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Biomedical subjects

I Johnson

Publications and source records attributed to I Johnson.

At least 19 recordsLinked to original sources
PubMed2007

Duration and distance of exposure are important predictors of transmission among community contacts of Ontario SARS cases.

We report attack rates and contact-related predictors among community contacts of severe acute respiratory syndrome (SARS) cases from the 2003 Toronto-area outbreak. Community contact data was extracted from public health records for single, well-defined exposures to a SARS case. In total, 8662 community-acquired exposures resulted in 61 probable cases; a crude attack rate of 0.70% [95% confidence interval (CI) 0.54-0.90]. Persons aged 55-69 years were at higher risk of acquiring SARS (1.14%) than those either younger (0.60%) or older (0.70%). In multivariable analysis exposures for at least 30 min at a distance of <or=1 m increased the likelihood of becoming a SARS case 20.4-fold (95% CI 11.8-35.1). Risk related to duration of illness in the source case at time of exposure was greatest for illness duration of 7-10 days (rate ratio 3.4, 95% CI 1.9-6.1). Longer and closer proximity exposures incurred the highest rate of disease. Separate measures of time and distance from source cases should be added to minimum datasets for the assessment of interventions for SARS and other emerging diseases.

Adolescent↗
PubMed2006

Observational study of bone-anchored hearing aid infection rates using different post-operative dressings.

INTRODUCTION: Avoidance of infection at the implant site is a crucial element to the success of bone-anchored hearing aid (BAHA) implantation. However, little evidence exists to suggest the best post-operative wound dressing to use. MATERIAL AND METHODS: We report our experience with 160 consecutive BAHA patients, using four types of post-operative BAHA wound dressing (Tri-adcortyl, Mepitel, Allevyn, and Acticoat 7 with Allevyn). Patients were reviewed at week one and week two post-operatively. Infection was defined as a positive wound swab culture or evidence of cellulitis at the BAHA site. RESULTS: Post-operative BAHA infection rates were 16 per cent, 50 per cent, 10 per cent and 5 per cent, for each of the four dressings respectively, and the mean number of additional visits to wound care clinic were 1.5, 3.7, one and 0.4, respectively. DISCUSSION: Acticoat 7 with Allevyn produced the lowest infection rate and thus became the dressing of choice for our BAHA programme.

Adult↗
PubMed2005

Benign paroxysmal positional vertigo: clinical characteristics of dizzy patients referred to a Falls and Syncope Unit.

BACKGROUND: Dizziness is a common symptom in older people that affects quality of life and increases the risk of falls. Benign paroxysmal positional vertigo (BPPV) is a common cause of dizziness that increases in prevalence with age, and is potentially curable. AIM: To compare patients with BPPV referred initially to a Falls and Syncope Unit (FSS group) with those initially referred to a Regional ENT/Balance Service (ENT group). DESIGN: Retrospective case-note review. METHODS: Medical notes, investigations and outcomes were reviewed for all patients. RESULTS: Of 59 patients with BPPV confirmed by Dix-Hallpike test, 31 (53%) were initially referred to the FSS (2.6 patients per month, 71% females) and 28 (47%) were initially referred to ENT (4.7 patients per month, 86% females). Compared to those referred initially to ENT, FSS patients were significantly older (mean +/- SD 69 +/- 13 vs. 55.4 +/- 13 years, p = 0.0003) and had dizzy symptoms for longer before diagnosis (median (range) 12 (4-120) vs. 6 (1-36) months, p = 0.0273). FSS patients were more likely to have more than one type of dizziness (16% vs. 0%, p = 0.001), more likely to have cerebrovascular or cardiovascular co-morbidity (13% vs. 4%, p = 0.0152) and were taking significantly more medications (3.2 vs. 1.7; p = 0.0271). Cure rates on intervention were similar (83% FSS, 86% ENT). DISCUSSION: BPPV is a potentially curable cause for dizziness in older people. Older people are frequently referred directly to Falls units, who will be seeing increasing numbers of patients with dizziness. A high index of suspicion allows early identification and treatment of this condition.

