Low-Power Wireless System for Continuous Measurement of Cardiovascular Parameters on a Single Limb

A novel low-power sensor wireless system for continuous and simultaneous measurement of the electrocardiogram (ECG) and the impedance plethysmogram (IPG) from a single limb has been designed and tested. This system is made up of an analog subsystem composed of two signal-conditioning channels, one for the ECG and one for the IPG that share the same voltage pickup electrodes, and a digital subsystem based on the BGM220PC22WGA microcontroller that is responsible for digitizing the signals and sending their data via Bluetooth Low Energy (BLE) to a processing unit. The consumption of the system has been analyzed using different settings, obtaining values that would allow a battery duration of up to 131 h, by performing four 30-s measurements every hour. The system was tested in one arm and one leg in a group of healthy volunteers to verify the functionality and to identify the best electrode positions to get high quality signals. Non-standard ECG leads are obtained in both one arm and one leg with an SNR of more than 30 dB. In the worst case, for measurements on the legs, the mean error of the RR intervals from each recording was 1.7 ms and the 95% confidence interval (+/- SD) was +/- 7.3 ms versus a reference system. This has made it possible to accurately obtain the Pulse Arrival Time (PAT) between the ECG and the simultaneously measured IPG signal, which allows more cardiovascular information to be obtained from the patient than with systems that acquire only the ECG signal.