This is an open-access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work, first published in JMIR mHealth and uHealth, is properly cited. The complete bibliographic information, a link to the original publication on https://mhealth.jmir.org/, as well as this copyright and license information must be included.
Mobile health interventions are intended to support complex health care needs in chronic diseases digitally, but they are mainly targeted at general health improvement and neglect disease-specific requirements. Therefore, we designed TrackPAD, a smartphone app to support supervised exercise training in patients with peripheral arterial disease.
This pilot study aimed to evaluate changes in the 6-minute walking distance (meters) as a primary outcome measure. The secondary outcome measures included changes in physical activity and assessing the patients’ peripheral arterial disease–related quality of life.
This was a pilot two-arm, single-blinded, randomized controlled trial. Patients with symptomatic PAD (Fontaine stage IIa/b) and access to smartphones were eligible. Eligible participants were randomly assigned to the study, with the control group stratified by the distance covered in the 6-minute walking test using the TENALEA software. Participants randomized to the intervention group received usual care and the mobile intervention (TrackPAD) for the follow-up period of 3 months, whereas participants randomized to the control group received routine care only. TrackPAD records the frequency and duration of training sessions and pain levels using manual user input. Clinical outcome data were collected at the baseline and after 3 months via validated tools (the 6-minute walk test and self-reported quality of life). The usability and quality of the app were determined using the Mobile Application Rating Scale user version.
The intervention group (n=19) increased their mean 6-minute walking distance (83 meters, SD 72.2), while the control group (n=20) decreased their mean distance after 3 months of follow-up (–38.8 meters, SD 53.7;
Besides the rating providing a valuable support tool for the user group, the mobile intervention TrackPAD was linked to a change in prognosis-relevant outcome measures combined with enhanced coping with the disease. The influence of mobile interventions on long-term prognosis must be evaluated in the future.
ClinicalTrials.gov NCT04947228; https://clinicaltrials.gov/ct2/show/NCT04947228
The circulatory disorders of peripheral arteries due to atherosclerotic lesions, also known as peripheral arterial diseases (PAD), are the third most frequent manifestations of cardiovascular diseases (CVD) after coronary and cerebrovascular arterial diseases [
A primary goal in CVD treatment is to slow down disease progression and avoid major adverse cardiac or limb events. Nonetheless, patients with PAD lag behind those with coronary artery disease (CAD) in terms of optimal treatment patterns [
The individual restrictions in the daily life of patients with PAD are more important than statistical facts regarding mortality and morbidity. Intermittent claudication causes a progressive reduction of the pain-free walking distance (PWD), and it is an expression of worsening PAD [
Supervised exercise therapy (SET) is a cornerstone in the conservative management of intermittent claudication [
Mobile health (mHealth) technologies increase incentives and provide digital support for patients with PAD on several treatment levels [
We developed a smartphone app named TrackPAD [
The TrackPAD pilot study aimed to answer the following research questions:
Is it feasible to implement the app into everyday practice?
Is TrackPAD suitable for recording patients’ daily and weekly SET performance?
Does the TrackPAD improve the prognosis of PAD and related QoL?
The primary outcome was defined as the change in the 6-minute walking distance using a standardized protocol at baseline and after 3 months of follow-up [
Aside from the 6-minute walking distance being objective and well-validated with respect to walking ability predicting mobility loss and mortality in PAD, it has an excellent test-retest reliability [
The secondary outcome measures were changes in physical activity and assessing the patient’s PAD-related QoL via PAD-QoL. The PAD-QoL questionnaire is a validated PAD-specific questionnaire [
This paper reports the results from the pilot study, including TrackPAD app usability tests for the target group (patients with PAD). In preparation for the pilot study, we conducted a recently published questionnaire study [
The TrackPAD pilot study was designed as a 2-armed randomized controlled trial and included patients with diagnosed and symptomatic PAD. It is a closed parallel-group trial (control and intervention groups were assessed simultaneously), with blinded assessors and face-to-face assessment components and a 3-month follow-up. Besides information regarding the pilot study, a call for participation was announced in a local newspaper (Westdeutsche Allgemeine Zeitung, local section for Essen and Duisburg) with the contact information provided, including the phone number and email address (trackPAD@uk-essen.de). In addition, potential participants were actively solicited during their outpatient clinic visits or their inpatient stay at the Department of Cardiology and Vascular Medicine, University Clinic of Essen. Willing patients were asked to register for the pilot trial at the front desk of the outpatient clinic.
