Hct/Hgb levels and power

[rmur17]

okay this thread is not about doping! Let's say a given cyclist was borderline anemic for several years in the 37-39 Hct (around 125-130 Hgb) range when tested -- for whatever reasons - perhaps a combination of an iron-poor diet, dilutional effects of training etc.

A starting baseline was Hct 38.1, Hgb 127 about eighteen months ago.

With an improved diet and modest supplementation of iron over ~nine months, last spring ('07) this person's blood level has risen to 40.5% Hct (135 Hgb).

A recent test after another ~ nine month span was 43.4 Hct (144 Hgb).

Overall the percentage change from 1.5 yrs ago was 13.4% and from nine months ago 7.2%.

If we assume the training volume and intensity, state of overall health, plasma volume etc. etc. was reasonably constant across this period such that the increase in Hgb/Hct truly reflect the hemoglobin status of the blood, what would one predict about the performance of the individual? We're mostly concerned about sustainable power to the pedals of course.

Or maybe more properly, the what would one expect to say about the performance potential of the individual relative to historic norms in the ~38% Hct range?

To keep it simple, let's focus on power @Vo2max or ~5MP and power at functional threshold FTP.

i've searched some old threads and, although suggestive, I'd like to hear current thoughts from those in the know.

thanks

 

[Urkiola2]

okay this thread is not about doping! Let's say a given cyclist was borderline anemic for several years in the 37-39 Hct (around 125-130 Hgb) range when tested -- for whatever reasons - perhaps a combination of an iron-poor diet, dilutional effects of training etc.

A starting baseline was Hct 38.1, Hgb 127 about eighteen months ago.

With an improved diet and modest supplementation of iron over ~nine months, last spring ('07) this person's blood level has risen to 40.5% Hct (135 Hgb).

A recent test after another ~ nine month span was 43.4 Hct (144 Hgb).

Overall the percentage change from 1.5 yrs ago was 13.4% and from nine months ago 7.2%.

If we assume the training volume and intensity, state of overall health, plasma volume etc. etc. was reasonably constant across this period such that the increase in Hgb/Hct truly reflect the hemoglobin status of the blood, what would one predict about the performance of the individual? We're mostly concerned about sustainable power to the pedals of course.

Or maybe more properly, the what would one expect to say about the performance potential of the individual relative to historic norms in the ~38% Hct range?

To keep it simple, let's focus on power @Vo2max or ~5MP and power at functional threshold FTP.

i've searched some old threads and, although suggestive, I'd like to hear current thoughts from those in the know.

thanks

Hello rmur17. About your question I would say that in the 1st place if that cyclist was competing with a 12.5-13 g/dL of Hgb that seems very low to me so it is possible that as you point out he/She was anemic or pseudoanemic, especially being confirmed than now he/she has a Hgb of 14.4 and Hct of 43.4%. This means that during that period of anemia or pseudo-anemia he/she was underperforming 100% for sure and just by correcting his/her levels he/she should notice an important improvement in condition. It is difficult though and maybe some matemathitians/engineers out there can help us out in predicting FTP based on the numbers before this physiological status and the new status. And even that it would be very theorical. The bottom line is that he/she sould be performing better with proper training and it is extrenely important to take care of nutrition/training dose and recovery so that he/she does not fall again in the whole.

I hope it helped. Not much info but I hope it helped.

Cheers.

 

[ctgt]

okay this thread is not about doping! Let's say a given cyclist was borderline anemic for several years in the 37-39 Hct (around 125-130 Hgb) range when tested -- for whatever reasons - perhaps a combination of an iron-poor diet, dilutional effects of training etc.

A starting baseline was Hct 38.1, Hgb 127 about eighteen months ago.

With an improved diet and modest supplementation of iron over ~nine months, last spring ('07) this person's blood level has risen to 40.5% Hct (135 Hgb).

A recent test after another ~ nine month span was 43.4 Hct (144 Hgb).

Overall the percentage change from 1.5 yrs ago was 13.4% and from nine months ago 7.2%.

If we assume the training volume and intensity, state of overall health, plasma volume etc. etc. was reasonably constant across this period such that the increase in Hgb/Hct truly reflect the hemoglobin status of the blood, what would one predict about the performance of the individual? We're mostly concerned about sustainable power to the pedals of course.

Or maybe more properly, the what would one expect to say about the performance potential of the individual relative to historic norms in the ~38% Hct range?

