DISSOLUTION OF MULTICOMPONENT MICROBUBBLES IN THE BLOOD-STREAM - 1 - THEORY

The problem of dissolution of a bubble in the bloodstream is examined. The bubble is assumed to be filled with a mixture of a sparingly wate r-soluble gas (osmotic agent) and air. The dissolution of the bubble h as three definite stages, In Stage 1, the bubble quickly swells in air . The swelling ratio depends on the surface tension, blood pressure, l evel of oxygen metabolism and initial mole fraction of osmotic agent i n the bubble. In Stage 2, the osmotic agent slowly diffuses out of the bubble. The squared radius decreases nearly linearly with time, at a rate proportional to the Ostwald coefficient and diffusivity of the os motic agent. In Stage 3, the partial pressure of the osmotic agent bec omes so high that it condenses into a liquid, In order to prolong the lifetime of 5-mu m bubbles in the bloodstream from < 1 s las found wit h pure air), the osmotic agent must have a low Ostwald coefficient (le ss than or equal to 10(-4)) and a relatively high saturated vapor pres sure at body temperature (greater than or equal to 0.3 atm = 3 x 10(4) Pa). (C) 1998 World Federation for Ultrasound in Medicine & Biology.