blood oxygen saturation immediately after breathhold

[growingupninja]

I have a question that someone here might be able to answer....

I started using a pulse O2 meter when doing dry training, mostly dynamic. It is a fingertip model, and also has a little heart rythym graph which is useful for showing vasoconstriction. My question is that after a hold, when I take my first few breaths, the device shows a sudden drop in O2, usually 5% to 10%, which then quickly climbs back to normal (98%+).

Why would my O2 drop suddenly when I start to breathe again? Does this have something to do with vasoconstriction and the location of the device (fingertip)? Or is it a function of blood pressure? Is this something that hook breathing (which I don't do out of the water) addresses? When I begin to breathe again my pulse also rises quickly, as I would expect.

Thanks.

 

[trux]

Yes, the O2 saturation is the most critical after the breath hold, and that's why it is very important to watch your buddy for some 30s after surfacing, when it is the most likely that he blacks out. There are several factors involved: the sudden decrease of the transpulmonary pressure, the release of vasoconstriction, the sudden drop of arterial pressure, and the change of chemistry due to the exhale of CO2 (Bohr saturation curve shift).

 

[growingupninja]

Thank you.

 

[Johan Andersson]

A very important factor is the fact that you use a fingertip sensor. There is a circulatory delay of several seconds (could be up to 20-30 sec) before the blood that is oxygenated in the lungs reaches the the fingertip.

To state it in a short way, in the pulmonary vein, the blood has a near 100% saturation almost immediately after the first post-apnea inhalation, but it takes time before this blood reaches peripheral arteries (such as in the finger). As a consequence, saturation can continue to fall at the site of measurement until the oxygenated blood reaches the site. The circulatory delay to the brain is shorter, but nevertheless, the lowest saturation in the cerebral circulation and highest risk for hypoxic loss of consciousness, should be in the immediate post-apnea period.

As trux said, because if this, you should not not interupt the supervision of your buddy until at the least 30 sec after surfacing.

 

[growingupninja]

A very important factor is the fact that you use a fingertip sensor. There is a circulatory delay of several seconds (could be up to 20-30 sec) before the blood that is oxygenated in the lungs reaches the the fingertip.

To state it in a short way, in the pulmonary vein, the blood has a near 100% saturation almost immediately after the first post-apnea inhalation, but it takes time before this blood reaches peripheral arteries (such as in the finger). As a consequence, saturation can continue to fall at the site of measurement until the oxygenated blood reaches the site. The circulatory delay to the brain is shorter, but nevertheless, the lowest saturation in the cerebral circulation and highest risk for hypoxic loss of consciousness, should be in the immediate post-apnea period.

As trux said, because if this, you should not not interupt the supervision of your buddy until at the least 30 sec after surfacing.

Thanks. It is all very interesting. Makes sense; the fingertip is a long way from the vitals. I was trying different ways to hook breathe to see if that would affect the reading but I wasn't seeing much of a difference--except if I breathe too shallow and hold the hook breaths longer the saturation just takes longer to start the sudden post apnea dip. I have noticed though that the magnitude of the dip is reduced (maybe 5-6%) if I am doing empty lung work; it is largest after a long, full lung dynamic (as much as 12%), and--I think--also more pronounced if my muscles are fatigued. I imagine that difference might have a lot to do with Bohr curve shift; on the empty lung work I wouldn't have as much accumulated CO2.