After screening based on inclusion and exclusion criteria and obtaining written informed consent, participants were randomized into 2 groups by the Center for Clinical Studies in Essen using the TENALEA software. The control group included participants with standard care and no further mobile intervention. The intervention group included participants receiving standard care and additional mHealth-based self-tracking of their physical activity using TrackPAD. The participants were stratified based on their 6-minute walking test (distances less than 362 meters, between 362 and 430 meters, and more than 430 meters) to ensure an even distribution of the walking speed between the two groups. After the randomization process, participants were not replaced, regardless of the reason for exclusion.
Both groups were strongly advised to continue with their SET according to the current standard guidelines [
The baseline and follow-up examinations took place at the Department of Cardiology and Vascular Medicine outpatient clinic. They included a 6-minute walking test and a measurement of the ankle-brachial index (ABI). The ABI Measurements were conducted using a Doppler probe on the tibial and anterior artery locations. According to the current European Society of Cardiology (ESC) guideline, the highest value was used for calculation and divided by the highest systolic brachial Doppler pressure [
The patients were asked to fill out a questionnaire package at both time points, including self-reported physical activity, demographic characteristics, and the PAD-QoL questionnaire. The PAD-QoL was translated into German by a native speaker and was pretested on 5 PAD patients not included in the study sample. The pretest did not reveal the need for any adjustments.
Main inclusion criteria were diagnosed and symptomatic PAD of the lower extremities, defined as Fontaine stage IIa or IIb. Fontaine stage IIa indicated intermittent claudication with a walking distance of more than 200 meters, whereas Fontaine stage IIb indicated intermittent claudication with a walking distance of fewer than 200 meters [
18 years of age or older
Diagnosis of lower extremity PAD based on either an ABI greater or equal to 0.9 in at least one leg, invasive or noninvasive imaging of stenotic lower extremity artery disease, or endovascular or surgical revascularization of lower extremity artery disease
PAD Fontaine stage 11a/b
Smartphone with the capacity to use TrackPAD (Android version greater than 5.0 or IOS version greater than 11.0)
Written informed consent prior to any study procedures, including a specified follow-up evaluation
Best-medical treatment in the last 2 months per standard guidelines
Wheelchair-bound, use of walking aid, or walking impairment due to another cause than PAD
Below or above-knee amputation
Acute or critical limb ischemia
PAD Fontaine Stage I, III, or IV
No German knowledge
Severe cognitive dysfunction
Congestive heart failure with NYHA III-IV symptoms
Active congestive heart failure requiring the initiation or up-titration of diuretic therapy
Angina pectoris with CCS class 3 to 4 symptoms, myocardial infarction, or stroke in the last 3 months
Active arrhythmia requiring the initiation or up-titration of anti-arrhythmic therapy
Severe valve disease
The mobile intervention TrackPAD was designed by Rocket Apes GmbH. There were no associations between the authors and the developer. Moreover, TrackPAD was only designed for study purposes and not commercial use. We did not change any content during the study period, and all content was frozen during the trial. The only dynamic component was the leaderboard, which was adjusted based on the training sessions performed by the participants. The participants set their weekly goal of SET units at the beginning of each week. As recommended by the 2017 ESC guideline [
Main views of the TrackPAD-app.
To account for a PAD-tailored solution, we included the following features (
Weekly goal adaptation: The app suggested a new weekly goal using an internal algorithm based on the completion rate of a user’s SET units during the previous week.
Feedback after SET units: The feedback after each SET unit contained PAD-specific information regarding leg pain levels, breathing, and overall exhaustion. Patients had to respond by choosing between 1 (minimum leg pain, no restriction in breathing, or minimum exhaustion) and 10 (maximum leg pain, maximum restriction in breathing, or maximum exhaustion) for each item.
Claudication reminder: Each SET unit started with a short reminder that the walking pace and incline must be adapted to reach a certain level of claudication to extend the PWD sustainably. The reminder popped up when each new SET unit was initiated and needed to be actively confirmed.
Personal achievements: The personal progress of each user was recorded to unlock achievement medals (eg, a notable increase in users’ physical activity, activity performed during public holidays, or successes like an increase of performed SET units per week).
Leaderboard: The leaderboard contained different categories (ie, number of steps in single training sessions, number of completed training sessions, total minutes of physical activity, and percent increase of physical activity). The different leaderboards showed individual placements compared to other users using TrackPAD.
Patient events: Information on upcoming Department of Cardiology and Vascular Medicine patient events focusing on vascular diseases were stored and easily accessible via the main menu.
PAD‑FAQ: An FAQ section was included to address common technical issues, important contact information, and general training advice. Instructions in case of increasing or new pain during the training were also included.
