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Biomedical subjects

G D Williams

Publications and source records attributed to G D Williams.

At least 37 records · Page 2Linked to original sources
PubMed1998

Infant pertussis deaths in New South Wales 1996-1997.

Since 1996, south-eastern Australia has been experiencing a pertussis epidemic which has resulted in the deaths of several infants, including four from NSW in the 12 months to July 1997. All were less than six weeks of age and died from overwhelming cardiovascular compromise despite intensive care support. This excessive infant mortality from a preventable disease demonstrates the need for better pertussis immunity in the community and for erythromycin treatment of all suspected cases and family contacts, especially infants.

Disease Outbreaks↗
PubMed1998

Removal of local field gradient artifacts in T2*-weighted images at high fields by gradient-echo slice excitation profile imaging.

Development of high magnetic field MRI techniques is hampered by the significant artifacts produced by B0 field inhomogeneities in the excited slices. A technique, gradient-echo slice excitation profile imaging (GESEPI), is presented for recovering the signal lost caused by intravoxel phase dispersion in T2*-weighted images. This technique superimposes an incremental gradient offset on the slice refocusing gradient to sample k-space over the full range of spatial frequencies of the excitation profile. A third Fourier transform of the initial two-dimensional image set generates an image set in which the artifacts produced by the low-order B0 inhomogeneity field gradients in the sample are separated and removed from the high-order microscopic field gradients responsible for T2* contrast. Application to high field brain imaging, at 3.0 T for human and at 9.4 T for immature rat imaging demonstrates the significant improvement in quality of the T2*-weighted contrast images.

Algorithms↗
PubMed1998

A birdcage coil tuned by RF shielding for application at 9.4 T.

The design and performance of an inductively fed low-pass birdcage radiofrequency (RF) coil for applications at 9.4 T are described where tuning is accomplished by mechanically moving a concentric RF shield about the longitudinal axis of an RF coil. Moving the shield about the RF coil effectively changes the mutual inductance of the system, providing a mechanism for adjusting the resonant frequency. RF shield tuning eliminates adjustable capacitors on the legs of the RF coil, eliminates current imbalances and field distortions, and results in improved B1 field homogeneity and high quality (Q) factors. RF shield tuning and inductive matching provide an isolated resonance structure which is both physically and electrically unattached. Experimental analysis of shield position on both B1 field homogeneity and resonant frequency is provided. Computer simulations of B1 field homogeneity as a function of shield position and shield diameter are also presented. Magnetic resonance microimaging substantiates the usefulness of this design.

Animals↗
PubMed1998

ECLS in pertussis: does it have a role?

OBJECTIVES: To investigate the value of extracorporeal circulatory life support (ECLS) in paediatric patients with severe Bordetella pertussis infection. DESIGN: Single case report and a review of the ECLS database. SETTING: Tertiary referral hospital paediatric intensive care unit. PATIENTS AND PARTICIPANTS: A single case report of an infant with B. pertussis infection is described. Despite receiving ECLS, this infant died from overwhelming cardiac and cerebral insults. Outcome for children receiving ECLS registered on the Extracorporeal Life Support Organization database is reviewed. MEASUREMENTS AND RESULTS: The mortality of infants receiving ECLS for B. pertussis infection is high, with only 5 survivors reported among 22 registered cases. The majority of nonsurvivors had evidence of circulatory collapse in addition to severe respiratory failure, and these patients commonly died of hypoxic-ischaemic cerebral insult. These data suggest the existence of a subgroup of patients with respiratory failure only, who may benefit from ECLS, and a larger subgroup who suffer ischaemic cardiac and cerebral insults which are unlikely to be improved by ECLS. CONCLUSIONS: The value of ECLS in patients with B. pertussis infection who present with major cardiac dysfunction is questionable. Such patients almost invariably have a poor outcome despite maximal therapy.

Diseases in Twins↗
PubMed1998

Association between age and blood loss in children undergoing open heart operations.

