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Biomedical subjects

P Dawson

Publications and source records attributed to P Dawson.

At least 73 records · Page 4Linked to original sources
PubMed1997

A comparison between the platelet activating properties of different contrast media used in radiology and MRI.

Previous studies have demonstrated that some intravascular radiographic contrast media (CM) used in angiography, especially non-ionic monomers, may cause platelet activation. This study was designed to elucidate which properties of the CM were responsible for this activity. Platelet activation engendered by CM was studied using flow cytometry to detect platelet degranulation (as CD62 expression) and fibrinogen binding. In order to elucidate the relevant characteristics of the CM responsible, contrast agents of differing structures, properties, formulations and osmolalities were studied; ionic and non-ionic, monomeric and dimeric. Gadolinium chelate MR enhancing agents and saline solutions of differing osmolalities were also investigated. Ionic dimeric sodium meglumine ioxaglate, non-ionic dimeric iodixanol and non-ionic dimeric iotrolan did not produce increased degranulation compared with saline controls. However, all agents produced a mild increase in bound fibrinogen. Experiments using saline solutions demonstrated that these effects are not attributable to the high osmolality of some CM. The broad comparison facilitated by this study shows that previous generalizations regarding platelet activation by CM, based on an ionic-non-ionic division, are not valid. We presume that some chemical structural property of the compounds is responsible and it is of note that the chemically distinct gadolinium chelates, gadolinium DTPA and gadolinium DTPA-BMA, also caused platelet activation to a similar degree. CD62 expression correlated with fibrinogen binding suggesting that at least one common pathway of platelet activation is involved.

Angiography↗
PubMed1997

Röntgen's other experiment.

Röntgen's fame today rests solely on his discovery of X-rays and takes no account of the fact that he was perhaps the leading experimental physicist of his time. One experiment he devised and brilliantly executed was, arguably, one of the most important of the 19th century. It was greatly celebrated at the time, yet today has been all but completely forgotten. With the aim of developing a more complete picture of Röntgen and his place in the history of physics, this paper describes the nature of the problem he tackled and gives an outline of his experimental approach to it. The significance of his achievement for the construction of the edifice of 19th century physics is explained.

Electromagnetic Phenomena↗
PubMed1997

Patterns of caregiving following the institutionalization of elderly husbands.

The purpose of this study was to examine the caregiving career of older women following the institutionalization of their husbands. Informed by the interpretive perspective in sociology and Hughes's (1971) concept of career, the study employed a longitudinal, prospective, and descriptive design and combined the quantitative and qualitative approaches. The data used in the analysis were drawn from a larger study designed to explore the transition to quasi-widowhood and wives' responses to their husbands' institutionalization. The caregiving career of wives was seen as a pattern of frequent visiting and increasing involvement in the provision of care. Over the nine-month period of the study, two caregiving patterns emerged that were distinguished by a variety of circumstances and interactions. Wives who relinquished aspects of caregiving were more likely to be caring for husbands who were, in large measure, cognitively impaired. These wives reported good morale, few symptoms of depression, change in marital closeness, and satisfaction with aspects of institutional care. Wives who continued to be heavily involved in caregiving were more likely to have husbands who were physically impaired. They had depression scores indicative of moderate to severe depression, reported no change in marital closeness, and were dissatisfied with aspects of institutional care.

Aged↗
PubMed1997

Spousal caregiving in the institutional setting: visiting.

The purpose of this study was to investigate the visiting experience of wives whose husbands had been admitted to a long-term care institution. The study employed a longitudinal and prospective design and combined qualitative and quantitative approaches. The data were drawn from a larger study designed to explore the transition to quasi-widowhood. This article reports on one aspect of spousal caregiving following the admission of a husband to a long-term care setting, i.e. visiting. In this study, wives visited frequently. Their reasons for visiting included love and devotion, duty and obligation, the monitoring of husbands' well-being and the provision of assistance to both husbands and staff. They engaged in task performance and social interaction during visiting. Their feelings of satisfaction and enjoyment with visiting were associated with their husbands' well-being and feeling useful. Over the 9-month period of the study, two patterns of visiting and involvement emerged that were associated with different outcomes related to depression, morale and satisfaction with institutional dimensions of care.

Adult↗
PubMed1996

The non-ionic isotonic contrast agents. Perspectives and controversies.