The local ethics committee of the University of Duisburg-Essen (18‑8355‑BO) approved this study. Written informed consent was collected from each participant before any study procedures, and contact information was delivered to each participant. Any changes will be communicated to the ethics committee. The pilot study started at the beginning of November 2018 and ended in March 2019.
Data were stored on an encrypted European server. No personalized data were shared with the developer, and they were only accessible to the study team.
To allow for missing data and loss to follow up, we aimed to recruit 23 to 25 participants per study arm. The results achieved an estimated power of
After screening and randomization, we included 46 participants in the pilot study, of whom 22 (48%) were randomized to the intervention group, and 24 (52%) were randomized to the control. During the follow-up, 7 (15%) participants dropped out, mainly due to personal reasons. For example, 5 (11%) participants withdrew due to the severe illness of a close relative, and 2 (4%) participants dropped out as a result of either worsening of a nonstudy-related disease or death (
Quantitative development of screened patients including reasons for dropouts and exclusions.
Patient characteristics at baseline.
|
Intervention group (n=19) | Control group (n=20) | |
Age (years), mean (SD) | 64.6 (9.8) | 65.6 (7.7) | .72 |
Sex (male), n (%) | 12 (63) | 9 (45) | .34 |
Obesity (BMI > 30 kg/m2), n (%) | 5 (26) | 1 (5) | .16 |
Prior MIa, n (%) | 2 (11) | 3 (15) | .85 |
Hypertension, n (%) | 12 (63) | 16 (80) | .41 |
Diabetes, n (%) | 4 (21) | 6 (30) | .21 |
Hyperlipidemia, n (%) | 12 (63) | 13 (65) | .42 |
Previous peripheral intervention, n (%) | 8 (42) | 5 (25) | .26 |
Previous peripheral bypass graft, n (%) | 3 (16) | 5 (25) | .68 |
Previous PCIb, n (%) | 4 (21) | 6 (30) | .69 |
Heart failure, n (%) | 2 (11) | 3 (15) | .85 |
Coronary arterial disease, n (%) | 6 (32) | 9 (45) | .51 |
Active/Former smoker, n (%) | 6/11 (32/58) | 8/10 (40/50) | .89 |
Fontaine stage IIa, n (%) | 12 (63) | 14 (70) | .44 |
Fontaine stage IIb, n (%) | 7 (37) | 6 (30) | .85 |
6-minutes walking distance (meters), mean (SD) | 407 (80.8) | 390.1 (66) | .35 |
ABIc | 0.75 (0.21) | 0.73 (0.18) | .46 |
Reported physical activity (days per week), mean (SD) | 2.4 (1.4) | 2.3 (1.9) | .35 |
aMI, myocardial injury.
bPCI, percutaneous coronary intervention.
cABI, ankle-brachial index.
Of the 20 participants who increased their 6-minute walking distance at follow-up, 18 (90%) belonged to the intervention group using TrackPAD. The remaining participant in the intervention group did not change his covered distance at follow-up. In contrast, except for 2 (10%) participants, 18 (90%) participants in the control group showed decreased 6-minute walking distance at follow-up.
The mean distance covered in the 6-minute walking test showed a significant increase in the intervention group overall (83.0 meters, SD 72.2), whereas the mean walking distance of the control group decreased on average (–38.8 meters, SD 53.7;
Both Fontaine stages showed similar trends, but the mean distance increase for the less progressed Fontaine stage IIa was more pronounced (intervention group: 97.0 meters, SD 78.6 vs. the control group: –35.3 meters, SD 55.9;
TrackPAD was linked to a mean increase in the 6-minute walking distance of the intervention group, regardless of the Fontaine stage (95% CI 48.2-117.8). In contrast, the control showed either a slight or missing increase (95% CI –63.9-3.6). In total, the difference between both means was 121.8 meters (Fontaine stage IIa: 132.3 meters; IIb: 106.4 meters). Depending on the Fontaine stage, this resulted in a 17% (IIb) to 23% (IIa) increase of the covered distance at follow-up (
Differences in the 6-minute walking distance within and between study and control group after 3 months of follow-up.
|
Fontaine IIa (n=26) | Fontaine IIb (n=13) | Fontaine IIa, IIb (n=39) | |||
Study (n=12) | Control (n=14) | Study (n=7) | Control (n=6) | Study (n=19) | Control (n=20) | |
Difference in meana (meters) | 97.0 | –35.3 | 59.4 | –47.0 | 83.0 | –38.8 |
Median (meters) | 89.9 | –22.0 | 30.0 | –22.5 | 60 | –22.0 |
SD (meters) | 78.6 | 55.9 | 57.0 | 52.2 | 72.2 | 53.7 |
95% CIb (meters) | 47.0-147.0 | –67.5-3.0 | 6.3-111.8 | –101.8-7.8 | 48.2-117.8 | –63.9-3.6 |
Difference in mean between both groups (meters) | 132.3 | 106.4 | 121.8 | |||
SD (meters) | 135.5 | 71.6 | 176.4 | |||
95%-CIc (meters) | 75.5-189.0 | 39.2-172.8 | 80.2-163.4 | |||
.01 | .01 | .01 |
a Positive mean indicates an improvement.
b.Difference between study and control group of the sub group.
cThe true difference of the population between both groups.