To keep it simple, let's focus on power @Vo2max or ~5MP and power at functional threshold FTP.

i've searched some old threads and, although suggestive, I'd like to hear current thoughts from those in the know.

thanks

I'm also interested in the answer to this question. I have given blood 50+ times, and never ever was refused for low iron until I started training more seriously. In the past 4 years, I have been deferred once, and 2-3 times they re-tested my HgB just to make sure (my blood didn't sink fast enough in the solution). Their threshold to give blood is 125.

One more question: What is the relationship between the HgB levels that Canadian Blood Services measure for, and the HcT levels that we all as cycling fans read about so much? Do they automatically vary in lockstep with each other, or are there other factors?

 

[Urkiola2]

I'm also interested in the answer to this question. I have given blood 50+ times, and never ever was refused for low iron until I started training more seriously. In the past 4 years, I have been deferred once, and 2-3 times they re-tested my HgB just to make sure (my blood didn't sink fast enough in the solution). Their threshold to give blood is 125.

One more question: What is the relationship between the HgB levels that Canadian Blood Services measure for, and the HcT levels that we all as cycling fans read about so much? Do they automatically vary in lockstep with each other, or are there other factors?

It is very kind of you to donate blood since it is a necessity in many hospitals...I just hope that finally all the new blood substitution solutions going on the clinical trials can finally be cleared and be used for the good og humanity and not for the enrichement of athletes and some people around them..

Anyways, I don´t know the Canadian theshold to give blood but if they refused you because your Hgb was 12.5 then you (I am assuming you are a male) could be in trouble in terms of performance. If you want to compete I would donate blood during the off-season, because during the season you can end up under anemic or pseudoanemic conditions. One bag of blood (pint) it is about 450ml and that represents, and pretty accurately..a drop of about 3%Hct and 1g/dL of Hgb. Also you have to check Ferritin levels which is a major player. Many people (including many physicians) only pay attention to iron levels. However iron levels are very voluble and they don´t necessarely reflect the iron status of your body. Ferritin is the storage form of iron and that is what you need to look for in the future. Very low ferritin levels take several months to get back up to normal with iron replacment therapy and proper rest. So that is something you should taking into account.

I hope it helped.

Cheers

 

[Alex Simmons]

It is very kind of you to donate blood since it is a necessity in many hospitals...I just hope that finally all the new blood substitution solutions going on the clinical trials can finally be cleared and be used for the good og humanity and not for the enrichement of athletes and some people around them..

Anyways, I don´t know the Canadian theshold to give blood but if they refused you because your Hgb was 12.5 then you (I am assuming you are a male) could be in trouble in terms of performance. If you want to compete I would donate blood during the off-season, because during the season you can end up under anemic or pseudoanemic conditions. One bag of blood (pint) it is about 450ml and that represents, and pretty accurately..a drop of about 3%Hct and 1g/dL of Hgb. Also you have to check Ferritin levels which is a major player. Many people (including many physicians) only pay attention to iron levels. However iron levels are very voluble and they don´t necessarely reflect the iron status of your body. Ferritin is the storage form of iron and that is what you need to look for in the future. Very low ferritin levels take several months to get back up to normal with iron replacment therapy and proper rest. So that is something you should taking into account.

I hope it helped.

Cheers

I have one 50+ y.o. female athlete that is susceptible to low ferritin levels, something we look out for when performance stall/falls.

 

[sidewind]

Some numbers from
http://www.ncbi.nlm.nih.gov/sites/entrez


Influence of blood donation on O2 uptake on-kinetics, peak O2 uptake and time to exhaustion during severe-intensity cycle exercise in humans.

Burnley M, Roberts CL, Thatcher R, Doust JH, Jones AM.
Department of Sport and Exercise Science, University of Wales Aberystwyth, Ceredigion, UK.

