In-ear wearable accurately measures heart rate

Under realistic clinical scenarios, an in-ear wearable photoplethysmography (PPG) device can match electrocardiography (ECG) for the measurement of heart rate, according to a recent study.

Ninety-seven patients provided a total of 2,048 hours of ECG and in-ear PPG recording, resulting in a per-participant average of 14.4 hours of recording. After quality filtering, the in-ear monitor demonstrated a 0.78-bp bias as compared with ECG measurement. The standard deviation was 2.54 bpm. [Front Digit Health 2022;4:909519]

The resulting average intraclass coefficient was 0.81 (95 percent confidence interval [CI], 0.78–0.84), while the Pearson’s correlation coefficient was slightly higher at 0.84 (95 percent CI, 0.80–0.86). The coefficient of determination was 0.71 (95 percent CI, 0.68–0.75), and the resulting mean absolute percentage error was 2.57 percent (95 percent CI, 2.24–2.90).

“The results prove that the in-ear PPG sensor can provide a valid heart rate measurement if further improved by filtering algorithms. Though achieving moderate results using all data points, applying the quality indicator of the in-ear sensor improved all statistical parameters by removing unreliable data points,” the researchers said.

“This is the first paper to describe a detailed validation of heart rate derived from a commercial in-ear PPG sensor in a realistic clinical setting,” they added.

A promising technology

The study enrolled adult patients who were suffering from refractory epilepsy and had undergone video-electroencephalography (EEG) monitoring. Alongside standard EEG and ECG recordings, patients were also given a commercial in-ear sensor, which was designed to measure PPG metrics. Nurses replaced the in-ear devices every 6 hours with a full-charged monitor.

The wearable in-ear device combines an LED element with a photodiode, a resistance-based temperature sensor, and an accelerometer, allowing it to collect measurements of heart rate, body temperature, user movement patterns, and the intervals between heart beats.

“In the grand scheme of clinical epilepsy practice, our main question remains as whether in-ear PPG-based measurements can be used for epileptic seizure detection,” the researchers said, noting that the present findings do support a potential role for such devices in epilepsy management.

“Since epileptic patients may ultimately benefit from continuous, real-time monitoring and seizure detection using the in-ear sensor, establishing its accuracy in this specific setting was a crucial first step,” they added.

Nevertheless, important study limitations remain. For instance, while all patients experienced seizures while in-ear monitoring was ongoing, it remains uncertain how much of the seizure-relevant data were cleared off by the quality filtering.

Moreover, the exact predictive value of in-ear heart rate, body acceleration, and other such PPG signatures for seizure detection remains unknown.

“To make the in-ear optical sensor suitable for usage in epilepsy practice, future research should focus on the feasibility of using the heart rate, acceleration, and PPG signals of the in-ear sensor to detect epileptic seizures and the impact of movement on the accuracy of the PPG-signal,” the researchers said.