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Biomedical subjects

T Johnston

Publications and source records attributed to T Johnston.

At least 19 recordsLinked to original sources
PubMed2006

Financial analysis of potential donor management at a medicare-approved transplant hospital.

The purpose of this study was to perform a financial analysis of severe brain injured (SBI) patient management to determine potential reimbursement versus net losses in relation to organ donation and transplantation at a transplant center. We undertook a retrospective analysis of financial records of medically suitable referrals to the organ procurement organization (OPO) from our institution for fiscal years 2002-2003. This included (1) hospital cost and reimbursement, (2) OPO reimbursement for actual donors, (3) financial returns on local transplant activity solely supported by local donor activity and (4) Medicare incentives for local organ donation. There were 48 potential and 18 organ donors for this period. The consent rate reduced from 50% to 25% if family was offered withdrawal of care. After reimbursements from OPO, Medicare incentives and kidney transplant activity solely supported by local organ donation were figured in, the total returns were 244% of total cost of SBI patient management. Aggressive proactive management of severely brain injured patients remains a good medical practice. For Medicare-approved transplant centers, there are additional financial incentives to aggressively treat these patients and pursue organ donation. Prematurely offering withdrawal of care negatively impacts on the organ donation process and hurts institutions financially.

Brain Injuries↗
PubMed2003

Characterization of cationic amino acid transporters and expression of endothelial nitric oxide synthase in human placental microvascular endothelial cells.

We investigated the expression and activity of arginine transporters and endothelial nitric oxide synthase (eNOS) in human placental microvascular endothelial cells (HPMEC). Using RT-PCR amplification products for eNOS, CAT1, CAT2A, CAT2B, CAT4, 4F2hc (CD98), rBAT and the light chains y+LAT1, y+LAT2, and b0+T1 were detected in HPMEC, but not B0+. Immunohistochemistry and Western blotting confirmed the presence of 4F2hc and CAT1 protein in HPMEC. 4F2hc-light chain dimers were indicated by a shift in molecular mass detected under nonreducing conditions. L-Arginine transport into HPMEC was independent of Na+ or Cl- and was inhibited by the neutral amino acid glutamine, but not by cystine. The Ki for glutamine inhibition was greater in the absence of Na+. Kinetic analysis supported a two-transporter model attributed to system y+L and system y+. Expression of eNOS in HPMEC was detectable by immunohistochemistry and ELISA but not by Western blotting. Activity of eNOS in HPMEC, measured over 48 h, either as the basal production of nitric oxide (NO) or as the accumulation of intracellular cGMP was not detectable. We conclude that HPMEC transport cationic amino acids by systems y+ and y+L and that basal eNOS expression and activity in these cells is low.

Amino Acid Transport Systems, Basic↗
PubMed2003

Changes in GABA(B) receptor mRNA expression in the rodent basal ganglia and thalamus following lesion of the nigrostriatal pathway.

Loss of striatal dopaminergic innervation in Parkinson's disease (PD) is accompanied by widespread alterations in GABAergic activity within the basal ganglia and thalamus. Accompanying changes in GABA(B) receptor binding have been noted in some basal ganglia regions in parkinsonian primates, suggesting that plasticity of this receptor may also occur in PD. However, the molecular mechanisms underlying the changes in receptor binding and the manner and extent to which different GABA(B) receptor mRNA subunits and splice-variants are affected remain unknown. This study used in situ hybridisation to examine the full profile of changes in expression of the known rat GABA(B) receptor genes and gene variants in the basal ganglia and thalamus of rats, brought about by degeneration of the nigrostriatal tract. All of the GABA(B) mRNA species examined showed unique expression patterns throughout the basal ganglia and thalamus. In addition, all exhibited a marked loss of expression (between 46 and 80%) in the substantia nigra pars compacta of animals bearing a complete 6-hydroxydopamine-induced lesion of the nigrostriatal tract, confirming the presence of these variants in dopaminergic neurones in this region. Further analysis of autoradioagrams revealed additional changes only in GABA(B(1a)) mRNA in discrete anatomical regions. Expression of the GABA(B(1a)) variant was significantly increased in the substantia nigra pars reticulata (33+/-2%), entopeduncular nucleus (26+/-1%) and the subthalamic nucleus (16+/-1%). Since these regions all receive reduced GABAergic innervation following nigrostriatal tract lesioning, it is possible that the increased expression occurs as a compensatory measure. In conclusion, these data demonstrate that GABA(B) receptor genes exhibit regional- and subunit/variant-specific plasticity at the molecular level under parkinsonian conditions.

