In the spaces between the internal organs in the body, is there air of a vacuum?
Neither, the body tends to fill the free spaces on the body with liquid (mostly water). If there were any spaces, the gasses on the blood would come out of solution, the there would be air (or at least gasses in the ratio at which blood dissolves them).
Any gaseous space that there might be in your body is not a vacuum. It’s probably at the same pressure as the external atmosphere, although it could possible be at a higher pressure of your muscles were somehow compressing it. If it were a vacuum, it wouldn’t be so for long; the liquids in your body would “boil” and fill it up with gas.
If you have gas in your body, GasX works well. Also anything with simethicone.