The sniff test is a fluoroscopic exam used to check how the. diaphragm (the muscle that controls breathing) moves during. activities such as breathing normally and inhaling rapidly. Your diaphragm normally moves down when you inhale, and up. when you exhale. Both the right and left sides of your diaphragm. should move in the right direction at the same time. During the sniff test, the radiologist will observe how your diaphragm. moves. You will be asked to sniff or quickly breathe in through. your nose. An injury or abnormality resulting in paralysis of the. phrenic nerve (the nerve responsible for diaphragmatic motion) can. be detected in this manner.