Clinical and research measurement techniques of the pulmonary circulation: the present and the future.

There has been a lot of progress in measurement techniques of the pulmonary circulation in recent years, and this has required updating of basic physiological knowledge. Pulmonary artery pressures (PAP) are normally low and dependent on left atrial pressure (LAP) and cardiac output (CO). Therefore, defining the functional state of the pulmonary circulation for the detection of pulmonary vascular disease or evaluation of disease progression requires measurements of PAP, LAP and CO. Invasive measurements have lately improved by a better definition of zero leveling and of the effects of intrathoracic pressure changes, and understanding of the inherent limitations of fluid-filled thermodilution catheters. The effects of LAP and pulmonary flow on PAP in health and disease are now integrated in the hemodynamic diagnosis of pulmonary hypertension. Development of alternative noninvasive approaches is critically dependent on their potential to quantify pulmonary vascular pressures and CO. Doppler echocardiography and magnetic resonance imaging are coming close. Both approaches are performant for flow measurements, but pressures remain indirectly assessed from flow velocities and/or structural changes. Doppler echocardiography or magnetic resonance imaging has been shown to be accurate, allowing for valid population studies, but with insufficient precision for single number-derived clinical decision making.