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Old 20th November 2008, 18:28   #1 (permalink)
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Hypercapnia and High Blood Pressure

I have just been listening to Alex Deas interview about his rebreather Alex Deas Interview, OR Apocalypse mCCR, eurotek '08 on Vimeo during this he states (about 15mins in to his talk) about carbon dioxide retention leading to significantly raised blood pressure.

My understanding is that carbon dioxide retention (ie hypercapnia) causes a respiratory acidosis. As breathing is mainly controlled via the brain stem in the respiratory centre where the drive to breathe is principally led by levels of carbon dioxide acting on chemoreceptors (secondary systems are hydrogen ions and oxygen). Hypercapnia thus leads to acute shortness of breath, headache and confusion. At a chronic level it can also act to increase the risk of oxygen toxicity and nitrogen narcosis.

However, I know nothing of how it can raise blood pressure. Particularly in such a short time of during a dive. Is Mr Deas confusing himself with pulmonary hypertension - this can happen in people with such as Chronic Obstructive Airways Disease (COAD). However, I am not aware that this relates directly to Blood Pressure.

Anyone able to shed some light?
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Old 21st November 2008, 02:27   #2 (permalink)
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Re: Hypercapnia and High Blood Pressure

Quote: (Originally Posted by craige) View Original Post
I have just been listening to Alex Deas interview about his rebreather Alex Deas Interview, OR Apocalypse mCCR, eurotek '08 on Vimeo during this he states (about 15mins in to his talk) about carbon dioxide retention leading to significantly raised blood pressure.

My understanding is that carbon dioxide retention (ie hypercapnia) causes a respiratory acidosis. As breathing is mainly controlled via the brain stem in the respiratory centre where the drive to breathe is principally led by levels of carbon dioxide acting on chemoreceptors (secondary systems are hydrogen ions and oxygen). Hypercapnia thus leads to acute shortness of breath, headache and confusion. At a chronic level it can also act to increase the risk of oxygen toxicity and nitrogen narcosis.

However, I know nothing of how it can raise blood pressure. Particularly in such a short time of during a dive. Is Mr Deas confusing himself with pulmonary hypertension - this can happen in people with such as Chronic Obstructive Airways Disease (COAD). However, I am not aware that this relates directly to Blood Pressure.

Anyone able to shed some light?
Good question. I wish I knew the answer but I will be watching this thread.
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Old 21st November 2008, 19:56   #3 (permalink)
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Re: Hypercapnia and High Blood Pressure

Why does it matter? Lots of things (exercise for example) dramatically increase blood pressure but so what?
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Old 22nd November 2008, 22:55   #4 (permalink)
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Re: Hypercapnia and High Blood Pressure

Hi,

I googled a bit. I found an article on
with title High output heart failure.
It says in its abstract: The symptoms and signs of heart failure can occur in the setting of an increased cardiac output and has been termed 'high output heart failure'. An elevated cardiac output with clinical heart failure is associated with several diseases including chronic anaemia, systemic arterio-venous fistulae, sepsis, hypercapnia and hyperthyroidism. The underlying primary physiological problem is of reduced systemic vascular resistance either due to arterio-venous shunting or peripheral vasodilatation. Both scenarios can lead to a fall in systemic arterial blood pressure and neurohormonal activation leading to overt clinical heart failure.

So it seems to be saying the BP falls rather than rises (because of vasodilation) but, what the heck, it kills you anyway. In a diving scenario I guess "high output heart failure" might well end up simply being labelled "heart attack"...... and we do get a lot of those.

Extract from hypercapnia: Definition from Answers.com :

Hypercapnia


Symptoms

Symptoms of early hypercapnia, where arterial carbon dioxide pressure, PaCO2, is elevated but not extremely so, include flushed skin, full Rebreather World - Rebreathers for Scuba Diving - the next step, extrasystoles, muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure. In severe hypercapnia (generally PaCO2 greater than 10 kPa or 75 mmHg), symptomatology progresses to disorientation,


No mention of the reason why though.










Googling elsewhere I found someone (Therapeutic Hypercapnic Acidosis: Pushing the Envelope -- Swenson 169 (1): 8 -- American Journal of Respiratory and Critical Care Medicine) experimenting on rabbits (had ideas for therapeutic use of hypercapnia): "Their control and sick hypercapnic rabbits had higher blood pressures, lesser lactic acidosis, and better oxygenation than did the normocapnic controls."

(Doesn't tell you what the mechanism is either).









Also isn't it generally accepted that anything which stresses you out is likely to raise your BP - and hypercapnia certainly does that, I speak from experience.


Hmm. Dunno. Your guess is better than mine!

Cheers,

Charles.

Last edited by solocavediver; 22nd November 2008 at 23:02..
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Old 25th November 2008, 21:33   #5 (permalink)
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Re: Hypercapnia and High Blood Pressure

Thanks for the responses.
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