A difference-in-difference regression with fixed effects for time (accounting for a progression of PAD) and individual participant (accounting for unobserved heterogeneity between the participants) estimating the percentage change in the treatment effect showed that the effect of receiving access to TrackPAD increased the 6-minutes walking distance about 28% (SE 0.04). This effect was significant to a confidence level of 99%.
The PAD-related quality of life (PAD-QoL) was assessed by the PAD-QoL questionnaire at baseline and follow-up. No relevant differences were observed at baseline between both groups. However, at follow-up, significant changes were noted in 3 factors of the PAD-QOL, with the most extensive change evident in the “symptoms and limitations in physical functioning.” The intervention group reported reduced limitations in their daily activity: “I have had to greatly reduce my activities because of my PAD” (Q1, intervention group: –1.6 meters, SD 1.4 vs control group: –0.1 meters, SD 1.0;
Excerpt of results from the PAD-QoL questionnaire survey [
Overall, changes in the PAD-QoL over the 3 months of follow-up showed a less intense subjective symptom perception and fewer limitations in daily life among the intervention group.
To compare the two groups in terms of physical endurance at baseline, we recorded the reported physical activity. Both groups did not differ in days of physical activity per week (intervention group: 2.9 days per week, SD 2.8 vs control group: 2.4 days per week, SD 1.9;
At follow-up, 37 (80%) participants reported an increase in their weekly physical activity (intervention group: n=15, 33% vs control group: n=16, 35%), resulting in a comparable rise in physically active days per week in both groups (intervention group: plus 0.3 days per week, SD 3.5 vs control group: plus 0.4 days per week, SD 2.6;
We considered intervention participants as active users if they performed at least 1 weekly training. During week 1, every participant was active. A dip from 19 (100%) to 14 (74%) active users was observed in week 2, increasing to 17 (89%) active users in week 3. During the following weeks, the activity remained stable, with 14 to 15 (70% to 75%, respectively) active users from week 5 to 12 (
TrackPAD-app usage of the intervention group during the 12 weeks of follow-up.
Week | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
Total training sessions (units)a | ||||||||||||
Active userb (n) | 19 | 14 | 17 | 16 | 15 | 15 | 15 | 14 | 15 | 14 | 14 | 15 |
Intervals per training session (units), meanc (SD) | 2.5 (2.8) | 2.8 (2.2) | 2.6 (1.7) | 2.0 (1.2) | 1.8 (1.2) | 2.3 (1.6) | 2.7 (2.8) | 2.4 (2.0) | 2.2 (2.3) | 2.1 (1.9) | 2.5 (2.1) | 2.7 (4.1) |
aTotal number of recorded training sessions for the respective week as assessed by the TrackPAD-App.
bActive user with at least one training interval in the corresponding week.
cMean number of intervals during one training session. Each training session could be paused if necessary, resulting in each training session being subdivided into several intervals.
The reasons for discontinued TrackPAD use by the nonactive users (n=5, 26%) from week 5 onward were assessed at follow-up. Reasons for discontinued TrackPAD use were related to personal circumstances (n=3, 16%) and technical issues (n=2, 11%). Of the 2 participants who stopped using TrackPAD for personal reasons, 1 was due to the illness of a close relative, and the other lost interest. One participant stopped using TrackPAD due to reported interference between the TrackPAD app and their Samsung Health app, and another participant stopped the training sessions due to several sequential app crashes (
The vast number of questions regarding functionality, aesthetics, and informational content of TrackPAD were reported as positive to extremely positive (4 or 5 stars out of 5;
Participants' statements regarding the trackPAD app in terms of functionality, aesthetics and information according to the user version of the Mobile Application Rating Scale [
The users’ feedback also included questions regarding the perceived impact of the TrackPAD with respect to their PAD disease (
Most users evaluated the app in all of the 3 categories positively. Only 3 (17%) users would “maybe” or are “unlikely” to recommend the app to people with existing PAD disease. Supporting the positive evaluation illustrate in Panel A (
App rating of the study group after study end according to the user version of the Mobile Application Rating Scale [
The data underlying this article will be shared at reasonable request to the corresponding author.
