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Biomedical subjects

W H Wallace

Publications and source records attributed to W H Wallace.

At least 19 recordsLinked to original sources
PubMed2006

Technical aspects of the Naval Dosimetry Center quality assurance programme.

The purpose of this paper is to describe the technical aspects of the Naval Dosimetry Center (NDC) quality programme. The Navy has been formally monitoring personnel for occupational exposure to ionising radiation since at least 1946. The current system, the DT-702/PD, is the Harshaw 8840 holder and 8841 card. New card and holder checks are performed to verify that the correct LiF elements and holder filters are in the correct location and are of the correct composition. Element correction coefficient (ECC) magnitude and repeatability are also verified. Several quality assurance parameters are checked by a specially designed shipping machine. Calibration cards are used to calibrate each reader and quality control cards are inserted throughout a group of field cards to verify reader operation during the read process. The success of the programme is measured by annual proficiency tests administered by the National Voluntary Laboratory Accreditation Programme and Pacific Northwest National Laboratories.

Calibration↗
PubMed2003

Comparative genomic hybridization and pathological findings in atypical teratoid/rhabdoid tumour of the central nervous system.

The atypical teratoid/rhabdoid tumour (AT/RT) is an uncommon tumour of the central nervous system in children, characterized by the presence of a rhabdoid cell component associated with variable combinations of primitive neuroectodermal tumour, mesenchymal and epithelial differentiation. Immunohistochemistry reveals a complex pattern of antigen expression and cytogenetic studies have demonstrated losses from chromosome 22. We have performed comparative genomic hybridization (CGH) on paraffin-embedded material from three cases of AT/RT. Two cases showed losses from chromosome 22 associated with other chromosome imbalances including losses from 1p in both cases. The third case demonstrated a loss from 8p as the sole abnormality. While monosomy or deletion from chromosome 22 is a useful diagnostic marker for AT/RT, it is not present in all cases. The variation in cytogenetic patterns reported for this tumour type raises the possibility that different genetic pathways may underlie this tumour phenotype and warrants the further definition of the cytogenetic spectrum for this rare tumour.

Adolescent↗
PubMed2001

Hypothalamic-pituitary-ovarian dysfunction after prepubertal chemotherapy and cranial irradiation for acute leukaemia.

BACKGROUND: We assessed adult hypothalamic-pituitary-ovarian function following treatment with chemotherapy and cranial irradiation for childhood acute lymphoblastic leukaemia. METHODS: The patients (n = 12) had median age at diagnosis of 4.7 years, and at assessment of 20.8 years. They collected a daily urine sample over two to five consecutive menstrual cycles (total of 41 cycles) for analysis of LH and steroid excretion. Blood sampling and ovarian ultrasound examination was performed in the early follicular phase. Sixteen healthy women with regular menstrual cycles were recruited as controls. RESULTS: Urinary LH excretion was significantly lower in patients throughout the cycle, particularly during the LH surge (P < 0.0001). The length of the luteal phase was significantly shorter in patients than in normal controls (12.2 +/- 0.3 versus 13.6 +/- 0.4 days, P = 0.01) with a high prevalence of short (< or =11 days) luteal phases (15/39 cycles). Luteal phase pregnanediol excretion was slightly but not significantly lower. Follicular and luteal phase excretion of oestrone was lower in patients than in controls (P = 0.01). Early follicular phase plasma oestradiol was also lower in the patient group (P = 0.032) although LH, FSH, inhibin A and B concentrations were similar. CONCLUSIONS: These data indicate that treatment for childhood leukaemia results in subtle ovulatory disorder in some patients, probably related to cranial irradiation. Follow-up of these women is required to detect any effect on reproductive potential.

Acute Disease↗
PubMed2001

Premature adiposity rebound in children treated for acute lymphoblastic leukemia.

