Bright Choice wrote:dsm wrote:Am always on the look out for symptoms of CO2 imbalance as that to me is the Achilles heel of the current ASV machines. They are designed to fix it *but* for known patterns such as CSR. They are also capable of inducing CO2 imbalance.
dsm - Very interesting post, thanks for sharing! I'd be interested in learning more about CO2 imbalance - that's new to me. Can you share a simplified explanation?
Thanks!
Bright Choice
I'll try to keep it very brief & simple as it is a topic that can go in all directions. Firstly my comments are mostly my opinions as I am not any kind of respiratory worker nor expert. NotMuffy is a widely recognized sleep expert and his expertise on SDB is well known here and in other forums. It is worth noting that NotMuffy (to the best of my memory) has not used cpap therapy directly (doesn't need to) so has the perspective of an expert who deals with lots of different SDB people who do use cpap machines of all types. That may or may not matter. I though think it does give a different perspective on *some* issues & perhaps the view on the importance of the placebo effect is one of those areas. That aside. Anything NotMuffy adds here is going to have more weight than most of the rest of us.
This is a simplified version of the factors & relates mainly to sleep.
I apologize in advance if I have not simplified it adequately, or have got any part of it wrong or is misleading.
CO2
CO2 in the blood is monitored by the body (respiratory chemoreceptors mostly near the brain) to determine what rate/depth of breathing is required at a point in time.
CO2 levels drive respiration.
If there is momentarily too much CO2 in the blood (what ever the trigger), a normal person's respiratory chemoreceptors detect this via the blood flow coming from the lungs, and signal to the respiratory system to breath deeper & faster to help 'blow off' the excess CO2. If there is momentarily too little CO2 in the blood, the respiratory chemorectotors normally signal the respiration to slow down or stop. This allows CO2 to build up as the body 'dumps' it into the blood. A yawn can be an example of a breath signaled to clear excess CO2 from the lungs. Hyperventilation also 'blows off' CO2 and usually leads to under-ventilation until all is back in balance. Not breathing causes CO2 to build up.
Prolonged periods either way can cause harm in particular from too little oxygen in our system ...
Respiration helps us obtain oxygen.
O2 (SpO2) or blood oxygen is what keeps our body & brain well (oxygen feeds the cells). A healthy oxygen level (along with a healthy CO2 level) is achieved by gas-exchange in the lungs (via the Alveoli). Breath-in & as long as the air gets freely to the alveoli, oxygen is taken into the blood and CO2 expunged from the blood. On breathing out of the air exiting the lungs takes out the excess CO2. The Oxygen level therefore depends to a large degree on the CO2 level in our blood as seen at the respiratory chemoreceptors (near the brain).
How this can get 'out of whack' is for example when we have too little CO2 in the blood, which signals slowing or stopping of breathing. That slowing or stopping of breathing if it lasts too long, can and does result in inadequate oxygen levels in the blood. If our O2 levels (SpO2) drop too low it can start to harm the cells - brain and body.
a CO2 imbalance has its own side effects that vary depending on level.
Too much CO2 in the blood can cause it to become excessively acidic. Too little can swing it the other way alkolosis. The PH balance in the blood is important.
The imbalances are called hypocania (too little CO2) & hypercapnia (too much CO2).
>>
Hypocapnia: causes cerebral vasoconstriction, leading to cerebral hypoxia and this can cause transient dizziness, visual disturbances, and anxiety. A low partial pressure of carbon dioxide in the blood also causes alkalosis (because CO2 is acidic in solution), leading to lowered plasma calcium ions and nerve and muscle excitability. This explains the other common symptoms of hyperventilation —pins and needles, muscle cramps and tetany in the extremities, especially hands and feet
Hypercapnia: symptoms and signs of early hypercapnia include flushed skin, full pulse, tachypnea, dyspnoea, extrasystoles, muscle twitches, hand flaps, reduced neural activity, and possibly a raised blood pressure. According to other sources, symptoms of mild hypercapnia might include headache, confusion and lethargy. Hypercapnia can induce increased cardiac output, an elevation in arterial blood pressure, and a propensity toward arrhythmias.
<<
Too little oxygen in the blood leads to hypoxia. Hypoxia gets bad very quickly. Stop breathing the 1st & worst damage is to the brain then the body.
In summary:
The CO2 levels in the blood provide the signals to the respiratory system as to rate & depth of breathing. The breathing helps provide oxygen needed by the body's cells to maintain good health.
CO2 and xPAP set up.
By incorrectly setting up a Bilevel or some ASV machines, it is possible to trigger hyperventilation & thus blow off too much CO2. It is also possible for some people to have an incorrect pressure setting on their machine that induces excessive numbers central apneas that in turn allow repeated excess levels of CO2 to build up which in turn lowers oxygen levels.
Deadspace.
When we breathe out there is what is called deadspace which is the part of the respiratory system that still holds air that didn't exit the body & thus still has discarded CO2 in it. In CPAP, deadspace extends into the mask & hose. The holes in the mask are there to allow the bulk of the expunged CO2 laden air to get away. But, we do need a certain level of CO2 to be re-breathed and if a CPAP machine has been set with too high an eep (end expiratory pressure - also can be referred to as epap) then the CO2 level in the air can remain too high. Some people with particular disorders may actually need their mask/hose modified to force them to hold even higher levels of CO2. Most people though, are not impacted by deadspace issues.
Hope this was not too complex. If yes hopefully someone else can simplify it further.
DSM
