Nitrous oxide: bowel distention
Nitrous oxide will move into air-filled cavities in the body that normally contain nitrogen; so as nitrous oxide transfers from the blood into the space, nitrogen transfers out. However, nitrous oxide is 34 times more soluble than nitrogen in blood. Thus, substantial quantities of nitrous oxide leave the blood and enter the bowel, but not much nitrogen can leave the bowel to enter the blood. The result is that during exposure to nitrous oxide, like in other compliant spaces, the volume of gas in the bowel increases. The amount of the increase depends on the alveolar partial pressure of nitrous oxide, the intestinal blood flow, and the duration of nitrous oxide administration.
It has been calculated that the volume of and enclosed air pocket can be doubled be inhalation of by 50% N2O and quadrupled by inhalation of 75% N2O after several hours.