Understanding the small vessels in the lungs and their function with a novel method of lung microvascular assessment in healthy patients and those with pulmonary hypertension.

Healthy controls and participants with Group 1 pulmonary arterial hypertension will undergo a novel invasive pulmonary microcirculation study utilising continuous thermodilution methodology within the pulmonary circulation. This procedure will be performed once in each individual by an experienced procedural Cardiologist at a quaternary pulmonary hypertension and advanced heart failure referral centre. The procedure involves a standard right heart catheterisation then follow on to indices of pulmonary microvascular function procedure via a multipurpose catheter placed in the left or right pulmonary artery and a Hexacath Rayflow microcatheter and Abbott PressureWireX placed in a subsegmental pulmonary artery. Absolute pulmonary artery flow and microvascular resistance are calculated by use of continuous thermodilation methodology using normal saline attached to RayFlow catheter via injector enabling constant pressure and flow delivery. Each participant undergoes the procedure one time, with procedural duration of approximately 30 minutes. Participation in the study ends after the procedure is completed, there is no further follow up. As this is a once off procedure, there is no risk of participant non-adherence. Each procedure will be conducted in accordance with a strict, standardised protocol developed by the investigative team. Only trained procedural cardiologists who have completed specific competency-based instruction in the study protocol will perform the procedure.