Introduction: Inertial sensors embedded into smart-eyewear (S-EW) technology offer new opportunities to evaluate cardiac and respiratory activity by head- head-ballistocardiography (H-BCG).
Aims: To test the feasibility of extracting cardiac mechanical activity and respiratory signals from H-BCG, from which to evaluate cardi-orespiratory coupling during controlled breathing at different rates.
Methods: Seven healthy volunteers (age: median [25th;75th] 25[25;27] years; BMI: 23.3[23.3;24.2] Kg/m2) were recruited. Three-axis linear ac-celeration (ACC) and 3-axis angular velocity (100 Hz) were acquired us-ing a S-EW prototype (�EssilorLuxottica, Milan, Italy), simultaneously with 1-lead ECG (512 Hz) signal (Movesense Flash, Movesense Ltd., Vantaa, Finland) as gold standard. Protocol in sitting position included 10 breaths at 4, 6, 8, 10 seconds/breath, respectively, for each phase. Respira-tory cycles were automatically identified on the displacement signal ob-tained by integrating the H-BCG posterior-anterior ACC component, while cardiac activity was derived from the head-foot ACC and roll, and morphological and temporal beat-to-beat parameters, such as JJ intervals, Peak-to-Peak Amplitude and Slope were extracted for each respiratory phase. Folded scattergrams were used to evaluate changes in the computed parameter with respect to the % of the respiratory cycle. Sinusoidal har-monics were fitted to derive several evaluation metrics, and statistical dif-ferences among protocol phases were assessed.
Results: Automatically extracting cardiac activity and respiration from H-BCG was feasible, from which cardiorespiratory coupling during a paced breathing protocol was evaluated. A higher feasibility was obtained at 6 and 8 sec per breath. Respiratory-modulated changes in both temporal (due to respiratory sinus arrhythmia) and morphological (probably due to preload) cardiac parameters were observed.
Conclusion: This preliminary work showed the feasibility of automati-cally assessing cardiorespiratory coupling from the head micromovements using S-EW technology, with the subject in sitting position during paced breathing, thus paving the way for future investigations during spontane-ous breathing in real-life settings.