The non-ionic isotonic contrast agents represent a new class of intravascular iodinated x-ray contrast agents. They are highly hydrophilic, resulting in low chemotoxicity, are non-ionic, thereby eliminating Coulomb interactions, and are formulated in solutions iso-osmolar with the respective body fluids. Invitro testing, organ specific toxicity studies and overall systemic toxicity assessments such as LD50 measurements all point to an excellent toxicity profile. This justify their application in high dose procedures where their low toxicity may be distinctly advantageous. Their iso-osmolality, possibly combined with a slower diffusion of the larger molecules across vessel walls and out of the vascular space, may play a significant role in producing better quality venous phase images following arteriography and arterial phase images following venous injection. This may have implications for the quality of IV-DSA, the venous phase of arteriograms, CT-portography and spiral CT arteriography.

Animals↗
PubMed1996

X-ray contrast-enhancing agents.

The author argues that, whatever important and rapid developments may be taking place in imaging technologies, there will be a continuing need for X-ray enhancing agents for a considerable time to come. Areas in which there are current developments, such as non-ionic dimers and compact dimers, are surveyed and a look to a possible future of blood pool and targetted agents is offered.

Contrast Media↗
PubMed1996

Contrast agents in magnetic resonance imaging.

The author gives a brief overview of the basic mechanisms of action of contrast enhancing agents in MR imaging and discusses agents currently available, and agents soon to be available, under the classification: extra-cellular fluid space marker agents, hepatobiliary agents and oral agents. Likely future developments in these and other areas are briefly surveyed.

Contrast Media↗
PubMed1996

Continuous extradural infusion of ropivacaine for prevention of postoperative pain after major orthopaedic surgery.

We studied 151 patients undergoing total hip or knee arthroplasty, or cruciate ligament reconstruction in a multicentre study in Australia and New Zealand. Patients were openly allocated randomly to one of five treatment groups or to a control group. General anaesthesia was induced after introduction of extradural block with 0.5% ropivacaine. After surgery, patients received an extradural infusion of 0.2% ropivacaine at 6, 8, 10, 12 or 14 ml h-1 or received no postoperative extradural infusion (control group). All patients had access to i.v. PCA morphine for supplementary analgesia. Morphine consumption was lower in all treatment groups compared with the control group, decreasing with increasing ropivacaine infusion rate. Median VAS scores were lower in all ropivacaine infusion groups compared with the control group for the first 10 h of the study; however by the end of the study, VAS scores were similar in all groups. The higher ropivacaine infusion rates caused a slower convergence of spread of the initial sensory block and a higher degree of motor block. The overall incidence of side effects was similar, with the exception of a higher incidence of urinary retention and hypotension in the groups receiving the higher rates of ropivacaine. The quality of treatment scores were similar for all treatment groups (Br. J. Anaesth. 1996; 76: 606-610).

Adult↗
PubMed1996

Phaeochromocytoma in pregnancy.

The Royal Women's Hospital, Melbourne, is a tertiary referral hospital with over 7,000 deliveries per year. We report 3 cases of phaeochromocytoma in pregnancy at the hospital in the 20-year period since 1976. The first case was unsuspected and resulted in a maternal death. The subsequent 2 cases were diagnosed antenatally with successful outcomes for both mother and baby. The 3 cases demonstrate the importance of an early antenatal diagnosis and the special management problems of phaeochromocytoma in pregnancy. The diagnosis of phaeochromocytoma should be considered in any pregnant women with severe hypertension, particularly if presenting before 20 weeks' gestation, labile, or associated with sweating, palpitations or headaches.

Adrenal Gland Neoplasms↗
PubMed1996

Short communication: renal function and the excretion of contrast agents.

The renal excretion of intravascular iodinated X-ray and gadolinium chelate MR contrast is examined theoretically. An expression is derived for the proportion of an administered dose of such an agent excreted in any given time in the face of varying levels of renal function. It is shown that a family of curves may be generated from which an estimate of this proportion for any time may be made. Some circumstances in which such knowledge may be useful are briefly discussed.

Algorithms↗
PubMed1996

Contrast media as extracellular fluid space markers: adaptation of the central volume theorem.

We present some theoretical observations on the pharmacokinetics of the conventional intravascular radiographic and gadolinium chelate MR contrast agents. These agents may be viewed from a physiological perspective as extracellular fluid (ECF) space markers. It can be shown that the passage of such agents through the body may be described by a variant of the "central volume theorem", if the central volume is taken to be that of the entire extracellular fluid. A consequence is that, in a manner akin to nuclear medicine techniques utilizing technetium-99m diethylene triamine pentacetic acid (DTPA), measures of glomerular filtration rate (GFR) related to total ECF volume rather than to the normal body surface area may be obtained from direct or indirect measurements of iodine or gadolinium plasma levels. Typical measurements are presented. A simple means is also described of generating curves of the fraction of contrast medium excreted from the body, applicable to both patients with normal and with abnormal renal function.

Biomarkers↗