Fig. 4. Transient behavior of vessel diameter after exposure to air embolism in control (filled circles) and surfactant-pretreated (open circles) animals. Numbers define the specific events: (1) air becoming entrapped, with no change in vessel diameter; (2) rapid, massive vessel constriction over air; (3) continual vessel constriction causing embolism breakup into multiple smaller bubbles; (4) gradual return to original vessel diameter, separating individual bubbles from one another.