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Exercise stress tests have been used for the diagnosis of pulmonary hypertension since the introduction of the haemodynamic definition of the disease in the 1950s. Paul Wood reasoned on the pulmonary vascular resistance (PVR) equation to show that pulmonary artery pressure (PAP) can increase as a result of resistance but also because of flow and/or left atrial pressure.1 One of his patients with borderline pulmonary hypertension on mitral stenosis and severe exercise-induced pulmonary hypertension is illustrated in figure 1. Right heart catheterisation studies in normal subjects showed that the average slope of the PAP–cardiac output relationship is 1 mm Hg/l per minute in young adults and increases to 2.5 mm Hg/l per minute after six to eight decades of life, and that left atrial pressure is transmitted upstream to PAP in an approximately 1:1 ratio.2 Cardiac output-associated high PAP may thus be amplified by an increased PVR due to pulmonary arteriolar remodelling, reflecting lung disease, and/or by upstream transmission of an increased pulmonary outflow pressure, reflecting left ventricular diastolic dysfunction.
What are the limits of normal? Pulmonary hypertension was traditionally defined by a PAP higher than 25 mm Hg at …