Breathing & Loop Gain: Insights on Sleep Apnea

Have you ever heard of the term “loop gain?” How about “eupnea?” Well, here are just some of the interesting topics we will discuss today. There’s so much to learn about breathing. This week we welcomed a returning guest, Patrick McKeown. He is a wealth of information. His book, The Breathing Cure, is definitely a must-read as well. Join me as we review some of the wonderful things we talked about during our conversation.

Breathing & Loop Gain…. So Much More to Learn

Well, I don’t think it matters how many times you actually talk about breathing. I know a reasonable amount about breathing. I’ve written about breathing. I’m doing a very intensive course still on breathing to learn more about it from the wonderful Dr Rosalba Courtney, who we’ve had as a guest on this podcast. It’s a six-month programme. Patrick, I’ve had Patrick on as a guest. 

He’s one of the first episodes three or four years ago on this Unstress podcast, where we do talk more about the Buteyko method. Patrick is just a wealth of information, and I love talking to him. I thought that PALM was really important. 

These are things that we should be using to assess our patients that have potentially sleep apnoea, and it was the P stands for Pharyngeal collapsibility because the airway collapses, and as we grow older, the tone of our airway becomes less toned and more susceptible to collapsibility. So pharyngeal collapsibility is important.

Arousal threshold

Arousal threshold is all about how easily you are awake, how a high arousal level means you wake up very easily. The loop gain was really something. I’m always learning, and I want to share it with you. I had to find out more about loop gain because when Patrick said people with the high loop gain of far less able to tolerate mandibular advancement splints. I think that’s a really important point. 

Loop gain is an engineering method used. I’m quoting here to measure the stability of the negative feedback chemoreflex control system. Within our brains, within our bodies, there are chemoreceptors that respond to carbon dioxide levels, to all different levels, but specifically to carbon dioxide levels. 

The overall loop gain of the ventilatory system reflects the ratio of the ventilatory response to the disturbance that elicited that response. Loop gain equals ventilatory response divided by ventilatory disturbance.

Eupnea, Apnea, and Hypopnea

It’s a way of assessing whether your response to a particular activity is adequate, I guess. Therefore, when breathing deviates from, and here’s another term, “Eupnea” – the point where ventilation matches metabolic demand. Eupnea is described as normal, healthy unlabelled breathing in a mammal, and it’s sometimes known as quiet breathing or resting respiratory rate – eupnea. 

There are terms like you become familiar with an “apnea” – where you actually stop breathing, or “hypopnea” where you have restricted breathing. But here’s a term you don’t hear very often for a very good reason, and that is eupnoea, normal, good, healthy and unlabelled breathing.

The Breathing Cure

Patrick’s book, The Breathing Cure, which I’m holding up for those watching, is just an amazing book. There’s so much information in here. It was published in 2021. It’s a brilliant book. If you’re wanting to explore more about breathing, then you could. It’d be hard to go further than this book, but “loop gain” was something that Patrick had mentioned, and I must admit it wasn’t something that I was particularly familiar with. 

When I got the book, I immediately went to page 404, quite a way into the book, and wanted to read about loop gain. I thought I’d share it with you. I don’t mind reading a bit of a book for you and informing you.

“Loop gain. After anatomical considerations,” which are fitness, this is mine in addition here, which is when you’ve put on weight thickening around the neck, fat around the neck, the flaccidity of laryngeal muscles and pharyngeal muscles which predispose you to collapse. That’s an important there – anatomical considerations. “High loop gain is the greatest contributing factor in obstructive sleep apnoea.” 

That’s a really important statement. “Affecting one-third of patients diagnosed with the condition. Patients with high loop gain have an exaggerated response to even small changes in the level of carbon dioxide.” 

Carbon dioxide levels

People think breathing is so much about oxygen, but it’s actually mainly about carbon dioxide levels because carbon dioxide levels in the lungs determine your pH. They balance out your acid-alkali balance. “And so it’s carbon dioxide level, which is really critical factor. And the pH in the blood is very narrow. So for it to work effectively, for example, to take oxygen onto the haemoglobin molecule, you need a pH of 7.35. 

To release carbon dioxide at the site where you need it, 7.45. So we work in a very narrow range of pH. That’s critically important. And that’s why balancing our pH, and that’s why carbon dioxide levels are so important. And that’s why breathing gently and slowly through the nasal passages from the diaphragm is what constitutes breathing well.”

“Patients with high loop gain have an exaggerated response, even to small changes in the level of carbon dioxide.” Now, this is important. For example, if someone was to hyperventilate and overdo it, they keep pushing out carbon dioxide level to such a degree that you would eventually pass out, which kind of slows your breathing right down and gives the body a chance for the carbon dioxide to build up again in your lungs. 

