The effect of afterload on the cardiodepressor reflex response to coronary artery occlusion in dogs

The acute hemodynamic responses to anterior and posterior wall ischemia were examined at different afterloads in 30 open-chest anaesthetized dogs. Regional and global left ventricular responses to acute ischemia were also measured before and following bilateral cervical vagotomy in 18 dogs. As the preocclusion afterload (mean aortic pressure) was progressively raised with intravenous methoxamine, a significant decrease in stroke volume occurred following circumflex artery occlusion, whereas no change in stroke volume occurred following occlusion of the left anterior descending artery. Bilateral cervical vagotomy completely inhibited the decrease in stroke volume during circumflex occlusion at high afterload. Vagotomy had no effect on the hemodynamic response to acute anterior wall ischemia. Reversible cold vagal block in paced hearts at high afterload unmasked compensatory inotropy in the nonischemic anterior myocardial segment during circumflex occlusion. Restoring vagal tone by rewarming attenuated the fractional shortening of the nonischemic segment. The results indicate that a relationship exists between myocardial wall tension and reflex cardioinhibition during acute posterior wall but not anterior wall ischemia in dogs.     

Isolated bilateral ostial coronary stenosis with proximal right coronary artery occlusion

The incidence of coronary ostial stenosis in patients undergoing coronary arteriography has been found to range between 0.07 and 0.25%. A slightly higher incidence has been observed in patients with angiographically confirmed coronary artery disease: between 0.13 and 2.7%. Bilateral ostial stenosis is even less common. Although cardiovascular syphilis is no longer a prominent condition, it must be considered in the differential diagnosis since it carries a very high risk (50%) of cardiovascular complications if left untreated. Ostial coronary stenosis occurs in 26% of patients with syphilitic aortitis. This paper reports on a 41-year-old Wasserman (WR)-positive woman with progressive angina caused by bilateral ostial coronary stenosis.     

A review of clinical trials in dietary interventions to decrease the incidence of coronary artery disease

Of the associations between dietary elements and coronary artery disease (CAD), the greatest body of evidence deals with the beneficial effect of reducing the dietary intake of saturated fatty acids and cholesterol. Furthermore, it is well established, on the basis of convincing evidence, that reduction in serum total cholesterol results in reduction in coronary morbidity and mortality, as well as in regression of other atherosclerotic manifestations.In fact, dietary intervention studies revealed that it is possible to reduce the incidence of coronary death and nonfatal myocardial infarction, as well as manifestations of atherosclerosis in cerebral and peripheral arteries, by reducing dietary intake of saturated fat and cholesterol. In two recently reported dietary interventions the incidence of coronary events, especially coronary mortality, and total mortality were reduced by increased intake of n-3 long-chain polyunsaturated fatty acids and by a modification of the diet toward a Mediterranean-type diet (rich in α-linolenic acid. In addition to those findings, the potential efficacy of the dietary newcomers phytostanol and phytosterol esters on reducing coronary incidence is discussed in the present review.     

Relation between regional function and coronary blood flow reserve in multivessel coronary artery stenosis

In the setting of chronic coronary stenoses, percent wall thickening (%WT) both at rest and during catecholamine stimulation can be abnormal despite normal resting myocardial blood flow (MBF). We hypothesized that this phenomenon is related to abnormal MBF reserve. Accordingly, 15 dogs were studied between 7 and 10 days after placement of Ameroid constrictors around the proximal coronary arteries and their major branches, at a time when collateral development had not yet occurred. %WT and MBF were measured at rest, after 0.56 mg/kg of dipyridamole, and at incremental doses of dobutamine (5-40 microgram. kg(-1). min(-1)). Resting %WT and MBF were normal in all four sham dogs. Resting transmural MBF was normal in all segments in the 11 study dogs, despite reduced (-2 SD of normal) %WT (<30%) in 40 of 82 segments. MBF reserve was reduced (<3) in segments with reduced %WT, and a close coupling was noted between resting %WT and MBF reserve. All segments showed an increase in %WT with dobutamine up to a dose of 20 microgram. kg(-1). min(-1), above which those with abnormal endocardial MBF reserve showed a "biphasic" response. It is concluded that, in the presence of chronic coronary stenoses, abnormalities in resting %WT as well as inducible reduction in %WT during pharmacological stress are related to the degree of abnormal MBF reserve.     

