Proportional pressure relations in the pulmonary arterial system

Background – Objectives: The pulmonary arterial system can be characterized by: 1.A constant product of Pulmonary Vascular Resistance (PVR) and Total Arterial Compliance (TAC) with Tau=PVRxTAC≈0.7 seconds (1). 2.A proportional relation exits between systolic and diastolic pulmonary artery pressure, sPAP, dPAP, with mean pulmonary artery pressure mPAP (2). Recently it was shown that the time constant Tau is affected by Pulmonary Arterial Wedge Pressure (PAWP), and thus not constant under all conditions (3). We therefore questioned how the product PVRxTAC = Tau depends on PAWP. Methods: We have studied proportionality of pressures in a group of patients (n=1054) and determined the contribution of Pulmonary Arterial Wedge Pressure. Results: We found that sPAP=1.61mPAP and dPAP =0.62mPAP, for all PAWP between 1 and 31 mmHg. Calculating PVR and TAC in the standard way as PVR=(mPAP-PAWP)/CO and TAC=PP/SV, with CO: Cardiac Output, PP: Pulse Pressure, SV: Stroke Volume, and HR: Heart Rate, it follows that: PVRxTAC=(1-PAWP/mPAP)/HReq. 1 Comparison with Tedford’s data (their fig 3C) is as follows: PAWP Tau-TedfordTau-Eq. 1 6 mmHg 0.43s 0.48s 45 mmHg 0.18s 0.18s Conclusions: These findings imply that for a certain PAWP and Heart Rate a hyperbolic relation remains, but the time constant Tau depends on the ratio of PAWP/mPAP and Heart Rate. A clinically measured low Tau could suggest a high PAWP.