There's really much more to this, than merely swallowing too much air while drawing, or acid content in PG. Scientists believe that nicotine (regardless of it's source) causes the LES (Lower Esophageal Sphincter), the muscle between the bottom of the esophagus and the top of the stomach, to relax more than it typically would. This relaxation allows a backwash of stomach acids and enzymes back up into the esophagus. Think of this muscle as sort of a one-way valve, designed too allow food IN to the stomach, but not to allow anything OUT, and thereby preventing anything (including stomach acid, enzymes, etc.) to back up into the esophagus. The esophagus is also biologically designed somewhat different than the stomach, in that it cannot tolerate those stomach acids and enzymes.
And I quote from the WebMD website: Impairing the function of the LES. "The nicotine in tobacco seems to lower the pressure in the lower esophageal sphincter," says Cheskin. The reduced pressure could allow stomach acids and enzymes to back into the esophagus." per the following website.
Heartburn & Tobacco: Effects of Smoking, Chewing, and More
There are literally hundreds, if not thousands of websites where this information is addressed. You can merely type "nicotine" and "GERD" or "Acid Reflux" into Google or any search engine, and look for more.
My own personal experience can attest to this. I am diagnosed with GERD, as well as Hiatal Hernia, which further complicates issues derived from the use of nicotine. For those unfamiliar, a Hiatal Hernia is when a small portion of one's stomach, protrudes up through the diaphragm (the muscles separating the stomach (and organs below), from the chest cavity above. This further distorts the region surrounding or adjacent to the LES causing additional acid backwash problems.
In spite of taking medicine on a regular basis to combat GERD, if I attempt to use nicotine levels much above 11mg, I will get into trouble with severe heartburn, and worse. Even 11 can affect this condition at times, and I need to be lower. I tend to try to use nicotine levels of 6mg or 0mg, to try to avoid this problem.