Feasibility and design of a novel smartphone app to deliver blood pressure-lowering high-resistance inspiratory muscle strength training

Introduction

Above-normal blood pressure (BP), defined as having a systolic BP (SBP) ≥120 mmHg and/or diastolic BP (DBP) ≥80 mmHg (1), is the primary modifiable risk factor for cardiovascular diseases, the leading cause of death in developed and developing countries. Above-normal BP is also a strong independent risk factor for chronic kidney disease and cognitive decline and dementia. Currently, ~55% of all adults in the United States have above-normal BP, with the prevalence increasing to ~70% among midlife and older adults (i.e., adults aged ≥50 years) (2) and, despite the availability of established therapies to lower BP, rates of BP control have been worsening over the past decade (3). The number of midlife and older adults is rapidly increasing, predicting a continued increase in above-normal BP-driven morbidity and mortality. Therefore, improving rates of BP control, particularly in midlife and older adults, is an important public health goal. Thus, there is a need to develop and implement novel BP-lowering strategies to decrease the risk of BP-associated chronic diseases and improve public health.

Lifestyle strategies such as losing weight, consuming a healthy diet, limiting sodium intake, and performing aerobic exercise are guideline-recommended first-line strategies to control BP in all adults with above-normal BP (1). However, adherence to these healthy lifestyle strategies is poor, with <40% of adults achieving recommended levels of each intervention (4-6). Some commonly cited barriers to achieving healthy lifestyle recommendations are time-availability, cost, transportation, and facility access (7-11). Accordingly, there is a need to establish novel BP-lowering lifestyle strategies that effectively lower BP while also overcoming these barriers to adherence.

High-resistance inspiratory muscle strength training (IMST) is a type of respiratory exercise that involves performing repeated forceful resisted inspirations through a handheld device; expiration is unimpeded (12). A single high-resistance IMST session involves performing 30 resisted breaths, requiring only 5–10 minutes per day. This makes high-resistance IMST a time-efficient intervention that overcomes the key time-availability barrier. Additionally, by using portable and affordable training devices, IMST can be performed at home or during travel, reducing transportation, facility access, and cost related barriers to adherence (13).

A high-resistance IMST protocol consisting of 30 breaths per day at a resistance of 75% maximal inspiratory pressure, performed 5–7 days per week for 6 weeks has been shown to lower BP in young adults (14,15), midlife and older adults with above-normal BP (16), and patients with obstructive sleep apnea (17,18), with BP reductions of 9 mmHg SBP and 4 mmHg DBP on average (19). Reductions in BP of this magnitude are clinically significant and would be expected to lower cardiovascular disease risk by as much as 30% if maintained (20). Importantly, this IMST protocol also has been shown to be safe, resulting in only minor adverse events. Adherence to the intervention has also been excellent, with >90% of all prescribed training sessions performed in all studies to date (21). In addition to lowering BP, high-resistance IMST also has been shown to improve markers of brain health (22), and increase whole-body exercise tolerance (23) and respiratory endurance (24), suggesting there are additional health benefits associated with this lifestyle intervention. As such, current research strongly supports the efficacy of high-resistance IMST for lowering BP.

These promising results have come from randomized controlled trials performed in clinical research centers with daily to weekly interaction between investigators and study volunteers, during which members of the study team guide study participants through the intervention. As such, instruction for using high-resistance IMST to lower BP has only been provided in highly controlled clinical research settings, requiring regular transportation to the research clinic, limiting wide-spread dissemination. Thus, there is a need to develop tools that independently guide users through a high-resistance IMST intervention, outside of the clinical research setting, in order to achieve widespread dissemination and implementation of this safe, effective, and time-efficient lifestyle intervention.

Digital health technologies have been effective for delivering other lifestyle interventions, such as aerobic exercise (13). This suggests that digital health technologies also may be effective tools to deliver and monitor high-resistance IMST interventions. In the United States, 89% of midlife adults and 76% of older adults own a smartphone (25), which is kept on their person at most times. With high smartphone utilization among the target population, it is likely that high-resistance IMST could effectively be delivered through a smartphone application (app).

Given the potential clinical impact app-delivered high-resistance IMST could have on BP control, the purpose of this study was to begin the process of developing a smartphone app that can independently deliver an IMST intervention. The goals were to collect feedback from target users (i.e., midlife and older adults with above-normal BP) to guide app development, design the conceptual model of the app, and finally to conduct beta and usability testing to show app feasibility, acceptability, and the potential for user engagement.

