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Biomedical subjects

D Leonard

Publications and source records attributed to D Leonard.

At least 19 recordsLinked to original sources
PubMed2006

Cement pressurisation in the acetabulum.

Cement pressurisation is an important step in total hip arthroplasty that determines the long-term integration at the cement-bone interface. Our aim was to evaluate the performance of a new pressuriser designed by us against the standard existing pressurisers in an in vitro experimental set-up using two parameters: cement penetration and cement pressurisation. A polypropylene cup model was designed to represent the acetabulum. DePuy's T-handle, Exeter and our own plunger type pressuriser were each tested for cement pressurisation in this acetabular model. Cement penetration and pressures were measured. The cement intrusion into the capillaries with the DePuy pressuriser was found to vary between 2 and 8 mm (mean: 5 mm at the pole and 4.6 mm at the rim), with the Exeter pressuriser it varied between 3 and 9 mm (mean: 5.8 mm at the pole and 7.8 mm at the rim) and with the plunger type pressuriser it varied between 4 and 6 mm (mean 5.2 mm at the pole and 4.8 mm at the rim). The peak pressure achieved with the DePuy pressuriser was 60 kPa whereas it was 70 kPa with the plunger type pressuriser. The mean penetration with the plunger type pressuriser was found to be better than the other types. The penetration was found to be more uniform with equal penetration at the rim as well as at the pole.

Acetabulum↗
PubMed2006

Validation of the small-punch test as a technique for characterizing the mechanical properties of acrylic bone cement.

This paper examines the validity of using the small-punch test technique as a means of quantifying the mechanical properties of acrylic bone cement under different test conditions. The elastic moduli calculated using the small-punch test method were compared with data measured using the international standard for acrylic bone resin, ISO 5833. Conclusions from the study indicate that the small-punch test is a reproducible miniature specimen test method that can be used to characterize the mechanical properties of retrieved acrylic bone cement as used in total joint replacement surgery. Moreover, the test conditions were found to influence the elastic modulus of acrylic bone cement. The test temperature had a greater effect on the elastic behaviour of the bone cement than the test medium.

Bone Cements↗
PubMed2005

Experimental investigation of geologically produced antineutrinos with KamLAND.

The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of 238U and 232Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained.

Journal Article↗
PubMed2001

Potential health and environmental issues of mercury-contaminated amalgamators.

BACKGROUND: Dental amalgamators may become contaminated internally with metallic mercury. This contamination may result from mercury leakage from capsules during trituration or from the long-term accrual from microscopic exterior contaminants that result from the industrial assembly process. The potential health risk to dental personnel from this contamination is unknown. METHODS: The authors assessed used amalgamators from the federal service inventory for the amounts of mercury vapor levels, as well as the visual presence of mercury contamination. They evaluated these amalgamators for potential mercury vapor health risk, using established National Institute for Occupational Safety and Health methods and American Conference of Governmental Industrial Hygienists standards. RESULTS: Ten of the 11 amalgamators assessed had measurable mercury vapor levels. Four amalgamators were found to have internal static mercury vapor levels above Occupational Safety and Health Administration ceiling limit thresholds. During a simulated worst-case clinical use protocol, the authors found that no amalgamators produced mercury vapor in the breathing space of dental personnel that exceeded established time-weighted federal mercury vapor limits. CONCLUSIONS: Amalgamators may be contaminated internally with metallic mercury. Although the authors detected mercury vapor from these units during aggressive, simulated clinical use, dilution factors combined with room air exchange were found to keep health risks below established federal safety thresholds. CLINICAL IMPLICATIONS: Dental personnel should be aware that amalgamators may be contaminated with mercury and produce minute amounts of mercury vapor. These contaminated amalgamators may require disposal as environmentally hazardous waste.

Air Pollution, Indoor↗
PubMed2000

Albuminuria in Australian Aboriginal people: prevalence and associations with components of the metabolic syndrome.

