Clinical validation of a novel wearable system for real-time telemetric transmission of transient changes of cardiac autonomic modulation induced by psychophysiological and physical stress

Background: Although clinical assessment of cardiac autonomic modulation (CAM) usually relies on off-line heart rate variability analysis (HRVa), measured under stationary conditions according to guidelines, there is a growing interest, in sports medicine and psychophysiology, for the reliable evaluation of acute changes of CAM occurring under real-world dynamics (i.e. acute stress induced by competitions or critical situations). The aim of this study was to test, with a standardized clinical protocol inducing enhancement of sympathetic/vagal modulation, the reliability of a novel system for continuous monitoring and telemetric transmission of transient CAM changes (Vi- BioBox), provided by real-time calculation of time-variant HRV parameters and Skin Potential Response (SPR). Methods: All measurements were performed in the laboratory for clinical electrophysiology. The Vi-BioBox system (Vi-grade, Udine) consists of a wearable wireless mini-recording device connected to a textile electrode garment (Nuubo, Spain) and hands electrodes. 3 ECG and 2 SPR signal are continuously recorded (1 KHz sampling-rate) and streamed in real-time to Wintax4 (Magneti-Marelli) data logging for real-time calculation and monitoring of spectral HRV parameters and of the Root Mean Square value of two SPR signals (SPRRMS) with a proprietary custom software (Vi-BioSoft). 10 healthy volunteers (mean age 32.4±16.8 y, 50% males) underwent a 5-steps protocol: 1) 10-minutes baseline supine; 2) 10-minutes Head-up tilting 70° (HUTT); 3) 10-minutes supine recovery); 4) 20-minutes mental stress ("Mensa" preliminary Tests); 5) exercise-test at bicycle-ergometer. 12- lead ECG was continuously recorded also with Mortara Surveyor/X-Scribe and Time-variant HRV parameters were also calculated off-line with Kubios (3.0.2) software. Statistical analysis was performed with SPSS 21. Results: The quality of the Vi-BioBox signals was optimal for reproducible real-time calculation and monitoring of time-variant HRV parameters. Baseline SPRRMS activity ranged between 0.01 and 0.8 mV, with wide interindividual variability. A significant (p<0.05) increment (up to 2.6 mV) was induced by HUTT, but not by physical exercise. SPRRMS and LF/HF had similar trend along test session. Good agreement was found between HRV parameters calculated in real-time, their off-line recalculation with Kubios software and those obtained from Mortara telemetry. Conclusion: Real-time monitoring of time-variant spectral HRV parameters and of SPRRMS was reliable and reproducible. SPRRMS is an independent sensitive marker of sympathetic activation, which anticipates increments of VLF, LF and is useful to interpret CAM underlying of LF/HF changes. Real-time monitoring of CAM may be useful to improve the mechanistic understanding of acute psychophysiological stress-reactions, dysautonomic syncope, arrhythmic events initiation and for telemedicine (i.e. continuous remote monitoring of CAM in patients with heart failure).