This study is testing whether a new type of home oxygen therapy, called high-flow nasal cannula (HFNC), can improve breathing comfort and quality of life for people with long-term lung or heart conditions who need oxygen after leaving the hospital.

HFNC delivers warm, humidified oxygen at higher flow rates than standard oxygen therapy, which may reduce shortness of breath, improve sleep, and make daily activities easier. The therapy will be provided using the myAirvo™3 device, which also allows doctors to check patients' oxygen levels, heart rate, and symptoms remotely. All patients will also wear a small device (RootiREX) to monitor heart rhythm, sleep quality, and detect breathing pauses at night.

Participants will try both treatments - HFNC and standard oxygen therapy - for short periods, in random order, so that researchers can directly compare the effects within the same patient. Each treatment period will last two weeks, with a short break in between.

The main goal of the study is to see whether HFNC reduces shortness of breath (measured by the modified Medical Research Council scale). Other outcomes include comfort, sleep quality, quality of life, oxygen levels, and how well patients are able to use the devices at home.

The study will last six weeks in total for each participant. Researchers expect that HFNC will improve breathing comfort, stabilize oxygen levels, and reduce the need for hospital visits during this time.

Inclusion Criteria: Adults (≥18 years) with chronic respiratory (e.g., COPD, interstitial lung disease) and/or cardiac disease (e.g., heart failure), Clinical indication for long-term oxygen therapy, Capability to manage home-based devices independently or with caregiver assistance Signed informed consent

Exclusion Criteria:

Life expectancy < 3 months Inability to comply with home follow-up procedures.