Mechanisms of Early Filling in the Left Ventricle
Abstract
Filling of the left ventricle (LV) occurs in two phases; early filling and late filling. Late filling, the mitral flow “A-wave”, is a result of the left atrial contraction. Early filling, manifest as the “E-wave”, is thought to be substantially due to diastolic suction (DS), a phenomenon whereby the LV aspirates blood and fills itself independent of atrial activity. The presence and importance of DS has been the source of much debate within the scientific literature, dating back to the early 20th century. It has been said that DS is important in order for the LV to fill efficiently as the heart adjusts to varying demands, for example, an increased heart rate due to exercise.
The presence of a favourable pressure gradient (PG) that drives blood flow from the LA towards the LV has been well established. Additional studies have shown that, under abnormally small end-systolic volumes (ESV), or, with impeding LV inflow, a negative transmural pressure is recorded, which was considered evidence of suction. The purpose of this study was to vary the working conditions of the heart in a porcine model, and measure DS in two different ways and compare these measures of DS to ESV as well as ejection fraction (EF). By varying the working conditions of the heart using drug interventions (isoproterenol, phenylephrine & metoprolol), as well as volume loading, the amount of DS at different states was determined.
The volume of filling due to suction, VDS, as well as the amount of energy resulting from suction (via a backwards decompression wave, BDW), are both indicative that ESV decreases as the amount of DS increases. As EF increased, both measures of DS also increased. Additionally, results for VDS display that DS is still present at ESV larger than baseline ESV. Finally, comparing the two measures of DS to each other showed good agreement.
DS is often suggested to be a result of elastic recoil of the LV after contracting below an unstressed state. However, our findings that VDS exists at large ESV would contradict that DS is only a result of elastic recoil, suggesting that further studies must be conducted focusing on DS at large ESV.
Description
Keywords
Physiology, Engineering--Biomedical, Engineering--Mechanical
Citation
Burrowes, L. (2017). Mechanisms of Early Filling in the Left Ventricle (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26865