AIMS/HYPOTHESIS: To examine the prevalence and associations with the metabolic syndrome of albuminuria among Australian Aboriginal people. METHODS: Early-morning urine specimens were collected as part of community-based risk factor surveys assessing the prevalence of diabetes and cardiovascular disease in eight remote communities, with a sample size of 1,075 people. Microalbuminuria was defined as urinary albumin : creatinine ratio 3.4-33.9 mg/mmol, macroalbuminuria as albumin: creatinine ratio equal to or greater than 34 mg/mmol. RESULTS: There were high prevalences of microalbuminuria (men 22.2 %, women 26.9 %) and of macroalbuminuria (men 10.4%, women 13.5%). There were highly statistically significant linear associations of microalbuminuria and macroalbuminuria with increasing number of coexisting components of the metabolic syndrome (hypertension, glucose intolerance, dyslipidaemia, insulin resistance, abdominal obesity): among people with zero, one, two and three to five of these conditions, respectively, prevalence of microalbuminuria was 16%, 20%, 36% and 32% (p < 0.001); prevalence of macroalbuminuria was 2%, 6%, 12% and 32% (p < 0.001). There were independent associations of microalbuminuria with hypertension (odds ratio, 95% confidence interval = 2.36, 1.63-3.42) and diabetes (2.10, 1.28-3.45): macroalbuminuria was independently associated with hypertension (6.39, 3.93-10.4), diabetes (3.49, 1.93-6.28) and abdominal obesity (4.56, 2.40-8.64) and had a weaker association with insulin resistance (1.99, 1.12-3.54). Dyslipidaemia and impaired glucose tolerance were neither independently associated with microalbuminuria or macroalbuminuria, nor was insulin resistance or abdominal obesity independently associated with microalbuminuria. CONCLUSION/INTERPRETATION: There was a strong clustering of albuminuria with components of the metabolic syndrome. Diabetes, hypertension and abdominal obesity are major contributors to high rates of albuminuria among Australian Aboriginal people.

Adolescent↗
PubMed2000

Cautery-assisted palatal stiffening operation for the treatment of obstructive sleep apnea syndrome.

Cautery-assisted palatal stiffening operation (CAPSO) is a recently developed single office-based procedure performed with local anesthesia for the treatment of palatal snoring. A midline strip of soft palate mucosa is removed, and the wound is allowed to heal by secondary intention. The flaccid palate is stiffened, and palatal snoring ceases. This prospective study evaluated the ability of CAPSO to treat obstructive sleep apnea syndrome (OSAS). Twenty-five consecutive patients with OSAS underwent CAPSO. Responders were defined as patients who had a reduction in apnea-hypopnea index (AHI) of 50% or more and an AHI of 10 or less after surgery. By these strict criteria, 40% of patients were considered to have responded to CAPSO. Mean AHI improved from 25.1+/-12.9 to 16.6+/-15.0 (P = 0.010). The Epworth Sleepiness Scale, a subjective measure of daytime sleepiness, improved from 12.7+/-5.6 to 8.8+/-4.6 (P<0.001). These results indicate that CAPSO is as effective as other palatal surgeries in the management of OSAS.

Adult↗
PubMed1999

Block of brain sodium channels by peptide mimetics of the isoleucine, phenylalanine, and methionine (IFM) motif from the inactivation gate.

