Monitoring a changing distance with sensors

Dear Arduino community,

I am trying to characterise the respiratory rate of individual through the expansion of the chest wall during breathing. To do this, I was looking into using sensors which can track a change in distance over time.

I was wondering whether it was possible to use PIR sensors to do this? I've read a number of posts and tutorials which utilise PIR sensors as motion detectors, but not distance trackers.

Alternatively, I've stumbled across ultrasonic sensors which seem to be more capable.

Can anyone offer some advice in regards to the capability of these sensors, or point me in the direction of similar work which has been carried out previously?

Thanks in advance!

It is normal to use a chest spring for this sort of thing. You can knit a sensor with conductive thread mixed with another thread which will change its resistance when it is stretched.

Ultrasonic or optical (Infra Red) sensors will measure these kinds of distances but they can't distinguish moving forwards from chest expansion.

Plus you also have to measure diaphragm expansion if you're serious about breathing properly. That's more complex. I haven't seen a sensor specifically for this, but I expect they exist in the medical devices market.