For many centuries the discipline of Yoga knew the importance of good breathing for good life. Intuitively we are aware that breathing, when done properly, helps us to control our stress. Yoga teaches us to control our breathing through appropriate asanas (postures), meditation and pranayama (controlled breathing).
Swami Sivananda – Founder Divine Life Society and author of “The Science of Pranayama”
In the West these techniques were brought to the main stream medical awareness, mainly through the seminal publication “Relaxation Response” of Dr Herbert Benson in 1975. The Relaxation Response is defined as your personal ability to make your body release chemicals and brain signals that make your muscles and organs slow down and increases blood flow to the brain [Ref.1]. There are many techniques for developing Relaxation Response or deep relaxation. In the list of techniques deep breathing, meditation and yoga asanas appear prominently. Breath meditation, in which you focus on your breath while seated in a comfortable position , can relieve stress [Ref. 2]. Yoga Nidra and many variants of the same (for example iRest® Yoga Nidra ) are known to provide deep relaxation and relief to PTSD (Post Traumatic Stress Disorder) sufferers [Ref.3].
Deep relaxation, if practiced regularly can strengthen our immune system and bring a host of other medical benefits. For example, relaxation can ease asthma symptoms by widening respiratory passages. In some cases it can help diabetics by reducing the need for insulin [Ref.4] and provide significant relief to chronic pain sufferers. We are slowly understanding the way stress reduction works in promoting good health. Studies show that Relaxation Response elicits gene expression changes in short term and long term practitioners. It is believed that this might be causing long term physiological changes for good [Ref.5]
Deep Breathing to control Blood Pressure and hypertension
Probably the most prominent benefit of deep relaxation, achieved through deep and slow breathing amongst other techniques, is in controlling high blood pressure [Ref.6]. These days most of us are always on the run and stressed due to the un-ending need to do more and perfectly all the time. This evokes a strong fight or flight response in us and in this process we often forget how to breathe. That is why we need to develop good breathing techniques and we need to use them instinctively.
Yoga provides a wide range of tools for deep relaxation, including breathing to discipline the mind. Pranayama, the fourth limb of Yoga, is a well-developed and elaborate set of techniques to control prana (the vital life force, including breathing). By practicing pranayama one can quickly transform oneself in terms of attitude and feelings [Ref.7]. It is mind boggling to know that people spend huge amounts of money on drugs to control stress, which is temporary any way, while relaxation techniques are available through proper breathing and yoga. It can be used anywhere and anytime and it is free.
 http://www.med.umich.edu/painresearch/patients/Relaxation.pdf (on Relaxation Response)
 Stankovic,L., 2011, Transforming Trauma: A qualitative feasibility study of integrative restoration (iRest) Yoga Nidra on combat related Post-Traumatic Stress Disorder, Int. J. of Yoga Therapy, 21, p.23-37.
 Dusek et.al., 2008, Genomic counter-stress changes induced by the relaxation response, http://www.ncbi.nlm.nih.gov/pubmed/18596974.
 M. Tiwari, 1995, Secrets of Healing, Lotus Press, Wisconsin, 548p.