# Breathe with Touch: A Tactile Interface for Breathing Assistance System

Bin Yu, Loe Feijs, Mathias Funk, Jun Hu

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Bin Yu, Loe Feijs, Mathias Funk, Jun Hu. Breathe with Touch: A Tactile Interface for Breathing Assistance System. 15th Human-Computer Interaction (INTERACT), Sep 2015, Bamberg, Germany. pp.45-52, 10.1007/978-3-319-22698-9_4. hal-01609385

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# Breathe with Touch: A Tactile Interface for Breathing Assistance System

Bin Yu, Loe Feijs, Mathias Funk, Jun Hu

Industrial Design Department, Technology University of Eindhoven

{B.Yu, L.M.G.Feijs, M.Funk, J.Hu}@TUE.NL

**Abstract.** Breathing techniques have been widely used as an aid in stress-reduction and relaxation exercises. Most breathing assistance systems present breathing guidance in visual or auditory forms. In this study, we explored a tactile interface of a breathing assistance system by using a shape-changing airbag. We hypothesized that it would help users perform the breathing exercise more effectively and enhance their relaxing experience. The feasibility of the tactile interface was evaluated from three aspects: stress reduction, breathing training and interface usability. The results showed that for most participants, the overall heart rate variability were improved after breathing training. Moreover, “Breathe with Touch” brought users better satisfaction during the exercise. We discuss these results and future design implications for designing tactile interfaces for breathing guidance.

**Keywords:** tactile interface; biofeedback; breathing assistance; relaxation

## 1 Introduction

In modern society, the pace of life is fast and the competition is fierce. An increasing number of people are suffering from chronic stress in their daily life. Breathing techniques have been widely used in mind-body practices for stress reduction and relaxation [1]. Breathing techniques offer a simple tool to improve the balance of autonomic nervous system, strengthen its capability to adapt to stress and further mitigate the negative effects of stress on the health [2]. With a variety of breathing assistance devices, individuals learn to regulate their breathing into an optimal pattern with the aim of stress reduction. But this is not an easy task for most people to achieve a real relaxed state physically and mentally; because besides an improved breathing skills, the users' psycho-physiologic relaxing experience also affects the stress mitigation. To put it simply, users should also “feel good” during a breathing exercise. Therefore, the interface of breathing assistance device should not only offer an effective breathing guidance, but also a “feeling good” relaxing experience.

In medical applications, breathing guidance is usually presented in graphic or numeric forms, which tend to be technical and performance-oriented. In recent years, several new audiovisual interfaces with more aesthetic qualities have been created for daily use. For instance, Yongqiang Qin et al. developed an immersive breathing train-
ing game “Balloon” to train the user to improve breathing pattern [3]. In [4], the au-
thors presented “Sonic Respiration” to provide breathing feedback by modifying the
quality of musical interface. However, very little work has explored the feasibility of
tactile interface for breathing guidance.

The sense of touch enables us to interact with real objects around us, meanwhile,
to perceive these interactions. In [5], the authors suggested that the characteristic bidirec-
tional property of touch sense provides a basis to further enhance motor learning
and somatic experience. Studies in [6] revealed that tactile feedback could also reduce
the perceived workload in learning tasks and enhance the user’s feeling of presence.
Moreover, stimulating the tactile sense can give people strong relaxing experiences or
even emotional experiences, which are beneficial for stress mitigation and health.
Therefore, tactile stimuli are often used as a way to reduce stress and make people
feel better, such as in massaging techniques and physiotherapy. Tactile feedback is
often integrated into multimodal interfaces to enhance the user experience. For example
in [7] the authors developed a breathing guidance system to provide the users with
an immersive experience through a multimodal interface of auditory, vibratile and
light stimuli.

