Static Apnea and blood pressure

Yes, that's a very valid question, and I wondered about it many times too. I suspect that the risk of a cerebral stroke, or cardiac incidents may be quite increased, but strangely I never saw any studies addressing it directly, although I have around 700 documents on freediving physiology in the Freediving Media Base. Well, it is possible it was studied and the information is there (or somewhere else on the web), but I cannot help directly. Perhaps one of the resident docs (for example Dr. Pernett or Dr. Fitz-Clarke) could peek in and tell us more, but they are not coming daily, so am not sure if they see this thread.

I also did not hear about any cardiac or cerebral incidents, apart from the accident of Benjamin Franz, which might have been a stroke induced by high blood pressure, although I think the diagnosis was that it was DCS related (I am not quite sure about it though).

well since you mentioned gills...

Breathing in the bitter cold: lungless frogs and a fish without erythrocytes Evolving Ideas

coldwater salamander lacks lungs, borneo frog breathes mostly through its skin, and the antarctic icefish has no myoglobin or red blood cells or hemoglobin in the blood.

These differ from marine mammals that have lots of myoglobin, hemoglobin, neuroglobin and cytoglobin for oxygen stores, as do humans but at much less amounts.

Well, first of all for those who don't know: 120/ 80 (Ideal blood pressure)
The 120 is when your heart is contracted and when your blood vessel are full of blood
The 100 is when your heart is relax and your heart is full of blood ready to pump it throught your body.

You always have the same amount of blood in your system, so what that leaves is the space withing the blood vessel them selve, hence why some one with high cholesterol has a higher pressure: same amount of blood and less space. Or on an other way, your scared of needles and you start to panic, your sympathic system kicks in and adrealine and all that other good stuff starts pumping, your blood vessel will dilate, you BP will drop drasticly and then you pass out (real fun, had that append to me a few times and can feel the blood droping to my feetrofl)

Ok, this goes pass my knowledge, so don't take me to word on this: The high BP is probably due to one of the many reflex associated with apnea. A constriction of the blood vessel in an effort to save oxygen. What coes, I have no idea. Is it dangerous, I'd be more worried if it was a constant 140/100+ all the time. I would see it more like an/areobic excersice, were you bring it to a work out level, and then bring it back down. If you heart is constanly at 100+ bpm, your asking for trouble. But bring it to 140/160 for a work out, and then come back down to a 60-80 is very healthy for you. I could definatly see it working the same For BP....But again don't Take my word for it....I'm just a lowly medical technician in the Canadian forces :blackeye

You have discovered a basic component of the diving reflex. BP rises during apnea. Here is a simple way to understand. BP = HR x SV x R where HR is heart rate (beats per minute), SV is stroke volume (volume pumped by the heart with each beat), and R is the resistance of the peripheral vasculature. Notice that BP changes according to how each of these three variables change. The body uses its baroreflex to control each variable to maintain BP within an acceptable range. This is done through baroreceptors in the aortic arch and right ventricle that monitor blood pressure and send signals to the brainstem which then sends output to the heart and peripheral arterioles to simultaneously adjust HR, SV, and R.

Let’s say your initial BP is 110/80. Disregarding pulsation and accounting for the shape of your pulse wave, this means your mean or average arterial pressure is about 90 mmHg. Your initial HR is 80 and SV is say 70 ml per beat. This means your baseline initial vascular resistance R is 0.016 units.

Now you do a static apnea. Initial positive chest pressure at TLC and small blood shift from immersion cause a small increase in BP followed by a small decrease during the Valsalva which lowers HR a bit. Then you put your face in cold water and HR goes a way down (bradycardia) from receptors in the face sending impulses via the trigeminal nerve which synapse on the reflex arcs in the brainstem. Selective vasoconstriction in the muscles happens to conserve oxygen during apnea, causing R to go up. Meanwhile various chemoreceptors sense oxygen and carbon dioxide levels and modify reflexes further. The net effect on BP depends on HR x SV x R. The fact that BP rises during apnea suggests that there is a dominant rise in R over a few minutes.

