People with interstitial lung disease (ILD) are frequently prescribed ambulatory oxygen, to increase oxygen levels in the blood during daily activities. The best way of delivering this type of oxygen has not been established. The aim of this study is to compare two devices for delivering oxygen in people with interstitial lung disease - the traditional method using portable cylinders and a newer method using a portable concentrator. The investigators hypothesise that oxygen levels during exercise will be significantly higher when using a portable cylinder, but this difference will be small.

Exercise-induced hypoxaemia (EIA) is very common in individuals with ILD, due to progressive lung fibrosis which results in impaired gas exchange. It is common for people with EIA to be prescribed ambulatory oxygen, in order to normalize oxyhaemoglobin saturation, improve oxygen delivery to the tissues and relieve breathlessness during daily activities.

Ambulatory oxygen is traditionally delivered via a refillable portable oxygen cylinder containing compressed gaseous oxygen. More recently, portable oxygen concentrators (POCs) have emerged as a solution to the problem of finite cylinder life and to improve portability. Because a concentrator is constantly extracting oxygen from air, oxygen supply can continue as long as the battery is charged. This is typically around eight hours, but POCs can be recharged from an AC or DC power source. Portable oxygen concentrators usually weigh around 3.5kg, which is significantly lighter than oxygen cylinders, and are much easier to maneuver. However, there are some theoretical disadvantages to POCs. Like all concentrators, they do not deliver 100% oxygen. Concentrations typically range from 85-95%, depending on the flow rate. Differences in pulse timing and peak pulse flow between POCs may affect the fraction of inspired oxygen (FiO2) that is delivered. However, the clinical implications of these differences have not been documented.

The aim of this study is to compare the effects of ambulatory oxygen delivered during exercise using the EverGo POC to ambulatory oxygen delivered with a standard portable cylinder in individuals with ILD. We hypothesise that oxyhaemoglobin saturation during exercise will be significantly higher when using a portable cylinder, but this difference will not be clinically important.

Inclusion Criteria:

• a confident diagnosis of ILD made according to established criteria and
• desaturate to less than 90% during a 6-minute walk test

Exclusion Criteria:

• primary diagnosis of a respiratory condition other than ILD (eg COPD)
• currently using continuous oxygen therapy
• oxyhaemoglobin saturation (SpO2) is less than 90% on room air
• unable to perform a 6-minute walk test or comorbidities that limit walking