In this study, we aim to investigate whether the tactile interface would help users
perform breathing exercise more effectively and enhance user experience during the
exercise. We present the concept of *"Breathe with Touch"*: a tactile interface of
breathing assistance device that provides breathing guidance through a shape-
changing airbag. The airbag inflates and deflates at a specific rhythm to simulate the
targeted respiratory pattern. We assume that the changes in the shape of airbag can be
mirrored by the user resulting in a better and more relaxing breathing pattern. The
tactile interface was evaluated from three aspects: the effect on stress reduction, the
efficacy of breathing guidance and the usability. We synthesized the results with val-
uable qualitative responses from users.

2 Design & Implementation

The concept "Breathe with Touch" entails a tactile interface for breathing exercises.
By touching the interface, the user follows the shape change of the interface to receive
the feedback information. To design the proper form of tactile feedback, we observe
the nature of human's breathing movement. Breathing is accompanied by diaphragm
fluctuation activities. As an individual inhale, the diaphragm contracts and flattens,
causing the expansion of the lungs. Conversely, on exhale, the diaphragm relaxes and
moves upward to reduce the space in the chest cavity (see Fig 1). The lungs are like
two air balloons inside of our body. The changes in its shape depend on the airflow.

<figure><img src="image_2.png" /><figcaption>Fig. 1. The shape change of the airbag might be naturally associated with breathing movements</figcaption></figure>
"Breathe with Touch" simulates human's breathing movements through the shape changes of an inflatable airbag. The expansion and contraction of the lungs are mirrored by the inflation and deflation of the airbag. We assume that this kind of natural mapping between the targeted behavior and the interface could minimize cognitive workload thanks to the intuitive interpretation of the interface. Besides, we think the gradual shape-changing process of airbag could render the breathing guidance in a more soothing way, which helps users slow down their breathing and calm down as well. A hand-sized ellipsoid airbag was made of thermoplastic textile covered by a layer of soft velvet. The user rests her hand on the airbag to "feel" the targeted breathing rhythm (see Figure 2b).

<figure><img src="image_3.png" /><figcaption>Fig. 2. (a). Touch Airbag schematic diagram. (b). The user's right hand on the airbag</figcaption></figure>

The breathing guidance is mapped to the airbag in the following way: when the airbag inflates, an inhale activity is implied. When the airbag deflates, an exhale activity is implied. The maximum volume of airbag is around 120ml that is the same size of a mouse approximately. This enables the user to identify subtle changes of the shape easily and accurately by hand. The sensitive tactile feelings from the hand and fingers ensure that users can receive the guidance precisely as well. An air pump and a solenoid vent valves implement the inflation and deflation of the airbag. During the inflation, the air-pump pumps air into the airbag and the valve is closed. During the deflation, the air-pump stops working and the valve turn opened. Then, with the hand own weight, the air will be pushed out of airbag gently.

In this study, we focus on the design and evaluation of the tactile interface. A feed forward system was built with a pre-set breathing rate of 6 breathing cycles per minute (c/min). According to literature [8], most people could achieve a high HRV level under a respiration of 6 c/min. The airbag starts from the deflated state to inflated state then return to deflated state again. The duration of this inflation/deflation process is 10 seconds and this process repeats for the whole training session. As shown in Fig 2(a), the proposed tactile interface in this work can be embedded into a complete closed-loop biofeedback breathing assistance system in our future research.

# 3 Study One: Evaluation of the effects on stress reduction

We administered the first user study to investigate whether the proposed tactile interface would enhance breathing training and reduce stress effectively. 12 subjects (six
females and six males, age range: 25 to 35) participated in the study. Each participant
performed two stress-induced tasks (mathematical test) before and after breathing
training. For each task, the physiological data (pulse signals and respiration data) and
subjective stress reports were collected.

