User Experience and Clinical Utility of a Smartphone-Based Application for Hwa-Byung Treatment: a protocol for a single-arm prospective pilot study

Abstract

Objectives

Hwa-byung (HB) is a Korean culture-bound syndrome characterized by suppressed anger and somatic symptoms, which affects a substantial proportion of the population and significantly impairs quality of life. While the Korean medicine clinical practice guideline for HB recommends mind–body therapies and psychotherapy as key interventions, their implementation in conventional clinical settings is limited by time, spatial barriers, and challenges in maintaining treatment continuity. Digital health technologies, particularly smartphone applications, offer accessible, personalized, and sustainable therapeutic solutions to address these challenges. Therefore, this study aims to evaluate the user experience and preliminary clinical utility of a smartphone-based stress management application in patients with HB through a single-center, single-arm, prospective intervention study.

Methods

Based on acceptance and commitment therapy (ACT) principles and HB clinical practice guidelines, the Hwa-free application integrates four primary components ACT-based educational videos, daily three-line journaling, diaphragmatic breathing training, and guided meditation audio content. Using the Hwa-Byung Diagnostic Interview Schedule, thirty participants aged 19-80 years, diagnosed with HB, will be recruited. After baseline assessments, participants will use the application daily for 4 weeks while continuing their existing stable treatments. The primary outcome is user experience, assessed using a structured questionnaire. Secondary outcomes include changes in HB symptoms, depression, anxiety, anger, psychological flexibility, quality of life, and heart rate variability, measured at multiple time points over 8 weeks. Safety will be monitored through adverse event reporting. In this exploratory study, preliminary data on the feasibility, acceptability, and potential clinical benefits of digitally delivered Korean medicine interventions for HB will be provided.

Conclusion

The findings will guide the design of future definitive randomized controlled trials and promote the broader integration of evidence-based digital therapeutics into Korean medicine practice.

INTRODUCTION

Hwa-byung (HB), literally meaning “fire illness,” is a culture-bound syndrome indigenous to Korea, characterized by suppressed anger and somatic symptoms [1]. Clinical manifestations include chest tightness, a sensation of heat rising, a lump in the throat or chest, palpitations, and sleep disturbances, all of which significantly impair quality of life and psychosocial functioning [1]. While HB has traditionally been associated with middle-aged women experiencing domestic and social stressors, recent epidemiological data indicate a 36.3% prevalence among the MZ generation in Korea, linked to female sex, poor subjective health status, HB trait, depression, and state anger [2].

The Korean medicine (KM) clinical practice guideline (CPG) for HB, developed to support evidence-based care, recommends mind–body therapies and psychotherapy as primary treatment modalities [3]. These approaches aim to restore psychophysiological balance and stabilize the autonomic nervous system, which is critical as patients with HB often express psychological distress through somatic symptoms [3]. Mind–body interventions support emotional regulation and overall mental and physical well-being [4, 5], while psychotherapy facilitates the expression of suppressed emotions and promotes emotional recovery [6].

However, conventional delivery of these interventions faces practical limitations: limited treatment time, spatial constraints, and challenges in providing individualized care and maintaining therapeutic continuity. For modern populations with demanding schedules, overcoming these barriers requires innovative approaches that transcend temporal and spatial boundaries. Digital health technologies, particularly smartphone applications, offer a promising solution [7, 8]. With widespread adoption and personalized features, mobile applications can deliver tailored therapeutic programs while enhancing accessibility and adherence [9].

Despite growing interest in digital therapeutics for mental health, few studies have examined their application in HB management. A recent survey of KM doctors revealed strong interest in developing digital therapeutics for HB, highlighting the potential for innovation [10]. Research on technology acceptance among mental health application users shows that, while appropriate design and content can yield high user satisfaction, sustained engagement remains challenging owing to variability in user needs and engagement measurement methods [11]. Therefore, HB management applications are needed to provide individualized tailoring to user needs.

Building on these foundations, we developed a smartphone application that combines mind–body therapies and psychotherapy based on the KM CPG recommendations for HB [3]. This study aims to explore the user experience and preliminary clinical utility of the stress management application in patients with HB through a single-arm prospective intervention trial. Specifically, we aim to: (1) investigate user experiences with the application, (2) assess changes in HB symptoms, (3) evaluate stress response alterations via heart rate variability (HRV), (4) examine changes in quality of life, and (5) determine the safety and user satisfaction of the application.

