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Biomedical subjects

K Johnston

Publications and source records attributed to K Johnston.

At least 55 records · Page 3Linked to original sources
PubMed1999

The role of a pre-scored multi-attribute health classification measure in validating condition-specific health state descriptions.

It is common to find specially constructed condition-specific health state descriptions used as the basis for benefit assessment in cost-utility analysis. For this approach to be valid it is necessary to have valid descriptors of health states. Yet the evidence demonstrating descriptive validity has been neglected in economic evaluation. This paper reports on the validity, reliability and feasibility of obtaining values from specially constructed condition-specific descriptions of breast cancer screening by mapping these descriptions into a pre-scored multi-attribute health classification measure (the EuroQol instrument) and comparing the values obtained with those derived from a time trade-off exercise. In doing so, it highlights the importance of descriptive validity in explaining why different valuation methods produce different results. Four descriptions typically associated with ex post true negative, false positive, true positive and false negative breast screening results were considered.

Adult↗
PubMed1999

What are surrogate outcome measures and why do they fail in clinical research?

Surrogate outcome measures have been of interest in clinical research for a long time because of their potential ability to save time and cost. The literature, however, has numerous examples of failed surrogate measures. The definition of a surrogate outcome measure, its consideration in clinical stroke research and some of the potential mechanisms for failure of surrogate measures will be discussed.

Biomarkers↗
PubMed1999

The use of ECGs to record heart activity.

Most ECG recorders are single- or multi-channel. PC-based recorders are slowly evolving. Electrodes must be placed precisely to ensure accurate recording.

Arrhythmias, Cardiac↗
PubMed1998

Valuing temporary and chronic health states associated with breast screening.

The aim of this study was to derive quality of life values for the four key breast screening outcomes (true negative, false positive, true positive and false negative), including the quality of life effects of the screening and treatment processes. In doing so, methodological issues in health status measurement were explored, in particular the valuation of temporary health states. The true negative and false positive descriptions were temporary health states, lasting for short term durations (12 months) and the true positive and false negative outcomes were chronic health states lasting for long term durations (rest of life). Descriptions of breast screening outcomes were valued using the time trade-off technique and the visual analogue scale. Paired comparisons between TTO values for states with the same duration found a difference between the true negative and the false positive time trade-off values but no difference for true positive and false negative descriptions. The TTO values for the false positive were low. The study highlights several important methodological issues such as the use of the two stage procedure for valuing temporary health states, the impact of duration on values, the impact of anchor points, and the importance of qualitative analysis of respondents values. Further empirical testing of all these issues is recommended.

Adult↗
PubMed1998

Assessment of a new dipstick test in screening for microalbuminuria in patients with hypertension.

The prevalence of elevated urinary albumin levels is significantly greater in hypertensive than in normotensive subjects. To determine the sensitivity and specificity of a new dipstick test for microalbunimuria (the Micral-Test), 171 hypertensive patients were studied at a union-sponsored hypertension treatment program. Sensitivity, specificity, predictive values, and correlation coefficients between urinary albumin concentration results obtained by the Micral-Test and by nephelometry were determined in three urine samples. Sensitivity values of the Micral-Test, compared with 24-h nephelometry, were 81%, 75%, and 92% in a 24-h, overnight, and random sample, respectively. Specificity values were 89%, 90%, and 63% in the three samples, respectively. Positive predictive value ranged from 41% to 67%, whereas negative predictive value ranged from 93% to 97%. Correlation coefficients between the logarithms of albumin concentrations obtained from the three different urine specimens using nephelometry fell between 0.71 and 0.78, whereas those obtained with the Micral-Test fell between 0.49 and 0.71, and across techniques, 0.29 to 0.53 (all P < .001). Results obtained with both nephelometry and the Micral-Test using overnight and random urine collections approximated those obtained with 24-h collection. These results, coupled with the ease and convenience of both specimen collection and the Micral-Test itself, support the use of the test as a valuable screening tool for microalbuminuria in patients with hypertension.

Adult↗
PubMed1998

Structures of SAP-1 bound to DNA targets from the E74 and c-fos promoters: insights into DNA sequence discrimination by Ets proteins.

