In hemodynamic terms, the mean pulmonary arterial pressure (PAP) can be described by
Equation 1: PAP = (CO x PVR) + PVP
where CO = cardiac output, PVR = pulmonary vascular resistance, and PVP = pulmonary venous pressure. The PVP is essentially the same as left atrial pressure. Therefore, increases in CO, PVR or PVP will lead to increases in PAP. Normally, mean pulmonary arterial pressure is about 15 mmHg, and the pulmonary arterial systolic and diastolic pressures are about 25 and 10 mmHg, respectively. Pulmonary venous pressure is about 8 mmHg. Therefore, the pressure gradient driving flow through the pulmonary circulation is rather small at about 7 mmHg (mean pulmonary arterial minus venous pressures). This is a much lower driving pressure than the systemic circulation where the arterial-venous pressure gradient is about 90 mmHg. Although the blood flow through the pulmonary circulation is essentially the same as the blood flow through the systemic circulation, the pulmonary vascular resistance is ten- to fifteen-fold lower than the systemic vascular resistance. This explains why the mean pulmonary artery pressure is relatively low.
Pulmonary hypertension experts have experience with all treatments available for PAH. They may not use every therapy frequently but they are comfortable with all forms of treatment including oral, inhaled, and continuously infused options. Many community physicians are comfortable with oral therapies but don’t have the staff such as nurse coordinators to obtain and coach patients through more advanced options. It is a good idea for PH patients to ask their physicians how many PH patients they treat and about how many are on each type of therapy.