Not long ago, I let a colleague insert an IV line in my hand. He swished saline back and forth between two syringes to create bubbles, then he injected the foamy liquid into my vein. We wanted to know if a new gadget—a small Doppler ultrasound—could hear the bubbles in my bloodstream. We hoped the gadget might be useful in monitoring divers for decompression sickness, otherwise known as “the bends.” When the bubbles passed the ultrasound, we happily heard a waterfall of clicks. Bubbles in the arteries can be deadly, but bubbles in the veins are usually harmless. I knew it was safe, and it was not my first
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