BACKGROUND: Although recent studies indicated young children are at risk for increased perioperative hemorrhage after open heart operations, the associations between patient age, blood loss and blood product transfusions have not been fully defined in children. METHODS: Perioperative blood loss and blood product transfusion data were recorded for 414 consecutive children undergoing open heart procedures. The children were in the following age groups: 1 month or younger, group 1; older than 1 month to 12 months, group 2; older than 1 year to 5 years, group 3; and older than 5 years, group 4. RESULTS: Postoperative blood loss and blood product transfusions were inversely related to age and differed significantly between the four age groups. Multiple preoperative and intraoperative factors that possibly influence hemostasis also differed significantly between age groups. Median units transfused within 72 hours differed significantly with age (p < 0.0001): group 1, 8 units (range, 1 to 19 units); group 2, 6 units (range, 0 to 21 units); group 3, 2 units (range, 0 to 23 units); and group 4, 0 units (range, 0 to 38 units). CONCLUSIONS: Blood loss and transfusions vary inversely with age. Per kilogram of body weight, neonates bled more and received more donor products than any other age group.

Age Factors↗
PubMed1998

Fibrinolysis in pediatric patients undergoing cardiopulmonary bypass.

OBJECTIVE: Thromboelastographic evaluation of the influence of fibrinolysis on blood loss and blood product transfusions in children during cardiac surgery. DESIGN: Prospective study. SETTING: University-affiliated, pediatric medical center. PARTICIPANTS: Two hundred seventy-eight consecutive children undergoing cardiac surgery. INTERVENTIONS: Blood sampling for coagulation tests, including native and protamine-modified thromboelastography. MEASUREMENTS AND MAIN RESULTS: Blood coagulation tests were measured before, during, and after cardiopulmonary bypass (CPB). Demographic data, perioperative blood loss, and blood product transfusions were prospectively recorded. Fibrinolysis was defined as thromboelastography of A30/MA less than 0.85 (MA, maximum amplitude; A30, amplitude 30 minutes after MA) and was noted in 3% of children pre-CPB, 16% during CPB, and 3% post-CPB. Fibrinolysis before CPB was associated with poor cardiac output. Fibrinolysis during CPB occurred in young children (aged 350 +/- 836 days) undergoing complex surgery with prolonged CPB (119 +/- 48.8 minutes) and deep hypothermia (25.6 degrees C +/- 4.7 degrees C). These patients received blood products after CPB and were not fibrinolytic after transfusion. They incurred similar blood loss (in mL/kg) and received similar volumes of blood products (mL/kg) as age-matched and surgery-matched patients without fibrinolysis. CONCLUSION: A group of children at risk for fibrinolysis during CPB was identified. However, fibrinolysis during CPB did not influence blood loss or the total volume of blood products transfused.

Blood Loss, Surgical↗
PubMed1998

Pharmacokinetics and side effects of milrinone in infants and children after open heart surgery.

UNLABELLED: We investigated the pharmacokinetics and side effects of milrinone in infants and children (< or = 13 yr) after open heart surgery in this prospective, open-label study. Milrinone binding to cardiopulmonary bypass (CPB) circuitry was also examined in out two groups. Children in the small dose group (n = 11) received two 25-microg/kg boluses with a final infusion rate of 0.5 microg kg(-1) x min(-1); those in the large dose group (n = 8) received a 50-microg/kg bolus and a 25-microg/kg bolus with a final infusion rate of 0.75 microg x kg(-1) x min(-1). Blood samples for milrinone concentration were drawn 30 min after each bolus, at steady state, and after discontinuing the milrinone infusion. Pharmacokinetics were evaluated using traditional and nonlinear mixed effects modeling analysis. Milrinone kinetics best fit a two-compartment model. Steady-state plasma levels in the small and large dose groups were within the adult therapeutic range (113 +/- 39 and 206 +/- 74 ng/mL, respectively). The volumes of distribution (Vbeta) in infants (0.9 L/kg) and children (0.7 L/kg) were not different, but infants had significantly lower milrinone clearance (3.8 vs 5.9 mL x kg(-1) x min(-1)). Thrombocytopenia (defined as platelet count < or = 100,000 mm(-3)) occurred in 58%, and the risk increased significantly with duration of infusion. Tachyarrythmias were noted in two patients. Milrinone did not bind to CPB circuitry. We conclude that milrinone is cleared more rapidly in children than in adults. The major complication was thrombocytopenia. IMPLICATIONS: Most pediatric dosing is based on data published for adults. Infants and children have kinetics that differ from adults. We studied the distribution of I.V. milrinone in infants and children after open heart surgery. Milrinone had a larger volume of distribution and a faster clearance in infants and children than in adults, and dosing should be adjusted accordingly.

