Blood Ph.

[Skindiver]

A while back i posted an opinion on hyperventilation and Mr Fattah wrote a interesting reply where he said that a blackout can actually be brought forward due to blood chemistry changes because of hyperventilation.
This was the single most compelling argument for me to avoid hyperventilation in a measured no - variables constant dive. Prior to this my stance was.. ' if i know i can make 40m then why not hyperventilate and do it more comfortably'.

I have since then become increasingly interested in freediving physiology for safety and performance sake. So..

Who can explain blood Ph, Whats neutral and normal?
How does it curve during and after breathe - up, and after repeditive dives ?
What is the value at the end of a long apnea ?
Are there differences in the blood Ph profile in static and constant apnea ?
What Ph settings / curves are we striving for and how does that impact on our blood O2 and C02 saga ?

I hope to achieve by your responses more knowledge than i currently do which is that my pool must be 7.2.

Mr Fattah et al ... stage!.. Please.

Greg Lewis - Monto.

 

[Ben Gowland]

I have been thinking about this for a while.

The only serious physiological change associated with decreasing blood pH (that I am aware of) is the effect that it has on haemoglobin saturation curves. Acidic conditions decrease the oxygen affinity of Haemoglobin.

This means that you will not absorb as much oxygen from the air in your lungs - bad.

Conversely, in the brain, acidic blood will mean that haemoglobin offloads its oxygen faster than normal, which is good.

Note: None of this alters the total oxgen absorbing capacity of haemoglobin - this merely changes the point at which O2 is absorbed/offloaded.

So what does this mean for diving? Well, it suggests that if your nervous system is well adapted fr hypoxia, then it may be beneficial to hyperventilate before breatholding. However if your brain needs high 02 levels to stay concious, then it is best not to hyperventilate.

The balance point is the critical issue here - I don't know how much ppO2 or O2 mol the brain needs to stay concious.

So that probably doesn't help that much in the end does it?

Sorry,

Ben

 

[efattah]

Delicate Balance

There is definitely a balance needed here. Too much hyperventilation and you definitely black-out prematurely; too little breathing and you risk a CO2 blackout, and too much wasted energy from early contractions. What I have found is that you should ventilate just enough to keep the contractions 'stable and comfortable.' Too much hyperventilating has clear symptoms. You will feel great until right at the end of the ascent, when suddenly you'll get huge contractions and your arms/legs may start tingling, vision fading. Shortly after you'll blackout or samba. That is the characteristic of an overly aggressive breathe-up; feeling great until right at the end when it all falls apart. Instead, you should start to feel the need to breathe at about the half-way point, around when you turn at the bottom; the contractions should start small, and gradually increase, still staying somewhat comfortable. There should be no 'sudden panic' feeling at the end.


Eric Fattah
BC, Canada

 

[Skindiver]

This seems to work nicely then..

I take it then that after a breathe - up, with Co2 being blown off, ones blood Ph should become alkaline. Alkaline blood now supports haemoglobin binding with o2 most efficiently. So far so good.

During breath hold Co2 begins to build up, gradually turning the blood acidic which supports efficient O2 release especially to the brain, where and when we need it in the latter part of the dive.

Have i got this right ?

Does the switch from alkaline to acid, happen fast enough to be of literal positive effect, as above, during a single breath - hold ? Or does the blood Ph take hours or more to change ?

Thanks for the replies.

Greg lewis - Monto.

 

[efattah]

Quick Enough

The pH changes rapidly during a breath-hold. Although the blood always gets more acidic, the more you hyperventilated, the less acidic it will get, and the less O2 it will release. However, when breathing up, the hemoglobin saturation is already 98%+, so hyperventilating will cause only a negligible increase in hemoglobin oxygen binding. So, all the hyperventilating does is change the O2 unloading at the end of the apnea.


Eric Fattah
BC, Canada

 

[Skindiver]

Aha. Getting somewhere now.

Ok.
I have a firm grasp of whats happening in the blood now. If breathing patterns can influence the blood Ph presumably widely and quickly enough why would diets designed to influence Blood Ph be neccessary. ?

What is neutral blood Ph ( 7.2 ?)
Does the Ph shift across 'neutral' from alkaline to Acid (on the Ph scale) or is the shift ' relative. ' ie does it start deeply alkaline and and finish less alkaline but still in the alkaline part of the scale ?

Thanks Mr Fattah.

Greg Lewis - Monto.

 

[efattah]

More answers

After hyperventilating your blood will definitely be very alkaline (? 8.0), and after a long apnea you will be very acidic (6.9-7 ?) I don't know the exact numbers.

Diets or electrolyte drinks which modify your blood pH cause a slightly different effect than just breathing or not breathing. This effect is much more complicated, and I'm not sure I'm qualified to try to explain it.

It has to do with your total blood store of bicarbonate. A person with lots of bicarbonate in their blood will experience a slower change towards acidic blood, due to the elevated quantity of buffer. So even if he starts at the same pH, because he has more buffer molecules, it takes him longer to reach the same level of acidity. Apnea practice gradually increases your bicarbonate, but after about 48 hours with no apnea your kidneys re-absorb most of the excess bicarbonate. Drinking bicarbonate or citrate drinks also increases your bicarbonate level. Immediately after a big static set your bicarbonate level will be way up, hence you can hold your breath for longer.

