, the intensity of the bands hybridized with FVIII and beta 0.9 probes increased proportionately. However, the intensity of the bands obtained with the probes pY3.4 and pBLUR (probes containing multiple repeat sequences) varied little with increasing DNA concentrations. The ratios of radioactivity obtained for the two probes FVIII/beta 0.9, were well correlated with the number of X-chromosomes in the samples. Calculations of the FVIII/beta 0.9 ratio for the five samples with the unknown karyotypes gave a correct prediction of the number of X-chromosomes in each case. CONCLUSION: Slot blot hybridization can be used as a method of prenatal quantitation of the number of X-chromosomes in chorionic villi samples. The method could be useful for rapid prenatal diagnosis of other numerical chromosomal abnormalities.

Adult↗
PubMed1993

Respiratory status and diuresis following treatment with dexamethasone.

The effect of dexamethasone therapy on fluid balance, lung function and requirement for respiratory support has been assessed. Ten premature infants were studied, they had a median gestational age of 28 weeks. None of the infants had any improvement in the respiratory status for 48 h prior to commencing dexamethasone. Fluid balance, pulmonary function and requirement for respiratory support were measured 12 h prior to and for 36 h after receiving dexamethasone. There were no significant changes in fluid input over the study period, but urine output increased significantly after 12 h of dexamethasone therapy (P < 0.02). Compliance of the respiratory system only significantly improved after 36 h of dexamethasone therapy (P < 0.03), this was associated with a significant change in the inspired oxygen concentration (P < 0.05). We conclude that the improvement in respiratory status resulting from dexamethasone therapy is preceded by a diuresis.

Dexamethasone↗
PubMed1993

Randomised trial of methods of extubation in acute and chronic respiratory distress.

Sixty infants (median gestational age 29 weeks) with acute and 60 infants (median gestational age 25 weeks) with chronic respiratory distress were randomised to be extubated either directly into a headbox or onto 3 cm H2O nasal continuous positive airway pressure (CPAP). Our aim was to test the hypothesis that extubation onto nasal CPAP rather than directly into a headbox was more likely to be associated with successful extubation in infants with acute rather than chronic respiratory distress. Overall the failure rate of extubation was approximately 33%, with no significant difference between the infants with acute and chronic respiratory distress. There was no significant difference in the failure rate of extubation among infants randomised to receive nasal CPAP or headbox oxygen in either the acute or chronic respiratory distress groups.

Acute Disease↗
PubMed1993

Vitamin A status in preterm and term infants at birth.

Vitamin A status was determined in infants born at term or prematurely to assess if vitamin A levels at birth were related to gestational age. Vitamin A levels were measured in cord blood samples from 13 infants born at term and in blood samples obtained within two hours of birth in 26 preterm infants (median gestational age 31 weeks, range 27-35). None of the preterm infants developed chronic lung disease. The vitamin A levels of the term infants (median 0.71 mumol/l, range 0.34 to 1.27) were significantly higher than those of infants born preterm (median 0.35 mumol/l, range 0.12 to 1.22), p < 0.01. Vitamin A levels correlated significantly with gestational age (vitamin A level = 0.024 gestational age (weeks) -0.23, r = 0.39, p < 0.02. We thus conclude that gestational age must be taken into account when interpreting vitamin A levels.

Chronic Disease↗
PubMed1993

Vitamin A levels at birth of high risk preterm infants.

Vitamin A levels were measured shortly after birth in preterm infants at high risk of developing chronic lung disease (CLD). Eleven infants, median gestational age 24 weeks, developed CLD. Their results were compared to 11 infants who, although they required mechanical ventilation for at least 48 hours, did not develop CLD. The median gestational age of this latter group was 30 weeks (range 27-35). The median vitamin A level of the infants who developed CLD was 0.62 umol/l (range 0.41-0.95), which was significantly higher than the median level of the infants who did not develop CLD, which was 0.36 umol/l (range 0.13-0.89). We conclude preterm infants who develop CLD are not predisposed to develop that complication by low vitamin A levels at birth.

Chronic Disease↗
PubMed1993

Vitamin A levels and feeding practice in neonates with and without chronic lung disease.

Infants with chronic lung disease (CLD) have been demonstrated to have low vitamin A levels. The aim of this study was to assess factors which influenced this association. Vitamin A levels of infants born at less than 32 weeks gestational age with and without CLD were determined and related to feeding practice. The infants with CLD had statistically significantly lower vitamin A levels on days 21 to 30 and days 31 to 40. From day 11 onwards, the median Vitamin A levels were less than 60% of the minimum acceptable level for a healthy child or adult. Infants with CLD required significantly longer mechanical ventilation and parenteral nutrition than controls and there was a significant positive correlation between duration of mechanical ventilation and parenteral nutrition (r = 0.83). Infants with CLD received significantly less vitamin A supplementation than the infants without CLD. Our results thus suggest that feeding practice explains the association of CLD and vitamin A deficiency in preterm infants.

