Accuracy of the Instantaneous Breathing and Heart Rates Estimated by Smartphone Inertial Units

Area of Science:

• Biomedical Engineering
• Cardiorespiratory Monitoring
• Wearable Technology

Background:

• Seismocardiography (SCG) and Gyrocardiography (GCG) utilize chest wall accelerations and angular velocities.
• Respiration causes signal interference, but smartphone integration offers potential.
• Accurate cardiorespiratory monitoring is crucial for health assessment.

Purpose of the Study:

• To evaluate the accuracy of smartphone inertial sensors for simultaneous heart rate and breathing rate measurement.
• To assess the performance of SCG and GCG in detecting heartbeats and respiratory acts.
• To validate inter-beat (IBI) and inter-breath (IBrI) interval estimations using smartphone sensors.

Main Methods:

• Acquired SCG and GCG signals from 10 healthy subjects at rest using smartphones.
• Compared smartphone-derived SCG/GCG data with electrocardiography and respiration belt signals.
• Analyzed heartbeat and respiratory act detection accuracy, sensitivity, and positive predictive value (PPV).
• Evaluated inter-beat and inter-breath interval estimations using Bland-Altman analysis and R-squared values.

Main Results:

• GCG demonstrated high sensitivity (97.3%) and PPV (97.9%) for heartbeat detection.
• SCG and GCG showed high accuracy for respiratory act detection (sensitivity >95%, PPV >92%).
• IBI and IBrI estimations exhibited strong linear relationships (R² > 0.999 and R² > 0.968) with minimal bias and narrow limits of agreement.

Conclusions:

• Smartphone inertial sensors can accurately measure instantaneous heart and breathing rates.
• SCG and GCG, when derived from smartphones, offer a viable non-invasive cardiorespiratory monitoring solution.
• This technology eliminates the need for additional specialized monitoring devices.