Adolescent↗
PubMed1998

Randomized, single-blinded comparative study of the efficacy of amoxicillin (40 mg/kg/day) versus standard-dose penicillin V in the treatment of group A streptococcal pharyngitis in children.

A 10-day course of amoxicillin at a dosage of 40 mg per kilogram per day was compared with conventional (lower dosage) penicillin V therapy in the treatment of culture-proven Group A streptococcal pharyngitis in children 3 to 18 years of age in a prospective, randomized, and single-blinded study. Children had to have signs and symptoms compatible with the diagnosis of streptococcal pharyngitis and to have a throat swab positive for Group A streptococci. A second throat culture was obtained 10 to 14 days after the completion of therapy. Serotyping was performed to help differentiate carrier states from reinfections. Of 161 children enrolled, 113 were evaluable; 55 received penicillin and 58 received amoxicillin. At the completion of therapy 70.9% (39/55) of patients in the penicillin group vs 87.9% (51/58) of patients in the amoxicillin group were asymptomatic (clinical cure, P = 0.025). At the completion of therapy, 54.5% (30/55) of patients in the penicillin group vs 79.3% (46/58) of patients in the amoxicillin group had negative throat cultures (bacteriologic cure, P = 0.005). The carrier rate (children who were well but who were still carrying the same serotype of Group A streptococcus) also differed between the groups: 13 (23.6%) in the penicillin group compared with six (10.3%) in the amoxicillin group. Amoxicillin at 40 mg/kg/day was significantly more effective than lower dosages of penicillin V for clinical and bacteriologic cure in the treatment of Group A streptococcal pharyngitis in children. The current perception that penicillin is declining in effectiveness may be due to inadequate dosing.

Adolescent↗
PubMed1997

Comparison of the effects of red cell separation and ultrafiltration on heparin concentration during pediatric cardiac surgery.

OBJECTIVE: To determine the effects of red cell separation and ultrafiltration on heparin concentration. DESIGN: Prospective study. SETTING: University-affiliated, pediatric medical center. PARTICIPANTS: Thirty-one children undergoing cardiac surgery. INTERVENTIONS: Blood sampled for heparin concentration and coagulation tests. MEASUREMENTS AND MAIN RESULTS: Thirteen infants under-went modified veno-venous ultrafiltration (UF) after cardiopulmonary bypass (CPB). In addition, residual blood in the CPB circuit was hemoconcentrated by UF and reinfused (UF group). Heparin concentration increased from 2.0 +/- 0.6 to 2.5 +/- 0.8 U/mL, following modified UF; while activated coagulation time (ACT) decreased from 701 +/- 177 to 627 +/- 107 seconds. Heparin concentration of CPB circuit residual increased from 1.9 +/- 0.7 to 3.1 +/- 1.0 U/mL. In 18 children (older than 1 year old), the residual blood in the CPB circuit was hemoconcentrated by cell separation (CS) and reinfused (CS group). Heparin concentration of CPB circuit residual decreased from 2.6 +/- 0.6 to 0.3 +/- 0.2 U/mL. After reinfusion, patient heparin concentration remained unchanged at < 0.05 U/mL. Thrombin time increased from 28 +/- 6 to 48 +/- 29 seconds and did not correlate with H. CONCLUSIONS: The plasma concentration of heparin increased after veno-venous modified UF of the patient. Heparin concentration also increased after UF of residual CPB circuit blood. In contrast, circuit blood hemoconcentrated by CS contained minimal heparin, and, when infused, did not increase patient's heparin concentration. ACT and thrombin time did not correlate with heparin concentration.