Chronic Disease↗
PubMed1993

Haemophilia: strategies for carrier detection and prenatal diagnosis.

In 1977 WHO published in the Bulletin a Memorandum on Methods for the Detection of Haemophilia Carriers. This was produced following a WHO/WFH (World Federation of Haemophilia) Meeting of Investigators in Geneva in November 1976, and has served as a valuable reference article on the genetics of haemophilia. The analyses discussed were based on phenotypic assessment, which, at that time, was the only procedure available. The molecular biology revolution in genetics during the 1980s made enormous contributions to our understanding of the molecular basis of the haemophilias and now permits precise carrier detection and prenatal diagnosis. WHO and WFH held a joint meeting on this subject in February 1992 in Geneva. This article is the result of these discussions.

Base Sequence↗
PubMed1992

Neonatal complications of extreme prematurity in mechanically ventilated infants.

Previous data have suggested that neonatal complications amongst preterm ventilated infants increase with decreasing gestational age and thus are likely to be greatest among ventilated infants of less than 28 weeks gestational age. The aim of this study was to test that hypothesis, thus we report the neonatal complications of 175 extremely preterm mechanically ventilated infants (gestational age less than or equal to 28 weeks). Of the infants 152 were ventilated because of respiratory distress syndrome (RDS) or respiratory distress of severe prematurity, 41% of these infants died. Amongst infants with RDS or respiratory distress of extreme prematurity, mortality was significantly increased in infants of gestational age less than or equal to 24 weeks and birth weight less than or equal to 1000 g. In this group 20% developed a pneumothorax, and mortality was inversely related to gestational age. In infants with RDS, 43% developed a periventricular haemorrhage and 37% were still oxygen-dependent at 28 days of age; neither of these complications was significantly related to birth weight or gestational age. Of infants with RDS 38% developed a patent ductus arteriosus and 16% developed retinopathy of prematurity. These data suggest that even amongst very immature infants there has been an impressive reduction in the neonatal complications of mechanical ventilation.

Gestational Age↗
PubMed1992

Evaluation of triggering systems for patient triggered ventilation for neonates ventilator-dependent beyond 10 days of age.

The performance of two triggering systems was compared during patient triggered ventilation (PTV) of infants ventilator-dependent beyond 10 days of age. Ten infants were studied who had a median gestational age of 26.5 weeks and a postnatal age of 15.5 days. PTV was administered via the SLE ventilator and the two triggering systems, an airway pressure monitor and the MR10 respiration monitor, were used in random order each for 30 min. The airway pressure trigger had a superior performance in that, although it did not differ significantly in delivered inflation volume or sensitivity to the MR10 respiration monitor, it had a shorter trigger delay (P < 0.01). Oxygenation improved in eight of the ten infants on the airway pressure trigger, but only in three on the MR10 respiration monitor. The reduction in PaCO2 was greater during PTV with the airway pressure trigger compared with the MR10 respiration monitor (P < 0.01). We conclude that the airway pressure trigger has a superior performance compared to the MR10 respiration monitor trigger in infants who are ventilator-dependent beyond 10 days of age.

Chronic Disease↗
PubMed1992

Lung function and the Hering Breuer reflex in the neonatal period.

Lung function and the occurrence of the Hering Breuer reflex during the neonatal period has been investigated. To assess the effect of extrauterine and intrauterine maturation on the strength of the reflex both preterm and term infants were recruited. Ten preterm infants, born at a median gestational age of 29.5 weeks (range 27-34) were studied serially over the first four weeks of life and 10 term infants were studied at a median postnatal age of 1.5 days (1-4). All of the infants were recruited from the neonatal unit and initially had had some form of respiratory distress. Respiratory rate, tidal volume and compliance were measured and end inspiratory occlusion performed in an attempt to provoke the Hering Breuer reflex. The Hering Breuer reflex was provoked in all infants on all occasions. There was no difference in the strength of the reflex between the preterm and term infants or preterm infants studied at different postnatal ages. All infants studied regardless of maturity or postnatal age had non-compliant lungs and a rapid respiratory rate. These data suggest a lack of intrauterine and extrauterine maturation of the Hering Breuer reflex in the neonatal period amongst infants with non-compliant lungs.

Aging↗