How Biochemistry Affects Breathing: Distinguishing Roles in Chemosensitivity

How did biochemistry impact our breathing? In today's session I wanted to delve into the ways that changes in the biochemistry in our body, such as our oxygen levels, our carbon dioxide levels, our ph levels actually impact our breathing and look at the ways that it's regulated and go into some of the depth of the details around three key areas. One being chemosensitive cells, one being chemoreceptors, and the other one being what are called acid sensing ion channels. And to dive into the functions of each and how they will regulate and control our breathing differently. So typically what's taught is that when we have a change in carbon dioxide, a chemoreceptor will pick that up and that will drive us to breathe differently. And it's a very small, little narrow area of it. And in fact the impact that the chemoreceptors has, whilst it does have an effect, it is not the primary way that we're actually breathing. So breathing is a behavior. And by behavior it means that we have these central passion generators and we've talked about these before. In our brain stem, particularly in the medulla oblongata, we have a small area called the Prebotzlinger complex, which is driving our inspiratory pattern. Just like the pacemaker of the heart. We have a pacemaker within our brainstem that's very primitive, it's amongst every single person that is just generating a continual pattern over and over again. Now this sets a particular rate in rhythm of breathing and it's learned as we get begin to regulate our nervous system. So at the moment I have a 7 week old baby and her breathing pattern is just all over the place. And I looked into this, I was a bit concerned that usually we're told babies are the best breathers, they're born without kind of trauma or stress or things like that and therefore their breathing is normal. However, I quickly learned that a baby's breathing rhythm is all over the place because that pre buck signature complex, whilst it's firing, it hasn't become conditioned via its nervous system being regulated. A baby learns to regulate its nervous system through parents, through caregivers. So that's very important to distinguish between anything to do with chemoreceptors and the fact that breathing itself is through a pacemaker. However, these particular pacemakers, the inspiratory pattern is generated by what we call the prebot singing complex. And the expiratory pattern is generated by called the parafasal nucleus. And essentially the paraphasal nucleus only comes on in two time, two particular areas, one Being exercise, when we get to moderate intensity exercise and we get an activation of our expiration and one being in REM sleep, when breathing is no longer controlled by our chemical receptors at all, it's just controlled by pattern generators only. Both of these have what we call chemosensitive cells, meaning it's going to pick up as the cerebral spinal fluid comes through the brain, the level of carbon dioxide and more so the level of ph. And there might be slight deviations even at resting, typically because we might be thinking, we might be having emotions and we have increase in arousal in our sympathetic nervous system. And that is going to drive a change in our rhythm and the pattern of our breath. But mostly it's going to be regular. However, when we start to exercise, we produce energy. Exercise creates metabolic activity and as a result of that, the byproduct of the production of ATP, particularly when we're in aerobic means to create energy, glucose plus oxygen equals water plus carbon dioxide. And that carbon dioxide dissolves into the blood. And when it dissolves into the blood, it dissociates into a hydrogen ion. And the hydrogen ion then gets buffered by the hemoglobin, but it creates more. The more CO2, the more acidic the blood environment gets. That then gets picked up by our chemoreceptors. So we have these behavioral breathing to begin with, even when we start to exercise, the system is going to make predictions of how much we should be breathing based off behavioral learning and memory. But then when there's a change in our CO2 level, our ph level, hemoreceptors pick this up and they try to fine tune our tidal volume, how deep we breathe. So ventilation in general is breathing frequency times bi tidal volume. So if someone is resting and they have six breaths per minute and they're breathing roughly 500 milliliters, but that's only going to be a 3 liters per minute breath, which is quite slow and quite low and probably not enough for most people with metabolic activity. But if we consider that the role of, of or the signal of CO2 rising generally means that there's a need for more oxygen to come in. CO2 and oxygen work together. We need oxygen to produce CO2, hence there's two oxygens in carbon dioxide. However, more CO2 being produced means more oxygen needs to come in. How do we get more oxygen into the body? We breathe more, but how do we breathe faster or do we breathe deeper? If we breathe faster, we lose more air to dead space. That trachea bronchi, bronchial roughly 150 milliliters. The faster we breathe, the less efficient we are with gas exchange. The deeper we breathe, however, the more efficient we are of gas exchange because the air pulls all the way down into the alveoli. So taking this a little bit of a larger breath is what actually CO2 is driving us to do. So breath hold training itself doesn't make the breath shallower, it makes it larger and slower, which is more gas exchange efficient. However, in exercise, there becomes an issue is that we have mechanical limitation to how deep we can breathe until we expend too much energy. And the role of the nervous system is to essentially try to make us as efficient as possible. So what tends to happen is when we hit our peak gas exchange and our peak kind of mechanical limitation to our tidal volume is then if CO2 continues to increase, the chemoreceptors will send a signal to the brain to start to generate a feeling, an affect, an emotion that is called air hunger. Okay. And that air hunger's role is to change your behavior, either slow you down in your pace of exercise, because you are now outside of homeostasis, or moving towards outside of homeostasis, or to change your breathing behavior. What's that? To send signals down to the prebotzling complex to start to fire faster. So the emotional component will drive respiration in terms of rate, and our metabolic systems will drive restoration in terms of our depth. However, there's a third thing we want to consider here, is when the ph gets to a critical point in terms of its acidotic state is so high, it then starts to open what are called acid sensing ion channels on our amygdala that are also aligned in our hypothalamus as well as our peripheral nervous system. And these channels are proton gated channels. And when there's a high level of hydrogen being H plus a proton, it opens the channels, it fuels the inside of our neuron. The energy then can be created in our mitochondria within the neuron. And that neuron can fire and wire to create plasticity to generate learning. So when we go into an acidotic state, not only do we get a change in our breathing, we also start to get initiation of learning, particularly learning with fear. Why is that? Because air hunger is an affect that's high arousal and it's a negative sensation. It's the closest thing we can get to fear in general. In fact, that's why leaning into doing air hunger tolerance work can help people with anxiety and stress when they get to a point where they're more grounded and regulated, they can be aware of that and have the top down control of their ability to manage those things. That is through exposure therapy. These acid sense and ion channels not only condition fear, they also condition pain, which is very interesting because pain again and air hunger are associated very well. People might feel as if they are struggling with pain, struggling with air anger when they are high intensity exercise. So when we get to a point where the ph level is critical now to survival, we get to a point in exercise called the respiratory compensation point where breathing frequency drives up so high through a generation of the feeling of fear and pain in our body to try and get us to stop to exercise. Now what does performance allow us to do? What does training allow us to do? It allows us to override these sensations, to push through to become more tolerant. So we're not becoming tolerant of the carbon dioxide itself. We've become intolerant of the sensation. We're building tolerance to the fear of the emotional state that we're in. So they're the considerations that we can make in the biochemical element of breathing. And if we break these three things down, we need to consider all three when we're working with clients. The level of the biochemistry, the psychology and the interaction of the training in the mind and the body together. Hope that gives you a little bit more of a depth of information of understanding the role between carbon dioxide ph and its interaction between breathing, mind, body and behavior.