Development of an Active Controlled Stretcher for an Ambulance

最近，在日本，病人在到达医院前在救护车运输过程中死亡的事件引起了极大的关注，称为DOA(即到达时死亡)。我们认为，在救护车运输过程中，患者病情恶化的一个因素是救护车与私家车相比相对较差，其特征是：振动、加速和减速。为了解决这一问题，人们对基于隔离救护车振动的担架的设计进行了大量的研究，但我们发现，在刹车引起脚对头加速的过程中，躺在担架上的人的血压会发生变化。当救护车在曲折或狭窄的道路上行驶时，尤其会出现血压变异(BPV)；反复进行加速或减速。由于强制改变血压可能会导致病情恶化，因此有必要使用担架来减小脚头加速的影响，减少运输过程中的BPV。因此，我们从一个略有不同的角度对救护车担架的设计进行了研究，因为还没有关于减少BPV的担架的设计研究。1994年，我们通过仿真分析研究了主动控制担架对降低BPV的影响。仿真结果表明，该系统能有效地降低BPV，运送病人更加舒适。为了减少患者的血压波动，我们于1995年为救护车设计了一种自动控制系统，并利用该系统进行了紧急制动试验。实验结果表明，通过根据救护车运行时自后而前的加速度连续控制担架在重力下的倾斜角，可以有效地降低脚部对头部的加速度。

Recently in Japan, a great deal of attention have been paid to the patient's death during ambulance transport before arriving at hospital, called DOA (Dead On Arrival). We consider that a deteriorating factor of the patient's condition during ambulance transport is a relatively poor ride of the ambulance compared with a private car characterized by : vibration, acceleration, and deceleration. To solve the problem, many researches have been made on the design of the stretcher based on the isolation of the ambulance vibration.We have, however, found that the blood pressure of human laying on a stretcher varies during a brake causing foot-to-head acceleration. The blood pressure variation (BPV) especially appears when the ambulance runs through a zigzag or narrow road ; the accelerations or decelerations are repeatedly performed. As the enforced change of the blood pressure may lead to deterioration of patient's condition, it is necessary to use a stretcher to decrease the effect of the foot-to-head acceleration and to reduce the BPV during transport. We have, therefore, worked on the design of the ambulance stretcher from a slightly defferent angle, since no such studies have been done on designing of a stretcher which reduces the BPV.In 1994, we investigated the effect of an actively controlled stretcher (ACS) on the reduction of the BPV by simulation analysis. The simulation results suggest that the ACS can effectively decrease the BPV and comfortably transport the patient. In 1995, we designed an ACS for an ambulance to reduce patient's blood pressure variation, and performed emergency brake tests using the ACS.The experimental results showed that the ACS can effectively decrease the foot-to-head acceleration by continuously controlling the tilying angle of the stretcher under gravity according to back-to-front acceleration of the running ambulance.