Pressure, volume and flow: studies of ventricular, valvular and vascular haemodynamics in the human cardiovascular system.

BACKGROUND: Pressure, volume and flow form the three pillars of quantification in cardiovascular physiology. Newer approaches to their assessment provide opportunities to further assess their interactions. METHODS: 4 projects were conducted. Project 1 evaluated mechanisms of myocardial oxygen supply:demand imbalance in 3682 healthy volunteers using aortic pressure-time integrals measured with radial arterial tonometry (AT) and generalised transfer function. Project 2 evaluated the acute left ventricular (LV) contractile response to transcatheter mitral valve replacement (TMVR) in 9 high-risk patients. Intraoperative left and right heart catheterisation, 3D transoesophageal echocardiography and pressure-volume analyses were performed at baseline, immediately following TMVR and late postTMVR. Project 3 mathematically evaluated the current definition of paradoxical lowflow, low-gradient aortic stenosis (PLFLGAS) by deriving an equation for LV enddiastolic volume in terms of mean pressure gradient, aortic valve area and LV ejection fraction. Project 4 evaluated feasibility and reproducibility of non-invasive LV pressure-volume and aortic pressure-flow quantification in 21 patients who underwent simultaneous AT and cardiovascular magnetic resonance imaging (CMRI). RESULTS: In project 1, more unfavourable age-related myocardial oxygen supply:demand profiles were seen in women than men, driven by sex differences in arterial aging, pressure wave reflection and cardiac ejection duration. In project 2, TMVR caused acute LV dilatation and reduction in contractility, but changes returned to baseline by a median time of 17 minutes. LV end-diastolic pressure and forward stroke volume were preserved at the three study timepoints. In project 3, the derived LV end-diastolic volume equation incorporating defining criteria for PLFLGAS could not mathematically resolve the combined input parameters based on current definitions, raising concerns regarding the internal consistency of the consensus definition. In project 4, non-invasive LV pressure-volume and aortic pressure-flow analyses, using simultaneous AT and CMRI, were feasible, reproducible and showed good and appropriately directed correlation to more conventional markers of cardiovascular function. CONCLUSIONS: Newer approaches to pressure, volume and flow assessment can lead to better understanding of the interactions between the ventricles, valves and vasculature in states of health and disease.