Hypercapnia or Hipoxia?

[wet]

Yes, the do mention CO2 in that part. Their claim PAO2 chemorecptors are playing more important role than pH and PACO2 chemoreceptors (as I already wrote) rather surpirsed me. That should be very easily verifiable, so I wonder that they would claim something like that if it was not true. On the other hand, I know very well, that hypercapnia alone (with no hypoxia associated to it) leads to bradycardia too, so I have rather serious doubts about their claim.

EDIT:

There is nothing wrong with the data, and nothing wrong with the experiments. The purpose of the experiments was not showing the influence of CO2, but the influence of facial thermo sensors and apnea. In this document they simply did not go into the depths to analyze hypoxia and hypercapnia in apnea separately, which itself would not be too bad. The only surprising is the menitoned claim about the PAO2 receptors, but since I do not now what led the to the conclusion, I cannot comment.

I've no criticism of the data or experiments per se. Respiration, whether pneic or apneic, is consumption (O2) and production (CO2) with many variables. I was surprised to see that the production side of respiration was so relatively insignificant in the written paper. They include many references to other things, virtually nothing about CO2.

DDeden

 

[trux]

They include many references to other things, virtually nothing about CO2.

Yes, I agree that it is strange, but if they claim that the diving reflex is controlled especially by PAO2 receptors, then their ignoring of the topic is comprehensible. I suspect though they are not right, but I would not expect they are wrong in such a fundamental and easily verifiable fact.

 

[naiad]

What do you think would be the result of these: Dry

With no warm-up, no breathe-up, no exercize prior,
laying on side or flat on soft bed or rug

1) passive exhale, body still, HR at 5th contraction:___,
continue 2 more contractions, stop. rest 5 minutes

2) passive exhale, body still until 1st contraction, then dogpaddle
moving limbs "swim" hard, HR at 5th contraction:___,
continue 2 more contractions, stop. rest 5 minutes

3) passive exhale, body still until 1st contraction, then
undulate spine (loach style) in synchrony with each contraction,
(limbs not independently paddling), HR at 5th contraction:___,
continue 2 more contractions, stop. rest 5 minutes

[If you want to try this, safety first:crutch ; and note any preferred changes]

My guess is that 3) would have the lowest HR, although 5 contractions might be too early to tell, maybe the HR at 10th one would give a clearer answer?

DDeden

I gave them a try, these are the results:

1) HR = 83
2) HR = 92
3) HR = 89

If I take a deep breath and hold it, my HR drops immediately to about 62, and then slowly increases. This does not happen with passive exhale or forced exhale. With all of them, it increases in the 'struggle phase'.

Lucia

 

[wet]

I gave them a try, these are the results:

1) HR = 83
2) HR = 92
3) HR = 89

If I take a deep breath and hold it, my HR drops immediately to about 62, and then slowly increases. This does not happen with passive exhale or forced exhale. With all of them, it increases in the 'struggle phase'.

Lucia

Thanks for sharing your results. (My slow response was due to thinking about it)
Makes sense that the least energetic static has the lowest heart rate.

You mention that HR drops a lot during a "forced inhale", but not a forced exhale.

I wonder if the hypothermic effect of diving in cold water would cause the HR in a forced exhale dive to drop down to the same level as in a forced inhale warm-dry static. The cold reaction on the face augments the divers response (MDR), doesn't it seem likely that that would trigger the slowed HR to about the same extent that the forced inhale would do?

I'm thinking about how we react automatically to a very cold blast of winter air onto the face, the first response is to shut the mouth and hold the breath (sometimes with a gasp like a forced inhale). This sudden cold can also sometimes induce a laryngospasm, I believe, but never a black-out or samba or contractions or squeeze AFAIK.

So the breath hold follows the cold (whether due to submersion in cold water or a blast of cold air), and then reduced HR conserves oxygen and the MDR engages.

These don't trigger shivering AFAIK. Shivering seems whole-body related, not just face-activated or breath activated, not sure though. Makes sense that shivering is an aerobic terrestrial or surface-related reaction, but I'm curious which skin thermosensitive receptors/nerves trigger shivering. That it also occurs while doing an apneic wet static in cool water means that muscular activity shuts it off, since shivering doesn't occur during active movement AFAIK.

DDeden

 

[naiad]

Thanks for sharing your results.

No problem.