Blood Transfusion↗
PubMed1997

Modest hypothermia preserves cerebral energy metabolism during hypoxia-ischemia and correlates with brain damage: a 31P nuclear magnetic resonance study in unanesthetized neonatal rats.

Recent studies have shown that mild to moderate (modest) hypothermia decreases the damage resulting from hypoxic-ischemic insult (HI) in the immature rat. To determine whether suppression of oxidative metabolism during HI is central to the mechanism of neuroprotection, 31P nuclear magnetic resonance (NMR) spectroscopy was used to measure high energy metabolites in 7-d postnatal rats under conditions of modest hypothermia during the HI. The rats underwent unilateral common carotid artery ligation followed by exposure to hypoxia in 8% oxygen for 3 h. Environmental temperature was decreased by 3 or 6 degrees C from the control temperature, 37 degrees C, which reliably produces hemispheric damage in over 90% of pups. The metabolite parameters and tissue swelling (edema) at 42 h recovery varied very significantly with the three temperatures. Tissue swelling was 26.9, 5.3, and 0.3% at 37, 34, and 31 degrees C, respectively. Core temperature and swelling were also measured, with similar results, in parallel experiments in glass jars. Multislice magnetic resonance imaging, histology, and triphenyltetrazolium chloride staining confirmed the fairly uniform damage, confined to the hemisphere ipsilateral to the ligation. The NMR metabolite levels were integrated over the last 2.0 h out of 3.0 h of HI, and were normalized to their baseline for all surviving animals (n = 25). ATP was 47.9, 69.0, and 83.0% of normal, whereas the estimator of phosphorylation potential (phosphocreatinine/inorganic phosphorus) was 16.9, 27.8, and 42.6% of normal at 37, 34, and 31 degrees C, respectively. There was a significant correlation of both phosphocreatinine/inorganic phosphorus (p < 0.0001) and ATP levels (p < 0.0001) with brain swelling. Abnormal brain swelling and thus damage can be reliably predicted from a threshold of these metabolite levels (p < 0.0001). Thus for all three temperatures, a large change in integrated high energy metabolism during HI is a prerequisite for brain damage. With a moderate hypothermia change of 6 degrees C, where there is an insufficient change in metabolites, there is no subsequent HI brain damage. In general, treatment for HI in our 7-d-old rat model should be aimed at preserving energy metabolism.

Analysis of Variance↗
PubMed1997

Ambulatory surgery. Preoperative assessment and health history interview.

Successful outcomes for the ambulatory surgery patient begin prior to admission. With skillful assessment, early identification of possible risk factors, appropriate interventions, and education to prepare the patient and the family for the care required preoperatively and postoperatively, many procedures previously requiring hospital admission can now be done through the ambulatory surgery department.

Ambulatory Surgical Procedures↗
PubMed1996

Chemical burns as assault injuries in Jamaica.

A three-fold greater incidence of chemical burn injuries in Jamaican hospitals, compared to burn centres in other industrial countries, underscores the problem of the use of common chemicals for assault weapons in this country. With the increased availability of guns for personal use, many Jamaicans learned the value of carrying household chemicals such as sulphuric acid from batteries or sodium hydroxide obtained from cleaning supplies. Chemicals carried in a container, such as one might carry mace, afforded a means of defence among the lower socioeconomic groups who could not afford handguns. This use of dangerous chemicals for defensive weapons has extended to the use of chemicals for assault. The pattern of chemical injury differs significantly from most reports in the literature in both prevalence and aetiology. This review was prepared to examine these injuries with a view to planning strategies for prevention.

Adult↗
PubMed1996

Attitudes towards parental presence at induction of anaesthesia.

