Neural Respiratory Drive in Pulmonary Hypertension

NRD can be assessed by measuring parasternal electromyogram (EMG). Readings are taken by applying two small electrodes in the second intercostal space either side of the sternum and one to the shoulder. The electrodes are similar to those used in ECG acquisition. Measurements are then taken during normal breathing and also during maximal breathing effort ('sniff' procedure). Tests may be taken with patient recumbent at 45 degrees and supine. The test is non-invasive, has been safely performed in patients in previous studies and is not anticipated to cause any harm or distress. The total time for measurements will be around 20 minutes per patient.

NRD will be calculated as root mean square of normal tidal breathing as a proportion of maximal inspiratory effort (maximum inspiration from functional reserve capacity, taken as a sniff manoeuvre). Measurements will be performed in a ward based setting at the patient's bedside.

At the end of the inpatient stay for diagnosis, some patients are commenced on treatment and followed up in clinic. It would be the intention of the investigators to reassess these patients at clinic to test NRD and compare how this changes over time compared to other clinical parameters.

In addition, we will collect further readings of NRD in these patients when they attend for their standard follow up appointment. For the majority of patients, this will be after 3-4 months. For a subset of patients with chronic thromboembolic pulmonary hypertension, this may be up to one year after initial readings because these patients may be suitable for surgical intervention, which is not done locally and usually takes place 6-12 months after diagnosis at SPVU.

As such, the investigators intend that a patient will take part in the study for 52 weeks maximum, with most patients taking part for 16 weeks, and the study will not require them to have any additional attendances at hospital outwith their standard hospital admission for diagnosis and clinic follow up.