Lim Einly, Salamonsen Robert Francis, Mansouri Mahdi, Gaddum Nicholas, Mason David Glen, Timms Daniel L, Stevens Michael Charles, Fraser John, Akmeliawati Rini, Lovell Nigel Hamilton
Department of Biomedical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia.
Artif Organs. 2015 Feb;39(2):E24-35. doi: 10.1111/aor.12370. Epub 2014 Oct 27.
The present study investigates the response of implantable rotary blood pump (IRBP)-assisted patients to exercise and head-up tilt (HUT), as well as the effect of alterations in the model parameter values on this response, using validated numerical models. Furthermore, we comparatively evaluate the performance of a number of previously proposed physiologically responsive controllers, including constant speed, constant flow pulsatility index (PI), constant average pressure difference between the aorta and the left atrium, constant average differential pump pressure, constant ratio between mean pump flow and pump flow pulsatility (ratioP I or linear Starling-like control), as well as constant left atrial pressure ( P l a ¯ ) control, with regard to their ability to increase cardiac output during exercise while maintaining circulatory stability upon HUT. Although native cardiac output increases automatically during exercise, increasing pump speed was able to further improve total cardiac output and reduce elevated filling pressures. At the same time, reduced venous return associated with upright posture was not shown to induce left ventricular (LV) suction. Although P l a ¯ control outperformed other control modes in its ability to increase cardiac output during exercise, it caused a fall in the mean arterial pressure upon HUT, which may cause postural hypotension or patient discomfort. To the contrary, maintaining constant average pressure difference between the aorta and the left atrium demonstrated superior performance in both exercise and HUT scenarios. Due to their strong dependence on the pump operating point, PI and ratioPI control performed poorly during exercise and HUT. Our simulation results also highlighted the importance of the baroreflex mechanism in determining the response of the IRBP-assisted patients to exercise and postural changes, where desensitized reflex response attenuated the percentage increase in cardiac output during exercise and substantially reduced the arterial pressure upon HUT.
本研究使用经过验证的数值模型，调查了植入式旋转血泵（IRBP）辅助患者对运动和头高位倾斜（HUT）的反应，以及模型参数值变化对该反应的影响。此外，我们比较评估了一些先前提出的生理反应控制器的性能，包括恒速、恒定流量脉动指数（PI）、主动脉与左心房之间的恒定平均压差、恒定平均泵压差、平均泵流量与泵流量脉动之间的恒定比率（比率PI或类似线性斯塔林的控制），以及恒定左心房压力（(\overline{P_{la}})）控制，考察它们在运动期间增加心输出量同时在HUT时维持循环稳定性的能力。尽管运动期间天然心输出量会自动增加，但增加泵速能够进一步提高总心输出量并降低升高的充盈压。同时，与直立姿势相关的静脉回流减少并未导致左心室（LV）抽吸。尽管(\overline{P_{la}})控制在运动期间增加心输出量的能力方面优于其他控制模式，但它在HUT时会导致平均动脉压下降，这可能会引起体位性低血压或患者不适。相反，维持主动脉与左心房之间的恒定平均压差在运动和HUT两种情况下均表现出卓越的性能。由于PI和比率PI控制强烈依赖于泵的工作点，它们在运动和HUT期间表现不佳。我们的模拟结果还突出了压力感受性反射机制在确定IRBP辅助患者对运动和姿势变化反应中的重要性，其中脱敏的反射反应减弱了运动期间心输出量的百分比增加，并大幅降低了HUT时的动脉压。