Inactivation of sodium channels is thought to be mediated by an inactivation gate formed by the intracellular loop connecting domains III and IV. A hydrophobic motif containing the amino acid sequence isoleucine, phenylalanine, and methionine (IFM) is required for the inactivation process. Peptides containing the IFM motif, when applied to the cytoplasmic side of these channels, produce two types of block: fast block, which resembles the inactivation process, and slow, use-dependent block stimulated by strong depolarizing pulses. Fast block by the peptide ac-KIFMK-NH2, measured on sodium channels whose inactivation was slowed by the alpha-scorpion toxin from Leiurus quinquestriatus (LqTx), was reversed with a time constant of 0.9 ms upon repolarization. In contrast, control and LqTx-modified sodium channels were slower to recover from use-dependent block. For fast block, linear peptides of three to six amino acid residues containing the IFM motif and two positive charges were more effective than peptides with one positive charge, whereas uncharged IFM peptides were ineffective. Substitution of the IFM residues in the peptide ac-KIFMK-NH2 with smaller, less hydrophobic residues prevented fast block. The positively charged tripeptide IFM-NH2 did not cause appreciable fast block, but the divalent cation IFM-NH(CH2)2NH2 was as effective as the pentapeptide ac-KIFMK-NH2. The constrained peptide cyclic KIFMK containing two positive charges did not cause fast block. These results indicate that the position of the positive charges is unimportant, but flexibility or conformation of the IFM-containing peptide is important to allow fast block. Slow, use-dependent block was observed with IFM-containing peptides of three to six residues having one or two positive charges, but not with dipeptides or phenylalanine-amide. In contrast to its lack of fast block, cyclic KIFMK was an effective use-dependent blocker. Substitutions of amino acid residues in the tripeptide IFM-NH2 showed that large hydrophobic residues are preferred in all three positions for slow, use-dependent block. However, substitution of the large hydrophobic residue diphenylalanine or the constrained residues phenylglycine or tetrahydroisoquinoline for phe decreased potency, suggesting that this phe residue must be able to enter a restricted hydrophobic pocket during the binding of IFM peptides. Together, the results on fast block and slow, use-dependent block indicate that IFM peptides form two distinct complexes of different stability and structural specificity with receptor site(s) on the sodium channel. It is proposed that fast block represents binding of these peptides to the inactivation gate receptor, while slow, use-dependent block represents deeper binding of the IFM peptides in the pore.

Algorithms↗
PubMed1999

Susceptibility to chlordecone-carbon tetrachloride induced hepatotoxicity and lethality is both age and sex dependent.

The present paper examines the susceptibility to chlordecone (Kepone, CD) and carbon tetrachloride across different ages (35, 45, and 63-days-old) in male and female Sprague-Dawley rats using different lengths of time on a CD diet (10 ppm). The principal findings are that the hepatotoxicity and mortality associated with CD-CCl4 interaction is highly age-dependent for both sexes. There was marked hepatotoxicity occurring in both sexes as they reached 45 days-of-age and females were considerably more susceptible than males to both CD-CCl4-induced hepatotoxicity and lethality. While 63-day-old females are more susceptible to the CD-CCl4 interaction than their male counterparts, the magnitude of the sex difference is diminished from that observed in 45-day-old rats. These findings challenge the hypothesis of Mehendale (1990, Med. Hypotheses 33, 289-299) that chlordecone (CD) pretreatment eliminates the well-established sex difference in CCl4-treated rats. In contrast to the CD-CCl4 findings, the sex difference in CCl4-induced hepatotoxicity was not age-dependent and was consistent over the three ages studied. The findings that CD-CCl4 interaction is highly age-dependent (within the 3 ages tested) but that CCl4-induced hepatotoxicity is not, suggest that the CD-CCl4 interaction acts via a mechanism that does not primarily involve CCl4 potentiation.

Age Factors↗
PubMed1999

Pre-hospital emergency medical services: a population based study of pediatric utilization.

OBJECTIVES: To examine emergency medical services (EMS) usage by children in one state. METHODS: Dispatch of an EMS vehicle in response to a call in the US is referred to as a "run". Runs for Utah for 1991-92 were linked to corresponding hospital records. Abbreviated injury severity scores (AISs) were assigned using ICDMAP-90 software. RESULTS: For the two year period there were at least 15 EMS runs per 100 children per year, with incomplete reporting from rural areas. EMS response and scene times were similar for all age groups, but interventions were less frequent for children under 5 years of age. When the principal AIS region of injury was the head, neck, or face, cervical immobilization was less frequent for children less than 5 years of age (54%) than for older children (76%) and immobilization was associated with improved outcome, using the crude measure of lower hospital charges. There was a similar association between splinting of upper extremity fractures and reduced hospital charges. Both associations did not appear to be due to differences in injury severity. CONCLUSIONS: The majority of EMS use by children is for trauma. Children less than 5 years of age are less likely to have an EMS intervention than older children. Whether the lower frequency of interventions is due to the lack of properly sized equipment on the vehicle, or to other factors, is undetermined.

Adolescent↗
PubMed1997

Synergy between anions and farnesyldiphosphate competitive inhibitors of farnesyl:protein transferase.

