What does diaphragmatic breathing have to do with my nervous system?
Your diaphragm is innervated by the phrenic nerves. These nerves (there is a right and a left) originate from your neck (cervical spine) at vertebrae C3-5. When any body part takes its innervation from levels that are so high up in the spine, we know it's an important one. This is also why anyone with a spinal cord injury at C5 or higher (C1-4) is much less likely to survive, since they are unable to breathe on their own.
Your phrenic nerves lie pretty close to parts of your vagus nerves, and the vagus nerves have to pass THROUGH the diaphragm (again there is a right and a left vagus nerve). Remember from above—your diaphragm has holes in it for your aorta, vena cava, and esophagus to pass through. The vagus nerves run along the esophagus, and pass through the same opening in the diaphragm in which the esophagus does.
So, what does that all mean?
Your vagus nerves are like a superhighway of information from your internal organs to your brain. They actually bypass the spine and spinal cord, and go directly into your brainstem! This is the oldest and most primitive part of our brains. Your vagus nerves take information from lots of places and send it up to the brain: your throat, voice box (larynx), ear, heart, lungs, esophagus, stomach, portions of the small and large intestines, and other abdominal organs (see pic 2).
80% of the information from the vagus nerves is going from the body to the brain. Only 20% is traveling down from the brain into the body! What this means is that the vagus nerves are imperative for telling your brain what is going on with your body at any given time. 75% of our parasympathetic nervous system (the rest and digest system, as opposed to fight or flight sympathetic system) is comprised of the vagus nerves alone!
So what are my vagus nerves telling my brain, and how does that relate to the diaphragm?
The vagus nerves play important roles in the following functions:
Immune system response
Mucus and saliva production
Skin and muscle sensations
Therefore, if your breathing is quick, shallow, or otherwise impaired; or your heart rate and blood pressure are rising—your brain knows it right away, and this starts to change the balance between the sympathetic and parasympathetic nervous systems!
Wow. So how exactly does diaphragmatic breathing help my nervous system?
By practicing a true diaphragmatic breath, one where the diaphragm flattens and descends into the abdomen, and ALL portions of the diaphragm are expanding, we start to slow and deepen the breath. This increases activity in our vagus nerves, lowers our heart rate and blood pressure, improves blood flow to our muscles and internal organs, and generally sends messages to the brain that everything is ok. This helps shift our nervous system into a "rest and digest" state (parasympathetic), rather than always being on high alert and more in the "fight or flight" state (sympathetic).
Does this mean that diaphragmatic breathing can lower my stress level?
Yes! There is a lot of evidence actually for this fact, both for physiological (body) stress, and psychological stress too. One study showed that just 10 minutes of diaphragmatic breathing lowered systolic AND diastolic blood pressure by 7 points (so both the top and bottom numbers of blood pressure decreased). And the control group that did 10 minutes of regular breathing had no change in their blood pressure!
Diaphragmatic breathing can also alter cortisol levels, which is our stress hormone. One small study had participants practice diaphragmatic breathing for 30 minutes, every other day for 8 weeks. And they found significant reductions in cortisol levels at the end of the 8 weeks, whereas again the control group didn't change (and actually increased their cortisol levels!). Check out pic 5 to see the results on a graph, from the same systematic review as above. This same study also found significant reductions in the resting breathing rate of participants who practiced diaphragmatic breathing, meaning their entire system had shifted into more of a parasympathetic state, even at rest.
What about psychological stress?
Yes! Another study (also reported in Hopper 2019) followed subjects for 8 months of both regular diaphragmatic breathing & exercise sessions. They surveyed participants at the 2, 4, 6, and 8-month marks. Over time their scores on a depression and anxiety questionnaire continued to improve, while the subjects who didn't get this intervention showed no change. The results of those practicing breathing & exercises were significant, both as compared to their own scores at the start of their program, and as compared to the control group.
What other medical conditions can benefit from diaphragmatic breathing?
A great 2020 review article by Hamasaki highlighted several studies that showed the positive effects of diaphragmatic breathing on a variety of medical conditions. (Of note though, most of the studies included in the review had small sample sizes.) The conditions that were improved by diaphragmatic breathing include:
Anxiety: decreased overall anxiety, decreased resting heart rate and breathing rate
Gastroesophageal reflux disease (GERD): improved overall quality of life, and decreased usage of medications (proton pump inhibitors). These changes were seen at the end of the 4-week intervention, and even maintained 9 months later!
Chronic obstructive pulmonary disease (COPD): improved resting breathing rate, exercise capacity, and overall quality of life
Asthma: reduced asthma symptoms (including hyperventilation) and improved quality of life
Cancer: In older subjects with breast or prostate cancer, improved overall quality of life. In combination with other relaxation techniques, improved weight gain and ability to eat in those with cancer-related eating problems.
Kids with constipation: in combination with additional physical therapy interventions (abdominal training, colon massage), improved frequency of bowel movements
Heart failure: improved ability to complete daily physical activity
Stroke: in combination with other breathing exercises, improved respiratory function, exercise capacity, and overall quality of life
So while of course nothing is fool-proof, continuing your diaphragmatic breathing practice outside of any other exercise you do will only further benefit your brain and body! Your nervous system will thank you, I promise. 😉
Cleveland Clinic: Vagus Nerve. https://my.clevelandclinic.org/health/body/22279-vagus-nerve
Hopper, S. I., Murray, S. L., Ferrara, L. R., & Singleton, J. K. (2019). Effectiveness of diaphragmatic breathing for reducing physiological and psychological stress in adults: a quantitative systematic review. JBI database of systematic reviews and implementation reports, 17(9), 1855–1876. https://doi.org/10.11124/JBISRIR-2017-003848
Hamasaki H. (2020). Effects of Diaphragmatic Breathing on Health: A Narrative Review. Medicines (Basel, Switzerland), 7(10), 65. https://doi.org/10.3390/medicines7100065