Breathing occurs without thought but is controlled by a complex neural network with a final output of phrenic motor neurons activating diaphragm muscle fibers (i.e., motor units). (Fogarty et al, 2018)
Diaphragmatic breathing, or belly breathing, is a deep breathing technique. This type of breathing increases the amount of oxygen delivered from lungs to blood. Diaphragmatic breathing triggers a response that can decrease stress and lower blood pressure. (Yau & Loke, 2021)
Diaphragmatic breathing may decrease stress as measured by physiologic biomarkers, as well psychological self-report tools. (Hoper et al, 2019) Also has shown efficacy to reduce motion sickness (Stromberg et al, 2015) and urinary incontinence (Toprak et al, 2022).
Over the last decade, studies have indicated that practicing diaphragmatic deep breathing at 6 or ≤10 breaths per minute can lead to arteriolar dilatation by activating pulmonary-cardiac mechanoreceptors and inhibiting sympathetic nerve activities and chemoreflex activation. Two-minute slow and deep breathing has been shown to reduce SBP and DBP by 8.6 and 4.9 mmHg, respectively, in hypertensive adults. Practicing slow and deep breathing over several weeks has also been showed to enhance baroreflex sensitivity and significantly increases heart rate variability. (Yau & Loke, 2021)
See the technique here: Diaphragmatic Breathing Exercises & Benefits (clevelandclinic.org)
To perform this exercise while sitting in a chair:
Fogarty MJ, Mantilla CB, Sieck GC. Breathing: Motor Control of Diaphragm Muscle. Physiology (Bethesda). 2018 Mar 1;33(2):113-126. doi: 10.1152/physiol.00002.2018. PMID: 29412056; PMCID: PMC5899234.
Hopper SI, Murray SL, Ferrara LR, Singleton JK. Effectiveness of diaphragmatic breathing for reducing physiological and psychological stress in adults: a quantitative systematic review. JBI Database System Rev Implement Rep. 2019 Sep;17(9):1855-1876. doi: 10.11124/JBISRIR-2017-003848. PMID: 31436595.
Stromberg SE, Russell ME, Carlson CR. Diaphragmatic breathing and its effectiveness for the management of motion sickness. Aerosp Med Hum Perform. 2015 May;86(5):452-7. doi: 10.3357/AMHP.4152.2015. PMID: 25945662.
Toprak N, Sen S, Varhan B. The role of diaphragmatic breathing exercise on urinary incontinence treatment: A pilot study. J Bodyw Mov Ther. 2022 Jan;29:146-153. doi: 10.1016/j.jbmt.2021.10.002. Epub 2021 Oct 20. PMID: 35248263.
Yau KK, Loke AY. Effects of diaphragmatic deep breathing exercises on prehypertensive or hypertensive adults: A literature review. Complement Ther Clin Pract. 2021 May;43:101315. doi: 10.1016/j.ctcp.2021.101315. Epub 2021 Jan 26. PMID: 33530033.