Investigation of the comparative activities of various inhibitors of farnesyl:protein transferase (FPTase) has led to the observation that the presence of phosphate or pyrophosphate ions in the assay buffer increases the potency of farnesyl diphosphate (FPP) competitive inhibitors. In addition to exploring the phenomenon of phosphate synergy, we report here the effects of various other ions including sulfate, bicarbonate, and chloride on the inhibitory ability of three FPP competitive compounds: Cbz-His-Tyr-Ser(OBn)TrpNH2 (2), Cbz-HisTyr(OPO42-)-Ser(OBn)TrpNH2 (3), and alpha-hydroxyfarnesyl phosphonic acid (4). Detailed kinetic analysis of FPTase inhibition revealed a high degree of synergy for compound 2 and each of these ions. Phosphorylation of 2 to give 3 completely eliminated any ionic synergistic effect. Moreover, these ions have an antagonistic effect on the inhibitory potency of compound 4. The anions in the absence of inhibitor exhibit non-competitive inhibition with respect to FPP. These results suggest that phosphate, pyrophosphate, bicarbonate, sulfate, and chloride ions may be binding at the active site of both free enzyme and product-bound enzyme with normal substrates. These bound complexes increase the potency of FPP competitive inhibitors and mimic an enzyme:product form of the enzyme. None of the anions studied here proved to be synergistic with respect to inhibition of geranylgeranyl transferase I. These findings provide insight into the mechanism of action of FPP competitive inhibitors for FPTase and point to enzymatic differences between FPTase and geranylgeranyl transferase I that may facilitate the design of more potent and specific inhibitors for these therapeutically relevant target enzymes.

Alkyl and Aryl Transferases↗
PubMed1997

T cell receptor (TCR) mini-gene mRNA expression regulated by nonsense codons: a nuclear-associated translation-like mechanism.

Premature termination codons (PTCs) are known to decrease mRNA levels. Here, we report our investigation of the mechanism for this downregulation using the TCR-beta gene, which acquires PTCs as a result of programmed rearrangements that occur during normal thymic development. We found that a mini-gene version of this gene, which contains only three TCR-beta exons, exhibited efficient downregulation in response to PTCs. This demonstrates that the full coding sequence is not necessary for appropriate regulation. Mutation of the translation start AUG and a downstream in-frame AUG that displayed similarity to the Kozak consensus sequence reversed the downregulatory response to PTCs. Thus, an AUG start codon is required to define the reading frame of a PTC. Specific suppressor tRNAs also reversed the downregulatory response, strongly implicating the involvement of a translation-like process. Remarkably, the addition of suppressor tRNAs or the inactivation of the start AUGs caused a dramatic rise in the levels of PTC-bearing transcripts in the nuclear fraction prepared by two independent methods. Collectively, our results provide evidence for a codon-based surveillance mechanism associated with the nucleus that downregulates aberrant transcripts encoding potentially toxic polypeptides from nonproductively rearranged genes.

Animals↗
PubMed1997

Are there ethnic differences in the association between body weight and resistance, measured by bioelectrical impedance?

OBJECTIVE: To describe ethnic differences in the relationship between body size and body composition. Knowledge about such differences is important when studying obesity-related complications, such as hypertension and non-insulin dependent diabetes, because it may not be possible to generalize results from one study population to other populations. DESIGN: Cross-sectional study. SUBJECTS: Four groups of different ethnic identity (2987 Caucasians (Danes), 243 predominantly Melanesian (Torres Strait Islanders from northern Australia), 206 Australian Aborigines and 146 Polynesians (New Zealand Samoans), aged 30-70 y, were studied. MEASUREMENTS: We examined associations between body weight and bioelectrical impedance, as a measure of body composition. RESULTS: Except for Australian Aborigines, associations (slopes) between body weight and resistance were generally constant in the different ethnic groups, once height and age differences had been considered, indicating that this relationship may involve a certain universality, that is independent of the population specificity for impedance measurement. Systematic differences in instrument readings or electrodes did not seem to be responsible for the differences found. CONCLUSION: With the exception of Australian Aborigines, there may be a constant relation between body size and body composition (total body water or fat free mass) of different ethnic groups, that depends on gender and age category only.

Adult↗