Microbubble dynamics visualized in the intact capillary circulation

Abstract

The potential for the use of contrast echocardiography to study myocardial perfusion has generated efforts to develop standardized echo contrast agents. The two methods used in this laboratory to generate microbubbles in solutions serving as contrast agents included the widely used hand-agitation method and the newer ultrasonic microcavitation (sonication) method. The latter has been demonstrated to generate smaller and more uniform microbubbles in an in vitro system. The present study was designed to observe, by direct microscopic examination of a cat mesentery preparation, the behavior and fate of the microbubbles in an in vivo system. The in vivo mesentery observations confirm the critical role of microbubble size in its unhindered passage through the capillary vasculature. The smaller and more uniform sonicated microbubbles passed rapidly through the microcirculation along with the red blood cells, whereas the larger microbubbles were observed to coalesce and interrupt the flow of blood and subsequently collapse or shrink.

Hyperpolarized3He microspheres as a novel vascular signal source for MRI

“…Gas suspensions were created using a handagitation technique (15) that resulted in large bubbles with significant size variability (mean diameter ϭ 31.8 Ϯ 10.4 m). However, an injectable bubble ideally should be encapsulated and approximately the size of a blood cell (16). This reduces the risk of embolism because the particles can safely pass through the capillaries of the circulatory system.…”

Contrast echocardiography in Canada: Canadian Cardiovascular Society/Canadian Society of Echocardiography position paper

“…These air bubbles strikingly increase the backscatter because of their high impedance to ultrasound propagation compared with blood. However, air bubbles present in agitated saline administered intravenously do not cross the pulmonary circulation because the larger bubbles are trapped by the microcirculation, while microbubbles small enough to pass through the pulmonary capillary bed (smaller than 8 μm) collapse within a few seconds before reaching the left heart cavities due to surface tension, surrounding pressure and gas diffusion from bubbles into the blood (12,13). Early applications of CE were therefore limited to using agitated saline to detect intracardiac and intrapulmonary shunts, confirm needle placement during pericardiocentesis, and enhance right-sided Doppler signals and two-dimensional images.…”

Echocardiography in stroke and transient ischaemic attack

“…A venous embolism must be passing the region of the fossa ovalis at the precise time that right atrial pressure exceeds left atrial pressure sufficient for the foramen to open. The foramen must also be large enough to accommodate an embolic particle; the passage of a few microbubbles that are usually only 15-20,m in diameter23 24 may not prove this. It is also thought that it is uncommon to find a source for venous emboli in patients with stroke and patent foramen ovale.25 However, this is an area of controversy because of the practical difficulty in venous imaging soon enough after admission because of stroke to detect primary rather than secondary thrombosis.…”