MATERIALS AND METHODS

1. Study design and setting

This single-center, single-arm, prospective intervention study is designed to explore user experiences and the clinical utility of a stress management smartphone application in patients with HB. The study will be conducted at Dong-Eui University Korean Medicine Hospital, Busan, Republic of Korea. The protocol has been approved by the Institutional Review Board (IRB) of Dong-Eui University Korean Medicine Hospital (approval number: DH-2025-15) and is registered with the Clinical Research Information Service (register number: KCT0011105). All procedures will be conducted in accordance with the Declaration of Helsinki and Korean Good Clinical Practice guidelines.

2. Participants

Participant recruitment is scheduled from October 2025 to August 2026.

1) Inclusion criteria

Eligible participants must meet the following criteria: (1) adults aged 19-80 years; (2) diagnosed with HB using the Hwa-Byung Diagnostic Interview Schedule (HBDIS) [12]; and (3) provided written informed consent after receiving a full explanation of the study.

2) Exclusion criteria

Participants will be excluded if they: (1) initiated new HB treatments (medication, KM treatment, or non-pharmacological therapy) or significantly changed the dosage/frequency of existing treatments within 4 weeks before enrollment; (2) participated in other interventional clinical trials within 4 weeks; (3) plan to start new HB treatments during the study period; (4) have unstable psychiatric disorders (schizophrenia, bipolar disorder) requiring treatment within 6 months; (5) are receiving treatment for severe chronic or terminal illnesses; (6) are considered unlikely to comply with study procedures; or (7) have any condition deemed inappropriate for participation by investigators.

3. Sample size

The target sample size is 30 participants. As an exploratory single-arm study focusing primarily on user experience, 25 participants are expected to provide sufficient data, based on previous research on technology acceptance in mental health applications [13]. This sample size is not designed to achieve statistical power for secondary clinical outcomes; rather, changes in these secondary measures will be analyzed to generate hypotheses for future definitive trials. To account for a 15-20% dropout rate, we aim to recruit 30 participants.

4. Intervention

The intervention involves 4 weeks of using the Hwa-free smartphone application (DYPHI Inc., Seoul, Republic of Korea), developed based on acceptance and commitment therapy (ACT) principles and KM CPG recommendations for HB (Fig. 1, Table 1) [3]. While ACT originated in Western behavioral science, the KM CPG for HB [3] recommends ‘psychotherapy’ as a primary intervention (Grade A) and specifically identifies ACT in its ‘Clinical Considerations’ as the only counseling technique with evidence for HB. The guideline also supports relaxation and meditation techniques for HB treatment. Accordingly, the Hwa-free application implements these guideline-based interventions. A multidisciplinary team—comprising four KM doctors, including two KM neuropsychiatrists, one clinical researcher, one psychotherapist, and three app developers—adapted the program from The ACT Workbook for Anger [14]. Over 1.5 years, the team held monthly consensus meetings to integrate ACT principles with KM theories (five-element theory) to ensure clinical and cultural validity. Table 2 presents the contents of this culturally adapted program, which was previously introduced in a case report [15].

Figure 1.

Screenshots of Hwa-free smartphone application interface. The application includes (A) ACT-based educational videos, (B) a three-line diary feature, (C) a diaphragmatic breathing training interface, and (D) a meditation and relaxation audio selection screen. These screenshots show the final clinical version of the application. All user data shown is dummy data generated for demonstration purposes, with no personally identifiable information included. ACT, acceptance and commitment therapy.

Table 1.

Main components of Hwa-free application

Components	Details
ACT-based video content	Weekly educational videos teaching participants how to understand and accept their emotions and thoughts.
Three-line diary	A daily journaling feature encouraging participants to reflect on and process their emotions. Entries are not stored on servers, emphasizing the reflective process itself rather than content preservation.
Diaphragmatic breathing training	An interface guiding users through proper diaphragmatic breathing exercises to help restore autonomic nervous system balance.
Meditation and relaxation therapy	Audio content for stress management through meditation and relaxation techniques.

ACT, acceptance and commitment therapy.

Table 2.

Main module and components of ACT

Week	Module	Components	Corresponding ACT process
1	Psychoeducation: HB	a) Understanding HB b) Etiology of HB c) Physiological changes during HB progression d) Treatment approaches for HB	Contact with the present moment (Awareness of Symptoms)
2	Mind observation and regulation	a) Observing mental experiences b) Practicing mind regulation techniques	Self-as-context, cognitive defusion
3	Understanding Hwa and Self-care	a) Theoretical understanding of Hwa in KM b) Authentic healing from HB c) Managing HB triggered by interpersonal relationships	Acceptance (Willingness)
4	Hwa and values	a) Relationship between HB and personal value b) Identifying individual values c) Acceptance of unmet desires d) Exploring forgiveness	Values, committed action

HB, Hwa-byung; KM, Korean Medicine.

