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ST. LOUIS, Mo. — In just four years the use of e-cigarettes by teenagers has grown by nearly 50 percent.  The Mayo Clinic just finished the first study about the effects of vaping on the lungs. Dr. Karen Swanson discusses their findings.  She says that people should never inhale anything but air into their lungs.  The study concludes that vaping-associated lung injury may be caused by toxic chemical fumes.