We hypothesized that the reduction of O2-carrying capacity caused by the withdrawal of approximately 450 ml blood would result in slower phase II O2 uptake (VO2) kinetics, a lower VO2peak and a reduced time to exhaustion during severe-intensity cycle exercise. Eleven healthy subjects (mean +/- S.D. age 23 +/- 6 years, body mass 77.2 +/- 11.0 kg) completed 'step' exercise tests from unloaded cycling to a severe-intensity work rate (80% of the difference between the predetermined gas exchange threshold and the VO2peak) on two occasions before, and 24 h following, the voluntary donation of approximately 450 ml blood. Oxygen uptake was measured breath-by-breath, and VO2 kinetics estimated using non-linear regression techniques. The blood withdrawal resulted in a significant reduction in haemoglobin concentration (pre: 15.4 +/- 0.9 versus post: 14.7 +/- 1.3 g dl(-1); 95% confidence limits (CL): -0.04, -1.38) and haematocrit (pre: 44 +/- 2 versus post: 41 +/- 3%; 95% CL: -1.3, -5.1). Compared to the control condition, blood withdrawal resulted in significant reductions in VO2peak (pre: 3.79 +/- 0.64 versus post: 3.64 +/- 0.61 l min(-1); 95% CL: -0.04, - 0.27) and time to exhaustion (pre: 375 +/- 129 versus post: 321 +/- 99 s; 95% CL: -24, -85). However, the kinetic parameters of the fundamental VO2 response, including the phase II time constant (pre: 29 +/- 8 versus post: 30 +/- 6 s; 95% CL: 5, -3), were not altered by blood withdrawal. The magnitude of the VO2 slow component was significantly reduced following blood donation owing to the lower VO2peak attained. We conclude that a reduction in blood O2-carrying capacity, achieved through the withdrawal of approximately 450 ml blood, results in a significant reduction in VO2peak and exercise tolerance but has no effect on the fundamental phase of the VO2 on-kinetics during severe-intensity exercise.

 

[INCE]

Interesting questions in the opening post. I did not see any direct answers yet as to how reduction/ increase in hct/hgb affects power specifically.Let me try.

Generally, I’d think the relationship would be tied to the efficiency (economy) of the individual at the time of testing.I will make some very broad but realistic assumptions:
-End aerobic zone at ventilary theashold,
-efficiency=25%,
-power vs. VO2 linear,
-V02 vs. hgb/hct linear,
-equilibrium stable conditions,
-withdrawal of 450 ml of whole blood=drop of 3%Hct,=1g/dL in Hgb

I would theorize that hct change from 38.1% to 43. 4% (13.4% change over starting) would be equivalent to taking two units of whole blood and would increase VO2 by 8% and wattage at ventilary threashold by 2-3%. Sounds like it its not much but significan. Does it make sense?

 

[rmur17]

Interesting questions in the opening post. I did not see any direct answers yet as to how reduction/ increase in hct/hgb affects power specifically.Let me try.

Generally, I’d think the relationship would be tied to the efficiency (economy) of the individual at the time of testing.I will make some very broad but realistic assumptions:
-End aerobic zone at ventilary theashold,
-efficiency=25%,
-power vs. VO2 linear,
-V02 vs. hgb/hct linear,
-equilibrium stable conditions,
-withdrawal of 450 ml of whole blood=drop of 3%Hct,=1g/dL in Hgb

I would theorize that hct change from 38.1% to 43. 4% (13.4% change over starting) would be equivalent to taking two units of whole blood and would increase VO2 by 8% and wattage at ventilary threashold by 2-3%. Sounds like it its not much but significan. Does it make sense?

thanks for the reply. I don't have any ex. phys. training so I struggle with things like this.

Now can I ask how you arrived at the 8% for Vo2max but only 2-3% for threshold?

thanks again

 

[Steve_B]

I am interested in this topic myself. My last blood test (December) says:
Hematocrit = 39.8 % (expected range 42 - 52)
RBC = 4.33 M/UL (expected range 4.50 - 5.50)
Hemoglobin = 13.7 G/DL (expected range 13.5 - 17.0)
No Ferritin results listed.

I was probably a little dehydrated for this test and I believe that is supposed to elevate 'crit results so it could be even worse than this.

My doctor didn't mark the RBC and 'crit as anything to worry about. Hmmmm... I'm going to call him to get a copy of the previous two blood tests to see if this has been a chronic issue.

 

[kant314]

is there a relationship between Hemoglobin and hct?

 

[rmur17]

is there a relationship between Hemoglobin and hct?

we seem to have lost Urkiola2 in the spam .

Roughly speaking, Hct% = Hgb (g/dl) x 3

 

[Urkiola2]

we seem to have lost Urkiola2 in the spam .

Roughly speaking, Hct% = Hgb (g/dl) x 3

Sorry, I have a cold these days and have a slow hand to write these days.
My hand will get a bit faster soon...