The adiposity rebound (AR), when body mass index begins to increase after its nadir in childhood, is a critical period for the regulation of energy balance and adult obesity risk. The aim of the present study was to test whether children treated for acute lymphoblastic leukemia (ALL) experience premature AR. This might, in part, explain their tendency to develop obesity. Timing of AR was assessed by visual inspection of body mass index plots in 68 patients treated for ALL in first remission. This sample comprised all eligible patients treated in Scotland between 1991 and 1998, age 30 months or less at the time of diagnosis. Timing of AR in patients was compared against a cohort of 889 healthy British children studied during the 1990s using the same method. AR occurred significantly earlier in the patients treated for ALL (chi(2) test, P < 0.001). The AR had occurred in 43% (29 of 68) of the patients and 4% (40 of 889) of the comparison group by age 37 months. At 49 months AR had occurred in 81% (55 of 68) of the patients and 21% (190 of 889) of the comparison group. Treatment of ALL is associated with a significantly advanced AR. This might, in part, explain the extremely high prevalence of obesity in long-term survivors. Clinical management should focus on minimizing excess weight gain during therapy to reduce long-term obesity risk.

Adipose Tissue↗
PubMed2000

Plasma exchange as successful treatment of thrombotic thrombocytopenic purpura post autologous bone marrow transplant in a child.

We describe the case of a small child with stage IV neuroblastoma who developed thrombotic thromobocytopenic purpura (TTP) post autologous bone marrow transplant. Pneumococcal sepsis may have been the cause, a previously unreported association in transplant-associated TTP. Despite the child's size (10 kg) and the severity of the disease early intensive treatment with whole blood exchange and subsequently plasma exchange with cryosupernatant proved to be rapidly effective, in contrast to previous reports on its ineffectiveness in this setting.

Body Weight↗
PubMed2000

Risk factors for excess weight gain in children treated for acute lymphoblastic leukaemia.

OBJECTIVE: To test whether excess weight gain in patients treated for childhood acute lymphoblastic leukaemia (ALL) was predictable using patient characteristics at diagnosis. DESIGN AND SUBJECTS: Longitudinal study of changes in body mass index (BMI) in all 98 patients treated in Scotland on treatment protocol MRC UKALL-XI who had reached at least 3y post-diagnosis in first remission. MEASUREMENTS: The influence of the following variables on changes in BMI, expressed as a standard deviation score (SDS), was tested using variable selection techniques and classification and regression trees: BMI SDS at diagnosis; age at diagnosis; gender; socioeconomic status; treatment. RESULTS: Prevalence of obesity (BMI SDS>2.0) was <2% at diagnosis, but increased to 16% at 3y. Gain in BMI SDS was significantly inversely influenced by BMI SDS at diagnosis (P<0.01) and age at diagnosis (P<0.01). CONCLUSION: Obesity is common in ALL by the end of therapy, and is more likely in children who are younger and thinner at diagnosis. Excess weight gain was not readily predictable from routinely collected information available at diagnosis and so all children treated for ALL should be considered 'at risk' of excess weight gain and the target of obesity prevention.

Age Factors↗
PubMed2000

Bone turnover and growth during and after continuing chemotherapy in children with acute lymphoblastic leukemia.

Children treated for acute lymphoblastic leukemia may develop reduced bone mineral density during treatment, but there is little information on the mechanisms involved. In a prospective, longitudinal study on 15 children with ALL, we undertook serial measurements of markers of bone and collagen turnover, insulin-like growth factor (IGF)-I and its binding proteins (IGFBPs)-3 and -2 during the second year of continuing chemotherapy. In eight patients we also measured lower leg length by knemometry. Height SD scores, lower leg length velocity, IGF-I, and markers of bone collagen turnover did not differ significantly from healthy children. However, bone alkaline phosphatase, a marker of the differentiated osteoblast, was lower (mean SD score, -0.64; p < 0.0001), whereas procollagen type III N-terminal propeptide (P3NP, a marker of soft tissue collagen turnover; mean SD score, +0.93, p < 0.05), IGFBP-3 (mean SD score, +0.76; p < 0.01), and IGFBP-2 (mean SD score, +1.24, p = 0.01) were all higher than in healthy children. IGFBP-3 decreased during episodes of afebrile neutropenia (p < 0.05). Within 3 mo after completion of treatment, bone ALP increased in all eight patients, but collagen markers showed little change. IGFBP-2 returned to normal posttreatment, but P3NP and IGFBP-3 remained significantly elevated compared with healthy children (mean SD scores, +1.51 and +1.36, respectively; p < 0.01). We conclude that continuing chemotherapy was associated with normal growth and bone collagen turnover but enhanced soft tissue collagen turnover. Bone bone alkaline phosphatase was low throughout treatment, which suggests impaired osteoblast differentiation resulting from a direct effect of chemotherapy on bone. Although the effect was reversible, the long-term implications for bone health in survivors remain uncertain.

