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Biomedical subjects

P Dawson

Publications and source records attributed to P Dawson.

At least 55 records · Page 3Linked to original sources
PubMed1998

The L-arginine/nitric oxide pathway contributes to the acute release of tissue plasminogen activator in vivo in man.

OBJECTIVE: Effective endogenous fibrinolysis requires rapid release of endothelial tissue plasminogen activator (t-PA). Using the nitric oxide synthase inhibitor, L-NG-monomethylarginine (L-NMMA), we examined the contribution of endogenous nitric oxide to substance P-induced t-PA release in vivo in man. METHODS: Blood flow and plasma fibrinolytic and haemostatic factors were measured in both forearms of 8 healthy male volunteers who received unilateral brachial artery infusions of substance P (2-8 pmol/min) and L-NMMA (1-4 micrograms/min). RESULTS: Substance P caused dose-dependent increases in blood flow (P < 0.001) and plasma t-PA antigen (P = 0.04) and activity (P < 0.001) concentrations confined to the infused forearm, but had no effect on plasminogen activator inhibitor type I (PAI-I) or von Willebrand factor concentrations. In the presence of L-NMMA, substance P again caused significant increases in blood flow (P < 0.001) and t-PA antigen (P = 0.003) and activity (P < 0.001) concentrations but these increases were significantly less than with substance P alone (P < 0.001, P = 0.05 and P < 0.01, respectively). L-NMMA alone significantly reduced blood flow in the infused arm, but had no measurable effect on t-PA or PAI-1 concentrations. CONCLUSIONS: The L-arginine/nitric oxide pathway contributes to substance P-induced t-PA release in vivo in man. This provides an important potential mechanism whereby endothelial dysfunction increases the risk of atherothrombosis through a reduction in the acute fibrinolytic capacity.

Adult↗
PubMed1998

The haemodynamic effects of iodinated water soluble radiographic contrast media: a review.

All classes of iodinated water-soluble radiographic contrast media (RCM) are vasoactive with the iso-osmolar dimers inducing the least changes in the vascular tone. The mechanisms responsible for RCM-induced changes in the vascular tone are not fully understood and could be multifactorial. A direct effect on the vascular smooth muscle cells causing alterations in the ion exchanges across the cell membrane is thought to be an important factor in RCM-induced vasodilatation. The release of the endogenous vasoactive mediators adenosine and endothelin may also play a crucial role in the haemodynamic effects of RCM particularly in the kidney. In addition, the effects of RCM on blood rheology can cause a reduction in the blood flow in the microcirculation. The purpose of this review is to discuss the pathophysiology of the haemodynamic effects of RCM and to offer some insight into the biology of the endothelium and vascular smooth muscle cells as well as the pharmacology of the important vasoactive mediators endothelin and adenosine.

Adenosine↗
PubMed1998

Lost children, living memories: the role of photographs in processes of grief and adjustment among bereaved parent.

Drawing on recent developments in the conceptualization of grief (Klass, Silverman, and Nickman, 1996; Walter, 1996) that note the importance of talking about lost loved ones as part of maintaining a "continuing bond" between the living and the dead, this article considers the role of photographs in parents' adjustment to life without their child and in their negotiation of a more "comfortable" relationship with the deceased. The contributions that photographs and other memorabilia make to parents' opportunities to remember their children's lives (as opposed to their deaths), to facilitating conversations and reminiscences about their living relationships, and to parents' ability to introduce "lost" children to people who didn't know them, are explored using examples drawn from a series of case studies of bereaved parents. Photographs and other artifacts arising from their children's living can be perceived as the illustrations of a developing story in which previous and present relationships may be represented and interrogated for meaning. It is argued that visual representations of children's lives, no matter how brief, are a crucial feature of the process of coming to terms with both the fact of the loss and the reality of the life that has been lived.

Bereavement↗
PubMed1998

An abilities assessment instrument for elderly persons with cognitive impairment: psychometric properties and clinical utility.

In this article the psychometric properties of an Abilities Assessment Instrument (AAI), developed to assess the self-care, social, interactional and interpretive abilities of older people with cognitive impairment (CI) related to dementia, are described. The sample consisted of 112 institutionalized older men with CI and 60 institutionalized older men without CI. The psychometric evaluation of the AAI indicated that: (a) it is reliable in terms of test-retest (Pearson's r range .93-.99), interrater (Pearson's r range .95- .99), and internal consistency evaluations (Cronbach's alpha .90-.98), as well as through confirmatory factor analysis; and (b) that it is valid with respect to content validity (CVI 87.3%), concurrent validity (Pearson's r correlations ranging from -.67-.80 on the London Psychogeriatric Rating Scale [LPRS], and from -.76-.85 on the Functional Assessment Stages Scale [FAST]), and construct validity with significant differences between subjects with and without CI (t values ranging from 5.13-9.30). The AAI is a reliable and valid instrument that can be used to provide assessment data.

Activities of Daily Living↗
PubMed1997

Splenic blood flow: evaluation with computed tomography.

RATIONALE AND OBJECTIVES: To study splenic perfusion with use of computed tomography (CT). METHODS: Twenty-six control patients without splenoportal disease, six with cirrhosis, and seven with other splenic disease were examined with electron-beam CT. Twenty-five milliliters of iohexol (300 mg of iodine per milliliter) was given intravenously at 10 mL/sec followed by a saline bolus. Multiple single-level axial sections were acquired 8-90 seconds after injection. Perfusion was calculated by dividing maximal splenic enhancement by the area under the circulation-corrected aortic time-enhancement curve. Subjective assessments of enhancement heterogeneity were made, and regional perfusion was calculated in 10 patients with heterogeneous enhancement. Total splenic volume and blood flow were computed in 21 patients. RESULTS: Mean perfusion (controls: 1.29 mL/min/mL, miscellaneous group: 1.07 mL/min/mL) was close to predictions. There was a trend toward lower perfusion in cirrhotic patients (0.87 mL/min/mL), but the difference was not statistically significant. Total splenic blood was increased in patients with cirrhosis (P < .01). Marked perfusion heterogeneity was observed in 41% of spleens, but by 2 minutes splenic enhancement was uniform. CONCLUSION: CT shows promise in the study of splenic blood flow.

Evaluation Studies as Topic↗
PubMed1997

Bolus dynamics: theoretical and experimental aspects.

This paper analyses the arterial enhancement produced by short intravenous boluses of iodinated contrast medium, with particular attention to the differences between various types of contrast media. A theoretical discussion is presented, followed by a small experimental study. The characteristics of the arterial time-attenuation curve are a function of the rate of contrast medium transit to the extracellular fluid (ECF), osmolality driven transit of water from the ECF into the plasma, direct effects on the heart and pulmonary circulation, the distribution of transit times in the cardiopulmonary circulation and recirculation. Theory predicts that while differences in peak arterial attenuation/peak height (PH) will be small, alterations in the areas under the time-attenuation curve (AUC) will reflect early-phase rate constants in the absence of major inotropic effects. The AUC should be higher for non-ionic than ionic media reflecting these lower rate constants. An experimental study on three healthy dogs confirmed these theoretical observations, with a slightly higher PH (6.5% higher) using a non-ionic medium but a substantially higher AUC (22% higher). (Differences significant at the 5% level, two-tailed paired t-test.) Our theoretical predictions and experimental findings suggest non-ionic media produce superior vascular enhancement, particularly shortly after injection. Possible clinical implications, particularly in dynamic enhanced computed tomography, are discussed.

Angiography↗