The same thing happens during a dive, but it is more complicated. There is very little data from BP during actual dives. HR drops as usual, but the 1997 chamber study on Enzo Maiorca and his daughters in Buffalo found a very intense vasoconstriction causing a huge rise in BP as high as 280/200! Why so high? I don’t know. Go figure. Stroke volume can drop to offset this a bit, but the left ventricle must be under a tremendous wall stress during contraction to generate such high pressures. This is the only invasive data I recall at the moment from an underwater study. Bedini’s group in Pisa have measured SV underwater using echocardiography. They found a small drop in SV.

In my opinion, what makes this really interesting is why the body chooses to raise BP so high. Does this always happen? Is this really necessary? Perhaps not. Why not just compensate by lowering SV and contractility further to keep BP constant. I don’t know the answer. Maybe it has something to do with cerebral autoregulation needed to maintain some mysterious variable in the brainstem related to gas levels. The brain is the master commander and it might like to selfishly satisfy its own needs first and treat the heart like a slave. Is the wisdom of the body really optimized here? Who knows.

There you go. An amazing system to regulate BP. Lots of complex feedback loops based on sensing of many variables, and lots of unanswered questions. If you want to do an interesting study, find a way to measure BP underwater safely during actual dives, along with HR, and send me your results.

Dr. Fitz-Clarke,

Thank you very much for commenting. Yes, the mechanism is rather clear, known, and well documented, but thank you for the great details anyway! However, the mechanisms or the reasons for the high BP are not really in the focus of the original question. The real question is whether such extreme pressures cannot harm freediver's health - cannot it lead to heart defects or malfunctions, or more importantly to a rupture of cerebral arteries or hemorrhage? Certainly not at a healthy individual, otherwise we would have couple of brain strokes at each competition, but are there any studies or statistics about relation between the high BP due to DR and cerebral or cardiac incidents? Well, I saw on the web that there is indeed a lot of relations between strokes and sleeping apnea, but there are likely more factors involved.

Recently, there where some articles published that adresses this effect. Respectively by Kjeld et al. and Heusser et al.

The rise in bloodpressure seems to have the goal to maintain a sufficient oxygen supply to the brain. The dive reflex seems to play only a marginal role. Kjeld found out that most of the arterial vasodilatation is caused by hypercapnia. Heusser found out that with an increase in oxygen desaturation, the sympatic system increased the bloodpressure.

More research is needed. But my hypothesis is that if the divereflex fails, hypertension kicks in to try to help the diver survive the dive. This is done at any expense... A stroke is a "minor" problem, compared with drowning.

It's true that stroke's don't happen at competitions, but this might be different if we let 60-year olds try maximal statics while they are on anticoagulants (asperine etc.).

I currently don't think that the increase in blood pressure is a good thing, and it is something on my to-do-list to find out.

It might however be intresting to see how the divereflex affects the bloodpressure in diving mammals, and if there is any relationschip between hypertension and death within these species.

Rik said:

The rise in bloodpressure seems to have the goal to maintain a sufficient oxygen supply to the brain. The dive reflex seems to play only a marginal role. Kjeld found out that most of the arterial vasodilatation is caused by hypercapnia. Heusser found out that with an increase in oxygen desaturation, the sympatic system increased the bloodpressure.

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Yes, also this is well known, well documented, and nothing really new. However, as already written, nobody questions the reasons of the high BP, or its positive effects. What was questioned it is the level of risk, or any studies about it.

trux said:

Yes, also this is well known, well documented, and nothing really new. However, as already written, nobody questions the reasons of the high BP, or its positive effects. What was questioned it is the level of risk, or any studies about it.

Click to expand...

Well, there are no long-therm studies concerning freedivers and organ damage due hypertension.

There are however studies and reports concerning patients with hypertensive crises. The majority of the article discusses organ damage due hypertension in general. Some suggest that multiple episodes of hypertension could cause Alzheimer.

