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，导致睡眠期间低氧血症。SAS对心力衰竭患者的影响日益受到关注。持续气道正压通气（CPAP）治疗作为一种治疗睡眠呼吸障碍的方法，即使对于心力衰竭患者也是广泛使用和有效的。然而，它不能令人满意地防止氧饱和度的降低，因为氧气是以恒定的流速施用的。本研究设计了一套控制系统，以提高CPCA治疗下的血氧饱和度，首先根据临床数据研究了血氧饱和度的动态变化，阐明了每天3小时的CPAP治疗会显著降低动脉压和心率。因此，推断保持氧饱和度应高于90%是至关重要的。其次，在上述研究的基础上，建立了一个二阶状态方程的氧动力学模型。只要心力衰竭引起的血氧饱和度下降不频繁发生，该模型就能适当地描述这一现象。结果发现，模型参数（增益和时间常数）的个体差异在3倍以内。该模型揭示了心率对氧饱和度的影响很小，与先前声称的观点相反。最后，使用状态预测方法的控制系统的设计，并示出，通过模拟，能够保持氧饱和度在90%以上，假设长期不呼吸不发生。

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.