Adolescent↗
PubMed2000

Subfertility following treatment for childhood cancer.

The majority of children with cancer can now expect to be cured. Recent advances in assisted reproduction have focused attention on the long-term fertility outcome for these survivors. This article summarizes the current state of our knowledge about who is at risk of subfertility after childhood cancer and discusses possibilities of fertility preservation that are currently being researched.

Child↗
PubMed2000

Human bone cell hyperpolarization response to cyclical mechanical strain is mediated by an interleukin-1beta autocrine/paracrine loop.

Mechanical stimuli imparted by stretch, pressure, tension, fluid flow, and shear stress result in a variety of biochemical responses important in bone (re)modeling. The molecules involved in the recognition and transduction of mechanical stimuli that lead to modulation of bone cell function are not yet fully characterized. Cyclical pressure-induced strain (PIS) induces a rapid change in membrane potential of human bone cells (HBC) because of opening of membrane ion channels. This response is mediated via integrins and requires tyrosine kinase activity and an intact actin cytoskeleton. We have used this electrophysiological response to further study the signaling events occurring early after mechanical stimulation of HBC. Stimulation of HBC at 0.33 Hz PIS, but not 0.104 Hz PIS, results in the production of a transferable factor that induces membrane hyperpolarization of unstimulated HBC. The production of this factor is inhibited by antibodies to beta1-integrin. Interleukin-1beta (IL-1beta and prostaglandin E2 (PGE2) were identified as candidate molecules for the transferable factor as both were shown to induce HBC hyperpolarization by opening of small conductance calcium-activated potassium channels, the means by which 0.33 Hz PIS causes HBC hyperpolarization. Antibodies to IL-1beta, but not other cytokines studied, inhibit the hyperpolarization response of HBC to 0.33 Hz PIS. Comparison of the signaling pathways required for 0.33 Hz PIS and IL-1beta-induced membrane hyperpolarization shows that both involve the phospholipase C/inositol triphosphate pathway, protein kinase C (PKC), and prostaglandin synthesis. Unlike 0.33 Hz PIS-induced membrane hyperpolarization, IL-1beta-induced hyperpolarization does not require tyrosine kinase activity or an intact actin cytoskeleton. These studies suggest that 0.33 Hz PIS of HBC induces a rapid, integrin-mediated, release of IL-1beta with a subsequent autocrine/paracrine loop resulting in membrane hyperpolarization. IL-1beta production in response to mechanical stimuli is potentially of importance in regulation of bone (re)modeling.

Antibodies↗
PubMed1999

Totally implantable central venous access devices for paediatric oncology patients.

BACKGROUND: Totally implantable central venous access devices (ports) have been available for over 10 years but have not achieved widespread use in paediatric oncology patients. We reviewed our experience with these devices over 9 years to assess their safety and acceptability. PROCEDURE: We conducted a retrospective review of insertion technique and reasons for removal of all ports placed in paediatric oncology patients in this hospital between 1989 and 1996, with follow-up until 1998. Acceptability of both ports and external catheters was assessed by a questionnaire in a subgroup of families attending the oncology clinic. RESULTS: One hundred forty-nine ports were inserted during the study period. The median catheter life was 399 days (4-1,406), with a total of 69,342 catheter days. Sixty-nine percent of ports were removed electively at the end of treatment; 8% required removal because of infection and 5% because of blockage. No ports were accidentally dislodged or damaged. Children experienced significantly less restriction of activity with a port compared to an external catheter and greatly preferred the cosmetic appearance. The need for needle insertion to access the port was not seen as a disadvantage by most families. CONCLUSIONS: Ports can provide satisfactory central venous access for the majority of paediatric oncology patients, with a low risk of line-related complications and a high degree of acceptability to children and their parents.

Adolescent↗
PubMed1999

Congenital hemihypertrophy and epithelioid haemangioendothelioma in a 10-year-old boy: a case report.

Epithelioid haemangioendothelioma has not been previously described in a patient with congenital hemihypertrophy and diabetes mellitus. Hepatic nodules were incidentally discovered on a routine US examination searching for known associated abnormalities. Pulmonary nodules were present on chest X-ray and CT of the lungs. The diagnosis was confirmed by open biopsy of a hepatic nodule. Despite significant disease progression the patient remains symptom free.

Child↗