Stabilization of Gas Emulsions

Under atmospheric conditions the stability of gas emulsions is critically dependent on their size. Surface tension effects lead to an elevated total pressure (i.e. Laplace pressure) inside the bubble, quickly leading to dissolution. For a 1 pm bubble with a = 50 mN m , the Laplace pressure, piapiKc o Jr, is nearly twice the atmospheric pressure (pam)- When injected into the bloodstream, efflux of gas from the bubbles is further enhanced by blood pressure, Pbiood-In order to overcome the overpressure effects on small gas emulsion bubbles, a 

The presence of the gas osmotic agent in the bubble lowers the partial pressures of blood gases in the bubble, thereby decreasing their tendency to diffuse out of the bubble. 

The kinetics for gas emulsion dissolution in the bloodstream were first elucidated by Epstein and Plesset in 1950, viz. 

The work of van Liew and Burkard fails to take into account another key factor in the bubbles fate, i.e. the possibility that the gas osmotic agent may condense into a liquid. Once this occurs, all ultrasound contrast is lost. This effect can be important, especially in light of the fact that in order to achieve low values of the Ostwald coefficient, the saturated vapor pressure must be decreased. A theory taking this into account was recently put forward by Kabalnov et In essence, the partial pressure of the gas osmotic agent in 

The effects of condensation can be dramatically decreased by decreasing the surface tension on the bubble surface, thereby lowering the Laplace pressure. 

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