SAP-1 is a member of the Ets transcription factors and cooperates with SRF protein to activate transcription of the c-fos protooncogene. The crystal structures of the conserved ETS domain of SAP-1 bound to DNA sequences from the E74 and c-fos promoters reveal that a set of conserved residues contact a GGA core DNA sequence. Discrimination for sequences outside this core is mediated by DNA contacts from conserved and nonconserved protein residues and sequence-dependent DNA structural properties characteristic of A-form DNA structure. Comparison with the related PU.1/DNA and GABPalpha/beta/DNA complexes provides general insights into DNA discrimination between Ets proteins. Modeling studies of a SAP-1/SRF/DNA complex suggest that SRF may modulate SAP-1 binding to DNA by interacting with its ETS domain.

Amino Acid Sequence↗
PubMed1998

Electrolyte concentration differences between left and right vitreous humor samples.

Between-eye differences in electrolyte concentrations were studied in 200 medico-legal autopsies using an ion-specific electrode system. Taking the highest of the paired vitreous potassium concentrations, cases < 15 mM/L were classified as biochemically nonputrefied (Cat.1, n = 124), cases 15 to 20 mM/L as early putrefaction (Cat.2, n = 51), and cases > 20 mM/L as biochemically putrefied (Cat.3, n = 25). Mean paired vitreous sodium for all cases (n = 200) was 112 to 173 mM/L (mean 148, standard deviation (SD) = 8.9); between-eye differences were 0 to 8 mM/L (0% to 5.1% of mean), averaging 1.5 mM/L (1%) and with only one case (in Cat.3) outside instrument accuracy (+/- 3 mM/L). Mean paired vitreous chloride for all cases was 73 to 124 mM/L (mean 109, SD = 7.8); between-eye differences were 0 to 9 mM/L (0% to 8.8% of mean), averaging 1.7 mM/L (1.5%) and with 5 of 200 cases outside instrument accuracy (+/- 3 mM/L). Thus between-eye concentration differences of sodium and chloride are tolerable using this methodology. Previous reports of greater variability likely reflect errors introduced by sample manipulation prior to analysis. By contrast, between-eye differences in potassium in Cat.1 cases were 0 to 2.34 mM/L (0% to 21.8% of mean) averaging 0.37 mM/L (3.3%). Significant and erratic between-eye differences in potassium undermine the usefulness of vitreous potassium in estimation of time of death.

Electrolytes↗
PubMed1997

Melatonin rescues dopamine neurons from cell death in tissue culture models of oxidative stress.

Dopamine (DA) neurons are uniquely vulnerable to damage and disease. Their loss in humans is associated with diseases of the aged, most notably, Parkinson's Disease (PD). There is now a great deal of evidence to suggest that the destruction of DA neurons in PD involves the accumulation of harmful oxygen free radicals. Since the antioxidant hormone, melatonin, is one of the most potent endogenous scavengers of these toxic radicals, we tested its ability to rescue DA neurons from damage/death in several laboratory models associated with oxidative stress. In the first model, cells were grown in low density on serum-free media. Under these conditions, nearly all cells died, presumably due to the lack of essential growth factors. Treatment with 250 microM melatonin rescued nearly all dying cells (100% tau+ neurons), including tyrosine hydroxylase immunopositive DA neurons, for at least 7 days following growth factor deprivation. This effect was dose and time dependent and was mimicked by other antioxidants such as 2-iodomelatonin and vitamin E. Similarly, in the second model of oxidative stress, 250 microM melatonn produced a near total recovery from the usual 50% loss of DA neurons caused by neurotoxic injury from 2.5 microM 1-methyl-4-phenylpyridine (MPP+). These results indicate that melatonin possesses the remarkable ability to rescue DA neurons from cell death in several experimental paradigms associated with oxidative stress.

Animals↗
PubMed1997

Stability of hybridization activity of Coccidioides immitis in live and heat-killed frozen cultures tested by AccuProbe Coccidioides immitis culture identification test.

