Why does breathing slowly make us feel better?
You’ve heard it before – during moments of overwhelm, take slow, deep breaths. There is no question that breathing slowly has benefits on our mood. Indeed, slow, paced breathing is a key component of mindfulness and meditation practices around the world. But how exactly does controlling our breath influence our physiology and ultimately impact our mental well-being?
Breath and the Nervous System
Before discussing some of the theories for how slow paced breathing impacts our health and mood, it may help to briefly review how we currently understand the connection between our breath and our body.
The nervous system, our body’s network of nerves that coordinates our movements and sensations, is divided into the central nervous system (which consists of our brain and spinal cord), and the peripheral nervous system (which involves the nerves going out into our bodies) (Figure 1). The peripheral nervous system is further divided into two categories: the somatic nervous system, which involves our voluntary control over our body, and the autonomic nervous system, which is responsible for automatic functions that we don’t have to consciously think about but need to survive, such as our heartbeat, digestion, and – you guessed it – breathing. In fact, breathing is unique in that it is the only autonomic function we have the power to control.
The autonomic nervous system can be broken down further (this is the last nervous system division, I promise!) into the sympathetic and parasympathetic nervous systems (Figure 2). The sympathetic nervous system, also known as the fight-or-flight system, is activated when we are stressed or afraid. This triggers sweating, an increase in heart rate, and the release of adrenaline and cortisol, all to prepare us to either fight or flee to avoid danger. The parasympathetic nervous system is also called the rest-and-digest system because it kicks into gear when we are relaxed, triggering processes like saliva production, contraction of digestive muscles, and a reduction in heart rate. Scientists have a theory for how slow breathing leads to a calmer state of mind. Deep, slow breaths – particularly the exhalations – are thought to activate the vagus nerve, which is the primary nerve of the parasympathetic nervous system (this idea has been discussed in a previous NeuWrite post By Brittany Fair). In this way, we may be able to directly activate the part of our nervous system that inhibits stress signals and puts our bodies in a state of ease simply by adjusting our breath.
Slow Breathing and the Lungs
The fundamental purpose of the breath is to bring in the oxygen needed by each and every cell in our bodies (including in our brains!), and to get rid of the carbon dioxide our cells produce as waste. The process by which our lungs transfer oxygen from the air we inhale to the bloodstream, and carbon dioxide from the blood back into the air we exhale, is called gas exchange. Research suggests that taking slow, deep breaths increases the efficiency of this gas exchange. This has been studied primarily in people with low levels of blood oxygenation. For instance, in one study, researchers took overall healthy people to a high altitude location (where there is a lower amount of oxygen in the air), which lead to reduced oxygen levels in their blood. Then they measured their blood oxygenation before, during, and after 15 minutes of slow, paced breathing . They found that the shift from spontaneous to slow and controlled breathing led to an increase in blood oxygenation which occurred quickly and lasted for the duration of the breathing exercise. This effect has also been shown in patients with conditions that lead to reduced blood oxygen, such as heart failure , as well as in people living permanently at high altitudes . Together, these findings suggest that slow, deep breathing helps our lungs do their job most optimally.
Slow Breathing and the Heart
In addition to the benefits of slow breathing on the efficiency of gas exchange in our lungs, scientists are also studying its effects on heart rate and blood pressure, two processes controlled by our autonomic nervous systems. Both heart rate and blood pressure fluctuate naturally over time, and their rhythms are intrinsically linked. Our nervous system has a specialized way to maintain a consistent blood pressure – the baroreflex. This involves increasing the heart rate when blood pressure drops, and decreasing heart rate when blood pressure rises. Together, these fluctuations are influenced by many complicated processes – however, one major contributor is the breath. For instance, when you inhale, your heart rate goes up, and after a short delay, your blood pressure goes up as well. This pattern is reversed when you exhale (Figure 3).
