[abstract] METHODS FOR PRODUCING MICROBUBBLES FOR MICROEMBOLISM STUDIES

Abstract

Clinical complications of air embolism are sometimes observed in cases of decompression sickness, either in aerospace or underwater applications. In this report techniques are presented for producing calibrated microbubbles for air embolism studies. These techniques enable further research concerning the microembolism process as seen in air embolism or related problems. The utilization of differential absorption techniques in conjunction with gas injection methods enables calibrated microbubbles to be produced within the diameter range of capillary dimensions. To produce the microbubbles nitrogen is blended with carbon dioxide, the 'diluent' gas, while THAM (tris hydroxymethyl aminomethane hydrochloride) was used as an absorbent removing the 'diluent' gas from the initial bubbles. Hence, bubbles are initially produced from a gas mixture and the 'diluent' gas reabsorbed to reduce the diameter further. A Coulter counter was used for immediate size measurement of the bubbles. The absorbent medium in which the bubbles were produced was evaluated on 9 control dogs to test the physiological inertness. Plasma surface tension and arterial pH was measured in 5 animals receiving increasing doses while, in the remaining 4, arterial blood pressure, heart rate, breathing frequency and pulmonary artery pressure were measured before, during and after the injections. The resulting changes were within acceptable physiological limits. Stable bubble patterns were produced with diameters as small as 14 microns and in quantities exceeding 10 to the power of 7. Size distributions around any given diameter were +- 2 microns for 80% of the bubbles. The techniques and apparatus presented in this study can be further utilized for examining the complex microembolism process. Various applications of these techniques include an assessment of microcirculatory filtration and pharmacological responses to air embolism.