An injectable foam that could make vericose veins disappear has passed a safety trial.

Dr. John D. Regan of Wake Forest University Baptist Medical Center said that Varisolve uses carbon dioxide, which can cause less burning than foams that are currently on the market.

Vericose, or "spider," veins are caused when the valves in the vessels fail, allowing blood to flow backward, expanding and twisting the veins. Varisolve, which is made from air and carbon dioxide, helps destroy vein walls and lessen their appearance, according to a release about the study.

The recent trial was meant to see if people with a heart defect known as a right-to-left shunt could tolerate the additional air in their blood. About one-fourth of the population has the problem without any symptoms.

In more than 90 percent of the 28 patients studied at six research sites across the country, tiny bubbles were detected in the blood during the procedure. However, no neurological, visual or cardiac changes were observed.

The study will continue until a total of 50 patients have been treated and monitored.