3 ms·

Hold your breath. I've done that with a fingertip pulse oximeter I have.

• peripitea 6y ago
  In my experience you need to hold your breath for a while (like 2-3 minutes) for blood O2 to start decreasing. Certainly doable (and safe as long as you're lying down away from water) but might take some practice getting used to the discomfort. You can hyperventilate a bit before to make it easier (though never do this in any other breath holding scenario).
  • jimworm 6y ago
    If you weren't doing this already, try holding your breath after exhaling to reduce the amount of oxygen stored in your lungs, then the wait wouldn't be as long - 2-3 minutes is a good breath hold!
    • peripitea 6y ago
      In my experience this isn't that much better from a discomfort perspective, because (I would guess -- not an expert on physiology) the lower available oxygen in the lungs also leads to a more rapid increase in blood CO2. It might be a bit better depending on your particular body though, so yes it's worth trying both out. Actually I just tried it and yeah for me at least the full-lungs version is obviously longer but takes less discomfort for my SpO2 to start to drop (like well before contractions start), whereas on exhale I get more discomfort (around 15s before contractions) before a similar drop.