For each participant, a PPG sensor was placed on the left index finger and a res-
piratory sensor was placed at the abdominal level. Pulse signals were measured by a
data acquisition unit developed by our lab, and then beat-to-beat intervals (RR inter-
vals) were calculated and transmitted to a Processing program for data storage. The
standard deviation of the beat-to-beat intervals (SDNN) was calculated as the index of
HRV. Respiration data was recorded by the ANT system<fnref n="1" /> with a sampling rate of 256
Hz. The participant's stress level were measured by the state component of a Spiel-
berger State-Trait Anxiety Inventory (STAIS)[9].

<figure><img src="image_4.png" /><figcaption>Fig. 3. (a). The experiment set up (b). Right hand on the airbag</figcaption></figure>

The experiment followed a procedure as shown in Figure 4. On arrival at the la-
boratory, the participants were instructed how to use the breathing assistance system.
The pulse sensor and respiration sensor were applied to the participants. Then partici-
pants were instructed to relax with their eyes closed for 5 minutes. After the resting
period and without moving, participants were instructed to open their eyes and com-
plete a pre-training mathematical task which lasted 10 minutes during which time
measurements of HRV and respiratory rate were calculated. After the task, partici-
pants completed a pre-training STAIS questionnaire. After further 5-minute rest with
eyes closed, then participants completed a 10-minute breathing training session with
"Breath with touch". The instructions given to participants were: "Please follow the
changes of the airbag to breathe, when the airbag inflates, you should breathe in.
When airbag begins to deflate, you should breathe out. This session will last for 10
minutes." After the training, participants completed a further 10-minute mathematical
task. Pulse signal and respiratory data were also recorded throughout this period.
Then, a post-training STAIS questionnaire was completed.

<footnote n="1">¹ ANT, the Netherlands, http://www.ant-neuro.com/</footnote>
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** The experiment procedure</figcaption></figure>

The HRV, respiration rate and STAIS were calculated in Pre-training and Post-training periods separately. Differences were analyzed using an independent t-test. All data are described as means ± standard deviation (SD). A p-value of <0.05 was considered to be statistically significant.

Physiological data were missing from two participants because of technical problems. As the index of HRV, SDNN showed different degrees of increase among all participants after the breathing training, as shown in Fig 5. The SDNN values of post-training period were significantly higher than pre-training period (49.5 ± 14.2 vs. 66.3 ± 20.4; Pre-training vs. Post-training, p<0.05). Regarding the results of respiration data, seven participants showed a slower respiration rate during post-training task. However, there were no significant differences before or after training (18±6 vs. 15±2 circles; Pre-training vs. Post-training).

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** HRV (SDNN) and respiration rate before and after the breathing training.</figcaption></figure>

Psychometric data from the STAIS questionnaires are shown in Figure 6. Nine participants reported a lower anxiety level during the post-training mathematics task; however, there were three participants showed a higher anxiety levels (subject #1, #4, and #5). The STAIS scores were not significantly different between Pre-training period and Post-training period (46±11 vs. 39±9 points; Pre-training vs. Post-training).
<figure><img src="image_7.png" /><figcaption>Fig. 6. Scores of STAIS questionnaires pre- and post- the breathing training (N=12)</figcaption></figure>

4 Study two: Evaluation of interface usability

As tactile interfaces are seldom used in breathing assistance, we conducted another study to investigate the user's perception on the usability of tactile interface. To gain more insightful feedback and recommendations for further design, ten students with interaction design background (four females and six males, age range: 20 to 35) were recruited for this study. All participants complete three 10-minute breathing training sessions using the same breathing guidance, but with three different interfaces: visual, auditory and tactile interfaces. The experiment follows a within-subjects design with counterbalancing to avoid carry-over effects.

We introduced visual and auditory interfaces for breathing assistance as shown in Fig 7. In visual interface, an ellipse with varying radius represents the breathing guidance. When the ellipse grows, an inhale process is implied. In auditory feedback, we used the changes in sound volume to present breathing guidance. An increasing sound volume prompted user to breathe in, and the fading sound implied breathing out. The usability of the interface was measured using an adapted Lund's USE Questionnaire [10]. The questionnaire was designed for three dimensions: ease of use, ease of learning and satisfaction. All the questions used a seven-point Likert scale (1=strongly disagree, 7=strongly agree).