Accidental Falls↗
PubMed2003

Narrowing of the balance function with centrality in Au+Au collisions at the square root of SNN = 130 GeV.

The balance function is a new observable based on the principle that charge is locally conserved when particles are pair produced. Balance functions have been measured for charged particle pairs and identified charged pion pairs in Au+Au collisions at the square root of SNN = 130 GeV at the Relativistic Heavy Ion Collider using STAR. Balance functions for peripheral collisions have widths consistent with model predictions based on a superposition of nucleon-nucleon scattering. Widths in central collisions are smaller, consistent with trends predicted by models incorporating late hadronization.

Journal Article↗
PubMed2003

Disappearance of back-to-back high-pT hadron correlations in central Au+Au collisions at sqrt[s NN ] =200 GeV.

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudorapidity range and full azimuth in Au+Au and p+p collisions at sqrt[s(NN)]=200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes previously observed in high-energy collisions. A strong back-to-back correlation exists for p+p and peripheral Au+Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Journal Article↗
PubMed2003

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC.

Azimuthal anisotropy (v(2)) and two-particle angular correlations of high p(T) charged hadrons have been measured in Au+Au collisions at sqrt[s(NN)]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high p(T) partons. The monotonic rise of v(2)(p(T)) for p(T)<2 GeV/c is consistent with collective hydrodynamical flow calculations. At p(T)>3 GeV/c, a saturation of v(2) is observed which persists up to p(T)=6 GeV/c.

Journal Article↗
PubMed2002

Coherent rho(0) production in ultraperipheral heavy-ion collisions.

The STAR Collaboration reports the first observation of exclusive rho(0) photoproduction, AuAu-->AuAurho(0), and rho(0) production accompanied by mutual nuclear Coulomb excitation, AuAu-->Au*Au*rho(0), in ultraperipheral heavy-ion collisions. The rho(0) have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrt[s(NN)]=130 GeV agree with theoretical predictions treating rho(0) production and Coulomb excitation as independent processes.

Journal Article↗
PubMed2002

Centrality dependence of high-p(T) hadron suppression in Au+Au collisions at sqrt[s(NN)]=130 GeV.

Inclusive transverse momentum distributions of charged hadrons within 0.2<p(T)<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt[s(NN)]=130 GeV. Hadron yields are suppressed at high p(T) in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high-p(T) hadron production in heavy-ion collisions at high energy.

Journal Article↗
PubMed2002

Azimuthal anisotropy of K(0)(S) and Lambda+Lambda production at midrapidity from Au+Au collisions at sqrt[s(NN)]=130 GeV.

We report STAR results on the azimuthal anisotropy parameter v(2) for strange particles K(0)(S), Lambda, and Lambda at midrapidity in Au+Au collisions at sqrt[s(NN)]=130 GeV at the Relativistic Heavy Ion Collider. The value of v(2) as a function of transverse momentum, p(t), of the produced particle and collision centrality is presented for both particles up to p(t) approximately 3.0 GeV/c. A strong p(t) dependence in v(2) is observed up to 2.0 GeV/c. The v(2) measurement is compared with hydrodynamic model calculations. The physics implications of the p(t) integrated v(2) magnitude as a function of particle mass are also discussed.

Journal Article↗
PubMed2002

Midrapidity Lambda and Lambda(macro) production in Au+Au collisions at the square root of [s(NN)]=130 GeV.

We report the first measurement of strange (Lambda) and antistrange (Lambda macro) baryon production from square root of [s(NN)]=130 GeV Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Rapidity density and transverse mass distributions at midrapidity are presented as a function of centrality. The yield of Lambda and Lambda; hyperons is found to be approximately proportional to the number of negative hadrons. The production of Lambda; hyperons relative to negative hadrons increases very rapidly with transverse momentum. The magnitude of the increase cannot be described by existing hadronic string fragmentation models alone.

