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Biomedical subjects

P A White

Publications and source records attributed to P A White.

At least 19 recordsLinked to original sources
PubMed2001

Causal judgments about relations between multilevel variables.

Three experiments presented stimulus information about cause and effect variables taking 3 quantitative values. Judgments tended to vary in accordance with considerations of conditions affecting the validity of causal inference from correlational data: whether causal candidates were presented simultaneously or in a temporal order such that one could affect the other and whether candidates were confounded with each other. The results supported a general hypothesis that causal judgments are moderated in accordance with acquired methodological intuitions. The fourth experiment showed that tendencies in correlation judgment were different from those in causal judgment, further supporting the hypothesis that causal judgment from multilevel variable information is, to some extent, determined by processes or conceptual frameworks specific to the domain of causal cognition.

Adult↗
PubMed2001

Right ventricular distension alters monophasic action potential duration during pulmonary arterial occlusion in anaesthetised lambs: evidence for arrhythmogenic right ventricular mechanoelectrical feedback.

Abnormal loading and distension of the right ventricle may induce arrhythmia through the process of mechanoelectrical feedback. Nonetheless, the electrophysiological effects of right ventricular distension are ill-defined and the mechanisms which underpin mechanoelectrical feedback in the right ventricle are unknown. We examined the effects of changes in right ventricular load (complete occlusion of both caval veins or the main pulmonary artery) in 14 anaesthetised lambs, instrumented with right ventricular surface electrodes and strain gauges for recording monophasic action potential and segment length, and an integrated conductance and micromanometer-tipped catheter for measurement of right ventricular pressure and volume. Caval occlusion did not alter right ventricular segment length and monophasic action potential duration. By contrast, pulmonary arterial occlusion increased the segment length and decreased the monophasic action potential duration at 25, 50 and 70% repolarisation by 29 +/- 6, 22 +/- 4 and 17 +/- 3 ms, respectively (all P < 0.01). Of the 42 pulmonary arterial occlusions, 38 were associated with early afterdepolarisations (EADs) which increased progressively in magnitude as the occlusion was maintained until, in 32, overt arrhythmia was observed. By contrast, none of the four occlusions in which EADs were not observed resulted in arrhythmia. As a result, the proportion of occlusions which resulted in arrhythmia were greater in those associated with EADs than in those which were not (P = 0.002). Right ventricular distension alters the pattern of repolarisation, precipitates early afterdepolarisations and results in a variety of ventricular arrhythmia, including ventricular tachycardia.

Action Potentials↗
PubMed2001

Correlation of in vitro susceptibilities to newer quinolones of naturally occurring quinolone-resistant Neisseria gonorrhoeae strains with changes in GyrA and ParC.

The in vitro activities of ciprofloxacin, trovafloxacin, moxifloxacin, and grepafloxacin against 174 strains of Neisseria gonorrhoeae isolated in Sydney, Australia, were determined. The strains included 84 quinolone-less-sensitive and -resistant N. gonorrhoeae (QRNG) strains for which ciprofloxacin MICs were in the range of 0.12 to 16 microg/ml. The QRNG included strains isolated from patients whose infections were acquired in a number of countries, mostly in Southeast Asia. The gyrA and parC quinolone resistance-determining regions (QRDR) of 18 selected QRNG strains were sequenced, and the amino acid mutations observed were related to the MICs obtained. The activities of moxifloxacin and grepafloxacin against QRNG were comparable to that of ciprofloxacin. Trovafloxacin was more active than the other quinolones against some but not all of the QRNG strains. Increments in ciprofloxacin resistance occurred in a step-wise manner with point mutations initiated in gyrA resulting in amino acid alterations Ser91-to-Phe, Ser91-to-Tyr, Asp95-to-Gly, and Asp95-to-Asn. Single gyrA changes correlated with ciprofloxacin MICs in the range 0.12 to 1 microg/ml. The Ser91 changes in GyrA were associated with higher MICs and further QRDR changes. QRNG strains for which ciprofloxacin MICs were greater than 1 microg/ml had both gyrA and parC QRDR point mutations. ParC alterations were seen in these isolates only in the presence of GyrA changes and comprised amino acid changes Asp86-to-Asn, Ser87-to-Asn, Ser87-to-Arg, Ser88-to-Pro, Glu91-to-Lys, and Glu91-to-Gln. QRNG strains for which MICs were in the higher ranges had double GyrA mutations, but again only with accompanying ParC alterations. Not only did the nature and combination of GyrA and ParC changes influence the incremental increases in ciprofloxacin MICs, but they seemingly also altered the differential activity of trovafloxacin. Our findings suggest that the newer quinolones of the type examined are unlikely to be useful replacements for ciprofloxacin in the treatment of gonorrhea, particularly where ciprofloxacin MICs are high or where resistance is widespread.