The relationship with Hct and Hgb is: 1g/dL of Hgb multiplied by 2.96 to get your % of Hct. It is a mathematical formula and as always, there will be some exceptions. However I have seen thousends of tests and the relationship is quite accurate. Mathematically speaking is 2.96 although a multiplication by 3 is usually aplied widely.

Cheers.

 

[jsirabella]

I am surprised with your background and knowledge I did not see a post in the Sodium Phosphate thread. I asked a few riders here who race about it and they all gave me a strange look that never heard of it. Have you any experience with it? Ofcourse you can post here or in that thread not to take it off subject.

-Js

It is very kind of you to donate blood since it is a necessity in many hospitals...I just hope that finally all the new blood substitution solutions going on the clinical trials can finally be cleared and be used for the good og humanity and not for the enrichement of athletes and some people around them..

Anyways, I don´t know the Canadian theshold to give blood but if they refused you because your Hgb was 12.5 then you (I am assuming you are a male) could be in trouble in terms of performance. If you want to compete I would donate blood during the off-season, because during the season you can end up under anemic or pseudoanemic conditions. One bag of blood (pint) it is about 450ml and that represents, and pretty accurately..a drop of about 3%Hct and 1g/dL of Hgb. Also you have to check Ferritin levels which is a major player. Many people (including many physicians) only pay attention to iron levels. However iron levels are very voluble and they don´t necessarely reflect the iron status of your body. Ferritin is the storage form of iron and that is what you need to look for in the future. Very low ferritin levels take several months to get back up to normal with iron replacment therapy and proper rest. So that is something you should taking into account.

I hope it helped.

Cheers

 

[Urkiola2]

I am surprised with your background and knowledge I did not see a post in the Sodium Phosphate thread. I asked a few riders here who race about it and they all gave me a strange look that never heard of it. Have you any experience with it? Ofcourse you can post here or in that thread not to take it off subject.

-Js

Sorry, I am just not into ergogenic aids (legal or ilegal) discussions. I don't want to get into that.

 

[Fday]

okay this thread is not about doping! Let's say a given cyclist was borderline anemic for several years in the 37-39 Hct (around 125-130 Hgb) range when tested -- for whatever reasons - perhaps a combination of an iron-poor diet, dilutional effects of training etc.

A starting baseline was Hct 38.1, Hgb 127 about eighteen months ago.

With an improved diet and modest supplementation of iron over ~nine months, last spring ('07) this person's blood level has risen to 40.5% Hct (135 Hgb).

A recent test after another ~ nine month span was 43.4 Hct (144 Hgb).

Overall the percentage change from 1.5 yrs ago was 13.4% and from nine months ago 7.2%.

If we assume the training volume and intensity, state of overall health, plasma volume etc. etc. was reasonably constant across this period such that the increase in Hgb/Hct truly reflect the hemoglobin status of the blood, what would one predict about the performance of the individual? We're mostly concerned about sustainable power to the pedals of course.

Or maybe more properly, the what would one expect to say about the performance potential of the individual relative to historic norms in the ~38% Hct range?

To keep it simple, let's focus on power @Vo2max or ~5MP and power at functional threshold FTP.

i've searched some old threads and, although suggestive, I'd like to hear current thoughts from those in the know.

thanks

I would expect very little change from this. There would be a difference but it should be less than you would expect looking at the oxygen carrying capacity alone. The reason for this is lower hct/hb levels is associated with lower blood viscosity, so it is easier for the body to deliver more cardiac output to make up for the lower oxygen carrying capacity and harder to deliver high cardiac output when the oxygen carrying capacity is high.

 

[Urkiola2]

I would expect very little change from this. There would be a difference but it should be less than you would expect looking at the oxygen carrying capacity alone. The reason for this is lower hct/hb levels is associated with lower blood viscosity, so it is easier for the body to deliver more cardiac output to make up for the lower oxygen carrying capacity and harder to deliver high cardiac output when the oxygen carrying capacity is high.