Journal Article↗
PubMed2002

The reproducibility of endometrial volume acquisition and measurement with the VOCAL-imaging program.

OBJECTIVES: To determine the intraobserver reproducibility of volume acquisition and repeatability of endometrial volume measurements using the VOCAL-imaging program (Virtual Organ Computer-aided AnaLysis). METHODS: Ten three-dimensional (3D) ultrasound datasets of the same endometrium were obtained from one patient during one scan session. For every 3D dataset, the endometrial volume was calculated by four different measurement techniques; three rotational methods and one conventional method. A single observer acquired each dataset and conducted all measurements. For the rotational technique, the manual mode was used to trace the myometrial-endometrial border through three different predefined rotations of 30 degrees, 15 degrees and 9 degrees . Endometrial volume was also measured in a conventional manner by scrolling through one of the multiplanar images and outlining the contour in another. Ten consecutive measurements were taken for each of the four measurement techniques so that 40 endometrial volume readings were obtained for each of the 10 3D-ultrasound datasets. RESULTS: Endometrial volume measurements were more reproducible with the rotational technique. Rotational methods employing a rotation step of less than 30 degrees were associated with coefficients of variation below 1% and intraclass correlation coefficients above 0.94. Within each of the 10 different scans, the homogeneity of the variance of measurements was significantly different according to the method of measurement (P = 0.022 to < 0.001). Post-hoc tests revealed that both the conventional and 30 degrees rotational methods resulted in a significantly smaller mean endometrial volume than both the 15 degrees and the 9 degrees rotational methods. CONCLUSIONS: Endometrial volume acquisition is reproducible and endometrial volume measurements are repeatable but they depend upon the technique of volume calculation in so much as rotational methods employing a rotation step of less than 30 degrees are associated with a significantly smaller variance in measurements and a significantly greater mean endometrial volume.

Adult↗
PubMed2001

d Macro and (3)He macro production in square root of s(NN) = 130 GeV Au+Au collisions.

The first measurements of light antinucleus production in Au+Au collisions at the Relativistic Heavy-Ion Collider are reported. The observed production rates for d macro and (3)He macro are much larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at CERN SPS energy. These analyses also indicate that the (3)He macro freeze-out volume is smaller than the d macro freeze-out volume.

Journal Article↗
PubMed2001

Measurement of inclusive antiprotons from Au+Au collisions at square root of s(NN) = 130 GeV.

We report the first measurement of inclusive antiproton production at midrapidity in Au+Au collisions at square root of s(NN) = 130 GeV by the STAR experiment at RHIC. The antiproton transverse mass distributions in the measured transverse momentum range of 0.25<p( perpendicular)<0.95 GeV/c are found to fall less steeply for more central collisions. The extrapolated antiproton rapidity density is found to scale approximately with the negative hadron multiplicity density.

Journal Article↗
PubMed2001

Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at square root of (sNN) = 130 GeV.

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons ( h(-)) in Au+Au interactions at square root of ([s(NN)]) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dN(h(-))/d(eta)/(eta = 0) = 280+/-1(stat)+/-20(syst), an increase per participant of 38% relative to pp collisions at the same energy. The mean transverse momentum is 0.508+/-0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h(-) yield per participant is a strong function of p( perpendicular). The pseudorapidity distribution is almost constant within /eta/<1.

Journal Article↗
PubMed2001

Pion Interferometry of square root of (s(NN)) =130 GeV Au + Au collisions at RHIC.

Two-pion correlation functions in Au+Au collisions at square root of [s(NN)] = 130 GeV have been measured by the STAR (solenoidal tracker at RHIC) detector. The source size extracted by fitting the correlations grows with event multiplicity and decreases with transverse momentum. Anomalously large sizes or emission durations, which have been suggested as signals of quark-gluon plasma formation and rehadronization, are not observed. The Hanbury Brown-Twiss parameters display a weak energy dependence over a broad range in square root of [s(NN)].

Journal Article↗
PubMed2001

Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt [s(NN)]=130 GeV.

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Journal Article↗