Late proximal coronary artery stenosis complicating percutaneous endovascular catheterisation procedures

Background

Late-onset proximal coronary artery stenosis caused by preceding percutaneous catheterisation procedures remains under-surveyed.

Methods

From 1993, all patients undergoing percutaneous coronary procedures and a second session within 3 years were included except those ever treated by coronary bypass surgery or chest radiotherapy during this 3-year period. Emergence of a new lesion or worsening of an initially insignificant lesion to >50% of diameter stenosis at the never-treated ostial/proximal coronary segment on the follow-up angiogram was defined as late coronary stenosis caused by the previous catheterisation procedure and was analysed.

Results

From January 1993 to December 2005, 3240 patients who underwent 5025 procedures met the inclusion criteria. Of them, 23 patients experienced an event of late coronary artery stenosis (overall incidence 0.46%), and interventional procedures, specifically shaped catheters (Voda, XB, Amplatz Left) and atherosclerosis vulnerability correlated with risks of adverse events. Most of these events could be managed by contemporary medical, interventional, or surgical strategies, yet hazards of mortality and long-term restenosis still existed from this catheter-induced complication.

Conclusions

Percutaneous catheterisation procedures could be complicated by late proximal coronary artery stenosis. Thus, when conducting these procedures, operators should select and manipulate catheters with caution, especially in patients with susceptible clinical characteristics.     

Coupled oxygen transport analysis in the avascular wall of a post-angioplasty coronary artery stenosis

The coupled oxygen transport in the avascular wall of a coronary artery stenosis is studied by numerically solving the convection-diffusion equations. Geometry, replicating residual stenosis after percutaneous transluminal coronary angioplasty (PTCA), is used for the analysis. Important physiological aspects, such as oxygen consumption in the wall, oxygen carried by the hemoglobin, non-Newtonian viscosity of the blood, and supply of oxygen from the vasa vasorum are included. Mean blood flow rate in the lumen is varied from basal to hyperemic conditions. The results show that the P(O2) in the medial region of the arterial wall is approximately 10 mmHg. The oxygen flux to the wall increases in the flow acceleration region, whereas it decreases at the flow reattachment zone. Near the location of flow separation there is a small rise and a sharp fall in the oxygen flux. The minimum P(O2) in the avascular wall, P(O2, min ), at the point of flow reattachment reduces to approximately 6 mmHg for a 300 micron wall thickness. For a thinner wall of 200 micron, the P(O2, min ) at the location of flow reattachment increases to 6 times that of a 300 micron wall. The P(O2, min ) in the wall decreases by 60% when volumetric oxygen consumption is increased by 30% for the same avascular wall thickness.     

Influence of stenosis on hemodynamic parameters in the realistic left coronary artery under hyperemic conditions

The current study investigates the hyperemic flow effects on heamodynamics parameters such as velocity, wall shear stress in 3D coronary artery models with and without stenosis. The hyperemic flow is used to evaluate the functional significance of stenosis in the current era. Patients CT scan data of having healthy and coronary artery disease was chosen for the reconstruction of 3D coronary artery models. The diseased 3D models of coronary artery shows a narrowing of >50% lumen area. Computational fluid dynamics was performed to simulate the hyperemic flow condition. The results showed that the recirculation zone was observed immediate to the stenosis and highest wall shear stress was observed across the stenosis. The decrease in pressure was found downstream to the stenosis as compared to the coronary artery without stenosis. Our analysis provides an insight into the distribution of wall shear stress and pressure drop, thus improving our understanding of hyperemic flow effect under both conditions.     

