Unsupervised Heart-rate Estimation in Wearables With Liquid States and A Probabilistic Readout

TL;DR

This paper introduces an unsupervised, energy-efficient heart-rate estimation method for wearables using a Liquid State Machine with a novel learning algorithm and fuzzy clustering, enabling personalized and accurate ECG analysis.

Contribution

It presents a new unsupervised approach that encodes ECG signals into spike trains, uses a Liquid State Machine model, and employs fuzzy c-means clustering with particle swarm optimization for heart-rate estimation.

Findings

High accuracy in heart-rate estimation across diverse subjects

Low energy consumption suitable for wearable devices

Effective handling of cardiac irregularities

Abstract

Heart-rate estimation is a fundamental feature of modern wearable devices. In this paper we propose a machine intelligent approach for heart-rate estimation from electrocardiogram (ECG) data collected using wearable devices. The novelty of our approach lies in (1) encoding spatio-temporal properties of ECG signals directly into spike train and using this to excite recurrently connected spiking neurons in a Liquid State Machine computation model; (2) a novel learning algorithm; and (3) an intelligently designed unsupervised readout based on Fuzzy c-Means clustering of spike responses from a subset of neurons (Liquid states), selected using particle swarm optimization. Our approach differs from existing works by learning directly from ECG signals (allowing personalization), without requiring costly data annotations. Additionally, our approach can be easily implemented on state-of-the-art spiking-based neuromorphic systems, offering high accuracy, yet significantly low energy footprint, leading to an extended battery life of wearable devices. We validated our approach with CARLsim, a GPU accelerated spiking neural network simulator modeling Izhikevich spiking neurons with Spike Timing Dependent Plasticity (STDP) and homeostatic scaling. A range of subjects are considered from in-house clinical trials and public ECG databases. Results show high accuracy and low energy footprint in heart-rate estimation across subjects with and without cardiac irregularities, signifying the strong potential of this approach to be integrated in future wearable devices.