Abstract
Recently, noncontact vital sign monitors have attracted attention because of issues related to the transmission of contagious diseases. We developed a real-time vital sign monitor using impulse-radio ultrawideband (IR-UWB) radar with embedded processors and software; we then evaluated its accuracy in measuring heart rate (HR) and respiratory rate (RR) and investigated the factors affecting the accuracy of the radar-based measurements. In 50 patients visiting a cardiology clinic, HR and RR were measured using IR-UWB radar simultaneously with electrocardiography and capnometry. All patients underwent HR and RR measurements in 2 postures—supine and sitting—for 2 min each. There was a high agreement between the RR measured using radar and capnometry (concordance correlation coefficient [CCC] 0.925 [0.919–0.926]; upper and lower limits of agreement [LOA], − 2.21 and 3.90 breaths/min). The HR measured using radar was also in close agreement with the value measured using electrocardiography (CCC 0.749 [0.738–0.760]; upper and lower LOA, − 12.78 and 15.04 beats/min). Linear mixed effect models showed that the sitting position and an HR < 70 bpm were associated with an increase in the absolute biases of the HR, whereas the sitting position and an RR < 18 breaths/min were associated with an increase in the absolute biases of the RR. The IR-UWB radar sensor with embedded processors and software can measure the RR and HR in real time with high precision. The sitting position and a low RR or HR were associated with the accuracy of RR and HR measurement, respectively, using IR-UWB radar.
Highlights
Real-time monitoring for vital signs such as respiratory rate (RR), oxygen saturation, heart rate (HR), blood pressure (BP) and body temperature is fundamental in many clinical contexts
The mean RRs measured for 2 min using radar highly agreed with those measured simultaneously using capnometry (CCC 0.969; 95% CI 0.951–0.981)
The concordance level of the mean HRs between radar and ECG was lower than that of the mean RRs between radar and capnometry (CCC 0.845; 95% CI 0.772–0.897), and the systematic bias of the mean HR was greater than that of the mean RR (Fig. 4A and Table 2)
Summary
Real-time monitoring for vital signs such as respiratory rate (RR), oxygen saturation, heart rate (HR), blood pressure (BP) and body temperature is fundamental in many clinical contexts. The signals from carotid pulsation on the surface of the neck were more prominent than respiration signals by a sufficiently wide margin to distinguish the two, in contrast to heartbeat signals on the anterior chest, which were difficult to distinguish from respiration signals This method requires the radar sensor to be placed a short distance (30 cm) from the neck and aimed with pinpoint accuracy at the carotid pulsation, which may be a major limitation for a noncontact vital sign monitor given that careful positioning of the device at close range may pose just as much risk as direct contact from the perspective of contagious disease prevention. We developed an IR-UWB radar sensor that features embedded processors and software and can perform simultaneous real-time HR and RR monitoring from the chest at a comfortable distance. We evaluated the accuracy and reliability of HR and RR measurements obtained using the new IR-UWB radar sensor and investigated the factors affecting the accuracy of the radar measurements, including patient posture
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