Methods

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013) except for registration in a database. The study was approved by the Institutional Review Board of the University of Colorado Boulder (No. IRB00000774) and individual consent was obtained from all individual participants. Individuals naive to IMST as well as participants from an IMST clinical trial (26) were recruited. Midlife and older adults who owned an Apple (Apple Inc., Cupertino, USA) or Android (Google LLC, Mountain View, USA) smartphone and reported having above-normal SBP (≥120 mmHg) were eligible to participate in a focus group and/or beta testing. A phone screening was conducted and only those who met the eligibility criteria were invited to participate.

Focus group protocol

Two focus groups were conducted prior to the development of an IMST app to gauge both general interest in the app and feedback on pre-planned app features. Formative approaches suggest five participants per focus group round are needed to guide technology development (27), we therefore sought to enroll at least five participants into each focus group. The focus groups were in-person audio-recorded sessions held in a university conference room. Each session was conducted by one moderator and two assistant moderators. The moderator facilitated the session, provided questions to guide the group, and prompted answers when necessary. One assistant moderator took notes on participants’ verbal responses, paying close attention to capture direct quotes. The second assistant moderator, who was familiar with the IMST intervention, took supplementary notes and was available to answer participants’ questions.

Focus group participants were provided with a brief introduction to the IMST device (POWERbreathe K3, POWERbreathe International Ltd., Warwickshire, United Kingdom) and the goal of the project. They were asked to share their thoughts on health apps in general, before moving on to more specific questions about what they would want to see in an IMST smartphone app. After obtaining general thoughts, feedback about the pre-planned features of the IMST app was obtained from the group. Pre-planned app features included (I) a dashboard; (II) an IMST training plan; (III) BP measurement and tracking; and (IV) notifications and reminders. The moderator used a semi-structured discussion guide (see Table 1). Research staff reviewed each focus group transcript and redacted any identifiable information. Redacted electronic transcripts of focus group discussions were analyzed using the protocol described below.

Qualitative analysis

Based on the work of Hill et al. (28,29), researchers developed a Consensual Qualitative Research (CQR) coding and data analysis protocol. In this protocol, two team members served as main assessors and a third team member served as the independent auditor. Prior to facilitating the focus groups, each team member independently responded to the focus group questions as they anticipated the participants would respond. This process illuminated the expectations of the team. All members of the team also noted any personal biases that might have made it difficult for team members to objectively assess the data. For example, if a team member had a negative view of mobile apps for health behaviors, this was noted. The CQR process involves five general steps. The first three steps were completed with individual focus group data. The last two steps examined all focus group data.

Step 1: domains

Participant responses from each transcript were reviewed independently by both assessors. These responses were used to identify domains, or key topic areas, under which all the focus group content could be categorized. Double coding, or classifying single responses into multiple domains, was allowed but kept to a minimum. If many responses were double coded, the domains were revisited to determine if they were broad enough to encompass all the responses. It was necessary that all responses given by focus group participants fit into a domain. An “other” category was acceptable, but to be used sparingly.

After independently categorizing all the focus group responses, the two assessors compared and critiqued the two lists to create a single list of domains based on consensus. The resulting product was a list of domains and the raw data (focus group responses) that fit each domain.

Step 2: core ideas

Once the list of domains was created and data was segmented into each domain, the assessors independently categorized data into multiple core ideas under each domain. These core ideas were more specific sub-categories that focused more on participant ideas for the app. After each assessor created a list of core ideas under each domain, the assessors compared the core ideas and came to a consensus. A final list was created and given to the auditor in Step 3.

Step 3: auditing of domains and core ideas

The auditor served as the check for the team. The raw data, list of domains, and list of core ideas were given to the auditor. The auditor determined if the raw data were listed under the correct domain, all important information had been abstracted from the raw data, and the wording of the core ideas was concise and reflective of the raw data. The auditor also suggested changes to the titles of each domain and whether domains should be combined or segmented. The auditor provided comments and feedback to the assessors who reviewed the feedback together. The assessors could have accepted or rejected any of the auditor’s comments, but they must have considered each one.

Step 4: cross analysis

After steps 1–3 were conducted with data from both focus groups, the assessors compared the results. All core ideas from each transcript were combined into one document and the assessors clustered the core ideas into categories, adjusting these ideas as needed. The auditor then examined the list of all categories and the core ideas within each category and provided feedback to the team. The assessors met again to review the auditor’s feedback and decide on a finalized list.

