Growing Attention on Improving Mental Health by Enhancing Breathing Experiences
Regular practice of slow and deep breathing has gained lots of attention thanks to its health benefits  such as enhancing ventilation efficiency of respiratory system, heart rate variability, and lowering of blood pressure [22, 63, 27, 49]. Breathing exercise also has physiological benefits such as reducing mental stress, anxiety, and depression, and promoting a generalized state of relaxation [27, 7]. Since breathing provides an efficient way to voluntarily and indirectly control our physiological state, including heart rate and heart rate variability [27, 65], it has been known as the oldest stress-reduction technique . Various types of techniques that involve slow, deep breathing such as yoga, Tai Chi, and some forms of meditation, have been practiced throughout history to increase well-being [61, 41].
A growing number of studies in Human-computer Interaction (HCI) have developed and explored new interfaces to assist people to regain and sustain attention to their inner body through breathing .
However, despite making many advances, most of the devices lack mobility and a convenience that enables them to be deployed and tested in natural daily-life environments. Also, their studies have neither examined pneumatic-tactile feedback for guiding breathing rate (BR) control, nor have they evaluated effectiveness to allow people to have various options for getting tactile biofeedback. Lastly, it is difficult to find a tactile biofeedback system that provides adaptive intensity to adjust to different body shapes and user’s preferences, due to the lack of feedback control ability.