Pressure & flow relationship in the pulmonary circulation in man

Background: Current gold standard pulmonary artery pressure measurements (PAP) are not accurate using a fluid filled catheter. High fidelity micromanometer tipped catheters are more accurate both at rest and during exercise. They have been used to examine the pattern of pulmonary artery pressure waveforms under various physiological conditions. A new thoracic impedance device has been developed, the Physioflow 1 ((c)Manatee, France), which has been shown to measure cardiac output (CO) accurately in a variety of respiratory conditions. It is known that PAP varies with changes in posture, sleep and exercise, and may sometimes appear normal at rest in early disease. Resting pressures vary daily. However, pressure and flow is linearly related in physiological ranges and the relationship is relatively constant. Changes in pressure-flow relationships may be missed at rest. It has been shown that response to a given treatment may be missed if measurements are based solely on resting PAP. For this reason the slopes of pressure-flow plots, are more useful than spot measures of pressure and flow. This has not adequately been explored in humans