Step 5: narrative write-up

After completing the steps of the CQR assessment, E.D.J. drafted a narrative write-up of the findings.

Clickable wireframe app prototype development

After collecting and analyzing focus group feedback, the clinic-based IMST intervention was translated into a storyboard guided by Persuasive System Design (30-32). Graphic designers used these storyboards to produce a series of computer-based digital prototypes called clickable wireframes. These wireframes were intended to represent a fully functional mobile app experience. The content of the wireframes came from the domains and core ideas produced from focus group data (Figure 1).

Figure 1 Example wireframe content. (A) The app home screen which allows users to navigate to all features of the app. (B) The Log breaths start screen which users see immediately prior to starting an IMST session. This page also provides links for users to view their entire day-by-day training plan and a link to common issues or mistakes experienced during IMST sessions. (C) The Log blood pressure start screen which users see immediately prior to measuring their blood pressure. Upon hitting “start” the app provides guidance on taking valid blood pressure measurements and records the measured blood pressures. (D) The session history screen, which provides an overview of IMST history (i.e., training session frequency and intensity) and changes in blood pressure that the user has experienced. IMST, inspiratory muscle strength training.

Beta testing protocol

The sample size for beta testing was based on published guidelines suggesting 5 to 10 beta testers are needed to identify the majority of acceptability concerns (33,34). Beta testing was conducted in two rounds. Data were analyzed after round one and the prototype was adjusted before a second round of beta testing was conducted with the upgraded wireframe with new participants. Each beta test consisted of a one-on-one session between a participant and a moderator lasting approximately one hour. Participants were emailed a link to access the prototype on their personal mobile device. Participants were instructed to place their mobile device on the table where two assistant moderators could track their movement as they navigated through the prototype. The beta test moderator then guided the participant through several tasks while the assistant moderators took notes on the participant’s ability to complete each task. Participants were instructed to narrate what they were doing to capture qualitative data. The moderator also asked about how the participant liked the app’s features and design and how easy it was to use. Each beta test was audio recorded. At the conclusion of each beta test, participants were asked to complete the Systems Usability Scale (SUS) (35), a validated tool for assessing usability and acceptability of technology-based products (36,37). The SUS contains 5 questions with negative statements (e.g., “I need technical support to use this system”) and 5 questions with positive statements (e.g., “I think the system is simple and easy to use”) and responses are on a 5-pt Likert scale (1= strongly disagree, 5= strongly agree). To calculate the SUS score, we subtract 1 from responses to the positive statements and we subtract responses to negative statements from 5. The sum of all the resultant scores is then multiplied by 2.5 for the final SUS score on a 0–100 scale with 100 representing the most useable digital tool and a score of 68 being the benchmark for acceptable usability (35-37).

Participants were also asked to complete a satisfaction survey and items were scored on a 1 (extremely dissatisfied/not at all helpful) to 5 (extremely enjoyable/very relevant) Likert-scale. The survey consisted of 21 items, with a maximum satisfaction score of 105. We considered a score of 82.25–84 (65–80%) to be considered high satisfaction as this is a benchmark across industries (38).

Statistical analysis

For beta testing qualitative analysis, identifiable information was redacted from beta test transcripts prior to qualitative analysis. Transcripts and beta testing notes were reviewed to determine how many tasks participants completed without assistance. For beta testing quantitative analysis, R Statistical Software (The R Foundation for Statistical Computing, Vienna, Austria) used to calculate means and standard deviations were calculated for satisfaction questionnaire and SUS items.

Results

Participants

Two focus groups were conducted with a total of 12 participants (n=5 and n=7 for focus groups 1 and 2 respectively; Table 2) in July and August 2023. Individual beta testing sessions were conducted with a total of 9 participants (n=4 and n=5 for the first and second rounds of beta testing sessions respectively; Table 2) in December 2023 and February 2024. A total of 5 participants (age 70.0±6.5 years; 3 females, 2 males) took part in both a focus group and a beta testing session; all 5 of these participants were White, 1 was Hispanic or Latino while 4 were not Hispanic or Latino, and 3 had been enrolled in a previous IMST trial while 2 where naïve to IMST.

