Aim of the study is to evaluate the role of chemoreceptor activity and ventilation perfusion mismatch on the genesis of exercise induced hyperventilation in Pulmonary hypertension patients. So the investigators tested the chemoreceptor response at rest, both with hypoxic and hypercapnic stimuli, and the ventilatory response during exercise analyzing its two components, alveolar and dead space ventilation.

Inclusion Criteria:

• age ≥18 and ≤ 80 years
• ability to understand the research protocol and willing to sign the study informed consent
• diagnosis of pulmonary arterial hypertension belonging to Class I and IV
• stable haemodynamic status and optimized medical treatment since at least 2 months
• ability to perform maximal cardiopulmonary exercise test and pulmonary diffusing capacity for carbon monoxide evaluation

Exclusion Criteria:

• relevant comorbidities
• usual contraindications for cardiopulmonary exercise test
• pulmonary hypertension associated to left heart and pulmonary disease, congenital heart diseases with evident cardiac shunts.