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What Causes Chronic Hyperventilation & What You Can Do About It

PART 2: Underlying Physiology of Chronic Hyperventilation

This article is the second of a series exploring the questions of what might be causing chronic and resistant over-breathing or hyperventilation (manifesting as stubbornly low carbon dioxide readings from a capnometer) and secondly what we might do to address such problems.

The articles are aimed primarily at people experiencing such issues, but I hope they'll be relevant to health practitioners too.

In part 1 I offered two initial hypotheses:

  • the first being that over-breathing is an entrenched stress response,
  • and the second being that over-breathing is a compensation for a problem in cellular energy production which disrupts the body's acid-alkali balance.

In this article we'll explore these two narratives in greater depth. In doing so, we'll cover the basics of acid-alkali (or acid-base) physiology, which will be necessary to understand the second causal account, but actually it has a bearing on the first too.

Hyperventilation and Stress

Let's start by reviewing hyperventilation in relation to stress. If you're one of my clients, or following the Stress Resilient Mind programme, hopefully this will be familiar to you.

Over-breathing is a problem in the short term because it causes a reduction in oxygen delivery to brain cells. The simple story we've focused on so far is that stress triggers a shift to faster, chest-based breathing and this typically means an increase in ventilation, which we can define as air exchanged per minute.

The mechanism behind the reduction in oxygen delivery is that increased ventilation (over-breathing) lowers blood CO2 which in turn causes:

  • vasoconstriction in the brain, and
  • a shift in the acidity of the blood, meaning the blood holds on to its oxygen.

But things get more complicated in either of the two scenarios that I've listed – that is, if over-breathing becomes an ingrained pattern to which the body adapts, or if over-breathing is not the real problem at all, but an adaptation to a deeper problem.

In either case we're going to need to understand more about acid-alkali balance in the body. I'll try to keep things as simple as possible but there's no denying it's a complex topic.

Acid-alkali Physiology

Acidity level is measured as pH. PH ranges from 1 to 14. This range is like a spectrum of acidity:

1= strongly acidic

7= neutral

strongly alkaline =14

The body doesn't have a uniform pH. Broadly speaking there are three “compartments” having distinct pHs:

  1. blood,
  2. intracellular fluid (just meaning the stuff inside of cells)
  3. extracellular fluid (in the body but outside of and between cells).

Some particular organs have their own specific pH needs but generally this three-way division applies.

Then you've also got the contents of the stomach and intestines, which technically aren't inside the body, and since they're not relevant to to our purpose, I won't be talking about these further.

The body regulates pH. What this means is that each compartment has an optimal pH, and if it drifts away from this point, the body takes steps to bring it back, because otherwise things don't work so well.

Blood pH

Blood is the most tightly regulated – in fact there is a very narrow range for blood pH and if you deviate only a small amount from pH 7.4 for arterial blood you'll die. (Venous blood is actually slightly different.)

Why is blood pH so important? The main reason is that haemoglobin in your blood, which transports oxygen from the lungs to cells, requires a very tight pH range to do its job. Too acidic, and haemoglobin can't bind to oxygen in the first place. Too alkaline and it will hold on too tightly, not delivering oxygen to the cells that need it.

Intracellular pH and Acid Production

Inside cells generally, pH is also important because there are lots of chemical reactions going on that work optimally at a particular pH range. Away from this range, things don't work as well and there'll be health consequences, but not so dire as a shift in blood pH.

Cells actually produce acids, as a natural consequence of their biochemical processes, in particular cellular energy metabolism. This is the controlled burning of fuels derived from food, to release energy. The main acid produced by energy metabolism is actually carbon dioxide. Another one is lactic acid, which I'll return to later since it's very relevant to stress and anxiety.

There are other sources of acidity in the body, notably certain food components, and also the microbiome, which is the population of micro-organisms in the gut. But cellular energy production is the main source.

This extra acid must be cleared out of the cell, otherwise it will build up and disturb the optimal pH. The extracellular fluid is actually slightly more alkaline, in order to aid the process of clearing acid from inside cells. The extracellular fluid is the least important in terms of acidity regulation, but even so, this extra acidity must be ultimately be removed from the body.

Carbon Dioxide

Again the main acid determining pH in the body is carbon dioxide, which when it dissolves in body fluid forms carbonic acid (a fairly weak acid). Carbon dioxide is produced inside cells but is moved out, and ends up in the blood stream. From there, it's breathed out through the lungs.

As you'll know if you've been following the Stress Resilient Mind programme, you don't want to get rid of carbon dioxide too fast – that's because carbon dioxide when dissolved in the blood is the main factor controlling the pH of the blood. Too little carbon dioxide in the blood causes potentially serious consequences. So you need the right concentration.

This is the main reason breathing needs to be well regulated: so that blood pH is balanced and the blood can do it's job of delivering up oxygen to cells.

pH Regulation & The Bicarbonate Buffer System

Let's take a closer look at how the body achieves this regulation of blood pH, or how it maintains blood pH at a stable point. For that we need to discuss something called the bicarbonate buffer system.

A buffer is something that reduces the impact of a change, or smooths it out.

Suppose you start exercising intensively – your system will suddenly create a lot of carbon dioxide (acid) which, without the bicarbonate buffer would pull your blood pH out of range – bad news. But the bicarbonate buffer smooths out the impact of that.

Let's take a look at how that happens. What follows is a little technical. I'll summarise the main points at the end.

I've said that CO2 is the main acid that affects blood pH, and when it dissolves it forms carbonic acid.

H2O + CO2 ↔ H2CO3

water carbon dioxide carbonic acid

(Some carbon dioxide also attaches to heamoglobin inside red blood cells, but we don't need concern ourselves with that.)

Now there's a further step involved, which is that carbonic acid dissociates into a bicarbonate ion plus a hydrogen ion.

So the full chemical formula is this:

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

H+ is a hydrogen ion, and the concentration of hydrogen ions is literally the definition of pH. So the more H+ we have in a fluid, the more acidic it is.

HCO3- is called bicarbonate, and it is alkaline.

(You may have heard of bicarbonate in the context of sodium bicarbonate, which is baking soda – more on this in a later article.)

Now this is starting to get complex, maybe more complex than we need. The bottom line is this:

  • We have three related substances in the blood – carbon dioxide, carbonic acid, and bicarbonate ions. Together these determine the concentration of hydrogen ions, which is the acidity or pH.
  • The body needs to regulate blood pH, or keep it tightly within healthy bounds. And it can do this by adjusting the levels of these substances, that is by ejecting them out of the body.

There are two body systems which take part in this regulation:

  • The primary regulation system is the lungs and breathing. We can get rid of carbon dioxide by breathing it out, and we can do that pretty quickly and easily.
  • The secondary system is the bicarbonate buffer system operating in the kidneys. The kidneys can pee out both hydrogen ions and bicarbonate ions, and can control the relative proportions of each of these being peed out or retained in the blood. The kidney system is slower, making changes over a time period of hours to days.


We've now covered the basics of acid-alkali physiology, at least enough to give us a better understanding of the two possible causal hypotheses for chronic over-breathing. And this is what we'll return to in the next article in the series (part 3).

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