CardboardHRV: Bridging Virtual Reality and Biofeedback with a Cost-Effective Heart Rate Variability System

We introduce CardboardHRV, an affordable and effective heart rate variability (HRV) biofeedback system leveraging Cardboard VR. Designed for easy access to HRV biofeedback without sacrificing therapeutic value, we adapted the Google Cardboard VR headset with an optical fiber modification. This enables the camera of the inserted phone to capture the photoplethysmography (PPG) signal from the user's lateral forehead, enabling CardboardHRV to accurately calculate the heart rate variability as a basis for biofeedback. Furthermore, we've integrated an engaging biofeedback game to assist users throughout their sessions, enhancing user engagement and the overall experience. In a preliminary user evaluation, CardboardHRV demonstrated comparable therapeutic outcomes to traditional HRV biofeedback systems that require an additional electrocardiogram (ECG) device, proving itself as a more cost-effective and immersive alternative.