These don't trigger shivering AFAIK. Shivering seems whole-body related, not just face-activated or breath activated, not sure though. Makes sense that shivering is an aerobic terrestrial or surface-related reaction, but I'm curious which skin thermosensitive receptors/nerves trigger shivering. That it also occurs while doing an apneic wet static in cool water means that muscular activity shuts it off, since shivering doesn't occur during active movement AFAIK.

If I do a wet static in cool water, I stop shivering for the first 1:30-2 minutes, but then the shivering starts again. This suggests that there is a reflex to stop shivering during apnea.

For me, shivering is an immediate reaction to being cold, and not to a drop in core temperature. If I get into a cold pool, I start shivering almost immediately.

 

[wet]

No problem.

If I do a wet static in cool water, I stop shivering for the first 1:30-2 minutes, but then the shivering starts again. This suggests that there is a reflex to stop shivering during apnea.

For me, shivering is an immediate reaction to being cold, and not to a drop in core temperature. If I get into a cold pool, I start shivering almost immediately.

When entering the cool pool, do you typically climb in and wade a bit, or, do you first dive in (submersed apnea) and do a little apneic dynamic swimming right off, to warm up, and then begin a static?
DDeden

 

[naiad]

I climb in and wade around a bit. If I am wearing my opencell suit I can stay for a while and do a few statics before the shivering starts, but if I am wearing a swimsuit the shivering starts as soon as I get in the pool. That is one of the reasons why I don't go swimming much.

 

[wet]

No problem.

If I do a wet static in cool water, I stop shivering for the first 1:30-2 minutes, but then the shivering starts again. This suggests that there is a reflex to stop shivering during apnea.

For me, shivering is an immediate reaction to being cold, and not to a drop in core temperature. If I get into a cold pool, I start shivering almost immediately.

When doing dry statics, you usually are in a warm environment, right? Have you ever done them in a cold environment? I'm guessing that a dry static in teeth-chattering weather would result in the same apnea effect: no-shivering, then shivering. OTOH, if you did a dry dynamic (apnea jogging in place?), no shivering would result even in cold, since the muscles are already engaged in producing heat.

AFAIK, Shivering is only triggered by cold when (non-resp.) muscles are inactive ie. static.

I noticed that when I skied cross-country (flat-land skiing) in extremely cold weather, with terrible wind chilling gusts of -40C, as long as I was whole-body active, I stayed warm even when not wearing very warm clothes (but always a wind-breaker and warm hat). However, as soon as I stopped to rest or cook a meal, I'd nearly freeze to death within a few minutes it took to start a campfire, and shivering became a life-saver.

At those times, inhaling cold air often caused me to hypoventilate and try to hold my breath, otherwise my inside throat and lung area would feel quite painful from the cold. As long as I was actively using my limbs, I could get by with a thin wind jacket over a few sweaters and snow pants and baclava hat, but a face scarf was essential to prevent loss of internal heat via respirational convection.

I usually skied on the frozen surface of the Mississippi River wetlands, occasionally the ice would have thin spots, where the water currents were fastest, I steered clear of those, since my free-diving instincts were no-where to be found! I'm still amazed at the beavers which lived in submersed dens in that cold water, they're a lot tougher than I was, that's for sure. I guess it helps to have a fur coat that holds air pockets in and cold water out.

Anyway, just some thoughts.

DDeden

 

[naiad]

When doing dry statics, you usually are in a warm environment, right? Have you ever done them in a cold environment? I'm guessing that a dry static in teeth-chattering weather would result in the same apnea effect: no-shivering, then shivering. OTOH, if you did a dry dynamic (apnea jogging in place?), no shivering would result even in cold, since the muscles are already engaged in producing heat.

I usually do dry statics in a warm environment. If I do them in a cold environment, I haven't noticed any actual shivering during apnea, but my times are much worse than normal.

I find it amazing how animals are so well adapted to the cold. Makes me wonder what is the matter with humans - we are supposed to be insulated with fat, but many less well adapted animals tolerate the cold much better. When I worked at the zoo, I was surprised how many animals would voluntarily stay outdoors in cold weather. It was very cold at one point, -7c, and small monkeys with hardly any body fat and not very dense fur seemed to be happy outdoors. Wild starlings were having a bath wherever there was a hole in the ice.

