基于CPLD高精度恒流源技术的呼吸体积描记系统的设计

Design of a Respiratory Inductive Plethysmography System Based on CPLD Precision Constant Current Source Technology

利用呼吸感应体积描记(RIP)技术测量呼吸参数已得到了越来越广泛的认可,针对人体呼吸运动引起传感线圈的电感量变化非常小(小于几百nH),一般系统难以保证精确性和适用性问题;硬件设计采用了高精度恒流源,锁相放大和自动增益控制放大电路,并详细分析了各部分电路的特性,包括在平静呼吸和用力呼吸模式下分别对14位测试者测量潮气量和呼吸频率,并且与德国耶格公司的肺功能仪所测量的结果对比;实验证明RIP系统在这两种模式下测量潮气量和呼吸频率等呼吸参数与速度描记仪存在显著的正相关关系,说明该系统工作良好、测量精确,操作简单、便于携带和低功耗,未来可以在临床上推广应用于长时间动态的呼吸监测。

Respiratory inductive plethysmography （RIP） technology for measuring parameters of breathing has been widely accepted. However, due to small changes （less than few hundred nil） of the inductance caused by the human respiratory movements, general stimula- ting signal that stimulates the inductive coils can hardly guarantee the precision and the suitability of RIP system. To solve this problem , this paper present a design combined the technologies of the precision constant current source, the lock--in amplifier and the automatic gain control amplifier. The electric circuit characteristics of the design was also elaborated in this paper. With the breathing measuring experiment on 14 subjects which measured tidal volume and breath rate under quiet breath and forced breath and compared with the result from the pneu- motachograph manufactured by JAEGER. The results show that breath rate and other respiratory parameters from our system have a high positive correlation with the those from pneumotachograph. The system was proved to be working at stable and measuring in a better preci- sion. , due to the simple operations, convenience in carrying and the low--power , the system will meet the future demands on the long time ambulatory respiratory monitoring in the clinical.