TBME presents

An Ear-Worn Vital Signs Monitor

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Cardiovascular disease (CVD) affects over one third of the U.S. population and is the current leading cause of death. Many key cardiovascular parameters such as the heart rate, stroke volume, pre-ejection period (PEP), and pulse transit time (PTT) have valuable applications in the field of CVD monitoring.

This work presents a wearable device that can obtain key cardiovascular metrics at a single location. The ear is chosen to be the sensor location due to its natural anchoring point and the availability of physiological signals. The device measures the electrocardiogram (ECG), ballistocardiogram (BCG), and photoplethysmogram (PPG) to obtain the heart rate, PEP, stroke volume, cardiac output, and PTT. The ear-worn monitor runs on a single coin cell battery, and transmits physiological signals in real-time via Bluetooth to a computer.

The heart rate can be obtained from the ECG, BCG, or PPG signal. Combining the timing information from the R-wave of the ECG to the J-wave of the BCG allows for the estimation of the PEP. Similarly, the timing information from the J-wave of the BCG to the peak of the PPG’s derivative allows for the measurement of the PTT. Additionally, the J-wave amplitude of the BCG is correlated to the stroke volume, which yields cardiac output when combined with the heart rate. Results from a clinical study on 13 subjects demonstrate this proof of concept device.

Further information can be found at the Massachusetts Institute of Technology’s (MIT) Medical Device Realization Center (MEDRC) website: http://medrc.mit.edu.

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