Participants will be instructed to use the application at least once daily throughout the 4-week intervention period. Existing treatments maintained for at least 4 weeks before enrollment will remain unchanged during the study period. A detailed ‘Concomitant Medication/Treatment Log’ will be maintained to record the type, dosage, and frequency of all concurrent treatments throughout the study to monitor potential confounding effects.

5. Outcome measures

1) Primary outcome

The primary outcome is user experience, assessed using a structured questionnaire at Visit 3 (Day 28 ± 7). This questionnaire was developed by the application development company (DYPHI Inc., Seoul, South Korea) based on its experience in digital therapeutics to specifically assess user experience related to the unique features of the application. The questionnaire evaluated: (1) treatment content assessment (perceived effectiveness and usability of ACT programs, emergency button functions, three-line diary, and symptom self-assessment); (2) app usage experience (frequency, convenience, and accessibility); and (3) overall improvement suggestions through open-ended questions. Responses are recorded on 5-point Likert scales and as qualitative free-text responses. To ensure reliability, the internal consistency of the questionnaire items will be verified using Cronbach’s alpha.

2) Secondary outcomes

Secondary outcomes include changes from baseline to Visit 2 (Day 14 ± 7), Visit 3 (Day 28 ± 7), and follow-up (Day 56 ± 7) in the following measures: HB scale, a validated 31-item instrument assessing HB traits and symptoms [16]; visual analog scale for HB symptoms, a 0-100 mm continuous scale measuring subjective symptom severity [3]; Beck Depression Inventory-II, a 21-item self-report assessing depression severity [17]; State-Trait Anxiety Inventory, a 40-item instrument measuring state and trait anxiety [18]; State-Trait Anger Expression Inventory, a 44-item questionnaire evaluating anger intensity and expression patterns [19]; Acceptance and Action Questionnaire-II, an 8-item measure of psychological flexibility and experiential avoidance [20]; EQ-5D-5L/EQ-VAS, a standardized measure of health-related quality of life [21]; and HRV indicators, including standard deviation of NN intervals, high frequency (HF), low frequency (LF), and LF/HF ratio [22].

3) Safety outcomes

Safety will be assessed by monitoring adverse events throughout the study period, including severity and causality assessments.

4) Application adherence

Application usage will be automatically tracked, including total days used, session duration, content-specific frequency, and overall usage patterns.

6. Study procedures

Table 3 shows the study schedule. After obtaining written informed consent (Visit 1, Day 0), participants will undergo baseline assessments, including demographics, medical history, physical measurements, vital signs, all outcome measures, and HRV testing. Eligible participants will be instructed on using the application and will use it daily for 4 weeks. Follow-up visits will occur on Days 14 ± 7 (Visit 2) and 28 ± 7 (Visit 3) for clinical assessments. A remote follow-up using mobile surveys will be conducted at Day 56 ± 7 to assess sustained effects and continued application use.

Table 3.

Study schedule

Procedure	Visit 1 (day 0)	Visit 2 (day 14 ± 7)	Visit 3 (day 28 ± 7)	Follow-up (day 56 ± 7)
Informed consent	○
Demographics	○
Medical history	○
Vital signs	○	○	○
Inclusion/exclusion criteria	○
User experience survey			○
HB Scale	○	○	○	○
VAS-HS	○	○	○	○
BDI-II	○	○	○	○
STAI	○	○	○	○
STAXI	○	○	○	○
AAQ-II	○		○	○
EQ-5D-5L/EQ-VAS	○		○	○
HRV assessment	○		○
Application adherence		○	○	○
Concomitant treatments		○	○
Adverse events		○	○

AAQ-II, Acceptance and Action Questionnaire-II; BDI-II, Beck Depression Inventory-II; EQ-5D-5L, EuroQol 5 Dimension 5 Level; EQ-VAS, EuroQol Visual Analogue Scale; HB, Hwa-byung; HRV, Heart Rate Variability; STAI, State-Trait Anxiety Inventory; STAXI, State-Trait Anger Expression Inventory; VAS-HS, Visual Analog Scale for Hwa-byung Symptoms.

7. Statistical analysis

All statistical analyses will be two-tailed at a 5% significance level and conducted under the intention-to-treat principle. Analyses will be performed using IBM SPSS Statistics 18.0 (IBM Corp., Armonk, NY, USA) and R version 4.3.1 (R Foundation for Statistical Computing, Vienna, Austria).