Coupled oxygen transport analysis in the avascular wall of a coronary artery stenosis during angioplasty

The coupled oxygen transport in the avascular wall of a coronary artery stenosis is studied numerically by solving the convection-diffusion equations. Two geometries replicating stenosis before and after percutaneous transluminal coronary angioplasty (PTCA) are used for the analysis. The results are compared to evaluate the effect of the degree of stenosis on oxygen transport. Important physiological aspects, such as oxygen consumption in the wall, oxygen carried by the hemoglobin, non-Newtonian viscosity of the blood, and supply of oxygen from the vasa vasorum are included. The results show that the PO2 in the medial region of the arterial wall is approximately 10mmHg. The oxygen flux to the wall increases in the flow acceleration region, whereas it decreases at the flow reattachment zone. Near the location of flow separation, there is a small rise followed by a sharp fall in the oxygen flux. The drop in the oxygen flux to the wall at the point of flow reattachment for pre-PTCA stenosis is four times that for post-PTCA stenosis. The minimum PO2 in the avascular wall, PO2,min, at this location decreases to approximately 6.0 and 4.2mmHg for post- and pre-PTCA stenosis, respectively. The drop in PO2,w and PO2,min at the point of flow reattachment for pre-PTCA is approximately 2 times that for post-PTCA stenosis. Thus, the present study quantifies the oxygen transport to the arterial wall before and after cardiovascular intervention.     

Adapting HIV prevention evidence-based interventions in practice settings: an interview study

Background

A knowledge broker (KB) is a popular knowledge translation and exchange (KTE) strategy emerging in Canada to promote interaction between researchers and end users, as well as to develop capacity for evidence-informed decision making. A KB provides a link between research producers and end users by developing a mutual understanding of goals and cultures, collaborates with end users to identify issues and problems for which solutions are required, and facilitates the identification, access, assessment, interpretation, and translation of research evidence into local policy and practice. Knowledge-brokering can be carried out by individuals, groups and/or organizations, as well as entire countries. In each case, the KB is linked with a group of end users and focuses on promoting the integration of the best available evidence into policy and practice-related decisions.

Methods

A KB intervention comprised one of three KTE interventions evaluated in a randomized controlled trial.

Results

KB activities were classified into the following categories: initial and ongoing needs assessments; scanning the horizon; knowledge management; KTE; network development, maintenance, and facilitation; facilitation of individual capacity development in evidence informed decision making; and g) facilitation of and support for organizational change.

Conclusion

As the KB role developed during this study, central themes that emerged as particularly important included relationship development, ongoing support, customized approaches, and opportunities for individual and organizational capacity development. The novelty of the KB role in public health provides a unique opportunity to assess the need for and reaction to the role and its associated activities. Future research should include studies to evaluate the effectiveness of KBs in different settings and among different health care professionals, and to explore the optimal preparation and training of KBs, as well as the identification of the personality characteristics most closely associated with KB effectiveness. Studies should also seek to better understand which combination of KB activities are associated with optimal evidence-informed decision making outcomes, and whether the combination changes in different settings and among different health care decision makers.     

Implementing evidence-based interventions in health care: application of the replicating effective programs framework

Background

For people with dementia, patient-centred care should involve timely explanation of the diagnosis and its implications. However, this is not routine. Theoretical models of behaviour change offer a generalisable framework for understanding professional practice and identifying modifiable factors to target with an intervention. Theoretical models and empirical work indicate that behavioural intention represents a modifiable predictor of actual professional behaviour. We identified factors that predict the intentions of members of older people's mental health teams (MHTs) to perform key behaviours involved in the disclosure of dementia.

Design

Postal questionnaire survey.

Participants

Professionals from MHTs in the English National Health Service.

Methods

We selected three behaviours: Determining what patients already know or suspect about their diagnosis; using explicit terminology when talking to patients; and exploring what the diagnosis means to patients. The questionnaire was based upon the Theory of Planned Behaviour (TPB), Social Cognitive Theory (SCT), and exploratory team variables.

Main outcomes

Behavioural intentions.

