Purpose

Windkessel impedance analysis has proven to be an effective technique for instituting artificial afterload on ex situ hearts. Traditional fixed parameter afterload modules, however, are unable to handle the changing contractile conditions associated with prolonged ex situ heart perfusion. In this paper, an adjustable afterload module is described comprising of three fully adjustable sub-components: a systemic resistor, a proximal resistor and a compliance chamber.

Methods

Using a centrifugal pump, the systemic resistor and compliance chamber were subjected to testing across their operating ranges, whereby the predictability of resistance and compliance values was evaluated. The components were then assembled, and the full module tested on three separate porcine hearts perfused for 6 h with success defined by the ability to maintain physiological systolic and diastolic aortic pressures across flow rate variability.

Results

For both the systemic resistor and compliance chamber, experimental measurements agreed with their theoretical equivalents, with coefficients of determination of 0.99 and 0.97 for the systemic resistor and compliance chamber, respectively. During ex situ perfusion, overall 95% confidence intervals demonstrate that physiological systolic (95–96.21 mmHg) and diastolic (26.8–28.8 mmHg) pressures were successfully maintained, despite large variability in aortic flow. Left ventricular contractile parameters, were found to be in line with those in previous studies, suggesting the afterload module has no detrimental impact on functional preservation.

Conclusions

We conclude that due to the demonstrable control of our afterload module, we can maintain physiological aortic pressures in a passive afterload working mode across prolonged perfusion periods, enabling effective perfusion regardless of contractile performance.

中文翻译：

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用于非原位心脏灌注的可调后负荷模块的实现

目的

弹性贮阻抗分析已被证明是对实行人工负荷的有效技术易地心。然而，传统的固定参数后负荷模块无法应对与延长的非原位心脏灌注相关的不断变化的收缩状况。在本文中，描述了一个可调后负荷模块，该模块包括三个完全可调的子组件：系统电阻器，近端电阻器和顺应性腔室。

方法

使用离心泵，对系统电阻器和顺应性腔室在其工作范围内进行测试，从而评估了电阻和顺应性值的可预测性。然后组装这些组件，并在三个独立的猪心脏上灌注6小时，测试整个模块的成功，其成功取决于在流速变化范围内维持生理收缩压和舒张主动脉压的能力。

结果

对于系统电阻器和顺应性腔室，实验测量值与理论等效值一致，系统电阻器和顺应性腔室的确定系数分别为0.99和0.97。在非原位灌注期间，尽管主动脉血流变化很大，但总体上95％的置信区间表明，可以成功维持生理收缩压（95–96.21 mmHg）和舒张压（26.8–28.8 mmHg）。发现左心室收缩参数与以前的研究一致，表明后负荷模块对功能保存没有有害影响。

结论

我们得出的结论是，由于对后负荷模块的明显控制，我们可以在较长的灌注周期内以被动后负荷工作模式维持生理主动脉压力，从而无论收缩性能如何均可进行有效灌注。