The definition of hiccup is the spasmodic contraction of the diaphragm that repeats several times per minute. There are several different causes for one to hiccup:
Eating too much food too quickly
Drinking too much alcohol
Swallowing too much air
A sudden change in stomach temperature, such as drinking a hot beverage and then a cold beverage.Emotional stress or excitementHiccups are the result of lack of oxygen or changes in breathing, or any activity that causes the diaphragm to undergo involuntary activity. I have concluded that it is not the smoke that causes the hiccup-the culprit is the reaction of nicotine in the bloodstream and brain.
Nicotine in tobacco smoke reaches the brain within 8 seconds of reaching the lungs. It reaches the muscles and the rest of the body soon after. The effects on the body are:
Nicotine increases the heart rate. This can be measured by checking the pulse before and after the cigarette.
Nicotine constricts blood vessels. This causes the blood pressure to increase and the blood circulation to slow down in the smaller blood vessels and a lowering of the skin temperature. These can be measured with blood pressure and skin temperature checks before and after the cigarette.
Nicotine acts as a relaxant for some muscles and causes tension in others. This can be demonstrated by measuring hand tremors before and after the cigarette.
Nicotine increases stomach secretions
Nicotine changes the brain activity
The respiratory and the circulatory system are most affected by tobacco use. Once in the bloodstream, nicotine activates cholinergic receptors. These receptors are usually activated by the neurotransmitter, acetylcholine, which is produced in the brain and by neurons in the nervous system. Acetylcholine and its receptors are involved in many functions; including muscle movement, breathing, heart rate, learning, and memory. Nicotine's chemical makeup is similar to the Acetylcholine and therefore able to activate the receptors. When nicotine gets into the brain, it attaches to acetylcholine receptors and mimics the actions of acetylcholine. But, it can disrupt the normal functioning of the nervous system where information adjusts the outgoing messages that control contraction or changing in breathing patterns, resulting in a hiccup.
This, in my opinion, is the reason why one of the side-effects of nicotine replacement theorapy is hiccups.