An Ear-Worn Vital Signs Monitor.

This paper presents a wearable vital signs monitor at the ear. The monitor measures the electrocardiogram (ECG), ballistocardiogram (BCG), and photoplethysmogram (PPG) to obtain pre-ejection period (PEP), stroke volume (SV), cardiac output (CO), and pulse transit time (PTT). The ear is demonstrated as a natural anchoring point for the integrated sensing of physiological signals. All three signals measured can be used to obtain heart rate (HR). Combining the ECG and BCG allows for the estimation of the PEP, while combining the BCG and PPG allows for the measurement of PTT. Additionally, the J-wave amplitude of the BCG is correlated with the SV and, when combined with HR, yields CO. Results from a clinical human study on 13 subjects demonstrate this proof-of-concept device.

A Low-Power, Dual-Wavelength Photoplethysmogram (PPG) SoC With Static and Time-Varying Interferer Removal.

This paper presents a low-power, reflectance-mode photoplethysmogram (PPG) front end with up to 100 µA of static interferer current removal and 87 dB attenuation of time-varying interferers. The chip nominally consumes 425 µW including signal chain circuits, red and IR LED drive power, clocks, digitization and I/O. Measured data shows the noise of the PPG signal to be dominated by the photodiode sensor photon shot noise.

A wearable cardiac monitor for long-term data acquisition and analysis.

A low-power wearable ECG monitoring system has been developed entirely from discrete electronic components and a custom PCB. This device removes all loose wires from the system and minimizes the footprint on the user. The monitor consists of five electrodes, which allow a cardiologist to choose from a variety of possible projections. Clinical tests to compare our wearable monitor with a commercial clinical ECG recorder are conducted on ten healthy adults under different ambulatory conditions, with nine of the datasets used for analysis. Data from both monitors were synchronized and annotated with PhysioNet's waveform viewer WAVE (physionet.org) [1]. All gold standard annotations are compared to the results of the WQRS detection algorithm [2] provided by PhysioNet. QRS sensitivity and QRS positive predictability are extracted from both monitors to validate the wearable monitor.

An ear-worn continuous ballistocardiogram (BCG) sensor for cardiovascular monitoring.

Traditionally, ballistocardiogram (BCG) has been measured using large and stationary devices. In this work, we demonstrate a portable and continuous BCG monitor that is wearable at the ear. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. With the ear as an anchoring point, the device uses a MEMS tri-axial accelerometer to measure BCG at the head. Morphological differences exist between head BCG and traditional BCG, but the principal peaks (J waves) and their vectors are preserved. The frequency of J waves corresponds to heart rate, and when used in conjunction with an electrocardiogram's (ECG) R wave, the timing of J waves yields the RJ interval. Results from our clinical study show linear correlation between the RJ interval and the heart's pre-ejection period during hemodynamic maneuvers, thus revealing important information about cardiac contractility and its regulation.

A wearable vital signs monitor at the ear for continuous heart rate and pulse transit time measurements.

A continuous, wearable and wireless vital signs monitor at the ear is demonstrated. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. The device monitors the electrocardiogram (ECG) in a single lead configuration, the ballistocardiogram (BCG) with a MEMS triaxial accelerometer, and the photoplethysmograms (PPG) with 660 nm and 940 nm LED sources and a static photocurrent subtraction analog front end. Clinical tests are conducted, including Valsalva and head-up tilt maneuvers. Peak timing intervals between the ECG, BCG and PPG are extracted and are shown to relate to pre-ejection period and mean arterial blood pressure (MAP). Pulse Transit Time (PTT) extracted from cross-correlation between the PPG and BCG shows improved results compared to the pulse arrival time (PAT) method for tracking changes in MAP.

A continuous, wearable, and wireless heart monitor using head ballistocardiogram (BCG) and head electrocardiogram (ECG).

Continuous and wearable heart monitoring is essential for early detection and diagnosis of cardiovascular diseases. We demonstrate a continuous, wearable, and wireless heart monitor that is worn at the ear. The device has the form factor of a hearing aid and is wirelessly connected to a PC for data recording and analysis. With the ear as an anchoring point, the heart monitor measures the ballistocardiographic (BCG) motion of the head using a MEMS tri-axial accelerometer, which is an electrode-less method to measure heart rate. Additionally, electrocardiogram (ECG) is measured locally near the ear using a single-lead configuration. The peak timing delay between the head ECG and the head BCG, or RJ interval, can be extracted in the presence of noise using cross-correlation. The RJ interval is shown to correlate to the heart's pre-ejection period during both Valsalva and whole-body tilt maneuvers.

The ear as a location for wearable vital signs monitoring.

Obtaining vital signs non-invasively and in a wearable manner is essential for personal health monitoring. We propose the site behind the ear as a location for an integrated wearable vital signs monitor. This location is ideal for both physiological and mechanical reasons. Physiologically, the reflectance photoplethysmograph (PPG) signal behind the ear shows similar signal quality when compared to traditional finger transmission PPG measurements. Ballistocardiogram (BCG) can be obtained behind the ear using 25mm×25mm differential capacitive electrodes constructed using fabric. The BCG signal is able to provide continuous heart rate and respiratory rate, and correlates to cardiac output and blood pressure. Mechanically, the ear remains in the same orientation relative to the heart when upright, thus simplifying pulse transit time calculations. Furthermore, the ear provides a discreet and natural anchoring point that reduces device visibility and the need for adhesives.