However, it is difficult to evaluate if these articles are relevant for freediving. Most reported cases on hypertensive crises adresses patiënts who already have any form of diseases that affect the outcome after an hypertensive crisis.

A relative easy way to screen for organ damage due hypertension, would be to evaluate if maximal performances would have effect at the retina of the diver. After a performance, a trained physican could evaluate if there is any hypertensive retinopathy like cotton wool spots or other exudates. This could give some insight if the hypertension in freediving would lead to organ damage.

Well, the association with Alzheimer could explain the behaviour of some of my colleagues in the club

On more serious note, your comments sound quite interesting, and I hope some of the physiologists specialized in freediving will look at it closer. Or perhaps they did already?

I am not quite sure about the training effect. If you look up terms like sleeping apnea together with blood pressure and strokes on the web, you get quite a lot of hits. And since sleeping apnea is not really being promoted as a good training for improving your health, but rather a quite dangerous disorder, I am afraid it may be rather disputable whether the high BP in sportive apnea can be really considered harmless.

Do these blood pressure spikes only occur on advanced freedivers or this is even a problem for beginners? I already have a slightly above normal blood pressure for my age (25yrs bp ~130/80) and I'm already living very healthy, so there's no risk factors I could additionally eliminate. So if sleeping apnea is very likely to cause hypertension, should I also stay away from freediving? I get quite a red and warm head, when training statics and often start to sweat. :hungover

Off topic, but interesting article, regarding genes, hemoglobin and skin color:

Fugates of Kentucky: Skin Bluer than Lake Louise - Yahoo! News

I once wondered re. AAT if more aquatic dive-foraging/shore-living human ancestors might have had a mottled blue-grey tint (camouflage, UV protectant).

Skin color is controlled by 7 different genes interacting, not just one. Humans have 2 skin pigments, Pheaomelanin is reddish, eumelanin is black, people tend to have some of each, depending on ancestral distance from equator. Presence of blood in capillaries blends with the skin tone to give the overall color.

The genetic trait in the article might provide some unique advantages in some ways (anti-malaria?), not sure about possible relationship to sleep apnea or blood pressure or freediving.

That some hemoglobin (carries oxygen to tissues via blood vessels) exists as methemoglobin (which can't carry oxygen) isn't necessarily a bad thing for breathold diving, perhaps myoglobin abundance increases as a result? Perhaps the affected Fugates had higher than normal myoglobin levels?

Is anyone here taking blood pressure reducing medicine and still freediving? I'm afraid that I might have to take it soon. Since my BP often is above 140/90 :ycard
Is it possible at all to continue freediving then?

Hi sai,
Since i expirience the same problem with BP i wonder when do you measure the BP, morning evening? after static? or after diving?
My BP in the morning is 120/80 but during the day it goes up a bit and after deep diving it takes some time to go back to normal-i need to make more checks to be sure with the numbers.
You can try to lower your BP with natural herbs like olive leafs infusion and other staff-read about it.
Alon.

Blood pressure can be raised by various causes, both benign as malign, and it varies during the day and the measurement is also dependent of the posture and method of measuring.

In doubt... ask your general physican to evaluate your blood pressure.

I measure my BP with a few minutes rest before. But I'm somehow already tensing up even by the thought of measuring BP now. Can't really imagine taking pills for the rest of my life since I'm only 25, average weight, no smoking anymore and 5-6 times sport per week.
Seems to be a genetic thing for me.

Measuring your blood pressure while being anxious about your blood pressure might be not good for your blood pressure.

Frankly, I wouldn't be too worried about a high blood pressure alone barring you from breath-hold diving. I have an similar blood pressure, and I am still diving.

There does exist medication that you can use while freediving, if you would need it in the future.

Do you have any other ideas why you would get a an high blood pressure? If stress is an factor, I would recommend to try to deal with that. There are also other lifestyle options that could lower your blood pressure, but that is something for your general physician to discuss with you.