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I am a regular blood donor and I am also a skydiver. We normally go to around 13,000 feet AGL (above ground level). Depending on how high above sea level the ground is, altitudes could be as high as 15,000 MSL (mean sea level) before a jumper is required to use supplemental oxygen.

At those altitudes hemoglobin is less effective at carrying oxygen, which is why hypoxia is a risk.

The following chart taken from this article about aviation and the body shows how oxygen levels decrease as altitude increases:

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What I would like to know is if there is any research into the effect blood donation has on the blood stream's oxygen capacity? Is it possible to say that x days after a donation, due to reduced hemoglobin levels, operating at 15,000 MSL would be equivalent to operating at 15,000 + x MSL without donation?

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The American Red Cross (redcrossblood.org/donating-blood/donation-faqs) says it takes 4-6 weeks to restore hemoglobin levels. –  kmm Feb 22 '13 at 17:40
    
Right but how much are hemoglobin levels reduced and what does that reduction do to the overall oxygen levels in the blood? If you lose x% of hemoglobin after donation then being at sea level would be equivalent to being at.... 5,000 feet MSL? Basically my question is: how much earlier will altitude affect the body after blood donation than without? –  Charles Wesley Feb 22 '13 at 17:42
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The oxygen-carrying capacity of the blood is:

amount of haemoglobin * % saturation

The average blood donation is approximately 10% of total blood volume. . Since the donation will have no effect on the % saturation, the oxygen-carrying capacity at each altitude will go down by 10%.

By inspection of the graph in the question, the % saturation goes down by 10% at 10,000 feet. So I conclude that donating 10% of blood volume is equivalent to ascending to 10,000 feet in terms of the effect upon the blood's oxygen-carring capacity.

Response to OP comments:

1) Anyone living at 5,000 feet will have adapted to that altitude in two ways. First of all the erythrocyte levels of 2,3 bisphosphoglycerate will be elevated to maintain unloading of oxygen from haemoglobin in the tissues. Secondly, the number of red cells per mL of blood will have increased, to restore oxygen delivery. Incidentally this increases blood viscosity which is deleterious in the long term. Tibetans living in the Himalaya have adapted genetically to prevent this effect on their blood viscosity.

2) The effect of air pressure is already included in the graph, since it shows the actual degree of saturation of the blood.

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I'm not sure that is right. If you lived in Denver which is 5,000 MSL then donating blood would be the equivalent of being at 15,000 MSL. At 15,000 MSL the time of useful consciousness can be as low as 30 minutes or worse depending on things like smoking or general health? –  Charles Wesley Feb 22 '13 at 18:25
    
Also the graph shows that the degradation of oxygen saturation isn't linear. In the linked article it noted that oxygen saturation is also tied to air pressure, so it's probably a more complex formula. –  Charles Wesley Feb 22 '13 at 18:30
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I have responded by editing my answer. –  Alan Boyd Feb 22 '13 at 18:57
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