However, there are non-bicarbonate buffers such as phosphate, sulfate and hemoglobin, and seals have very elevated levels of non-bicarbonate buffers. Also, the total volume of blood plasma (i.e. hydration) affects the amount of CO2 that can dissolve directly into your blood, creating a larger CO2 store, which also acts like a buffer. CO2 is very soluble in water (plasma) but O2 is not, thus a hyperhydrated diver has a much elevated CO2 store, but he cannot store extra oxygen.


Eric Fattah
BC, Canada

 

[Ben Gowland]

Spot on Eric,

Just to add on to the earlier part about oxygen dissassociation at the end of a breath hold - the blood pH at the end of a breathold still affects how much O2 you absorb - at that time. Remember that your lungs are always offloading some oxygen right until the very end of a breathold. This means that the pH of blood coming through the lungs at that time will pick up less O2 if the blood is acidic, then that blood goes back to the heart, then up to the brain.

Having alkaline blood at the start of a breathold is bad because it means that the blood will offload less O2 in the brain at the start of the breathold. So the key is to stabilise the blood pH as near to neutral as possible for the duration of breathold.

The bottom lines here are - Total O2 storage capacity (slightly trainable through apnea), blood buffering capacity (partly training, partly diet) and nervous system resistance to hypoxia (presumably training? - I don't know if this has been investigated in humans).

Ben

 

[Skindiver]

Bombing my new found theories..

Thanks to Mr Fattah and Mr Gowland for your valuable responses.

Ben your last post materialises into a visualisation of two bubble streaks just below the surface coming straight for my new battleship. Im steering hard to starboard but...

Surely having alkaline blood at the start of a breath hold means that the transition to acid will take longer. As per your first post alkaline blood loads O2 Better. The longer you stay alkaline the better / more / longer you can load O2 from the lungs ?

Surely one doesnt need a high O2 unload in the brain in the early stages of Breath - hold. As reserves start running low and you start finding you brain needs more air, the blood has become more and more acid releasing O2 Better. I like this theory.

Im not talking about heavy alkaline blood as after hyperventilation. Rather a text book breathe - up.

C'mon. Abort those torps... Unless of course you are maintaining that neutral Ph does the best average of both jobs... and you have a plan to maintain neutral Ph by means other than not breathing - up and somehow avoiding inevitable Co2 Build up.?

 

[Ben Gowland]

Re: Bombing my new found theories..

Originally posted by Skindiver
[Surely having alkaline blood at the start of a breath hold means that the transition to acid will take longer. As per your first post alkaline blood loads O2 Better. The longer you stay alkaline the better / more / longer you can load O2 from the lungs ?

Yes. Absolutely.

Surely one doesnt need a high O2 unload in the brain in the early stages of Breath - hold.

It shouldn't be a problem unless the blood gets REALLY alkaline.

As reserves start running low and you start finding you brain needs more air

It shouldn't if you remain calm.

, the blood has become more and more acid releasing O2 Better. I like this theory.

Yes - but remember that only 5-10 seconds earlier - that blood (which is now in the brain) was in the lungs - and since it was acidic - it couldn't pick up the 02 very well. That is the point here.

Unless of course you are maintaining that neutral Ph does the best average of both jobs... and you have a plan to maintain neutral Ph by means other than not breathing - up and somehow avoiding inevitable Co2 Build up

That's the idea - hence the importance of buffering capacity - as Eric pointed out.

QUOTE]

The other thing that I wanted to bring up is that we are only discussing the importance of blood pH to 02 dissociation here. Alkali or acid blood may well have negative effects that we are not aware of i.e. increased metanbolic rate etc.

 

[efattah]

Right

Acidic blood has many advantages; decreased heart rate & metabolic rate, increased sympathetic nervous activity, splenic contraction, blood shift etc...

Eric Fattah
BC, Canada

 

[Ben Gowland]

Yes Eric, but I have always had a problem with all that sort of research - which is not strictly 'controlled', and you can never tell if the effects that you speak of are due to low O2, High CO2, or even just reactions to immersion, ambient pressure etc.

I have read loads (perhaps not as much as you, mind) of papers over the years on apneic research and am always depressed to see how badly controlled so many of these experiments are. Which is really a shame for people like you and me because it means that we can't be sure if we can make sensible decisions based on the results.

However, if you do know of well-controlled experiments into this area then please get in contact, as I would love to see some quality research on these subjects.

Ben

 

[efattah]

Not so difficult

Measuring the effect of acidic blood is easy to control. The subject simply inhales 20% O2, 74% N2 and 6% CO2. At that point he can continue breathing the mixture, or he can hold his breath, and in each case they measure his metabolic rate etc...


Eric Fattah
BC, Canada

 

[Ben Gowland]

But theat means that you are not controlling for apnea - which is the problem that I have with this kind of research, when you are trying to make inferences for apneic activities.

Ben

 

[Ben Gowland]

Sorry - that wasn't specific enough - I mean that breathing different mixtures beforehand and then holding breath is unrealistic. The real need is for invasive research to measure in situ responses in the core and extremities whilst breatholding

a) with prior hypocapnia
b) normally
and
c) with prior hypocapnia

And such research would answer our questions nicely. Unlikely to happen though eh? Who's going to fund that sort of stuff?

Ben

 

[Ben Gowland]

my apologies again!

c) with prior hypercapnia