could someone explain the main points of the O2 dissocation curve?

[ronaldo23]

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Kaplan really emphasizes this curve is super important, but i don't understand it that well conceptually...can someone briefly explain why it shifts what the shifts mean etc (in layman's terms)

 

[JasoniusUW]

Alright, here it is cut and dry.

X axis, tension, I prefer to think of PO2 (partial pressure of oxygen)
Y axis, Hb saturation

More pO2 means more saturation (you're stuffing the oxygen in under high pressure)
Less pO2 smaller gradient, not as much oxygen forced in

Now that curve is sigmoidal (S-shaped) but it can be shifted:

It shifts left [MORE AFFINITY: it packs MORE oxygen under LESS pressure - easier to pack/saturate] if:
-decreasing temperature
-decreased 2,3-BPG
-decreased [H+] - basic
-carbon monoxide exposure

It shifts right [LESS AFFINITY: it packs LESS oxygen despite MORE pressure - HARDER to pack/saturate] if:
-increasing temperature
-increased 2,3-BPG
-increased [H+] - MORE ACIDIC

Now here's how you remember it

When you exercise, you want LESS affinity to dump MORE oxygen INTO tissues
what happens during exercise?
1. body heats up
2. lactic acid makes an acidic environment

In the lungs, you want more loading, air is (hopefully) cooler than metabolic tissue requiring oxygen, and blood in lungs coming from the body is basic due to higher HCO3- concentration from CO2 storage. Therefore you want higher saturation/loading in the lungs. You want less saturation ability/dumping in systemic tissues.

 

[amikhchi]

I'm pretty sure it's the other way around, left-shifted is more saturated (hence more affinity) and right-shifted is less saturated (less affinity)

 

[rocuronium]

I'm pretty sure it's the other way around, left-shifted is more saturated (hence more affinity) and right-shifted is less saturated (less affinity)

You are correct. If JasoniusUW switches 'left shift' and 'right shift' all the points are correct.

 

[JasoniusUW]

Oops! Sorry, wrote that during my 4 am insomnia spat.

 

[ronaldo23]

does an altitude increase= left shift? and why do athletes sometimes train in high altitudes?

 

[rocuronium]

does an altitude increase= left shift? and why do athletes sometimes train in high altitudes?

The answer to your first question is quite difficult, as it depends on what stage of acclimatization you are at. Simply put, people who have lived at altitude for long periods of time usually have some sort of respiratory alkalosis, which would be a left shift. If you want to know more, I'd love to discuss it with you.

As for the second part of your question, athletes train at altitude because the low PO2 causes an increased production of red blood cells. More RBCs = increased oxygen carrying capacity, etc.

 

[JasoniusUW]

The answer to your first question is quite difficult, as it depends on what stage of acclimatization you are at. Simply put, people who have lived at altitude for long periods of time usually have some sort of respiratory alkalosis, which would be a left shift. If you want to know more, I'd love to discuss it with you.

As for the second part of your question, athletes train at altitude because the PO2 causes an increased production of red blood cells. More RBCs = increased oxygen carrying capacity, etc.

I thought those people just have more RBC's and are more 'barrel-chested' (Quechas)
It is also harder conditions to train in higher altitudes initially, acclimatizing can take hours to days. It's training under harsher conditions...and getting more RBC's at the end hahah. Bonus.

 

[rocuronium]

It's interesting that you mention the barrel chest trait. Generally people with a barrel chest have a harder time ventilating, so I am curious as to how it provides an advantage to those at altitude.

 

[physics junkie]

OP, here is an explanation of the curve in terms of its actual use.

When blood reaches your lung to be oxygenated it is exposed to a high oxygen partial pressure of PO2=100mmHg. This forces hemoglobin to bind oxygen as you can see on your curve you have 100% oxygen saturation at this level. By the time the blood reaches your tissue the PO2 is decreasing down to a minimum of 40mmHg. Keep this in mind for the next part.

Now, your body has a lot of mechanisms in play to allocate oxygen distributon to tissues based on their need(obviously muscle needs to use more oxygen than blood going through your skin) but one of the cooler ones is called the Bohr Effect. What happens is when blood reaches the tissue the waste products produced by tissue metabolism, CO2 and H+, influence how strongly the oxygen is bound to the hemoglobin. The H+ binds to the hemoglobin and decreases the affinity of hemoglobin for oxygen shifting the curve to the right. This causes more oxygen to be released at the same PO2. So now more oxygen is released into your cells.

When hemoglobin returns to the lungs carrying carbon dioxide and that bound H+ there is a lot of bicarbonate in the blood as well(HCO3-). What happens is the high PO2 in the lungs(100mmHg) causes carbon dioxide and hydrogen to dissociate from the hemoglobin. H+ undergoes a reaction with HCO3- to produce H2 and CO2 that is exhaled. Now that the H+ is removed from the hemoglobin the curve is going to shift to the left so you can bind more oxygen at the PO2 of 100mmHg 😱.

There is a lot more to this that you will learn in respiratory physiology but I hope this storyline helps this thing make sense to you.

 

[JasoniusUW]

It's interesting that you mention the barrel chest trait. Generally people with a barrel chest have a harder time ventilating, so I am curious as to how it provides an advantage to those at altitude.

Heritability studies in the Andes

In the mid-1800s, Denis Jourdanet, an early researcher into high-altitude adaptation, described the high-altitude native as having a ‘vast chest [that] makes him comfortable in the midst of this thin air' (Houston, 1987). This is one of the earliest descriptions of what may be the most commonly cited characteristic of New World high-altitude natives: the relatively large ‘barrel chest'. Alberto Hurtado (Hurtado, 1932) commented on this characteristic in Andean populations and postulated that the enlarged chest could allow for increased lung volumes and thereby increase oxygen uptake. Whether this chest morphology is a genetic characteristic has been the subject of numerous studies.

http://jeb.biologists.org/cgi/conte...k&searchid=1&FIRSTINDEX=20&resourcetype=HWFIG

Something we learned in comparative animal physiology. Heh yeah, I know what you mean, barrel chest is usually associated with some respiratory pathology.

 

[rocuronium]

Quite interesting indeed! Thanks for the link.