Anti-Infective Agents↗
PubMed2001

Integrons and gene cassettes in the enterobacteriaceae.

Integrons were detected in 59 of 120 (49%) urinary isolates of Enterobacteriaceae by PCR using degenerate primers targeted to conserved regions of class 1, 2, and 3 integrase genes. PCR sequencing analysis of the cassette arrays revealed a predominance of cassettes that confer resistance to the aminoglycosides and trimethoprim.

Aminoglycosides↗
PubMed2001

Validation and utility of novel volume reduction technique for determination of parallel conductance.

The parallel conductance volume, created by the conductivity of structures surrounding the ventricular blood pool, can be estimated by using a saline dilution technique. This paper examines the use of a novel volume reduction method, during a standard vena caval preload reduction maneuver, as an alternative to the routinely used saline dilution method to calibrate conductance catheter measurements in the left (LV) and right ventricle (RV) of animals and humans. The serial reproducibility of both methods was examined by measurement of percent difference, and by assessing the coefficient of repeatability 1) between two measurements within the same subject, 2) between the two techniques, and 3) interobserver variability. The effect of ventricular size and contractile state on the volume reduction technique was also observed. It was essential to ensure the technique was not affected by inotropic state. The volume reduction technique and saline dilution method were repeated at three different loading states (baseline, 5, and 10 microg x kg(-1) x min(-1) of dobutamine). The coefficient of repeatability between serial measurements was similar for both the volume reduction and saline dilution methods, and good interobserver variability was demonstrated. The volume reduction technique was compared with the saline dilution technique over a large range of ventricular sizes. No significant difference was observed in the RV or LV of adult humans or in the LV of neonatal pigs and children. There was no significant effect on either the saline dilution or the volume reduction technique as the inotropic state increased. In conclusion, the volume reduction technique is neither affected by ventricular size nor contractile state, is repeatable between different observers, and can be used to substitute the saline dilution method when preload reduction of the ventricle is being employed.

Adult↗
PubMed2000

Failure of stroke volume augmentation during exercise and dobutamine stress is unrelated to load-independent indexes of right ventricular performance after the Mustard operation.

BACKGROUND: Impaired right ventricular function has been implicated as a cause of reduced maximal exercise capacity after the Mustard operation for transposition of the great arteries. METHODS AND RESULTS: Fourteen asymptomatic survivors of the Mustard operation were studied. Each underwent conventional cardiac catheterization, and after satisfactory hemodynamics were confirmed, load-independent indexes of ventricular function were derived by conductance catheter during dobutamine infusion (0, 5, and 10 microg x kg(-1) x min(-1)). Seven patients also underwent upright exercise testing on a bicycle ergometer with analysis of respiratory gas exchange by continuous mass spectrometry. Accessible pulmonary blood flow was measured at each workload with an automated acetylene rebreathing technique. All patients exercised to a satisfactory end point (respiratory quotient >1.1). Maximum oxygen consumption during exercise was impaired compared with predicted values (mean, 77%; P:<0.02). Both exercise and dobutamine infusion were associated with an increase in cardiac index and heart rate and a reduced stroke volume index response. This was despite significantly improved indexes of myocardial contraction (end-systolic pressure volume relation, P:<0.001), preload recruitable stroke work index (P:<0.01), VA coupling (P:<0.001), and isovolumic relaxation (P:<0.001) during dobutamine infusion. There were no changes observed in end-diastolic pressure-volume relations, but there was failure to augment ventricular filling manifest by absence of change in dV/dt (P:=NS). CONCLUSIONS: The stroke volume response to exercise stress is reduced in patients after the Mustard operation. A similar failure to augment stroke volume occurs during dobutamine stress despite appropriate responses in load-independent indexes of contraction and relaxation. This is due to failure to augment right ventricular filling rates during tachycardia, presumably as a result of impaired AV transport, consequent to the abnormal intra-atrial pathways.

Cardiac Surgical Procedures↗
PubMed2000

Mixed viral infection identified using heteroduplex mobility analysis (HMA).

It is now recognised that mixed viral infection, or infection of an individual with two or more distinct strains of a single viral species, often occurs particularly with RNA viruses. Current methods for detection of mixed infection normally involve genotyping or cloning and DNA sequencing. These methods are not always accurate or sensitive at detecting mixed infection and cannot be used for large numbers of samples. Furthermore subsequent sequence determination of the coinfecting viruses is labour intensive. This paper describes a simple, generic method based upon PCR and heteroduplex mobility analysis (HMA) that can be used to rapidly determine mixed infection with two strains of the same virus. The utility of this method is illustrated with hepatitis C virus (HCV) and TT virus (TTV) as examples. PCR-HMA detected mixed infection in 3 (8%) of 38 sera from intravenous drug users (IVDU) and 28 (30%) of 70 TTV-positive sera from Australia, China, and Vietnam. HMA can also be used to screen recombinant colonies to identify the sequences of the coinfecting viruses. The methods described here could be applied to analyse any PCR product containing two or more divergent sequences, whether derived from viruses, bacteria, or eukaryotic organisms.

