Noncontact Vital Sign Monitoring Using IR-UWB Radar

Overview

Background: Contact sensors can cause injuries and infections in newborn infants with fragile skin. The impulse radio ultra-wideband (IR-UWB) radar is recently demonstrated in adults as a contactless method to measure heart rate. The purpose of this study is to assess heart rate (HR) in neonates using IR-UWB radar and evaluate its accuracy, compared to the electrocardiogram (ECG) in the neonatal intensive care unit (NICU). Methods: HR is recorded in newborn infants using both IR-UWB radar 35 cm away from the chest and ECG simultaneously in the NICU. The HR data during sleeping/calm state are automatically collected by a software algorithm. A total values averaged from a 30-second window every 10 s is used for the analysis. Data acquired on the same patient with standard electrocardiogram has been used for comparison.

Vital sign is recorded by the radar and bedside ECG simultaneously in supine position within an open-air crib. The three electrodes of the ECG are attached at the standard positions and connected to the BSM-6501K patient monitor (Nihon Kohden, Tokyo, Japan), and vital signs are recorded and extracted. The data from the radar is connected to a computer through a USB interface, and signal processing has been automatically performed by a software algorithm described by our previous study. A Fourier transform decomposes a signal with respect to time into a frequency component. Vital sign is recorded continuously, and digital outputs are extracted from periods when no large noise or fluctuation occurs in both methods. While vital sign acquisition is significantly interfered with moving extensively, being in nursing care, repetitive myoclonus, hiccupping, flopping, or crying, the IR-UWB radar system stops the measurements and deletes the motion-contaminated observations automatically by itself. To investigate the artifact and interference by body movement during measurement, the level of movement is integrated based on the change of distance of the body from the radar. The radar transmits dozens of these signals (frames) to the computer every second, and the frame would not be changed if there was no movement within the range of the radar. However, if there is any movement, the difference of two frames (previous - current) is calculated.