A non-contact vital signs monitor
A non-contact vital signs monitor
复制标题
DOI：
10.1615/critrevbiomedeng.v28.i12.290
复制
发表时间：
2000-01-01
影响因子：
--
通讯作者：
Burrow, M
中科院分区：
文献类型：
--
作者：
Matthews, G;Sudduth, B;Burrow, M
肺和心脏的扩张和收缩导致胸壁的运动，可以检测和监测胸壁的运动以确定呼吸和心率。原型非接触式生命体征监测器 (VSM) 已经开发出来，它使用极低功率、高频多普勒雷达来检测这些运动。 VSM 中嵌入的数字信号处理 (DSP) 技术用于从结果波形中提取心率和呼吸率信息。10 GHz 原型 VSM 是在 20 世纪 80 年代中期使用模拟技术为空军开发的。其目标是在 100 米的距离内评估阵亡士兵的临床状况，然后再投入资源援助该士兵。 1997 年开发了原始 VSM 的更新和改进版本。该设备设计用于在较短距离内运行，使用更高频率的载波，并使用数字信号处理技术提供更具体的心率和呼吸率信息。VSM 雷达系统是一个简单的零差接收器。它使用调频连续波 (FM-CW) 传输运行，从而允许非常低的功率水平。 35 GHz 工作频率下的安全人体功率密度暴露水平为 10 mW/cm(2)。使用均匀分布和 2 cm x 3 cm 的天线孔径进行简单近似，得出天线表面的功率密度为 0.017 mW/cm(2)，比安全水平低近 1000 倍。当 VSM 的天线对准受试者的胸壁时，VSM 能够测量和区分由心脏和肺部的机械活动引起的微小运动。当受试者的胸壁移动时，返回信号的确切相位会发生变化。为了避免出现与相位相关的死点，使用相位相差 90 度的两个信号将信号解调为基带 (DC)。产生的两个“时变直流”信号代表与目标位置变化相对应的相位角的正弦和余弦，在本例中是胸壁的运动。目前的VSM工作频率为35GHz，相应的波长仅为8.6mm。这提供了足够灵敏的响应，可以检测心脏功能引起的微小运动。生命体征监视器有几个可能的应用领域。事实上，它是非接触式的，这使得它对于监测烧伤病房、新生儿重症监护病房或创伤中心的患者特别有吸引力，因为在这些地方连接电极要么不方便，要么不可行。迄今为止的结果表明运动信号的心脏成分与心电图 (ECC) 之间存在很强的相关性。通过仔细的信号处理和分析，可以从表面运动波形中提取有关心脏状况、功能或性能的临床有用信息。这可以为心脏病专家目前可用的诊断和监测工具提供安全、廉价且无痛的补充。尽管在过滤对象的总体运动方面存在需要克服的技术障碍，但 VSM 比测量心率和呼吸率的传统方法具有显着的进步。
The expansion and contraction of the lungs and heart result in movement of the chest wall that can be detected and monitored to determine respiration and heart rate. A prototype noncontact Vital Signs Monitor (VSM) has been developed which uses very low power, high frequency Doppler radar to detect these motions. Digital signal processing (DSP) techniques, imbedded in the VSM, are used to extract heart and respiration rate information from the resultant waveform.A 10-GHz prototype VSM was developed for the Air Force in the mid-1980s using analog technology. The objective was to assess a fallen soldier's clinical condition at distances up to 100 meters before committing resources to assist that individual. An updated and improved version of the original VSM was developed in 1997. This device was designed to operate at shorter distances, use a higher frequency carrier, and provide more specific heart and respiration rate information using digital signal prdcessing techniques.The VSM radar system is a straightforward homodyne receiver. It operates using frequency modulated continuous wave (FM-CW) transmission, which allows for very low power levels. The safe human power density exposure level at its operating frequency of 35 GHz is 10 mW/cm(2). A simple approximation using uniform distribution and an antenna aperture of 2 cm by 3 cm gives a power density at the antenna face of 0.017 mW/cm(2), nearly a factor of 1000 below the safe level.When the VSM's antenna is trained on the chest wall of a subject, the VSM is capable of measuring and distinguishing minute movements resulting from the mechanical activity of the heart and lungs. As the subject's chest wall moves, the exact phase of the return signal changes. To avoid the possibility of phase-related dead spots, two signals differing in phase by 90 degrees are used to demodulate the signal to baseband (DC). The two resulting "time-varying DC" signals represent the sine and cosine of a phase angle corresponding to the changing position of the target, in this case the motion of the chest wall. The current VSM operates at a frequency of 35 GHz with a corresponding wavelength of only 8.6 mm. This provides a response sensitive enough to detect the small motions caused by cardiac function.The Vital Signs Monitor has several possible application areas. The fact that it is noncontacting would make it especially attractive for monitoring patients in burn units, NICUs, or trauma centers, where attaching electrodes is either inconvenient or not feasible. Results to date indicate a strong correlation between the cardiac component of the motion signal and an electrocardiogram (ECC). With careful signal processing and analysis, it may be possible to extract clinically useful information about cardiac condition, function, or performance from the surface-motion waveform. This could provide a safe, inexpensive, and painless addition to the diagnostic and monitoring tools currently available to cardiologists. Although there are technical obstacles to overcome in filtering gross motions of the subject, the VSM offers significant advances over conventional methods of measuring heart and respiration rate.