Focus group feedback

Among focus group participants, enthusiasm for IMST in general, and an IMST smartphone app in particular, was high. Comments in support of IMST and app-delivered instruction included:

• “If I were given this (IMST) device and the app, I would use it. If I were told it was likely to lower my blood pressure, absolutely I would use it religiously.”
• “I think this app would be fun to use. I like the idea of doing research on myself—seeing how what I do improves my health.”
• “Right now, you use the (IMST) device and it goes back in the box. With an app, it’s interactive it would elevate the device in terms of usefulness.”
• “The most powerful thing about IMST is seeing if it works. If I have a place to track my blood pressure, along with the sessions, I could see how they are linked and it would be motivating.”

The domains of content, user interface/experience, facilitators, and marketing along with core ideas were derived from focus group transcript analyses (Table 3).

Content

Across both focus groups, participants discussed the content they like and dislike in smartphone apps. The most common features that participants requested in a potential IMST app were simple instructions, a record of training data, and easy to interpret results. It should be noted that several participants emphasized the importance of simple and straightforward directions for training and using an IMST device. When discussing record keeping, participants noted they enjoy being able to track their progress over time. Progress tracking was also considered an app incentive which is discussed further below. Participants explained they would like to understand how the IMST data relates to their health and usage of the device. For example, it was mentioned that it may be beneficial to list what BP ranges are normal and high.

User interface/experience

Both focus groups included discussions about smartphone app features that affect the user experience and how they interface with the app. The main topics discussed regarding this theme included simplicity, visual appeal, diverse presentation of content, and interactivity. Similar to participants’ thoughts on IMST and device instructions, it was commonly found that the app should be very simple to use. Regarding visual appeal, a few participants felt that large bold fonts would be preferable for older adults. When discussing potential graphics for the app, each focus group had differing ideas. Many individuals in the first focus group noted they wanted a professional visual experience. One participant explained, “I don’t really care for cutesy things. You know, we’re all adults. I really, that kind of irritates me when it’s animated, cutesy, bright, sparkly colors.” In contrast, some participants in the second focus group noted that they enjoyed avatars, graphics, and badges that are utilized in popular smartphone apps such as Duolingo (Duolingo Inc., Pittsburgh, USA).

Participants also discussed multiple ways app content could be presented to fit user needs. Some suggestions for data presentation included desktop compatibility, graphical data to demonstrate progress, and downloadable data for the user or their physician. Lastly, interactivity was also discussed among focus group participants. Participants mentioned that the app should communicate with the user if training is being done correctly. For example, participants suggested the app could give guidance on breathing cadence if the user were breathing too quickly or slowly.

Facilitators

Potential features that could incentivize and facilitate the use of the IMST app were discussed. App reminders were considered a positive way to promote continued use. One participant explained, “Using (IMST phone app) incentive is, they’re reminding you. You get the reminder. You’re going to use it, and you can tell the difference.” Participants also discussed how visualizing progress (e.g., reductions in BP) and personalized training content could be incentivizing. Other facilitators included behavior change techniques like receiving positive feedback based on adherence to the program or reduction in BP and personalized content using machine learning. One participant noted that shopping apps often curate content to be direct to the user based on past behavior and this could be a motivator to continue using the app.

Marketing

Focus groups discussed potential costs, insurance coverage, advertising, and the importance of trusted sources related to the potential smartphone app. Participants thought that the retail price of an IMST digital device [$599 USD (POWERbreathe K3, 2023)] was too high, but expressed interest in an app compatible with the mechanical device which has a less expensive price point at around $70 USD. Insurance coverage was also discussed as a facilitator toward use of the device and app. One participant suggested, “there might be some cost issues for the digital. That might make it undesirable.” Another participant mentioned the app should be free after purchase of an IMST device. Several participants brought up how the smartphone app and the IMST device might be marketed to the public. It was a common thought among the participants in the second focus group that they would be more inclined to use the IMST app if it was recommended by a trusted source such as a physician.

Beta testing results

Task completion

In round one of beta testing, participants were able to navigate to almost all app components; however, several participants needed assistance to find where to log blood pressure measurements, find resources on lowering blood pressure, and find where to test their maximal inspiratory pressure (Table 4). Between rounds, the main dashboard of the prototype was modified based on this feedback. In round two, participants easily navigated to all app components, indicating a usable design had been achieved.

