Development and validation of an integrated wearable system for continuous cardiorespiratory monitoring using photoplethysmography and optical respiratory detection

Abstract Cardiovascular diseases remain the leading cause of mortality worldwide, with ischaemic heart disease the leading contributor and acute myocardial infarction accounting for the majority of ischaemic heart disease deaths. This study presents the development and technical validation of a low-cost, integrated wearable system for multi-parameter cardiorespiratory monitoring designed to support heart-attack detection algorithms. The system comprises two devices: a wristband incorporating a MAX30105 photoplethysmography sensor for cardiac pulse-wave and SpO $$_2$$ acquisition, and a chest band featuring novel optical respiratory detection and an MPU6050 inertial measurement unit for respiratory rate and movement monitoring. Both devices use ESP32-C3 microcontrollers with Bluetooth Low Energy connectivity to a custom mobile application enabling real-time visualization and cloud-based storage. Validation was conducted against clinical-grade reference equipment (ADInstruments physiograph and EDAN iM8 monitor) in 43 healthy volunteers, yielding 50 acquisitions: 30 at rest and 20 post-physical activity. This is a technical feasibility study in healthy young volunteers; validation in clinical populations remains future work. Heart rate showed the closest agreement with the reference (percentage error ±1.94%, $$r=0.99$$ post-activity; limits of agreement $$-6.21$$ to 4.21 BPM), followed by respiratory rate (±3.47%, $$r=0.99$$ ). SpO $$_2$$ error remained within tolerance (1.64% at rest, 2.98% post-activity) but showed weak correlation with the reference owing to range restriction in a healthy cohort, and is not yet suitable for applications requiring absolute saturation values. This study demonstrates that a low-cost, multi-sensor wearable system can achieve accuracy meeting the prespecified feasibility criterion ( $$<\pm $$ 5% error) in a healthy young cohort, establishing technical feasibility as a prerequisite to validation in the cardiovascular patient populations for which the system is ultimately intended.