Animals↗
PubMed2001

Multiple renal arteries do not pose an impediment to the routine use of laparoscopic donor nephrectomy.

UNLABELLED: Since the first description by Ratner and collegues in 1996, laparoscopic live-donor nephrectomy is gaining wide acceptance in an attempt to minimize the donor morbidity, length of hospital stay and length of time to return to work. It is unknown whether multiple renal arteries pose additional problems with laparoscopic donor nephrectomy. In November 1998, our institution initiated laparoscopic donor nephrectomy program. In the ensuing 19 months, we performed 25 living donor renal transplants, 24 of them using laparoscopic donor nephrectomy. The left kidney was procured in all cases. Eight donor candidates (33%) had two or more renal arteries (two arteries in five patients and three patients). RESULTS: In six cases (25%), findings at surgery differed from the CT angography results (in four cases, CT angiogram reported fewer arteries than were found at surgery and in two cases it reported more). We found no significant differences in both donor outcomes and recipient, based on the presence or absence of multiple renal arteries. Among donor outcomes, we found equivalent results for donor warm ischemia time total donor operating time, and donor length of stay. For recipient outcomes, we found no significant differences between groups for the incidence of acute tubular necrosis (ATN), graft survival and most recent serum creatinine. In one case, we constructed two arteries into a single conduit on the backtable prior to transplantation. However, in most cases with multiple arteries, we implanted the arteries separately into the recipient external iliac artery. Based on this experience, we do not find the presence of multiple renal arteries to be a barrier to the successful use of kidney grafts procured by laparoscopic donor nephrectomy.

Adult↗
PubMed2001

Nouns and verbs in Australian sign language: an open and shut case?

Results of the noun-verb pair comprehension and production tests from the Test Battery for Auslan Morphology and Syntax (Schembri et al., 2000) are re-presented, re-analyzed, and compared to data from two other cases also dealing with noun-verb pairs: the Auslan lexical database and a comparison of Auslan and American Sign Language (ASL) signs. The data elicited through the test battery and presented in this article confirm the existence of formationally related noun-verb pairs in Auslan in which the verb displays a single movement and the noun displays a repeated movement. The data also suggest that the best exemplars of noun-verb pairs of this type in Auslan form a distinct set of iconic (mimetic) signs archetypically based on inherently reversible actions (such as opening and shutting). This strong iconic link perhaps explains why the derivational process appears to be of limited productivity, though it does appear to have "spread" to a number of signs that appear to have no such iconicity. There appears to be considerable variability in the use of the derivational markings, particularly in connected discourse, even for signs of the "open and shut" variety. Overall, the derivational process is apparently still closely linked to an iconic base, is incipient in the grammar of Auslan, and is thus best described as only partially grammaticalized.

Journal Article↗
PubMed2000

Climate change and the adaptability of agriculture: a review.

The assessment of climate change impacts on agriculture has emerged as a recognizable field of research over the past 15 years or so. In a relatively short period, this area of work has undergone a number of important conceptual and methodological developments. Among many questions that have been debated are the adaptability of agriculture to climate change and the importance of land management adjustments in reducing the adverse effects of climate change. In turn, this latter focus has spawned a discussion regarding the nature of adaptation and the ability of agriculture to respond to sudden and rapid climatic changes. In this paper we present an overview of this debate. It is argued that the first generation of climate change impact studies generally ignored the possibility that agriculturalists may adjust their farming practices in order to cope with climate change or to take advantage of new production opportunities. This conceptual oversight has been largely eliminated over the past five years or so. However, questions remain surrounding the likelihood that various adaptive strategies will actually be deployed in particular places. In this paper, we stress the importance of studying adaptation in the context of decision-making at the individual farm level and beyond.