Because carbon dioxide is a waste product of energy, you’re producing energy. “So this response, this exaggerated, having a high loop gain is an exaggerated response to even small changes in the level of carbon dioxide. During an apnoea, breathing temporarily stops. This makes it impossible for CO2 to leave the lungs. The gas accumulates in the blood.”

“When a patient has a high loop gain, ventilation becomes exaggerated when breathing resumes this faster and harder breathing after an apnoea leads to a sudden drop in blood CO2. As the level of CO2 in the blood becomes too low, the brain fails to adequately signal to breathe, causing a central apnoea.” So that’s the critical point. 

You know, when you stop breathing, it upsets the balance of carbon dioxide in the, blood, in the lungs, and your obstructive sleep apnoea becomes a central sleep apnoea, and we haven’t done enough podcasts on central sleep apnoea, but you can see how this delicate balance of breathing well is so critically important to so many things in our body. 

The balance of pH as an alkali in the body determines, for example, smooth muscle. Smooth muscles contract when that balance goes out of balance. People who have a resistance to managing their high blood pressure.

I was talking to a doctor just last week about drug-resistant hypertension, and they were having trouble balancing out and finding the correct medication for this patient who didn’t matter what prescription of hypertensives they were giving them, they were having trouble controlling hypertension. It was interesting because the response to this was to use ultrasound and to oblate – to do hypothermy, to actually destroy, I think, the nerves supply to the kidneys, which were involved in regulating blood pressure. 

I asked the doctor, “Had you ever thought of this connection with breathing?” Because if you hyperventilate or if your breathing goes out of balance and your CO2 is out of balance, then smooth muscle will contract, and blood vessels have smooth muscle in them. They had never even thought of breathing as a factor in drug-resistant hypertension.


Another way this manifests itself is in young children who suffer from bedwetting. Enuresis, we’ve talked about this on several podcasts. But enuresis bedwetting, beyond the age when a child is toilet trained, they generally stop wetting their bed at night. They will get up at night to go to the bathroom rather than wet the bed. 

But this in these cases that we’ve seen in our practise, where children of eight, ten or even 12 years old are still wetting their bed, and they’ve gone to see a urologist, neurologist, psychologist. Again, no one has thought of breathing and its effect on body chemistry, which in turn affects smooth muscle, which is what the bladder is made of to cause enuresis. 

The use of micropore tape on the mouth at night to slow the breathing down. This cured this child’s problem within one or two nights. And these people had spent tens of thousands, not tens of thousands, but thousands of dollars and many hours and many distressing hours, consulting all sorts of specialists and many distressing hours for this child who actually couldn’t go to sports camps or sleepovers because she was so embarrassed that she may wet the bed. It was life-altering. 

But for us adults, getting up at night to go to the bathroom is also a reflection in many cases of sleep-disordered breathing. Now, getting up not to go to the bathroom can be a reflection of other things – undiagnosed diabetes or poorly controlled diabetes, certain medications, of course, prostate problems in men as we get older. 

But a common factor that is often overlooked is getting up at night to go to the bathroom to urinate. And I’m surprised when I take history in my practise of this being the case not just once, but maybe even two or three times in the night. And yet breathing has been overlooked.

This story this week with Patrick McKeown, The Breathing Cure, was wonderful. Always so good to connect with him. As I said, it doesn’t matter how often I do programmes on breathing, I learn something new every single time, and I’m sure you do too. This is a subject we’re going to revisit again and again because we keep on learning new things. Loop gain was such an important thing because it gives us a clue as to whether a patient may be able to use mandibular advancement splints. 

Now, these are splints that fit in the mouth to keep the airway open. It holds the jaw, as the name implies, a mandibular advancement mandible being the lower jaw, keeping the jaw advanced forward at night. The tongue is attached to the lower jaw, which drops back at night. How do you keep your jaw forward while you’re asleep? 

Well, you can do it while you are awake. You can do it while you’re listening to me. But it’s very difficult to do it at night. That’s why there are many designs of splints that keep the mandible forward and keep the airway open.

But not everybody can tolerate it. There are many reasons why people can’t tolerate a splint. One has to do with their jaw joints, and that is an important factor. Another is to do with this loop gain. If you have an exaggerated response to small changes in the level of CO2, which in turn change an obstructive sleep apnoea problem to a central apnoea problem, we have a breathing centre in the brain that has nothing to do with the obstruction of the airway. 

A central apnoea is a different story from an obstructive sleep apnoea. This is tying all these complex things together and as I keep saying, the more I learn, the more I realise I have to learn. 

I only wish I knew as much as I thought I did when I graduated all those years ago. That’s what makes health so interesting and enjoyable, and intellectually stimulating. I hope this finds you well. Until next time.



This podcast provides general information and discussion about medicine, health, and related subjects. The content is not intended and should not be construed as medical advice or as a substitute for care by a qualified medical practitioner. If you or any other person has a medical concern, he or she should consult with an appropriately qualified medical practitioner. Guests who speak in this podcast express their own opinions, experiences, and conclusions.