reply: We appreciate Kilner's (1) interest in our simulation study evaluating the significance of cardiac looping on pumping function of the heart using the finite element model (4). Although he agreed with us that the conservation of momentum of blood flowing into chamber contributes only modestly to the ejection, he pointed out another aspect of cardiac looping as a potentially potent modulator of cardiac function.
According to Kilner et al. (3), the salient feature of the looping is the redirection of flow in the ventricular chamber that facilitates the atrioventricular coupling through the momentum of the blood flow. Especially, vigorous inflow during exercise pushes the ventricular wall while being decelerated and stores elastic energy in the wall. Recoil of the stretched ventricular wall not only boosts the ejection flow but pulls the atrium to enhance its filling. However, we again question such a hypothesis because of the following reasons.
First, even with the high-inflow velocity, for example 1.3 m/s as reported by Kilner et al. (2), the roughly estimated kinematic energy of inflow [1/2 × 90 ml × 1.06 g/cm3 × (1.3 m/s)2 ≈ 0.081 J] is much smaller than the external work done by the myocardium with high contractility (e.g., 90 ml × 180 mmHg ≈ 2.1 J).
Second, although under relatively low heart rate (100 beats/min), we have confirmed that the end-diastolic ventricular shape does not differ appreciably even if the fluid is not included for simulation.
The concept of atrioventricular coupling is very attractive, but the quantitative analysis may not support it. Similar simulations are needed to evaluate such an effect using the whole heart model with both ventricles and atria to accurately answer this question.
No conflicts of interest are declared by the author(s).
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