Satisfaction and systems usability survey result

Beta testing participants completed a short satisfaction survey and the SUS (35) about the mobile app prototype (Table 5). Some features, like instructional videos, were not added to the prototype until round two and, therefore, were not assessed in the satisfaction survey until round two. Overall, participants were satisfied with the app prototype’s features and found them useful. The prototype was also rated over the benchmark of 68 as acceptable usability in both rounds (35-37). The usability score was 81.25±9.24 from round one beta testing participants and 84.00±6.75 from round two participants, resulting in an SUS score from all beta testing participants 82.63±7.55. At the end of their beta testing session, participants in both rounds were asked if they would use the IMST mobile app if it were available on the market. All 9 beta testing participants (100%) responded affirmatively that they would use the app.

Discussion

In the current study, the feasibility and potential design of a smartphone app for delivering BP-lowering high-resistance IMST was evaluated by performing iterative focus groups and beta testing with target app users, midlife and older adults who reported having above-normal SBP. In the focus groups, enthusiasm for IMST delivered by a smartphone app was high, supporting future efforts to develop such an app. The focus groups also provided important feedback on potential app functionality and design that drove the development of app wireframes. Through beta testing, the app wireframes were found to be usable and these target users exhibited significant interest in utilizing the IMST app for lowering BP. Collectively, these findings support further development of a smartphone app for delivering high-resistance IMST as an avenue to translate this lifestyle intervention out of the clinical research setting and into the public health domain.

Research indicates that mobile apps for BP management are impactful (39,40). Mobile app interventions have clinically significant effects on SBP, improve medication adherence, and promote BP-lowering lifestyle strategies like eating a healthy diet and being physically active (39,41). Furthermore, mobile apps are acceptable intervention tools among adults with high BP (42,43). Reasons for the adoption of BP management mobile apps are to track BP over time and to be reminded to measure BP (42). Similarly, the most common combination of features in effective BP management apps are self-monitoring, educational information, automatic feedback, and reminders and alerts (40). In the current study, it was found that focus groups also wanted the IMST app to remind them to complete the IMST sessions and to measure BP, see their own BP trends, associate their session progress with BP outcomes, provide resources about other health behaviors like nutrition and physical activity, and provide educational information on the mechanisms of action of IMST (e.g., how it works).

An important limitation of this study is that we were missing important demographic information such as education level and the brand of smartphone owned by each of our participants. These factors may influence participant feedback and would shed light on the generalizability of our findings to the larger population. However, within our study we did have congruence between the demographic factors of our focus group and beta testing participants. This includes five participants who completed both arms of this study. Therefore, there is likely to be strong internal validity between the two arms of this study.

Barriers to hypertension management app adoption include app usability, and lack of evidence as to the effectiveness of the app (44). To combat these barriers, the IMST mobile app will have been rigorously tested for usability and effectiveness. Accordingly, once the app design is finalized, the next step will be to assess the efficacy of app-delivered IMST via randomized controlled trials. For example, app-delivered IMST could be compared to home BP monitoring as a usual care control for lowering BP and improving other markers of cardiovascular health. After the efficacy of app-delivered IMST for lowering BP has been established, dissemination and implementation research can begin. This should include testing app-delivered IMST in underserved groups with unequal access to health care. It is anticipated that, once finalized, this combination of a novel and effective IMST intervention with a rigorously tested mobile app will be a potent tool for controlling BP.

Conclusions

Overall, above-normal BP is a highly prevalent risk factor for developing cardiovascular diseases and other chronic health problems. Despite the availability of efficacious therapies for lowering BP, rates of BP control remain poor, in part due to low adherence to established interventions. IMST delivered via a smartphone app is a low-barrier lifestyle strategy that has high potential to support sustainable BP management, which can be broadly disseminated into the general population.

Acknowledgments

None.

Footnote

Data Sharing Statement: Available at https://mhealth.amegroups.com/article/view/10.21037/mhealth-24-33/dss

Peer Review File: Available at https://mhealth.amegroups.com/article/view/10.21037/mhealth-24-33/prf

Funding: This work was supported by the National Institutes of Health (R41HL167375 to D.R.S. and K01HL153326 to D.H.C.).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://mhealth.amegroups.com/article/view/10.21037/mhealth-24-33/coif). K.J.N. is employed as a Scientist at Klein Buendel Inc. A.N.B. is employed as a Research Project Coordinator at Klein Buendel Inc. S.E.F. is employed as the Creative Director of Klein Buendel Inc. D.R.S. was the PI for NIH grant R41HL167375. This grant provided the funds to support the research presented in this manuscript. D.H.C. received salary support for this research from NIH grant K01HL153326. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Institutional Review Board of the University of Colorado Boulder (No. IRB00000774) and individual consent was obtained from all individual participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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