Ejection Fraction is Maintained during Preload Adjustment

Hypothesis: Venous occlusion impairs cardiac ventricle filling to end-diastolic volume (EDV). As EDV preload is reduced, ejected stroke volume (SV) is simultaneously lowered. The EDV mediation of SV output reflects the Frank-Starling Mechanism and compels a presented hypothesis that ejection fraction ratio EF=SV/EDV might remain constant during preload adjustment. Methods: Pressure volume (PV) loop datasets (n=34) recorded from female swine left ventricles 1 were provided for studied post-processing. Each dataset was analyzed to compute EF in the natural steady-state. Following EF measurement, inferior vena-cava occlusion (IVCO) measures of EDV i were noted at each IVCO beat i and EF constancy was applied to estimate each beat i stroke volume as SV i ~ EF x EDV i . Results: SV estimates were computed during early IVCO (beats 1 ≥ 5) and during a second phase of beats (beats 6 ≥10). Shown in Table 1, SV predictions exhibited near-unity slopes of proportion to direct SV measures. [Table: see text] Conclusions: A normal left ventricle appears to preserve EF during a preload reduction. This result highlights a possibility to quantify contractile mechanism aberrations if adjustment causes EF to change. For purposes of functional computation and modeling, the SV prediction also facilitates a useful forecast 2 of each IVCO beat i end-systolic volume as ESV i = EDV i - SV i ~ EDV i x (1- EF). 1. Habigt, M., et al., Nonlinearity of end-systolic pressure–volume relation in afterload increases is caused by an overlay of shortening deactivation and the Frank–Starling mechanism. Nature-Scientific Reports 2021. 11(3353): p. 1-11. 2. Marcus, E., A Study of Mechanisms Influencing Left-Ventricle End-Systolic Pressure Volume Relationship Measures, in COMPARATIVE PHYSIOLOGY: From Organisms to Omics in an Uncertain World, A.P. Society, Editor. 2022, American Physiology Society: San Diego EM's salary is supported by the Boston Children's Hospital Cardiology Department This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.