I may be wrong because maybe you did not explain yourself properly, but if you did so, your assumption seems to be wrong. Please explain yourself in a more scientific way or however you think. I am sorry but your hypothesis is not understandable to me. Thanks

 

[Fday]

I may be wrong because maybe you did not explain yourself properly, but if you did so, your assumption seems to be wrong. Please explain yourself in a more scientific way or however you think. I am sorry but your hypothesis is not understandable to me. Thanks

In a prior life I was an anesthesiologist. Believe it or not, anesthesiologists worry about xoygen delivery to the tissues under all sorts of conditions, especially regarding the effects of hemodilution from blood loss and polycythemia (too many red cells, a pathologic condition). We worry especially about when it is really necessary to transfuse to prevent complications like heart attack from the inability to deliver oxygen to the heart when blood loss has occurred. Hence, this has been pretty well studied. You could probably pick up any basic anesthesia text and this will be discussed.

Anyhow, how much fluid one can push through a pipe of any given size depends on the pressure gradiant and the viscosity. The lower the viscosity the more flow there will be. Lower viscosities occur with lower HCT. I did a little search and here are a few links that while not directly related to this discussion, goes to the gist of what I am trying to say.

Summary paper

mice study

bypass study

book extract

Compensation is not total

 

[Urkiola2]

In a prior life I was an anesthesiologist. Believe it or not, anesthesiologists worry about xoygen delivery to the tissues under all sorts of conditions, especially regarding the effects of hemodilution from blood loss and polycythemia (too many red cells, a pathologic condition). We worry especially about when it is really necessary to transfuse to prevent complications like heart attack from the inability to deliver oxygen to the heart when blood loss has occurred. Hence, this has been pretty well studied. You could probably pick up any basic anesthesia text and this will be discussed.

Anyhow, how much fluid one can push through a pipe of any given size depends on the pressure gradiant and the viscosity. The lower the viscosity the more flow there will be. Lower viscosities occur with lower HCT. I did a little search and here are a few links that while not directly related to this discussion, goes to the gist of what I am trying to say.

Summary paper

mice study

bypass study

book extract

Compensation is not total

Great to talk/discuss with an anesthesiologist. That is very impresive, as I personally have high respect for your field for the huge knowledge of general medicine and physiology involved.

Maybe we are not making our points across.
I know that anthesthesiologists are very concerned always with oxygen delivery since it is a crucial part of your job. Especially important as you better than I know, dealing with hypovolemia and hypovolemic shocks is one of the situations anesthesiologists deal with the most and plasma expanders like Hidroxiethyl Starch (HES), albumin, Gelofusine (Gelatin) or Dextran (branched polysaccharide) are widely used by anesthesiologists under hypovelemic situations. So I understand that from your point of view and your experience hypo and hypervolemia are terms and situations that you control very well. I have no doubt about your knowledge about oxygen carrying capacity and delivering to the tissues.
I believe that what you claim has to do with viscosity and in situations like the one you mention (polycythemia vera) the blood flow will be decreased due to the increased viscosity as we can apply Poiseuille's Equiation.
However the situation in which anesthesiologists work is different than the situation we can observe in athletes like it is the case of the post by rmur17. In general medicine and especially during surgery a Hct of 40% or 50% as you know is pretty much irrelevant since the patient is perfectly stable and oxygenized. However in terms of exercise situation a decrease from a physiological normal Hgb levels of 14g/dL to 13g/dL you could have some consequences in terms of performance. An average citizen will probably not tell such a small decrease but an athlete will defenetely tell it. In that situation we are dealing with neither hypo/hypervolemia but dealing with exercise performance and oxygen delivery to the cells. Since O2 is bound to Hgb, if your Hgb levels decrease your O2 carrying capacity will be drecreased to the tissues and especially important this will be during high intensity exercise. An increase in Cardiac Output will not have an effect to compensate the lower Oxygen carrying capacity since during maximal exercise you will reach your Maximal Cardiac Output with low or high Hgb levels. To me the only thing that can change to compensate the decrease in oxygen carrying capacity is 2,3 DPG (2,3 diphosphoglycerate) which could increase in order to increase the unload of O2 bound to Hgb. However and something that it is my day-to-day thing when an athlete decreases his/her Hgb and Hct they can defenetely tell a decrease in their performance. When these athletes bring back their normal physiological Hgb/Hct their performance goes back to normal.
Same thing happens with EPO or blood transfussions. Even when you can be dealing with a hypervolemia the oxygenation to the tissues will be much larger increased due to a higher levels of Hgb and therefore oxygen carrying capacity.

Cheers.

 

[Fday]

Great to talk/discuss with an anesthesiologist. That is very impresive, as I personally have high respect for your field for the huge knowledge of general medicine and physiology involved.

