Pulmonary hypertension diagnostic study of choice
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Richard Channick, M.D.; Assistant Editor(s)-in-Chief: Ralph Matar, Lisa Prior, Ann Slater, R.N.
Overview
Pulmonary hypertension (PH) is a pathological condition of the pulmonary vasculature present in several disease states and leading to hemodymical derangement. PH is defined as an elevated mean pulmonary artery pressure (PAP) as measured by right heart catheterization at rest.
Diagnosis
The diagnostic approach to PH aims to:
- Confirm the diagnosis of PH
- Determine the classification group of PH
- Specify the possible etiology for PH, if present
- Evaluate the hemodynamic status of the patient
A physical examination is performed to look for typical signs of pulmonary hypertension. These include extrasounds, murmurs and signs of RV failure.
Further procedures are required to confirm the presence of pulmonary hypertension and exclude other possible diagnoses. These generally include:
- pulmonary function tests,
- blood tests,
- electrocardiography (ECG),
- arterial blood gas measurements,
- X-rays of the chest (followed by high-resolution CT scanning if interstitial lung disease is suspected), and ventilation-perfusion or V/Q scanning to exclude chronic thromboembolic pulmonary hypertension.
- Biopsy of the lung is usually not indicated unless the pulmonary hypertension is thought to be due to an underlying interstitial lung disease. But lung biopsies are fraught with risks of bleeding due to the high intrapulmonary blood pressure.
- Clinical improvement is often measured by a "six-minute walk test", i.e. the distance a patient can walk in six minutes. Stability and improvement in this measurement correlate with better survival.
- Although pulmonary arterial pressure can be estimated on the basis of echocardiography, pressure sampling with a Swan-Ganz catheter provides the most definite measurement. PAOP and PVR can not be measured directly with echocardiography. Therefore diagnosis of PAH requires a cardiac catheterization. A Swan-Ganz catheter can also measure the cardiac output, which is far more important in measuring disease severity than the pulmonary arterial pressure.
Normal pulmonary arterial pressure in a person living at sea level has a mean value of 12–16 mm Hg (1600–2100 Pa). Definite pulmonary hypertension is present when mean pressures at rest exceed 25 mm Hg (3300 Pa). If mean pulmonary artery pressure rises above 30 mm Hg (4000 Pa) with exercise, that is also considered pulmonary hypertension.
Diagnosis of PAH requires the presence of pulmonary hypertension with two other conditions. Pulmonary artery occlusion pressure (PAOP or PCWP) must be less than 15 mm Hg (2000 Pa) and pulmonary vascular resistance (PVR) must be greater than 3 Wood units (240 dyn•s•cm-5 or 2.4 mN•s•cm-5).