There is actually a statistical measure of how much your heart rate fluctuates over time – heart rate variability (HRV). HRV is specifically defined as the variation in the time between each heart beat. If having a variable heart rate sounds scary, just think about how much our heart rates vary naturally throughout the day depending on whether we are resting or exercising, calm or anxious, and so on. This natural variation is not considered an arrhythmia, and is actually often used as a marker of good autonomic nervous system functioning. Our heart’s ability to adjust how much blood is being pumped throughout the body at any given time is critical for us to properly adapt to changing situations and switch between the fight-or-flight and rest-and-digest divisions of our nervous system. In fact, studies have found that higher HRV has been associated with greater baroreflex sensitivity , cardiovascular health , and ability to tolerate stress . On the other hand, HRV decreases naturally as we age [10-11], and lower HRV has been associated with anxiety , post-traumatic stress disorder , and cardiovascular disease [14-15]. So what does slow breathing have to do with this? Various studies have shown that when people engage in slow, paced breathing, particularly at around 6 breaths per minute, their HRV and baroreflex sensitivity are maximized , and this effect can persist after the breathing exercise . Scientists think that increases in HRV indicate activation of the parasympathetic nervous system (the rest-and-digest system), which is in line with the theory described earlier about slow breathing activating the vagus nerve to help us calm down.
It is noteworthy that the breathing frequency of 6 breaths per minute pops up often in the research. Interestingly, it seems to come up in different cultural practices as well. One study reported that recitation of the Ave Maria prayer and of the Buddhist mantra om-mani-padme-om (the jewel is in the lotus) slowed respiration to almost exactly 6/min and enhanced HRV and baroreflex sensitivity .
Slow Breathing and the Brain
Studying the psychological impacts of breathing interventions is actually more challenging than studying the physiological impacts, because it is difficult to tease apart the effects of the breathing activity itself from mental processes that may occur when we focus on our breath. For instance, when you engage in slow, paced breathing, you may also experience focused attention, mental imagery, and emotional regulation. It’s hard to say whether it’s the breathing activity or the focused attention/imagery/etc. (or a relationship between the two) causes the improvement in mental well-being. Of course, scientists are curious, and the difficulty of a problem never stops them from trying to learn and better understand. To get at this problem, they have used techniques to measure brain activity like EEG (electroencephalography; recording of electrical activity on the scalp), and fMRI (functional magnetic resonance imaging; measuring changes in blood oxygenation in the brain), along with surveys or questionnaires to measure psychological and behavioral outcomes during slow breathing exercises.
In general, slow breathing techniques have been associated with EEG patterns that are thought to reflect inward focus and meditative states [19-21]. These patterns were also associated with feelings of vigor and energy and reduced feelings of anxiety, depression, and anger [19-20]. Further, fMRI studies have found that slow breathing techniques were associated with a higher blood oxygenation signal (indicating increased brain activity) in various brain regions related to voluntary breathing and regulation of internal bodily states . These findings support the general theory that slow breathing is beneficial on our psychology. However, they don’t really get at how this happens.
One recent mouse study (also discussed in Brittany Fair’s NeuWrite post on breath) from Dr. Mark Krasnow’s lab at UC San Francisco is the first of its kind to really tackle the question of exactly how slow breathing is connected to a state of mental calmness . They found a specific group of cells located within the breathing center of the brainstem that, when made non-functional, resulted in animals that were surprisingly calm. These particular cells connect to another brainstem region called the locus coeruleus, which itself connects to every part of the brain and plays a big role in arousal and stress. These animals also happened to show different patterns of breathing – they took fewer fast-paced breaths and more slow breaths. This study suggests a specific mechanism by which signals from our breath can influence our brain to promote states of calm or stress.
Breathe Slowly and Prosper
There is little question that slow, paced breathing helps to calm us down. Slow breathing has been implemented in mindfulness and meditation practices throughout cultures and time, and these practices are connected with improved mental health overall [24-25]. However, how the act of slow breathing – apart from its connection to mindfulness and meditation – impacts our physiological and psychological well-being is a question scientists are still trying to answer. So far we have learned that slow, deep breathing may allow our lungs to function most optimally, benefit our cardiovascular functioning, activate our parasympathetic (rest-and-digest) nervous system, and reduce the activity of cells that send stress signals throughout our brain. Overall, if you are looking for a way to bring more calm into your life, it is safe to say that practicing slow breathing more regularly can only help.
 Figure 1 taken from MacMillan Higher Ed. on May 26, 2022
 Figure 2 taken from https://imotions.com/blog/nervous-system/ on May 26, 2022
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