Pulmonary Hypertension

Excerpt

Pulmonary hypertension (PH) encompasses a heterogeneous group of disorders with the common feature of elevated pulmonary artery pressure. It is divided into five clinical groups based on pathophysiology, hemodynamic characteristics, clinical features, and management.

TABLE 1: Clinical classification of PH

HIV: human immunodeficiency virus; LVEF: left ventricular ejection fraction; PAH: pulmonary arterial hypertension; PCH: pulmonary capillary hemangiomatosis; PVOD: pulmonary veno-occlusive disease.

Apart from the clinical classification, PH also has a hemodynamic classification that aids diagnosis. A mean pulmonary artery pressure (mPAP) >20 mmHg is considered above the upper limit of normal. However, a mere elevation in mPAP is insufficient to define PH, as this could be due to an increase in cardiac output (CO) or pulmonary artery wedge pressure (PAWP). Hence the sixth World Symposium on Pulmonary Hypertension (WSPH) and the European Society of Cardiology (ESC)/European respiratory society (ERS) guidelines inculcated pulmonary vascular resistance (PVR) as well as PAWP to hemodynamically define PH as described in Table 2.

TABLE 2: Hemodynamic classification of PH

mPAP: mean pulmonary artery pressure; PAWP: pulmonary artery wedge pressure; PVR: pulmonary vascular resistance; WU: Wood units

These measurements are obtained during right heart catheterization (RHC) at rest in the supine position. The latest ESC/ERS guidelines inculcated the definition of exercise PH as a change in mPAP/CO slope between rest and exercise >3mmHg/L/min. However, this definition cannot differentiate between pre-capillary and post-capillary PH. The change in PAWP/CO slope > 2 mmHg/L/min between rest and exercise might be able to differentiate between pre and post-capillary PH but measuring PAWP during exercise is challenging.

As seen from the above table, all PH groups can have pre and post-capillary components contributing to their PH. These patients should be classified based on the presumed predominant underlying cause of the increased pulmonary artery pressures. Patients with PAH are typically characterized by pre-capillary PH in the absence of other conditions that can cause pre-capillary PH, such as those seen in group 3 and group 4 PH.