Biomedical subjects

J A Schaar

Publications and source records attributed to J A Schaar.

3 recordsLinked to original sources

PubMed2005

The role of shear stress in the destabilization of vulnerable plaques and related therapeutic implications.

American Heart Association type IV plaques consist of a lipid core covered by a fibrous cap, and develop at locations of eccentric low shear stress. Vascular remodeling initially preserves the lumen diameter while maintaining the low shear stress conditions that encourage plaque growth. When these plaques eventually start to intrude into the lumen, the shear stress in the area surrounding the plaque changes substantially, increasing tensile stress at the plaque shoulders and exacerbating fissuring and thrombosis. Local biologic effects induced by high shear stress can destabilize the cap, particularly on its upstream side, and turn it into a rupture-prone, vulnerable plaque. Tensile stress is the ultimate mechanical factor that precipitates rupture and atherothrombotic complications. The shear-stress-oriented view of plaque rupture has important therapeutic implications. In this review, we discuss the varying mechanobiologic mechanisms in the areas surrounding the plaque that might explain the otherwise paradoxical observations and unexpected outcomes of experimental therapies.

Arterial Occlusive Diseases↗

PubMed2002

Effect of temperature increase and freezing on intravascular elastography.

Intravascular ultrasound (IVUS) elastography is a technique that assesses the local strain in the vessel wall and plaque. The strain is an important parameter for characterization of different plaque components. These regions are related to plaque vulnerability. IVUS elastography was validated in vitro using human coronary and femoral arteries. These experiments were performed on specimens that were stored frozen and measured at room temperature for practical issues. The aim of this study is to determine the influence of freezing and measuring the tissues at room temperature (23 degrees C instead of 37 degrees C) on the elastic properties. Four human coronary, one carotid and one femoral arteries were first measured at 23 degrees C and next at 37 degrees C. Additionally they were stored at -80 degrees C for up to 24 h and finally measured at 23 degrees C. Acquisitions at intraluminal pressures of 80 and 100 mmHg were performed using an EndoSonics 20 MHz Visions catheter. Elastograms were determined from the IVUS rf-data (sampled at 100 MHz in 12 bits) that were obtained from a digital interface. Qualitative and quantitative analysis of the elastograms obtained from fresh and frozen specimens measured at 23 degrees C reveals that storage of the specimen at -80 degrees C has no significant influence. In vitro experiments can be performed at room temperature after storage of the tissue at -80 degrees C without significant affection of the information with respect to measuring fresh ex vivo material at body temperature.

Journal Article↗

PubMedDate not supplied

Optical coherence tomography.

BACKGROUND: Optical coherence tomography (OCT) is a light-based imaging modality that can be used in biological systems to study tissues in vivo with near-histologic, ultrahigh resolution. The rationale for intravascular application of OCT is its potential for in vivo visualisation of the coronary artery microstructure. METHODS AND RESULTS: The principle is analogous to pulse-echo ultrasound imaging; however, light is used rather than sound to create the image. Low-coherent near-infrared light is emitted by a superluminescent diode and reflected by the microstructures within biological tissues. The echo time delay of reflected light waves is converted into a two-dimensional spatial image. The intensity of the reflected light waves is translated into an intensity map. Experimental studies confirmed the ability of intravascular OCT for plaque characterisation and accurate assessment of vascular structures that are close to the luminal surface. Preliminary clinical experience proved in vivo feasibility of intravascular OCT. A variety of atherosclerotic plaque structures including thin cap fibroatheromas can be visualized in vivo. CONCLUSIONS: Intravascular OCT allows for accurate assessment of vessel structures close to the luminal side. Clinical application is feasible. To date, however, the clinical relevance of OCT findings in coronary arteries is unclear and further validation of OCT imaging is mandatory.

Coronary Artery Disease↗