Baseline demographic and clinical characteristics will be summarized using means ± standard deviations for continuous variables, and frequencies (%) for categorical variables. Normality of continuous variables will be assessed using the Shapiro-Wilk test.

For the primary outcome, user experience survey results will be summarized using descriptive statistics. Questionnaire item consistency will be evaluated using Cronbach’s alpha. Secondary outcomes—changes in clinical scales and HRV parameters over Baseline, Week 2, Week 4, and Week 8—will be analyzed using linear mixed models. Models will include time as a fixed effect and participant as a random effect to account for within-subject correlations and missing data. Additionally, sensitivity analyses will be conducted to evaluate the effect of concomitant treatments by including concurrent therapy as a covariate in the linear mixed models. Safety data will be summarized as frequencies and percentages.

Missing data will be handled using multiple imputation to minimize bias, with sensitivity analyses conducted using the last observation carried forward method.

DISCUSSION AND CONCLUSION

This protocol outlines an exploratory study investigating the user experience and preliminary clinical utility of a smartphone-based stress management application in patients with HB. To our knowledge, this represents the first systematic evaluation of a KM CPG–based digital therapeutic intervention designed specifically for HB [3].

The study addresses a critical gap in HB management. Although the KM CPG for HB recommends mind–body therapies and psychotherapy [3], traditional clinical delivery faces practical constraints that limit accessibility and long-term adherence [10]. Digital health technologies provide a scalable solution to these barriers [7, 8]. By translating evidence-based KM approaches into a mobile app, we aim to expand the reach and sustainability of therapeutic interventions beyond conventional clinical settings.

ACT is chosen as the theoretical foundation of the application based on empirical evidence and clinical rationale. ACT emphasizes psychological flexibility and acceptance of internal experiences rather than symptom elimination, aligning with the emotional suppression and experiential avoidance typical of HB [6]. Previous research consistently shows the effectiveness of ACT in managing the core components of HB, including anger, depression, somatic symptoms, and emotional distress [6, 23-27]. Specifically, numerous studies show online ACT interventions reduce depressive symptoms and improve physical well-being [25-27], supporting a digital ACT approach for HB. Integration of ACT principles with KM mind–body practices, the application offers a culturally adapted approach that respects context while leveraging modern psychological frameworks.

Several methodological considerations warrant discussion. First, the single-arm design without a control group limits causal inference regarding treatment effects. However, this exploratory design is appropriate for assessing user experience and feasibility. Emphasizing qualitative user feedback alongside quantitative symptom measures will yield rich data to guide future controlled trials. Second, participants were allowed to continue their stable treatments rather than requiring treatment discontinuation. This pragmatic approach enhances external validity, reflecting real-world clinical scenarios where digital interventions act as adjuncts rather than standalone treatments. Third, including HRV as a physiological outcome warrants comment. Autonomic nervous system dysregulation is increasingly recognized as a key pathophysiological mechanism in stress-related conditions, including HB [28]. HRV offers an objective, non-invasive measure of autonomic function and may help detect changes preceding or accompanying subjective symptom improvements [22]. Combining psychological self-reports with physiological assessments offers a more comprehensive evaluation of intervention effects.

Several limitations should be acknowledged. The small sample size limits statistical power for detecting modest effects and prevents subgroup analyses. The single-center design in a Korean city may limit generalizability to other populations or settings. The 4-week intervention, suitable for initial feasibility assessment, may be insufficient to capture long-term effects or sustained behavioral changes. Additionally, the absence of a control group prevents definitive conclusions about treatment-specific effects versus non-specific factors, including attention or expectancy. Despite these limitations, this study holds important implications for clinical practice and research. If the application shows an acceptable user experience and preliminary clinical benefit, it would provide proof-of-concept for digitally delivered KM interventions in HB. The findings will guide the design of larger randomized controlled trials to establish efficacy. Beyond HB, this work may model the development of evidence-based digital therapeutics in other KM areas centered on mind–body interventions. The study also advances cultural psychiatry by exploring how culture-bound syndromes can be addressed through culturally adapted digital interventions.

In conclusion, this protocol outlines a rigorous exploratory study to provide preliminary data on the feasibility, acceptability, and potential clinical utility of a smartphone-based intervention for HB. By integrating KM approaches with contemporary digital health technologies, this work advances the modernization and accessibility of evidence-based care for this culturally significant condition. The knowledge gained will guide future definitive trials and support the broader integration of digital therapeutics into KM practice.