Maybe we are not making our points across.
I know that anthesthesiologists are very concerned always with oxygen delivery since it is a crucial part of your job. Especially important as you better than I know, dealing with hypovolemia and hypovolemic shocks is one of the situations anesthesiologists deal with the most and plasma expanders like Hidroxiethyl Starch (HES), albumin, Gelofusine (Gelatin) or Dextran (branched polysaccharide) are widely used by anesthesiologists under hypovelemic situations. So I understand that from your point of view and your experience hypo and hypervolemia are terms and situations that you control very well. I have no doubt about your knowledge about oxygen carrying capacity and delivering to the tissues.
I believe that what you claim has to do with viscosity and in situations like the one you mention (polycythemia vera) the blood flow will be decreased due to the increased viscosity as we can apply Poiseuille's Equiation.
However the situation in which anesthesiologists work is different than the situation we can observe in athletes like it is the case of the post by rmur17. In general medicine and especially during surgery a Hct of 40% or 50% as you know is pretty much irrelevant since the patient is perfectly stable and oxygenized. However in terms of exercise situation a decrease from a physiological normal Hgb levels of 14g/dL to 13g/dL you could have some consequences in terms of performance. An average citizen will probably not tell such a small decrease but an athlete will defenetely tell it. In that situation we are dealing with neither hypo/hypervolemia but dealing with exercise performance and oxygen delivery to the cells. Since O2 is bound to Hgb, if your Hgb levels decrease your O2 carrying capacity will be drecreased to the tissues and especially important this will be during high intensity exercise. An increase in Cardiac Output will not have an effect to compensate the lower Oxygen carrying capacity since during maximal exercise you will reach your Maximal Cardiac Output with low or high Hgb levels. To me the only thing that can change to compensate the decrease in oxygen carrying capacity is 2,3 DPG (2,3 diphosphoglycerate) which could increase in order to increase the unload of O2 bound to Hgb. However and something that it is my day-to-day thing when an athlete decreases his/her Hgb and Hct they can defenetely tell a decrease in their performance. When these athletes bring back their normal physiological Hgb/Hct their performance goes back to normal.
Same thing happens with EPO or blood transfussions. Even when you can be dealing with a hypervolemia the oxygenation to the tissues will be much larger increased due to a higher levels of Hgb and therefore oxygen carrying capacity.

Cheers.

I didn't say there would be no effect from changing the hct but that it will not be as great as many might think as many different things affect oxygen delivery to the tissues. A 10% increase in hct does not result in a 10% increase in capability and vice-versa. And, there is a point where increasing hct further will not result in an improve performance. There are so many variables it is almost impossible to say what the optimum hct for optimum performance would be. You suggest that maximum cardiac output is fixed and not dependent upon hct. There is no evidence to support that view.

I personally think that filling pressure is a much bigger deal in affecting how an athlete performs than the normal variations in hct. For instance, if an athlete exercises and does not replenish fluids lost through sweat the hct will go up but the filling pressure will go down. Wonder if the potential of the athlete goes up or down as the hct goes up under the situation of dehydration?

The capillaries do not care if the oxygen demand of the tissue is due to athletic demands or some other reason. In fact, the two major areas of concern regarding medical research look at delivery of oxygen to the brain and to the heart. The heart is nothing more than an exercising muscle so what is learned there can be applied directly to what happens in the legs. The major difference between exercising muscle and non-exercising tissue is blood flow can only occur in the muscle when it is relaxed, not during contraction. The physiology of this is pretty well understood and the current best understanding be found in any cardiac anesthesia test. Otherwise, the physiology of blood flow through the capillaries (the only part of the vascular system where oxygen can leave the vessels to get to the tissues) is pretty much the same for all the tissues.

My point is that it is complicated. Changing one thing may have adverse influences on another thing. Many things affect oxygen delivery to the tissues including all the variables that can affect maximum cardiac output, the blood pressure, and all the things that can affect the oxyhemoglobin dissociation curve, and how much right left physiolgic shunting is occuring in the lungs, and how easily the blood flows through the tissues, beyond the simple question of how much hemoglobin is in the blood. And then, exercise can affect other variables like electrolyte concentrations that can adversely affect the ability of the muscles to contract optimally that has nothing to do with hemoglobin concentraiton but everything to do with performance. Wishing it to be simple does not make it so.

