Oxygen administration method for heart failure patients with sleep-disordered breathing

睡眠呼吸暂停综合征（SAS）是一种睡眠呼吸紊乱，在睡眠中导致低氧血症。SAS对心力衰竭患者的作用越来越受到关注。持续气道正压通气（CPAP）作为一种治疗睡眠呼吸障碍的方法，在心力衰竭患者中应用广泛且有效。但由于给氧流量恒定，不能很好地防止氧饱和度的下降。为了提高CPCA处理下的氧饱和度，本研究设计了一套供氧控制系统。首先根据临床资料研究了血氧饱和度的动态变化，明确了每天3小时CPAP可显著降低动脉压和心率。因此，可以推断，保持氧饱和度在90%以上是至关重要的。其次，在上述研究的基础上，以二阶状态方程的形式构建了氧动力学模型。在心力衰竭引起的血氧饱和度下降不经常发生的情况下，可以保证模型能恰当地描述这些现象。模型参数（增益和时间常数）的个体差异在3倍以内。这个模型揭示了心率对氧饱和度的影响很小，这与之前的观点相反。最后，设计了一种使用状态预测方法的控制系统，并通过仿真表明，在不发生长期不呼吸的情况下，能够将氧饱和度保持在90%以上。

Sleep apnea syndrome (SAS) is a sleep-disordered breathing that causes hypoxemia during sleep. The effect of SAS on patients with heart failure attracts increasing attention. As a treatment for the sleep-disordered breathing, continuous positive airway pressure (CPAP) treatment is widely used and effective even for heart failure patients. However it cannot prevent the decrease of oxygen saturation satisfactorily, because the oxygen is administrated with a constant flow rate. In this research, a control system of oxygen administration is designed in order to improve the oxygen saturation under the CPCA treatment.First the dynamics of the oxygen saturation was studied based on clinical data and it was clarified that the 3 hours per day CPAP causes decrease of the artery pressure as well as of the heart rate meaningfully. As a result it was deduced that to keep the oxygen saturation should above 90 percent is vital. Second, based on the above study, a model of the oxygen dynamics was constructed as a second order state equation. It was assured that the model appropriately describe s the phenomena provided that the oxygen saturation drops caused by the heart failure do not occur very frequently. It was found that the individual difference of the model parameters (gain and time constant) is within 3 times. This model revealed that the heart rate has little effect on the oxygen saturation, against the previously claimed view. Lastly, a control system using the state predictive method was designed, and shown, by simulation, to be able to keep the oxygen saturation above 90 percent assuming that long term non-breathing does not happen.