The implementation of novel technologies, specifically mobile interventions, can substantially change the landscape for the treatment of CVD [
SET is one of the most relevant interventions in the conservative treatment of PAD, but barriers to exercise are still high. Besides low motivational aspects, intermittent claudication limits the sustainability of regular SET performance. Moreover, the requirements of primary care for patients with PAD focus on other priorities other than CVD in general [
Mobile technologies are increasingly used for health purposes, even among older adults who have demonstrated a lower uptake of technologies compared to younger people [
In this study, we gathered TrackPAD use input from the patients’ perspective, and we observed a high level of user acceptance. Overall, we found satisfaction in terms of functionality, aesthetics, and informational content. Studies combining eHealth and PAD are rare, but the same trend of mobile technology user acceptance was observed in patients with noncommunicable diseases. A review of eHealth interventions for cancer survivors showed mobile interventions are promising tools [
Improvement was demonstrated through the visual information within TrackPAD and the clear assignment of pictograms or pictures. The weakness of the gestural concept resulted from the advanced age of the user group, which is often inexperienced in using mHealth and requires an age-adapted presentation [
Since we designed a platform for both iOS and Android, some technical issues occurred due to the different technical implementations of the provider. The various mechanisms for counting steps presented a considerable challenge in designing a comparable app for both platforms. Depending on the manufacturer, step counts work either over a physical hardware mechanism and a software-based solution. This issue might become less relevant when it comes to personal use [
The disadvantages of simple activity tracking are known and common limitations in studies. The performance of systems trained with data in the laboratory setting substantially deteriorates when tested in real-life conditions [
Comparing the 6-minute walking distance between both groups in our study, we saw a significant increase in the mean walking distance of 80 meters in the intervention group using TrackPAD. Remarkably, we did not find any decrease in the walking distance within the intervention group, whereas 90% (n=18) of the control group did worse at follow-up compared to baseline. One reason for the longer walking distance might be because of the younger age of the study participants. Previous studies reported a mean age of more than 70 years, whereas the intervention group using TrackPAD had a mean age of 64. The higher increase may also be due to comparatively minor restrictions since two-thirds of the participants were classified as Fontaine stage IIa (PWD of more than 200 meters). The ease of initiating exercise among the Fontaine stage IIa patients with PDA compared to patients with higher Fontaine stages might be linked to better endurance during exercise and higher motivation in general. Moreover, the small sample size allows for substantial individual changes within the intervention group, leading to an upward deviation.
Although the covered distance in the 6-minute walk test only increased significantly in the intervention group, the self-reported physical activity increased in both groups at follow-up. An accurate assessment of physical activity using the PDA-QoL questionnaire seems questionable in the entire study population and has previously been described as a common issue [
We also observed an increase in PAD-QoL regarding “symptoms and limitations in physical functioning” within the intervention group. The association between increased physical activity and an increased PAD-QoL has been reported in other studies [
The main limitation of this study was the small sample size of the intervention group. Since we have analyzed some patient characteristics (ie, Fontaine stage IIa and IIb) separately, the sample size per group decreased even further. However, the Fontaine stage allowed us to control for the differences in the participants’ physical capability. Although we saw a relevant change in the primary outcome variable after follow-up, recordings of background activity during the follow-up period were available due to privacy restrictions. Based on the study design of this pilot, no blinding of the study participants was feasible, and motivational differences must be considered. Further research is needed to address this issue.
Using the smartphone–based tool TrackPAD, we found a significant increase in the mean 6-minute walking distance at follow-up, indicating a prognostically relevant change in walking ability in patients with moderate PAD. TrackPAD also bolstered a shift in the subjective symptom perception and fewer noticed limitations in terms of PAD-QoL. Thus, the TrackPAD app seems feasible and suitable for the target group of patients with PAD in terms of SET performance. Participants substantially valued the experience of using an app in the management of their care. Still, a further adaption of the visual presentation and the gestural concept that follows a patient-centered approach is needed.
CONSORT-eHEALTH checklist (V 1.6.1).
ankle-brachial index
coronary artery disease
European Society of Cardiology
mobile health
peripheral arterial disease
peripheral arterial disease–related quality of life CVD: cardiovascular disease
pain-free walking distance
quality of life
supervised exercise training
This work was supported by the Stiftung Universitätsmedizin (D/106-21637) and the Deutsche Forschungsgesellschaft (DFG; DFG 969RA/12-1).
None declared.