Results

Out of 1,269 professionals working in 85 MHTs, 399 (31.4%) returned completed questionnaires. Overall, the TPB best explained behavioural intention. For determining what patients already know, the TPB variables of subjective norm, perceived behavioural control and attitude explained 29.4% of the variance in intention. For the use of explicit terminology, the same variables explained 53.7% of intention. For exploring what the diagnosis means to patients, subjective norm and perceived behavioural control explained 48.6% of intention.

Conclusion

These psychological models can explain up to half of the variation in intention to perform key disclosure behaviours. This provides an empirically-supported, theoretical basis for the design of interventions to improve disclosure practice by targeting relevant predictive factors.

Trial Registration

ISRCTN15871014.     

Coronary flow measurements on the isolated rat heart following experimental coronary artery stenosis]

A stenosing proliferation of the vascular wall was produced by exposing the Ramus descendens of the rat's left coronary artery to continued mechanical stimulation. Two weeks after the operation the hearts were perfused according to a modified Langendorff method, and the flow rate was measured under aerobic conditions and following short-time anoxia. Under either experimental conditions, the flow rate proved to be significantly decreased.     

Plasma tissue factor in coronary artery disease: further step to the understanding of the basic mechanisms of coronary artery thrombosis

Tissue factor is a cell surface protein that is expressed constitutively by monocytes, macrophages and fibroblasts, but also by some other cells in response to a variety of stimuli. The main function of the tissue factor is to form a complex with factor VII/VIIa that converts factors IX and X to their active forms. Tissue factor is also involved in the pathophysiology of systemic inflammatory disorders, coagulopathies, atherosclerotic disease, tumor angiogenesis and metastasis. Increased tissue factor expression either locally in the coronary plaques or systematically on circulating blood elements of patients with acute coronary syndromes may be responsible for increased thrombin generation, thus leading to platelet activation and fibrin formation. Tissue factor therefore plays a pivotal role in the initiation of thrombotic complications in patients with coronary artery disease.     

Chronic coronary artery stenosis induces impaired function of remote myocardium: MRI and spectroscopy study in rat

Our purpose was to study morphological, functional, and metabolic changes induced by chronic ischemia in myocardium supplied by the stenotic vessel and in the remote area by MR techniques. A new technique of image fusion is proposed for analysis of coronary artery stenosis involving coronary MR angiography and spectroscopic imaging. Cine-MRI was performed 2 wk after induction of coronary stenosis. Global heart function and regional wall thickening were determined in 11 Wistar rats with stenosis and compared with 7 control rats. Two weeks after stenosis was induced, spin-labeling MRI for measurement of perfusion was performed in 14 isolated hearts. In eight isolated hearts with coronary stenosis, MR spectroscopy was performed, followed by angiography. 31P metabolite maps were fused with three-dimensional coronary angiograms. Induction of stenosis led to reduced segmental wall thickening (control: 75 +/- 9%, ischemic region: 9 +/- 3%, P < 0.05 vs. control) but also to impaired function of the remote region and lower cardiac output. Perfusion was reduced by 74.9 +/- 4.0% within ischemic segments compared with a septal control region. The phosphocreatine (PCr)/ATP ratio as a marker of ischemia was reduced in the region associated with stenosis (1.09 +/- 0.09) compared with remote (1.27 +/- 0.08) and control hearts (1.43 +/- 0.08; P < 0.05). The histological fraction of fibrosis within the ischemic region (12.8 +/- 1.4%) correlated to ATP signal reduction from remote to the ischemic region (r = 0.71, P < 0.05), but not to reduced wall thickening. Coronary narrowing caused declining function accompanied by diminished PCr/ATP, indicating impaired energy metabolism. Neither decline of function nor PCr signal decline correlated to fraction of fibrosis in histology. In contrast, reduction of ATP correlated to fibrosis and therefore to loss of viability. Impaired function within the ischemic region is associated with decreased PCr. Function of the remote region was affected as well. The fusion of PCr metabolite maps and the coronary angiogram may help to assess coronary morphology and resulting metabolic changes simultaneously.