OBJECTIVE: To determine the attitudes of South African anaesthetists with regard to allowing parents to be present during the induction of anaesthesia in children, and to determine the source and extent of resistance to this controversial practice. DESIGN: Questionnaire survey consisting of three parts and based on a previous study. SETTING: Southern Africa. PARTICIPANTS: All practising anaesthetists, specialist and non-specialist, on the mailing list of a major pharmaceutical company. RESULTS: Responses were obtained from 222 anaesthetists from 80 different localities in southern Africa. The majority of the respondents were specialist anaesthetists in private practice with between 5 and 15 years' experience. Of the respondents 55% agreed that it was acceptable to allow parents to be present at induction and that this did not compromise the child's safety; 117 claimed that there was resistance to the practice, perceiving the matron and nursing staff as the major source of resistance, both currently and in the past. Lack of facilities and loss of operating theatre sterility were cited as the main reasons for resistance. CONCLUSION: Although the practice is still controversial, the majority of anaesthetists who responded to the survey would be happy to allow parents to accompany children at induction. It should be catered for and encouraged according to certain guidelines.

Anesthesia↗
PubMed1995

Application of the accurate assessment of intracellular magnesium and pH from the 31P shifts of ATP to cerebral hypoxia-ischemia in neonatal rat.

The authors present a high field in vivo demonstration of our 2-dimensional calibration methods for determining magnesium ion concentration ([Mg]), under conditions of fluctuating pH, from the three 31P NMR chemical shift differences of ATP. The effect of 3 h of hypoxic-ischemic insult (HI) on intracellular brain [Mg] was evaluated by using a well established 7-day-old rat model of cerebral HI. During the final hour of HI, there was a significant increase (P < 0.001) in free magnesium as well as in the ratio of total [Mg]/[ATP]. The normal, HI, and early (1-2 h) recovery values of free [Mg] were 0.336 +/- 0.015, 0.519 +/- 0.104, and 0.337 +/- 0.071 mM, respectively. These results are consistent with the temporal changes in [ATP]. Our assessment of [Mg] and pH for this high error measurement is general for most in vivo applications and may be routinely implemented.

Adenosine Triphosphate↗
PubMed1995

A computer simulation of the static magnetic field distribution in the human head.

Distortion of the static magnetic field inside the human head is dependent on regional tissue susceptibility variations and geometrical shape. These effects result in resonance line broadening and frequency shifts and consequently, intensity and spatial errors in both magnetic resonance imaging (MRI) and magnetic resonance (MR) spectroscopy. To calculate the field distortion due to the susceptibility's geometry, two dimensional (2D) finite element analysis was applied to simulate the field distribution in a 2D model of the human head, placed in a uniform magnetic field. The model contains air-filled cavities and sinuses, and the remainder is treated as water. The magnetic field deviation was evaluated using gray scale plots and histograms of the magnetic field. The shifts in parts/million and broadening of the histograms correspond to the NMR of the sampled region. The field distribution of the human head was also experimentally mapped using the DANTE tagging sequence. The calculated and experimental field maps are in good agreement. Thus, geometric considerations with uniform susceptibilities are sufficient to explain most of the static magnetic field distribution in the human head.

Air↗
PubMed1995

Methods used in studies of drink-drive control efforts: a meta-analysis of the literature from 1960 to 1991.

We searched the drink-drive control literature over the past three decades, finding over six thousand documents. After detailed review of the abstracts and papers, 125 studies contained separate empirical evaluations of the effects of 12 DWI control policies and enforcement efforts (administrative license suspension, illegal per se, implied consent, preliminary breath test, mandatory jail sentence, mandatory community service, mandatory license suspension, limits on plea bargaining, mandatory fines, selective enforcement patrols, regular police patrols, and sobriety checkpoints). The 125 studies contained 664 distinct analyses that formed the basis for meta-analysis. All of the DWI control efforts were associated with reductions in drink-driving and traffic crashes. The DWI control literature is limited by the preponderance of weak study designs and reports that often fail to include basic data required for meta-analysis. Because of the poor quality of much extant research, we were limited to simple gain scores or percent change estimates in the current study. Further research that does not include appropriate research designs and analytic methods will be of limited utility. We recommend that all future reports include effect estimates and standard error estimates, minimum data required for effective meta-analysis.

Accidents, Traffic↗