Base Sequence↗
PubMed2000

Characterisation of two new gene cassettes, aadA5 and dfrA17.

Escherichia coli INS33 was isolated from the urinary tract of an infected patient. It was resistant to ampicillin, chloramphenicol, spectinomycin, streptomycin, sulfafurazole, tetracycline and trimethoprim. PCR screening revealed the presence of a class 1 integron that harboured two new gene cassettes, designated dfrA17 and aadA5. The new dfrA17 cassette was 91% identical to the known dfrA7 cassette. The aadA5 cassette was 95% identical over the first 830 bp to aadA4, but lacked the IS26 element found at the 3' end of this truncated cassette. Cloning and expression of the cassette region demonstrated that dfrA17 conferred high level resistance to trimethoprim but aadA5 conferred resistance to spectinomycin but not to streptomycin.

Amino Acid Sequence↗
PubMed2000

Human cytomegalovirus strains associated with congenital and perinatal infections.

The genotypes of human cytomegalovirus (HCMV) isolates from pediatric patients differs from those of infected adults in Australia. Genotypes were determined by PCR amplification of glycoprotein B (gB) sequences, with subsequent analysis by restriction fragment length polymorphism, single-stranded conformation polymorphism, heteroduplex mobility analysis and direct DNA sequencing. Restriction fragment length polymorphism analysis of gB showed genotypes gB1 (39%) and gB3 (30%) were more prevalent in infected children and two new genotypes (gB6 and gB7) were found. Single-stranded conformation polymorphism was used to group isolates into 22 further subtypes and suggested longitudinal co-infection or viral mutation was occurring over time. Heteroduplex mobility analysis was found to be the most accurate and concise of the four methods used for genotyping HCMV isolates. DNA sequencing was used to confirm the results obtained from heteroduplex mobility analysis, and identified two isolates that were incorrectly genotyped by restriction fragment length polymorphism analysis. Heteroduplex mobility analysis efficiently genotyped all samples and allowed estimation of sequence variation between isolates. These data suggest certain gB genotypes are associated more commonly with childhood infections, and these differ from strains associated with invasive disease in HIV patients.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Causal judgment from contingency information: the interpretation of factors common to all instances.

Participants made judgments about stimulus materials in which there were 2 possible causes of an outcome. One of these was a common factor, a factor present in all instances presented for judgment, and the other was a positive covariate of the outcome. Instead of interpreting the positive covariate as the cause, participants consistently preferred an interpretation in which the common factor was the cause and the positive covariate enabled the cause to produce its effect. Participants' judgments of both interpretations were predicted by the proportion of instances that were confirmatory for the interpretation and not by deltaP. The findings support a hypothesis that people have a multirole conceptualization of causality including, in addition to the roles of cause and effect, that of an enabler, a factor the presence of which ensures that a thing is in a state of readiness to produce a particular effect.

Adult↗
PubMed2000

A comparison of six commercial assays for total and free prostate specific antigen (PSA): the predictive value of the ratio of free to total PSA.

OBJECTIVE: To evaluate the clinical utility of six commercial assays for free prostate specific antigen (fPSA) and the derived ratio of fPSA to total PSA in distinguishing between patients with prostate cancer or benign prostate hyperplasia (BPH). MATERIALS AND METHODS: Each assay was evaluated against a panel of serum samples comprising those from patients with prostatic disease, other malignancies, normal subjects and sera containing substances which might interfere with the immunoassay. RESULTS: The levels of total (tPSA), fPSA and their ratio (f/tPSA) were compared among the different samples. All assays showed similar specificities for prostate carcinoma but differed in the positive predictive values of f/tPSA. CONCLUSIONS: Although all six assays were equimolar, there were differences in calibration, particularly for fPSA. The ability of f/tPSA to discriminate between benign and malignant prostatic disease depended on the assay used. The f/tPSA is not valid when the tPSA and fPSA assays are obtained from different manufacturers.

Calibration↗
PubMed2000

Simplified hepatitis C virus genotyping by heteroduplex mobility analysis.