 

[Waterysmile]

I noticed that when I skied cross-country (flat-land skiing) in extremely cold weather, with terrible wind chilling gusts of -40C, as long as I was whole-body active, I stayed warm even when not wearing very warm clothes (but always a wind-breaker and warm hat). However, as soon as I stopped to rest or cook a meal, I'd nearly freeze to death within a few minutes it took to start a campfire, and shivering became a life-saver.

DDeden

This has been my experience too. When engaged in activity I produce plenty of heat that keeps me warm - one cold snowy day (probably just above 0 Celsius I went for a walk in shorts, t-shirt, boots and gloves and that was enough.

 

[naiad]

Same with me. When I have done outdoor jobs in cold weather, it's the hard work that keeps me alive.

 

[wet]

I usually do dry statics in a warm environment. If I do them in a cold environment, I haven't noticed any actual shivering during apnea, but my times are much worse than normal.

I find it amazing how animals are so well adapted to the cold. Makes me wonder what is the matter with humans - we are supposed to be insulated with fat, but many less well adapted animals tolerate the cold much better. When I worked at the zoo, I was surprised how many animals would voluntarily stay outdoors in cold weather. It was very cold at one point, -7c, and small monkeys with hardly any body fat and not very dense fur seemed to be happy outdoors. Wild starlings were having a bath wherever there was a hole in the ice.

Well our thin fat layer is pretty good (it does protect the body core), but a very limited part of the system. If there is no wind, most furred/feathered animals (even equatorial animals) do well as long as their food is abundant, (snow monkeys in Japan) because of their fast metabolism, which produces heat (that is usually dumped by activity, panting, breathing, maybe sweating). OTOH, Hibernators do the opposite, they slow down metabolism to reduce food requirements during the winter. The heat conserving thermal rete mirabile (not the gas rete mirable) counter current heat exchange in birds feet, whale's tongues, human legs means less food is required to warm the body core and extremities.

Counterintuitively, in very cold weather, if you feel cold (outer), then you are warm (body core), but if you don't feel cold (outer) then you may be hypothermically cold (inside) and in danger. Again, it's complex.
DDeden

 

[wet]

This has been my experience too. When engaged in activity I produce plenty of heat that keeps me warm - one cold snowy day (probably just above 0 Celsius I went for a walk in shorts, t-shirt, boots and gloves and that was enough.

Yeah, while skiing flat land, if the wind was minimal I rarely needed extra clothes. I liked keeping a pace just about walking (which because of the equipment was actually a bit harder), warm but just below sweating. Sweat was bad, to be avoided, as even a mild breeze can quickly chill wet clothes when at rest stops, although in dry winter sunny conditions it dries ok.

DDeden

 

[wet]

Hypoxia in the blind mole rat: oxygen conservation masters
They can live in tunnels with only 3% oxygen and high in CO2.
I'd guess being blind is beneficial there, much less O2 cost.
[Dolphins, especially river dolphins lost much of their visual capacities
(colorblind, smaller eyes) and replaced with improved sonar.]

ScienceDaily: Blind Mole Rats Shed Light On Diseases Caused By Lack Of Oxygen

DDeden

 

[wet]

Hypoxia & cell energy (from PHYSORG.COM)

Researchers at Johns Hopkins have discovered how cells fine-tune their oxygen use to make do with whatever amount is available at the moment.
Too little oxygen threatens life by compromising mitochondria that power it, so when oxygen is scarce, cells appear to adjust by replacing one protein with an energy-efficient substitute that "is specialized to keep the motor running smoothly even as it begins to run out of gas," says Gregg Semenza, M.D., Ph.D., a professor of pediatrics and director of the vascular biology program in the Institute for Cell Engineering at Hopkins. "This is one way that cells maintain energy production under less than ideal conditions." A report on the work is in the April 6 issue of Cell.

"Cells require a constant supply of oxygen," Semenza says, "so it's vital for them to quickly react to slight changes in oxygen levels." The protein-swap is how they do it.

In the mitochondria, the tiny powerhouses found in every cell, energy is produced by passing electrons through a series of relay stations called cytochromes until they eventually join with oxygen to form water. [Please see my question at bottom DD] This final step is directed by the protein cytochrome coxidase, or COX for short. If electrons react with oxygen before reaching COX, they generate "free radicals" that can damage or destroy cells. The mitochondria are designed to produce energy without excess free radical production at normal oxygen levels.

