A hiccup is a spasm of the diaphragm and the muscles surrounding it. The spasms create a fast contraction, which draws air in. The fast draw causes your vocal chords to close, causing that iconic “hic”.
A 60 year old man was admitted to the hospital with acute pancreatitis. Pancreatitis is a horrifically painful condition that can be life threatening. In this case, it was a close call, and the doctors found several gallstones, which are often a cause. They inserted a nasogastric tube in preparation for what was going to be a long day, and ran into a problem.
They took the tube out. The hiccups continued. They tried a spoonful of sugar (which has been reported to help). Nothing.
They tried stimulating the back of pharynx. No dice.
They tried Valsalva’s maneuver (I’ve heard of that to make your ears pop but never from hiccps), sinus massage, and got creative and massaged his eyeballs. Nothing.
They broke out the sedatives and the muscle relaxers. NOTHING.
Finally, after TWO DAYS (I really hope they took care of the pancreatitis in the meantime) they went to perform a routine rectal examination. Stuck a finger in the rectum, and...silence. The first silence in two days. The silence continued for several hours, and then the hiccups came back. It was time to try again.
The patient stayed hiccup free for the next five days and was discharged from the hospital. I seriously hope he was ALSO pancreatitis free.
And now the question arises: how the HECK did this work!?!
What actually happened was that the hiccups were caused by continued firing from the vagus or phrenic nerves. These are both nerves that innervate the area around the diaphragm. The phrenic nerve controls the motor stimulation of the actual diaphragm, but the vagus nerve heads toward the esophageal plexus and the diaphragm as well, passing through the diaphragm and on down toward the thoracic cavity. If either one of these nerves started sending signals spasmodically, you might end up with the hiccups.
BUT, both of these nerves ALSO send and receive signals from the thorax, including from the gut and gastrointestinal tract. So if you have spasms going on in these nerves, stimulation via pressure in the rectum (which is very sensitive to pressure), might help. In this case it seems that the big deal was the vagus nerve, which has much more innervation in the rectum.