Long term oxygen therapy (LTOT) increases the life span of patients with chronic obstructive pulmonary disease who have low oxygen levels. However, even when on oxygen therapy at home, from time to time patients still have low oxygen levels especially when walking which can be harmful.

The investigators have designed a new system of delivering oxygen to overcome the above problem. The system measures the oxygen saturations of a patient and subsequently adjust the flow of oxygen to meet a pre-set oxygen saturation target.

Hypothesis: the investigators intelligent oxygen therapy system is better at reducing low levels of oxygen during a 6 minute walk than usual ambulatory oxygen for patients with chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis.

For patients with chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF), disease progression leads to hypoxic respiratory failure necessitating the use of long-term oxygen therapy (LTOT). However a number of studies have shown that despite being on LTOT at home many patients with COPD still experience episodes of intermittent hypoxia (reduction in oxygen saturation <90%). These episodes occur during rest, sleep, talking, walking and sleep. These episodes of intermittent hypoxia can be harmful as they can lead to the development of ischaemic heart disease, induce pulmonary hypertension and affect brain function.

In order to reduce these episodes of intermittent hypoxia, the investigators have designed an auto-titrating, closed-loop oxygen system which automatically adjust the flow of oxygen to match a given oxygen saturation target. This allows individualisation and optimisation of oxygen therapy for every patient.

Mechanism of action:

A pulse oximeter is attached to the ear or finger of a patient. This send the oxygen saturation reading to a control centre (located in a mobile phone). The control centre is pre-programmed to maintain a set oxygen saturation target. The control centre outputs a signal to a flow meter which regulated the outflow of oxygen.

In this study, the investigators will recruit patients with COPD on LTOT and patients with IPF on LTOT or ambulatory oxygen to undergo three 6 minute walk tests (6MWT). The first will be on air (practice walk), the second will be on their usual ambulatory oxygen and the third on the auto-titrating oxygen system. The order of the second and third walks be randomly selected. The patient will be blinded as to which type of oxygen they will be receiving in the second and third walk.

Hypothesis: the investigators iO2t system is better at preventing and treating oxygen desaturations that occur during a 6MWT than usual fixed flow ambulatory oxygen therapy

Inclusion Criteria:

• COPD and on LTOT
• IPF on LTOT or ambulatory oxgen

Exclusion Criteria:

• Unable to mobilise for a 6 minute walk test
• Unable to consent to study,
• Partial pressure of oxygen < 6.0 kilopascals (kPa) or Partial pressure of carbon dioxide > 8kilopascals on air,
• Exacerbation of the underlying lung disease in the previous 4 weeks
• Unstable cardiovascular disease (e.g. arrhythmia, hypertension/hypotension or angina)
• Pregnancy