The study evaluates the rest and exercise hemodynamics of patients presenting either idiopathic fibrotic pulmonary disease or pulmonary fibrosis secondary to connective tissue disease.

Patients with fibrotic pulmonary disease of the above origin will undergo detailed assessment of functional status with the following examinations: pulmonary function tests, echocardiogram, 6 minute exercise test, cardiopulmonary exercise test (in the absence of contra-indications) and finally right heart catheterization. Hemodynamic assessment will take place at rest and at exercise following the exercise protocol that was recommended by Herve et al (ERJ 2015) using a cycle ergometer at bedside.

The purposes of the study are:

1. to evaluate the response of the hemodynamic parameters at exercise compared to the resting parameters in this patient group.
2. to discriminate between precapillary from postcapillary etiology of pulmonary hypertension.
3. to correlate non-invasive parameters of functional limitation with invasive hemodynamic parameters.
4. to assess the prognostic role of exercise induced pulmonary hypertension in the specific patient group.

Inclusion Criteria:

1. diagnosis of pulmonary fibrosis secondary to connective tissue disease, according to the American College of Rheumatology/European League Against Rheumatism (ACR-EULAR) revised classification criteria , or diagnosis of idiopathic fibrotic diffuse pulmonary disease according to American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines
2. Forced vital capacity (FVC) ≥ 40 %

Exclusion Criteria:

1. Presence of contra-indications to exercise tests, such as acute myocardial infarction, unstable angina, uncontrollable arrythmia or skeletal disease that limits the ability to exercise.
2. History of pulmonary embolism during the year before enrollment
3. Presence of severe valvular disease.
4. Current treatment with vasoactive drugs of the pulmonary circulation
5. Pulmonary wedge pressure (PAWP) at rest > 15 mmHg

Patients are currently followed up in the Respiratory Clinics of the investigator's hospital and will be enrolled if suitable after having signed the form of consent.