Agriculture↗
PubMed1999

In vivo assessment of failed trophoblastic invasion of the spiral arteries in pre-eclampsia.

OBJECTIVE: To assess the ability of colour/pulsed Doppler ultrasound to detect failed physiologic change of the spiral arteries in pregnancies complicated by pre-eclampsia. DESIGN: Prospective matched-pairs case controlled study. SETTING: Tertiary referral teaching hospital. SAMPLE: Sixteen women with severe pre-eclampsia and 16 normotensive controls. METHODS: Colour/pulsed Doppler assessment of blood flow in the uterine arteries and spiral arteries in central and peripheral parts of the placental bed. MAIN OUTCOME MEASURES: Impedance to blood flow in the spiral arteries in pre-eclamptic group compared with normotensive controls. RESULTS: In women with pre-eclampsia there is significantly higher impedance to blood flow in spiral arteries compared with normotensive women. CONCLUSIONS: Ultrasound colour/pulsed Doppler based investigation of blood flow in the spiral arteries in ongoing pregnancy can detect failed physiological change of these vessels in pre-eclampsia. This is in concordance with histologic data.

Arteries↗
PubMed1999

Taxometric analysis of impression management and self-deception on the MMPI-2 in child-custody litigants.

The typology of impression management (IM), a deliberate attempt to create a positive social image, and self-deceptive positivity (SDP), an unintentional concealment of symptoms, were examined using taxometric procedures with MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989) underreporting scales in several custody-litigant samples. IM was identified as a taxon using several procedures and estimates of the base rate that were consistent (.40, .37, .31, .36, .37). SDP was better characterized as a dimensional construct. Means and estimated validities for MMPI-2 underreporting scales in this sample are reported. IM and SDP appear to be distinct and measurable underreporting constructs on the MMPI-2.

Adult↗
PubMed1997

Stimulation of megakaryocyte and platelet production by a single dose of recombinant human thrombopoietin in patients with cancer.

BACKGROUND: Thrombocytopenia is frequently encountered in patients with cancer. It is associated with an increased risk for clinically important bleeding episodes, which increases the demand for platelet transfusion. OBJECTIVE: To assess hematopoietic response to and clinical tolerance of recombinant human thrombopoietin, a recently cloned novel cytokine. DESIGN: Phase I and II clinical cohort study. SETTING: The University of Texas M.D. Anderson Cancer Center, Houston, Texas. PATIENTS: 12 patients with sarcoma who had high risk for severe chemotherapy-induced thrombocytopenia. INTERVENTION: A single intravenous dose of thrombopoietin (0.3 to 2.4 micrograms/kg of body weight) 3 weeks before chemotherapy. MEASUREMENTS: Peripheral blood and bone marrow evaluation before and after thrombopoietin administration. RESULTS: A single dose of thrombopoietin was associated with an increase in platelet counts (mean increase from baseline, 61% to 213%; P = 0.002) in a dose-related manner. This increase began by day 4 in most patients and peaked on a median of day 12. This sustained response was associated with a prolonged serum thrombopoietin half life (20 to 30 hours). The platelets appeared morphologically normal and showed normal aggregation in response to various agonists. Platelet response was accompanied by a dose-related increase in bone marrow megakaryocytes (as much as 4-fold); the expansion of the bone marrow progenitors of myeloid, erythroid, multipotential, and megakaryocytic lineages; and the marked mobilization of progenitors (maximum, 5.7-fold to 10-fold) of multiple cell lineages in the peripheral blood. Treatment was well tolerated, and no serious adverse events occurred. CONCLUSIONS: Thrombopoietin, administered as a single dose, is a potent stimulus for prolonged platelet production in humans. It merits further evaluation for the prevention and treatment of thrombocytopenia.

Antibodies↗
PubMed1997

Screw osteosynthesis compared with wire osteosynthesis in advancement genioplasty: a retrospective study of skeletal stability.