It is possible to say if I increase hemgolbin concentration the expected tendency is going to be to improve performance but it is not going to be possible to predict how much.

 

[Urkiola2]

I didn't say there would be no effect from changing the hct but that it will not be as great as many might think as many different things affect oxygen delivery to the tissues. A 10% increase in hct does not result in a 10% increase in capability and vice-versa. And, there is a point where increasing hct further will not result in an improve performance. There are so many variables it is almost impossible to say what the optimum hct for optimum performance would be. You suggest that maximum cardiac output is fixed and not dependent upon hct. There is no evidence to support that view.

I personally think that filling pressure is a much bigger deal in affecting how an athlete performs than the normal variations in hct. For instance, if an athlete exercises and does not replenish fluids lost through sweat the hct will go up but the filling pressure will go down. Wonder if the potential of the athlete goes up or down as the hct goes up under the situation of dehydration?

The capillaries do not care if the oxygen demand of the tissue is due to athletic demands or some other reason. In fact, the two major areas of concern regarding medical research look at delivery of oxygen to the brain and to the heart. The heart is nothing more than an exercising muscle so what is learned there can be applied directly to what happens in the legs. The major difference between exercising muscle and non-exercising tissue is blood flow can only occur in the muscle when it is relaxed, not during contraction. The physiology of this is pretty well understood and the current best understanding be found in any cardiac anesthesia test. Otherwise, the physiology of blood flow through the capillaries (the only part of the vascular system where oxygen can leave the vessels to get to the tissues) is pretty much the same for all the tissues.

My point is that it is complicated. Changing one thing may have adverse influences on another thing. Many things affect oxygen delivery to the tissues including all the variables that can affect maximum cardiac output, the blood pressure, and all the things that can affect the oxyhemoglobin dissociation curve, and how much right left physiolgic shunting is occuring in the lungs, and how easily the blood flows through the tissues, beyond the simple question of how much hemoglobin is in the blood. And then, exercise can affect other variables like electrolyte concentrations that can adversely affect the ability of the muscles to contract optimally that has nothing to do with hemoglobin concentraiton but everything to do with performance. Wishing it to be simple does not make it so.

It is possible to say if I increase hemgolbin concentration the expected tendency is going to be to improve performance but it is not going to be possible to predict how much.

I defenetely agree that it is quite impossible to predict an exact performance or a %gain in performance solely based on Hct%. To me there is no way you can do that and I agree with you. However, and please don't get offended, as this is a friendly argument I always have with cardiologists and also anesthesiologists because they look more at the big picture and hemodynamics than at the cellular level. There are many studies showing that a decrease in Hgb levels (from a physilogical individual homeostasis) and therefore Hct will result in impaired exercise performance due to a decreased O2 carrying capacity. Otherwise the term "anemia" or "pseudoanemia" would not exist. As a matter of fact, it is thought that Anemia is the no.1 disease in the world...However in the vast majority of cases is not disgnosed simply because to carry a regular life a person would not tell unless it is a severe anemia. I have seen people as you as well for sure with Hct's of 30% and barely feeling it for the day-day activities...or others with 25% and just feeling a bit tired...something that it is still amazing to me (used to work with athletes) and you may be right due to the increased cardiac output to make it up for the lower "viscosity". However this is not the case of athletes, that I can tell you for sure. If your Hct is 45% and you decrease it to 38% you bet you will be decreasing your performance and you will struggle more on the races. As I mentioned that is one of the many "features" of overtraining and I see that everyday. You can tray it yourself. Withdraw 2 bags of blood (roughly 1L). Filter the contents except the erythrocytes and reinfuse the plasma with the rest of elements in it back so that you will recover your plasma volume and electrolyte and other elements to achieve homeostasis. The only thing you would be missing would be the packed red blood cells. Then go on your bike and go racing or a high intensity training. Regardless of the efforts of your heart, arteries, arterioles and any other vessels as well as any hemodynamic mechanism ossible to "save your butt" you will hurt on the bike like yoiu never had before, that is for sure.
About Cardiac Output, yes there is a limit. THat is the endocardium. Your heart can try to increase it but there is an anatomical self-defense mechanism by the one your Cardiac Output cannot increase more and that is the endocardium. That is a typical question of residency/medical/physiology exams to "trick" you.

Anyways, I am tired of writing too much today...I think I may bee anemic.. ..Just kidding!.

Cheers.