## 4 Discussion
### Applicability for Physiological Pump Control  
In addition to the outpatient application, the proposed evaluation method of myocardial function has the potential to be utilized in the development of an algorithm for physiological pump control to automatically change and maintain pump speed at an optimal value for a current state of myocardial function. Numerous reports represent the application results of LVAD electric parameters for myocardial function assessment. For instance, [PERSON] et al. reported on the noninvasive identification of regurgitant pump flow, ventricular ejection, nonopening of the aortic valve, and collapse of the ventricle wall [30]. Moreover, there are reports on controllers monitoring aortic valve opening [31], detecting the suction state of the ventricle [32], and based on physical activity level index [33]. Previously, an LVAD controller based on the use of pulsatility ratio of pump flow rate and pressure head was reported [14; 15; 16]. The pulsatility index of pump motor current was used to determine the safety range of LVAD speed to avoid valve regurgitation and suction state of the ventricle during support [13]. There is a report theoretically assessing the Starling-like pump controller and justifying the use of flow pulsatility as the measure of choice [12]. Besides, the method for cardiac contractility assessment using only pump flow and pump speed was reported [11]. All the listed control methods are representatives of physiological pump control, which is supposed to automatically optimize the pump speed in a safety range for a specific state of the patient's CVS. However, these methods have certain shortcomings which do not allow us to use them in clinical practice. The main issue is that medical practitioners cannot rely on automatic algorithms based on not clearly understandable nonmedical parameters. Most control algorithms are non- or semiautomatic themselves, due to the need for manual selection of reference intrinsic parameters for a specific patient. It should be noted that the main parameters that need to be constantly evaluated under CF operating conditions are blood flow rate through the pump and pressure at the pump inlet (preload) and pump outlet (afterload) [34; 35]. Other disadvantages are linked to methods of determination of these parameters, which are: (1) Direct measurement, and (2) estimation through indirect methods using readily available intrinsic LVAD parameters (e.g., pump speed and electric current or power consumption) to derive flow rate via a process model [7; 36; 37; 38; 39; 40; 41; 42; 43]. Direct measurement increases invasiveness which is not always necessary or available in long-term support. And the second approach has limitations in accuracy caused by the low system efficiency of rotary blood pumps (RBPs), which makes it difficult to assess the direct correlation between electric and hydraulic parameters of the system [7; 42; 43; 44; 45; 46; 47]. For instance, the maximum efficiency of CF RBP typically does not exceed 30 % [48; 49; 50; 51]. Such a low efficiency can be explained by various energy losses in the whole system, i.e., electric, mechanical, and hydraulic losses [52; 53]. Mainly, conversion of mechanical energy into hydraulic becomes low efficient, due to the substantially larger ratio between the clearance gap and the diameter of the impeller in miniaturized blood pumps compared to industrial pumps with large impellers. This inflicks higher energy losses compared to other loss types [54; 55]. Our group has also deeply investigated the relationship between pump power consumption and blood flow rate [56]. This relationship was studied for two generations of CF RBPs: (1) The first generation of Sputnik LVAD that was successfully implemented into clinical practice [57; 58], and (2) the second generation under development, which is aimed at miniaturization and reducing the risk of blood cell trauma [44].