App-Based Versus Standard Six-Minute Walk Test in Pulmonary Hypertension: Mixed Methods Study

Dario Salvi, Emma Poffley, Lionel Tarassenko, Elizabeth Orchard, Dario Salvi, Emma Poffley, Lionel Tarassenko, Elizabeth Orchard

Abstract

Background: Pulmonary arterial hypertension (PAH) is a chronic disease of the pulmonary vasculature that can lead to heart failure and premature death. Assessment of patients with PAH includes performing a 6-minute walk test (6MWT) in clinics. We developed a smartphone app to compute the walked distance (6MWD) indoors, by counting U-turns, and outdoors, by using satellite positioning.

Objective: The goal of the research was to assess (1) accuracy of the indoor 6MWTs in clinical settings, (2) validity and test-retest reliability of outdoor 6MWTs in the community, (3) compliance, usability, and acceptance of the app, and (4) feasibility of pulse oximetry during 6MWTs.

Methods: We tested the app on 30 PAH patients over 6 months. Patients were asked to perform 3 conventional 6MWTs in clinic while using the app in the indoor mode and one or more app-based 6MWTs in outdoor mode in the community per month.

Results: Bland-Altman analysis of 70 pairs of conventional versus app-based indoor 6MWDs suggests that the app is sometimes inaccurate (14.6 m mean difference, lower and upper limit of agreement: -133.35 m to 162.55 m). The comparison of 69 pairs of conventional 6MWDs and community-based outdoor 6MWDs within 7 days shows that community tests are strongly related to those performed in clinic (correlation 0.89), but the interpretation of the distance should consider that differences above the clinically significant threshold are not uncommon. Analysis of 89 pairs of outdoor tests performed by the same patient within 7 days shows that community-based tests are repeatable (intraclass correlation 0.91, standard error of measurement 36.97 m, mean coefficient of variation 12.45%). Questionnaires and semistructured interviews indicate that the app is usable and well accepted, but motivation to use it could be affected if the data are not used for clinical decision, which may explain low compliance in 52% of our cohort. Analysis of pulse oximetry data indicates that conventional pulse oximeters are unreliable if used during a walk.

Conclusions: App-based outdoor 6MWTs in community settings are valid, repeatable, and well accepted by patients. More studies would be needed to assess the benefits of using the app in clinical practice.

Trial registration: ClinicalTrials.gov NCT04633538; https://ichgcp.net/clinical-trials-registry/NCT04633538.

Keywords: GPS; cardiology; exercise test; mobile apps; pulmonary hypertension.

Conflict of interest statement

Conflicts of Interest: None declared.

©Dario Salvi, Emma Poffley, Lionel Tarassenko, Elizabeth Orchard. Originally published in JMIR mHealth and uHealth (https://mhealth.jmir.org), 07.06.2021.

Figures

Figure 1
Figure 1
Architecture of the SMWT system: (a) patients’ app, (b) physiologists’ app, and (c) web interface for physicians.
Figure 2
Figure 2
Bland-Altman plot of the difference between the 6-minute walk test distance as measured by the app in indoor mode and as observed by the physiologist during a 6-minute walk test in clinic. 6MWD: 6-minute walk test distance.
Figure 3
Figure 3
Absolute difference of the 6-minute walk test distance as measured by the physiologist and as measured by the mobile phone app in indoor mode. 6MWD: 6-minute walk test distance; 6MWT: 6-minute walk test.
Figure 4
Figure 4
Bland-Altman plot of the difference between the 6-minute walk test distance as observed by the physiologist during a 6-minute walk test in clinic and as measured by the app in outdoor mode within 7 days of the clinic test. 6MWD: 6-minute walk test distance.
Figure 5
Figure 5
Outdoor, community-based 6-minute walk test distances over time of the top 5 patients who contributed with the most 6-minute walk tests. 6MWD: 6-minute walk test distance.
Figure 6
Figure 6
Histogram of the number of community-based 6-minute walk tests per patient per month. 6MWT: 6-minute walk test.
Figure 7
Figure 7
SpO2 and heart rate for a test where the SpO2 increases during exertion and the heart rate decreases. SpO2: peripheral oxygen saturation.
Figure 8
Figure 8
Bland-Altman plots of the differences between 19,356 matched samples of SpO2 and heart rate values measured simultaneously by two different pulse oximeters during 38 6-minute walk tests (6MWTs). SpO2: peripheral oxygen saturation.

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Source: PubMed

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