OBJECTIVE: To compare the skeletal stability of wire and screw fixation after advancement genioplasty. DESIGN: Retrospective study. SETTING: Teaching hospital and private practice, South Africa. SUBJECTS: 40 Patients who required advancement genioplasty, 20 in each group. INTERVENTIONS: Advancement genioplasty measurements made on cephalometric radiographs before and immediately after operation, and at least 6 months later. MAIN OUTCOME MEASURES: Comparison of horizontal and vertical measurements. RESULTS: In the screw (rigid) group mean horizontal advancement was 6.3 mm followed by a relapse of 0.3 mm during the follow up period. The corresponding figures for the wire (non-rigid) group were 5.8 and 0.5 mm. The two differed significantly in the degree of vertical change but the result is clinically unimportant. There was no difference in the degree of horizontal change. CONCLUSION: There was no difference in skeletal stability between the two groups.

Adolescent↗
PubMed1997

Expect the worse or hope for the best? Prenatal diagnosis of geleophysic dysplasia.

Geleophysic dysplasia is a rare, autosomal recessive disorder which causes disproportionate short stature associated with severe physical handicaps, but is compatible with survival into adulthood. We present a case, a first-born child, where genetic counselling difficulties arose following ultrasound recognition of short-limbed dwarfism in association with polyhydramnios and an initial incorrect prenatal diagnosis of lethal chondrodysplasia. After birth of the surviving affected infant, the parents had great difficulty accepting that there had been a prenatal misdiagnosis and they were greatly disappointed by our inability to predict the postnatal survival of an infant to whom no hope of life had previously been given. The correct diagnosis was not made until the proband was nearly 1 year old, and the true prognosis then became clearer. This experience underlines the relative ease of prenatal recognition of skeletal growth abnormalities compared with the considerable difficulties experienced in reaching a precise diagnosis. Thus, following prenatal diagnosis of unspecified chondrodysplasia when parents seek definite information about the prognosis, the temptation to be either overpessimistic or overoptimistic should be avoided.

Abnormalities, Multiple↗
PubMed1996

An in vitro study of the efficacy of mouthguard protection for dentoalveolar injuries in deciduous and mixed dentitions.

Sports-related dental trauma remains a risk for children and adolescents. Although mouthguards provide protection, up to 25% of dentoalveolar injuries can occur with a mouthguard in place. This study examined the effect of mouthguard protection in an in vitro model. A total of 97 sheep mandibular segments with incisors at four developmental stages (early deciduous, ED, n = 37; middle deciduous, MD, n = 20; late deciduous, LD, n = 18; mixed dentition, PD, n = 22) was used. Customised pressure formed mouthguards (MG) provided protection from trauma produced by a servohydraulic materials testing machine to test incisors. Injuries were examined clinically, radiographically and by dissection. Mean forces required to produce dentoalveolar injury were significantly greater in test (with MG) teeth than control (no MG) teeth. Mean forces to produce injury in test teeth decreased with resorbing root lengths. Deciduous incisors differed in injury type: subluxations and horizontal root fractures predominated in test teeth; lateral luxations and horizontal root fractures in control teeth. Predominant injuries in test and control permanent incisors were enamel infractions and subluxations. The magnitude of lateral luxation measurements of individual teeth was reduced significantly by mouthguard protection in both deciduous and permanent dentitions. The mouthguard tended to increase the mobility of the teeth it encompassed and, in some instances, promoted dentoalveolar injury of adjacent teeth.

Alveolar Process↗
PubMed1995

A human parthenogenetic chimaera.

In mice, parthenogenetic embryos die at the early postimplantation stage as a result of developmental requirements for paternally imprinted genes, particularly for formation of extraembryonic tissues. Chimaeric parthenogenetic<==>normal mice are viable, however, due to non-random differences in distribution of their two cell types. Species differences in imprinting patterns in embryo and extra-embryonic tissues mean that there are uncertainties in extrapolating these experimental studies to humans. Here, however, we demonstrate that parthenogenetic chimaerism can indeed result in viable human offspring, and suggest possible mechanisms of origin for this presumably rare event.

Animals↗