Olufsen Mette S, Alston April V, Tran Hien T, Ottesen Johnny T, Novak Vera
Department of Mathematics, North Carolina State University, Campus Box 8205, Raleigh, NC 27695, USA.
Cardiovasc Eng. 2008 Jun;8(2):73-87. doi: 10.1007/s10558-007-9050-8.
In this study we describe a model predicting heart rate regulation during postural change from sitting to standing and during head-up tilt in five healthy elderly adults. The model uses blood pressure as an input to predict baroreflex firing-rate, which in turn is used to predict efferent parasympathetic and sympathetic outflows. The model also includes the combined effects of vestibular and central command stimulation of muscle sympathetic nerve activity, which is increased at the onset of postural change. Concentrations of acetylcholine and noradrenaline, predicted as functions of sympathetic and parasympathetic outflow, are then used to estimate the heart rate response. Dynamics of the heart rate and the baroreflex firing rate are modeled using a system of coupled ordinary delay differential equations with 17 parameters. We have derived sensitivity equations and ranked sensitivities of all parameters with respect to all state variables in our model. Using this model we show that during head-up tilt, the baseline firing-rate is larger than during sit-to-stand and that the combined effect of vestibular and central command stimulation of muscle sympathetic nerve activity is less pronounced during head-up tilt than during sit-to-stand.
在本研究中，我们描述了一个模型，该模型可预测五名健康老年人从坐姿变为站姿以及进行头高位倾斜时的心率调节情况。该模型将血压作为输入来预测压力反射放电频率，进而用于预测传出性副交感神经和交感神经输出。该模型还包括前庭和中枢指令刺激对肌肉交感神经活动的综合影响，这种影响在姿势改变开始时会增强。然后，将预测为交感神经和副交感神经输出函数的乙酰胆碱和去甲肾上腺素浓度用于估计心率反应。心率和压力反射放电频率的动态变化通过一个具有17个参数的耦合常延迟微分方程组进行建模。我们推导了灵敏度方程，并对模型中所有参数相对于所有状态变量的灵敏度进行了排序。使用该模型我们发现，在头高位倾斜期间，基线放电频率高于从坐姿到站姿期间，并且在前庭和中枢指令刺激对肌肉交感神经活动的综合影响在头高位倾斜期间不如从坐姿到站姿期间明显。