The results are shown in Figure 7. In terms of “Ease of Use”, all of three interfaces received high scores; there were no significant differences between tactile, auditory and visual interfaces (19±2 vs. 17±2 vs. 17±2; Tactile vs. Auditory vs. Visual). In terms of “Ease of Learning”, there were also no significant differences between three interfaces (19±2 vs. 18±2 vs. 17±2; Tactile vs. Auditory vs. Visual). In terms of “SATISFACTION”, the score of visual interface was significant lower than tactile and auditory interfaces (15±3, 14±3 vs. 11±2; Haptic, Auditory vs. Visual, respectively, p<0.05). From the open-ended interview, we got more positive feedback about tactile interface. More than 70% participants chose the tactile interface as their favorite interface. Specifically, they expressed a strong interest in working with the tactile interface and emphasized that it was more comfortable due to the touch experience.
<figure><img src="image_8.png" /><figcaption>Fig. 7. The results of Evaluation of interface usability</figcaption></figure>

# 5 General discussion

During a breathing training, users need to recognize the breathing guidance and follow it to regulate their breathing. In other words, the breathing training is a learning process, in which the users should take an active role, rather than just being exposed to it. Therefore, in breathing training, although the learning tasks are very simple (i.e. to regulate breathing to a specific rate), some participants still regard it as a serious task, which keep them away from a pure relaxation. We think this might be an interesting “paradox” in the design of self-training system for relaxation. It appeals to us and drive us to think about the interaction design in these products or systems that aim to promote relaxation. The training session requires user’s mental effort to achieve optimal training effect, such as improved breathing skills, positive imagination or more concentration. However, such mental effort of learning might leads to new stress.

In this design, we tried to lower the workload and enhance the relaxing experience by using a tactile interface. The touch airbag was used as a tangible communication media between the training system and the user. It is assumed that the user can adapt her breathing movements to an optimal pattern more effortlessly by mirroring the shape changes of the tangible interface. The results of user study confirm that the proposed “natural-mapping” interface could help the users perform breathing exercise more spontaneously. The users do not need to put much effort into understanding the instructions, and the transition between inflation and deflation of airbag might naturally trigger a slow and smooth transition between inhalation and exhalation.

The effectiveness of tactile breathing guidance in aiding relaxation and reducing stress was shown by the results of SAITS self-report. However, there is no significant reduction of stress level during the post-training mathematics task. There might be two possible explanations. For most participants, it was their first time to use breathing assistance system; the unfamiliarity with the system brings about new stresses. We also have reservations about the acute effect of 10-minute breathing exercise on stress reduction. Although in some clinical use [11], the minimum time of each training session could be 5 minutes; a short-period exercise may be repeated several times throughout a day to achieve a greater effect on stress mitigation. From physiological measurements, the results suggested that there was a significant improvement in HRV
during the post-training task, which suggests that tactile breathing training could enhance the users' physical ability to adapt to stress.

The users' ratings on the usability of visual, auditory and lighting interface were shown in Fig 7. The tactile interface shows the potential in improving user experience during the relaxation exercise as seen from significantly higher user ratings on satisfaction. Improvements in user experience were also evidenced by the participants' feedback from the interviews at the end of the experiment. During a breathing training process, repeated breathing instructions become boring easily. This is a major problem of most breathing guidance systems for long-term use. To some extent, the touch airbag shifts the focus from the superficial interface to users' own regulating behavior, which helps to relieve users of tedium. Besides, the users thought tactile feedback offers a condition for them to perform breathing training with eyes closed, which also helped relax. They also gave us a lot of insightful recommendations for further design of the interface, for instance, changing the size or position of airbag, integrating the airbag into regular items, and combining tactile and auditory feedback.

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