Frozen hyphal suspensions of Coccidioides immitis were evaluated for suitability as positive control cultures in the AccuProbe C. immitis culture identification test. The genetic probe hybridization activity of heat-killed and viable frozen cultures, stored at -20 and -70 degrees C and tested over a 10-month period, was compared to that of a freshly grown culture, and the results were evaluated based upon the manufacturer's established positive and negative photometric light unit (PLU) cutoff values. All C. immitis suspensions produced positive hybridization values well above the positive and negative cutoff values, and no significant decrease in hybridization activity was observed with the frozen cultures after 10 months of storage. The frozen, heat-killed suspensions produced PLU values with less variability (coefficient of variation, 8% over 10 months than the fresh or frozen viable cultures and were deemed the most stable and sale form of positive control material to use.

Coccidioides↗
PubMed1997

UK breast screening programme: how does it reflect the Forrest recommendations?

OBJECTIVE: To compare the UK breast screening programme with the Forrest Report recommendations of 1986. SETTING: The UK breast screening programme. METHODS: A postal survey of 97 local breast screening programmes in the United Kingdom. The main outcome measures were the frequency of screening, the use of two view screening on incident screens, reading of screening mammograms, assessment procedures and visits, staffing levels, and the use of building and equipment. RESULTS: Eighty two (85%) of the questionnaires were completed and returned. All programmes screen every three years, as Forrest intended, with the exception of one health region which screens more often. The national policy is to use two views on incident screens where there is a clinical indication. None the less, 14% of programmes are using, or intending to use, two views on all women. Double reading of mammograms is not recommended in the United Kingdom outside Scotland, but is used by 88% of programmes. All programmes have access to the equipment required for the assessment techniques recommended by Forrest. Variation exists between programmes in the procedures women can expect to receive at their initial assessment visit and in the total number of assessment visits. Sixty eight per cent of programmes' breast screening budgets cover the staff required for a multidisciplinary team as defined by the Forrest Report. Ninety three per cent of screening programmes are organised around static sites, with 86% of these also using mobile vans. CONCLUSIONS: The national programme is following recommendations about the frequency of screening, but there seems to be some divergence from policy as regards the use of double reading, two views at incident screening, and the multidisciplinary team covered by the programmes' breast screening budget. Further research is needed on the effectiveness and cost effectiveness of two view incidence screening, double reading, and non-radiologists as readers. Investigation is also needed of the costs and effects of the variation between programmes in the number of assessment visits a woman may have.

Breast Neoplasms↗
PubMed1996

Attitudes about skin cancer prevention: a qualitative study.

BACKGROUND: Skin cancer represents a significant threat to the health and well-being of Americans. By engaging in both primary and secondary preventive behaviors, individuals can reduce their risks of developing skin cancer. METHODS: Focus groups were used as a qualitative technique to explore the similarities and differences between those who practiced skin cancer prevention (a high-concern group) and those who did not (a low-concern group). Transcripts from the discussions were analyzed to identify themes regarding participants' attitudes, beliefs, and practices about skin cancer prevention. RESULTS: Seven themes emerged from the data: 1) benefits of sun exposure; 2) salience of skin cancer prevention; 3) perceived seriousness of the sun's harmful effects; 4) personal connection to skin cancer; 5) media attention regarding skin cancer; 6) problems with sunscreens; and 7) preventive health "have-tos." CONCLUSIONS: To improve skin cancer prevention, health education interventions must attend to individuals' attitudes about sun exposure and address the barriers related to them.

Adult↗
PubMed1996

Hematologic emergencies in the intensive care unit.

Hematologic emergencies in the oncology population may require an admission to the intensive care unit (ICU). Syndrome of inappropriate antidiuretic hormone, hypercalcemia, tumor lysis syndrome, and disseminated intravascular coagulation are diseases defined in this article. These are common conditions in oncology patients that are reduced or prevented with close monitoring and accurate assessments. The purpose of this article is to introduce intensive care nurses to these disease entities so they will have a better understanding of the care involved with an oncology patient in the ICU unit.

Critical Care↗
PubMed1996

An introduction to music therapy: helping the oncology patient in the ICU.

Oncology and critical care patients have unique and complex problems. With the explosion of technology and advances in medicine, many intensive care units are seeing an increase in oncology patients. Intensive care units are stressful and frightening; music therapy is a noninvasive holistic approach to bridging the gap between oncology patients and intensive care units.

Holistic Nursing↗