Evaluation of a New 6 Minute Walk Test Smartphone App in Patients With Pulmonary Hypertension (The 6-APP Study)

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.