Heteroduplex mobility analysis (HMA) was used to genotype hepatitis C viruses (HCV) with PCR fragments derived from the 5' untranslated region (5'-UTR) or the NS5b region. HCV 5'-UTR fragments were amplified from 296 serum samples by use of a combined reverse transcription-PCR assay, and the genotypes of isolates were determined by sequencing. HCV genotype distributions in Australia were 39% for genotype 1a, 15% for 1b, 3% for 1a/b, <1% for 2a/c, 5% for 2b, 34% for 3a, <1% for 3b, and 1% for 4, and 1% of patients were infected with more than one genotype. Pairwise HMA of subtypes 1a, 1b, 2a/c, 2b, 3a, 3b, 4a, and 6a demonstrated that five distinct heteroduplex patterns were formed between the eight subtypes. A reference panel that contained a representative of each pattern (1a, 2b, 3a, 4a, and 6a) was used for genotyping. The pattern of heteroduplexes formed when a test isolate was mixed with the five reference isolates was correlated with the genotype, as determined by sequencing. Genotypes determined by HMA correlated exactly with sequencing results within the groups 1, 2, 3a, 3b/4, and 6. HMA was also used to simplify the identification of mixed infection with two HCV genotypes. In further studies, with amplicons from the NS5b region, HMA classified isolates into their respective subtypes, and the heteroduplex mobility ratio correlated closely with nucleotide sequence variation at the isolate, subtype, and genotype levels. HMA provides an adaptable, inexpensive, and rapid method of genotyping HCV that requires fewer resources than DNA sequencing.

5' Untranslated Regions↗
PubMed2000

Causal attribution and Mill's methods of experimental inquiry: past, present and prospect.

J. S. Mill proposed a set of Methods of Experimental Inquiry that were intended to guide causal inference under every conceivable set of circumstances in which experiments or observations could be carried out. The conceptual and historical relationship between these Methods and modern models of causal attribution is investigated. Mill's work retains contemporary relevance because his insights show how research can progress into presently uncharted waters. Following Mill, it is proposed that people use many different methods of causal attribution, the nature of which remains to be ascertained, and that the conditions that affect choice of method include the need to eliminate alternative causal candidates, whether single or multiple events are to be explained, the use of intervention or experiment as opposed to mere observation, and practical concerns.

Causality↗
PubMed2000

Causal judgment from contingency information: relation between subjective reports and individual tendencies in judgment.

In two experiments, participants made causal judgments from contingency information for problems with different objective contingencies. After the judgment task, the participants reported how their judgments had changed following each type of contingency information. Some reported idiosyncratic tendencies--in other words, tendencies contrary to those expected under associative-learning and normative rule induction models of contingency judgment. These idiosyncratic reports tended to be better predictors of the judgments of those who made them than did the models. The results are consistent with the view that causal judgment from contingency information is made, at least in part, by deliberative use of acquired and sometimes idiosyncratic notions of evidential value, the outcomes of which tend, in aggregate, to be highly correlated with the outcomes of normative procedures.

Adult↗
PubMed1999

Transmission of hepatitis C within Australian prisons.

Transmission of hepatitis C virus (HCV) within prisons has long been suspected but has not been satisfactorily documented. We present four cases of HCV infection occurring during periods of continuous imprisonment. Each subject was HCV seronegative on entering prison and on repeat testing after 4-52 months in prison, but subsequently became seropositive. Two subjects gave a history of injecting drug use, and the most likely means of infection in the other two subjects were lacerations from barbers shears and lacerations arising from physical assault. There is an urgent need for detailed study of the incidence of HCV infection and the modes of transmission in prisons.

Adult↗
PubMed1999

Characterisation of a chloramphenicol acetyltransferase determinant found in the chromosome of Pseudomonas aeruginosa.

The open reading frame (ORF) in the Pseudomonas aeruginosa chromosome, whose product resembles the chloramphenicol acetyltransferases (CAT) belonging to the CATB family, was cloned and shown to confer resistance to chloramphenicol (Cm) in Escherichia coli. The determinant was therefore named catB7 and the corresponding protein CATB7. When the copy number and expression signals were identical, the catB7 gene conferred resistance to Cm at a level slightly lower than those of three other catB genes. CATB7 resembles other CATBs in that it acetylates Cm but not 1-acetoxy-Cm. For CATB7, the K(m) values for acetyl-CoA and Cm were 5.0-5.4-fold higher than the corresponding values for each of the three other CATB proteins (CATB1, CATB3 and CATB5) examined and the Vmax was 5-6 fold lower. Using PCR, the catB7 gene was found in all six P. aeruginosa strains examined but not in any other species of pseudomonad tested. Weak CAT activity was detected in crude cell extracts from five of the six P. aeruginosa strains. However, this activity did not correlate with the Cm susceptibility of the strains, indicating that catB7 is not likely to be the major determinant of intrinsic Cm resistance in P. aeruginosa.

Amino Acid Sequence↗