Equipment for recording inaudible sounds

["rowan drury" rowandrury]

Dear Nature Recordists

I am working on a project with an artist who is trying to record sounds fro=
m
inside the human body. We are looking in to ways to record sounds such as
blood flowing, valves opening, stomach acid, etc. So far he has use
traditional medical equipment such as electronic stethoscopes, these have
given some sounds but they are often muffled. It has been suggested that we
could try using the same equipment used in the recording of nature and
animals that make very small sounds (insects) and to record ultrasounds of
bats, etc.

I am looking to get some advice on what might be a good set of equipment to
use, which recommended microphones, etc, might be able to record small
sounds through the skin.

Any suggestions greatly appreciated and any questions welcome
Regards
Rowan Drury