Ha ha - now I've got your attention.......
This is an old thought that has popped back into my head due to 2 recent threads which I've brought into one (denounce me at will )
SWBO - 'traditional' theory claims that in the last 10m of ascent the pressure drops so significantly that Oxygen 'offloads' from the blood into the lungs.
There is a difference between oxygen LEAVING the blood to go into the lungs and; the rate of diffusion from lungs to blood REDUCING. Either one could cause a SWBO, but the former requires the PO2 in the alveolar gas to be lower than the PO2 in the pulmonary artery.
Now, ahem, it's been a while since I read any of the classic literature on SWBO. Does anyone have a reference that PROVES that alveolar PO2 gets so low and that pulmonary artery PO2 exceeds it?
The 'exhale in last 5m' technique is based on the common theory - i.e. that if oxygen has to leave the blood to enter the lungs - you'd want the volume of gas that it is joining to be as small as possible so that the ppO2 of alveolar gas increases faster and thus results in less 'offloading'.
However, if the O2 transfer is merely reducing and hasn't 'reversed', then exhaling could aggrivate the situation by reducing the amount of O2 molecules available to transfer to the blood (albeit at a slow rate).
None of this takes account of any of the blood flow or arterial pressure aspects of exhaling v holding it in - which probably have a greater bearing - but I thought it was worth pointing out.
Any comments/refs from those still in touch with the classic literature?
Ben
This is an old thought that has popped back into my head due to 2 recent threads which I've brought into one (denounce me at will
SWBO - 'traditional' theory claims that in the last 10m of ascent the pressure drops so significantly that Oxygen 'offloads' from the blood into the lungs.
There is a difference between oxygen LEAVING the blood to go into the lungs and; the rate of diffusion from lungs to blood REDUCING. Either one could cause a SWBO, but the former requires the PO2 in the alveolar gas to be lower than the PO2 in the pulmonary artery.
Now, ahem, it's been a while since I read any of the classic literature on SWBO. Does anyone have a reference that PROVES that alveolar PO2 gets so low and that pulmonary artery PO2 exceeds it?
The 'exhale in last 5m' technique is based on the common theory - i.e. that if oxygen has to leave the blood to enter the lungs - you'd want the volume of gas that it is joining to be as small as possible so that the ppO2 of alveolar gas increases faster and thus results in less 'offloading'.
However, if the O2 transfer is merely reducing and hasn't 'reversed', then exhaling could aggrivate the situation by reducing the amount of O2 molecules available to transfer to the blood (albeit at a slow rate).
None of this takes account of any of the blood flow or arterial pressure aspects of exhaling v holding it in - which probably have a greater bearing - but I thought it was worth pointing out.
Any comments/refs from those still in touch with the classic literature?
Ben
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