Semenza's team noticed that one particular component of the COX protein complex, COX4, comes in two different forms, COX4-1 and COX4-2. Under normal oxygen conditions, the cells' mitochondria contain mostly COX4-1. The researchers suspected that COX 4-2 might be the active protein under stressful, low-oxygen conditions, which the researchers refer to as hypoxia.

To test the idea, the team compared the growth of human cells in normal oxygen conditions (what's generally present in normal room air) compared to cells grown in hypoxia. In low oxygen, liver, uterus, lung and colon cells all made COX4-2. The researchers then exposed mice to hypoxia for a few weeks and found that they too showed increased levels of COX4-2.

In 1992, Semenza's team had discovered a protein which they called HIF-1 (for hypoxia-inducible factor 1) that cells make in response to hypoxia. HIF-1 turns on genes that help cells survive when oxygen is low, such as during a heart attack or stroke. The researchers set out to figure out if the sensor protein HIF-1 triggers the COX-swapping.

By examining the gene control regions of COX4, they found that the HIF-1 sensor switched on COX4-2 activity when oxygen is low. And they learned that because COX4-1 already is in the mitochondria, the swap for COX4-2 occurs when the sensor turns on yet another gene that produces an enzyme to specifically chew up COX4-1. Engineering human cells to lack this enzyme and subjecting them to low oxygen, the scientists found the cells unable to rid themselves of COX4-1.

"It's remarkable that the one-celled yeast also swap COX subunits in response to hypoxia, but because they lack HIF-1, they accomplish the swap in a completely different way," says Semenza. "This suggests that adapting mitochondria to changes in oxygen levels may be a major challenge for most organisms on Earth."

Source: Johns Hopkins Medical Institutions

Question: I think they are referring to metabolic water production here: "passing electrons through a series of relay stations called cytochromes until they eventually join with oxygen to form water". But water is Oxygen plus Hydrogen (protons). Oxygen plus electrons = ?? Chemist help!

DDeden

 

[naiad]

Interesting - maybe this is part of the mechanism of 'O2 tolerance'.

 

[trux]

Question: I think they are referring to metabolic water production here: "passing electrons through a series of relay stations called cytochromes until they eventually join with oxygen to form water". But water is Oxygen plus Hydrogen (protons). Oxygen plus electrons = ?? Chemist help!

Hydrogen is a single proton-electron pair (unless we speak about the less stable isotopes like Deuterium [proton + electron + neutron] or Tritium [proton + electron + 2 neutrons]). When the atom contains unequal number of positively and negatively charged particles (protons vs. electrons), we call them ions (electrically charged). So a single proton would be an H+ ion. It means if the described process needs extra electrons for generating a molecule of water, then there already must be the H+ ions (protons) + oxygen somehow present.

 

[wet]

OK, I checked wikipedia, found some info I'll add later. I was mainly trying to see if there was a link to neuro- cyto-hemo- myo-globins, especially neuroglobin which connects to protection against strokes. Darn complexity again!

Also I was thinking of ancient humans on seashores, did they have to live next to freshwater rivers or not? I've read that although humans can't drink seawater, brackish water is much more tolerable, and since we produce metabolic water from food digestion (as above) and also that we sweat out salt and also our mucus is salty (that can be sneezed or blown out), the excess salts can at least be managed to a certain degree. IOW we can't drink only plain saltwater, but by combining these methods, plus drinking coconut water and rainwater when available, it seems more sustainable on seashores far from rivers where our ancestors would have had to deal with the large land predators (tigers, lions) that waited to ambush prey at freshwater rivers.

DDeden

 

[ukfinswimmer]

The best literature to read is Peter Lindholm's PhD thesis (Uni of Stockholm, 2002). Full citation:

Lindholm, P. (2002). Severe hypoxemia during apnea in humans: influence of cardiovascular responses. PhD Thesis. Karolinska Institutet; Stockholm, Sweden.

Best wishes.

Alaric.

 

[trux]

Alaric, Peter Lindholm's thesis was already referred to at the begining of this thread in the post #32, and the post also includes a link to the document (what is always helpful when posting references to a forum). However, although I read the thesis, I see nowhere in it any discussion of neuro- cyto-hemo- myo-globins that David asks above. It only briefly mentions hemoglobin, but without any deeper information (and indeed, it is not the purpose of the document)