Evaluation of a New 6 Minute Walk Test Smartphone App in Patients With Pulmonary Hypertension

Pulmonary Arterial Hypertension (PAH) is a progressive illness that; if not diagnosed early or left untreated, can be a severe life limiting condition . It is a chronic disease of the pulmonary vasculature, with vascular proliferation and remodelling of the small pulmonary arteries leading to a progressive increase in pulmonary vascular resistance (PVR). This can ultimately lead to right heart failure and premature death . The predominant symptom of PAH is dyspnoea on exertion, with a decrease in exercise capacity, and most patients present with this symptom .

PAH is an uncommon condition, affecting about 6000 patients in the United Kingdom , and due to its rarity, the NHS commissions 7 centres to care for patients with PAH. Oxford University Hospital NHS Foundation Trust works closely with the Royal Brompton Hospital to provide care for patients with PAH in Oxfordshire and the surrounding region.

The six-minute walk test (6MWT) is a standard method for measuring exercise capacity in patients with cardiopulmonary disease such as PAH. The 6MWT measures how far a patient can walk in 6 minutes. Walking is an activity performed every day, by most patients except for those most severely limited. By assessing patients' ability to exercise, the 6MWT provides a global assessment of respiratory, cardiovascular, neuromuscular and cognitive function. The 6MWT does not differentiate what limits the patient, nor does it assess maximal exercise capacity. Instead, the 6MWT allows the patient to exercise at a daily functional level, and is a useful tool for assessing changes after a therapeutic intervention, and correlates with a subjective improvement in dyspnoea .

In PAH the 6MWT is used to evaluate patients' response to treatment, with an increase in 6MWT distance of greater than 42m being considered a clinically significant improvement . Furthermore, change in 6MWT distance correlates with VO2 max (maximum rate of oxygen consumption measured during exercise), NYHA class (classification of patients' daily limitation) and mortality in PAH patients, providing an objective assessment of disease progression, prognosis and response to treatment. It is a universally accepted test as it is safe and easily performed by the patient.

The 6MWT has become the primary end-point for many trials, and as a surrogate invalidated survival outcome for all placebo controlled trials of PAH therapy . It is used by regulatory bodies to determine whether a treatment should be approved. However, there is much discrepancy between whether it is the total distance walked at baseline prior to treatment, a decrease in total distance walked over time or a percentage increase in walking distance that correlates best with survival outcome. The investigators hypothesize that it is all 3 of these measures, and that having a validated and more reproducible 6MWT would help assess patients and guide treatment strategies better.

The test is usually performed in hospital, by walking along a hospital corridor, where many factors on the day of the test can affect patients' performance, including tiredness, unfamiliarity with the environment or anxiety. The test typically requires 2 physiologists to monitor the distance walked by the patient, their oxygen saturations by pulse oximetry, and to record symptoms felt during the test. To improve the assessment of a patient's exercise capacity using a 6MWT, the investigators hypothesize that the test would reflect more the patient's functional status, if it were undertaken prior to the hospital outpatient appointment. The investigators have designed a mobile-phone "app" that allows patients to perform the 6MWT within the patient's home environment. This is felt to be more appealing to the patients, and would reduce the time spent in hospital on the day of their outpatient appointment.

The 6MWT app is categorised as a mobile-health (m-health) system, a form of telehealth whereby healthcare is delivered at a distance using smartphones. By utilizing biometric collection devices such as a pulse oximeter monitor with Bluetooth capability, m-health can be used to measure the oxygen saturation levels in the blood from patients, and transmit them to a secure server, allowing them to be reviewed by cardiologists and other healthcare professionals.

The evidence-base for m-health as a tool for assessing physical fitness is increasingly established. This new approach not only offers the opportunity for reliable collection of data, but provides the infrastructure to do this at scale and will allow decisions on patients' health to be based on more frequent and more accurate information.

There are no known risks to undertaking a 6MWT in the community as walking is an activity of daily living, and all patients are encouraged to walk daily.

The population to be studied will be those with PAH who are currently assessed with a 6MWT. Once the app has been validated, patients with any type of cardiorespiratory disease who are assessed with a 6MWT could use the app, for example patients with chronic obstructive airways disease, heart failure, renal failure, and pre-transplantation work up.

The 6MWT results form part of the NHS data set collected by NHS England for patients with PAH, and it would be beneficial to have a more reproducible assessment, whose results could be compared between the 7 centres providing care for these patients. At present, there is much variability in how 6MWTs are performed between units, and the app would reduce this variability.

The 6MWT has been undertaken at the John Radcliffe hospital for 5 years and the investigators will also retrospectively analyse the data from the 6MWT that have previously been undertaken. The data on patients will be pseudo-anonymised, i.e. no personal information like name, surname or address, will be used, but the investigators will keep date of birth, gender, diagnosis, dates and results of the 6MWT, date and causes of death. As part of the clinical care team, reviewing the data is part of the normal standard of care for patients with PHT. The data is collected on the Solus cardiac reporting system and can be extracted from this database. The data will be pseudo-anonymised by the Principle Investigator for analysis, and then shared with the wider research team. The data will be analysed to look at distance walked, and change in oxygen saturation and heart rate during the test. The investigators will analyse the data over time, to look for changes in these parameters and correlate these with outcome data, i.e. mortality.

The study aims at demonstrating that patients are able and willing to use the app for the 6MWT and the measurements obtained by the app are comparable to the ones obtained in hospital.