Pulmonary vascular resistance and compliance relationship in pulmonary hypertension

Abstract

Right ventricular adaptation to the increased pulmonary arterial load is a key determinant of outcomes in pulmonary hypertension (PH). Pulmonary vascular resistance (PVR) and total arterial compliance (C) quantify resistive and elastic properties of pulmonary arteries that modulate the steady and pulsatile components of pulmonary arterial load, respectively. PVR is commonly calculated as transpulmonary pressure gradient over pulmonary flow and total arterial compliance as stroke volume over pulmonary arterial pulse pressure (SV/PApp). Assuming that there is an inverse, hyperbolic relationship between PVR and C, recent studies have popularised the concept that their product (RC-time of the pulmonary circulation, in seconds) is "constant" in health and diseases. However, emerging evidence suggests that this concept should be challenged, with shortened RC-times documented in post-capillary PH and normotensive subjects. Furthermore, reported RC-times in the literature have consistently demonstrated significant scatter around the mean. In precapillary PH, the true PVR can be overestimated if one uses the standard PVR equation because the zero-flow pressure may be significantly higher than pulmonary arterial wedge pressure. Furthermore, SV/PApp may also overestimate true C. Further studies are needed to clarify some of the inconsistencies of pulmonary RC-time, as this has major implications for our understanding of the arterial load in diseases of the pulmonary circulation. @ERSpublications Empiric estimates of pulmonary arterial load are prone to errors and may result in overestimation of RC-time

Acute hemodynamic effects of inhaled sodium nitrite in pulmonary hypertension associated with heart failure with preserved ejection fraction

“…This observation provides further physiological support for the role of exogenous administration of sodium nitrite for nonGroup 1 PH patients. Tedford et al demonstrated that elevated pulmonary capillary wedge pressure was associated with lower Cpa for any given PVR (shifting the resistance-compliance curve down and to the left), although there is still some debate about this in the literature (25,32). We found no difference in the baseline resistance-compliance relationship between patient groups.…”

Heart Rate Dependence of the Pulmonary Resistance x Compliance (RC) Time and Impact on Right Ventricular Load

“…Measurements of pulse wave velocity and changes in impedance with increasing heart rate should be considered as part of ongoing research efforts. Alternatively, simplified equations for resistance, compliance, and the RC time may not reflect true physiologic values [2]. Ea (Pes/SV) is known to be heart rate dependent and estimating compliance as SV/PP, which is mathematically similar, could be influenced by heart rate even if ‘true’ compliance is not.…”

“…Therefore, calculated mPAP may underestimate the pulsatile loading in cohort D and while we witnessed absolute increases in resistive and pulsatile load, it is not possible to truly assess the relative contributions of each. Finally, PAC is clearly a lumped simplification for compliance, and while it has been validated against 3-element Windkessel model calculations, some of this theory has been debated [2]. …”

“…Despite this general dependence, individual RC time constants still display variance as recently highlighted by Chemla [2]. We and others have shown that elevations in left heart filling pressures, estimated by pulmonary artery wedge pressure (PAWP), reduce the RC time to account for some of this scatter [3–5].…”

Pulmonary Arterial Compliance in Acute Respiratory Distress Syndrome: Clinical Determinants and Association With Outcome From the Fluid and Catheter Treatment Trial Cohort*

“…Future studies should assess the echocardiographic correlates of C PA and PVR in ARDS enabling non-invasive assessment in ARDS. An additional limitation is that SV/PP represents a lumped simplification for compliance and some of this theory has recently been debated (39). Other parameters such as pulmonary artery elastance are also important lumped parameters of RV afterload, although they too have limitations and how to best estimate pulmonary artery elastance remains controversial (40).…”