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Definition of PH

Pulmonary hypertension (PH) is pathophysiologic consequence of vasculopathic changes in the pulmonary vessels that may occur as a result of predisposing factors. Pulmonary arterial hypertension (PAH) is characterised by the presence of precapillary PH in absence of other causes of precapillary PH and of postcapillary (=venous) PH.

PAH is defined by specific hemodynamic criteria obtained via right heart catheterization (RHC), including a mean pulmonary arterial pressure (mPAP) >25 mm Hg, a normal or reduced cardiac output, and a postcapillary pressure <15 mmHg.

The upper limit of normal mPAP is 20 mmHg. The significance of a mPAP between 21 and 24 mmHg is unclear. The definition of PH on exercise as mPAP >30 mmHg as assessed by RHC is not supported by published data, and healthy individuals can reach much higher values. Thus no definition for PH on exercise as assessed by RHC can be provided at the present time.

Important definitions

PH is a haemodynamic and pathophysiological condition defined as an increase in Ppa ≥25 mmHg at rest as assessed by right heart catheterisation. PH can be found in multiple clinical conditions. The definition of PH on exercise as Ppa >30 mmHg as assessed by right heart catheterisation is not supported by published data. PAH (group 1) is a clinical condition charecterised by the presence of pre-capillary PH in the absence of other causes of pre-capillary PH such as PH due to lung dieseases, chronic thromboembolic PH, or other rare diseases. PAH includes different forms that share a similar clinical picture and virtually identical pathological changes of the lung microcirculation.

PH: pulmonary hypertension; Ppa: mean pulmonary arterial pressure; PAH: pulmonary arterial hypertension.

Haemodynamic definitions of pulmonary hypertension1
Definition	Characteristics	Clinical group(s)
Pulmonary hypertension (PH)	Mean PAP ≥25 mmHg	All
Pre-capillary PH	Mean PAP ≥25 mmHg PWP ≤15 mmHg CO normal or reduced1	1. Pulmonary arterial hypertension 3. PH due to lung diseases 4. Chronic 5. PH with unclear and/or multifactorial mechanisms
Post-capillary PH	Mean PAP ≥25 mmHg PWP >15 mmHg CO normal or reduced2	2. PH due to left heart disease
Passive Reactive (out of proportion)	TPG ≤12 mmHg TPG >12 mmHg

¹ All values measured at rest.
² High CO can be present in cases of hyperkinetic conditions such as systemic-to-pulmonary shunts (only in the pulmonary circulation), anaemia, hyperthyroidism, etc.

CO = cardiac output; PAP = pulmonary arterial pressure; PH = pulmonary hypertension; PVVP = pulmonary wedge pressure; TPG = transpulmonary pressure gradient (mean PAP - mean PVVP).