Utility of a smartphone based system (cvrphone) to accurately determine apneic events from electrocardiographic signals

Abstract

Background: Sleep disordered breathing manifested as sleep apnea (SA) is prevalent in the general population, and while it is associated with increased morbidity and mortality risk in some patient populations, it remains under-diagnosed. The objective of this study was to assess the accuracy of respiration-rate (RR) and tidal-volume (TV) estimation algorithms, from body-surface ECG signals, using a smartphone based ambulatory respiration monitoring system (cvrPhone).

Methods: Twelve lead ECG signals were collected using the cvrPhone from anesthetized and mechanically ventilated swine (n = 9). During ECG data acquisition, the mechanical ventilator tidal-volume (TV) was varied from 250 to 0 to 750 to 0 to 500 to 0 to 750 ml at respiratory rates (RR) of 6 and 14 breaths/min, respectively, and the RR and TV values were estimated from the ECG signals using custom algorithms.

Results: TV estimations from any two different TV settings showed statistically significant difference (p < 0.01) regardless of the RR. RRs were estimated to be 6.1±1.1 and 14.0±0.2 breaths/min at 6 and 14 breaths/min, respectively (when 250, 500 and 750 ml TV settings were combined). During apnea, the estimated TV and RR values were 11.7±54.9 ml and 0.0±3.5 breaths/min, which were significantly different (p<0.05) than TV and RR values during non-apnea breathing. In addition, the time delay from the apnea onset to the first apnea detection was 8.6±6.7 and 7.0±3.2 seconds for TV and RR respectively.

Conclusions: We have demonstrated that apnea can reliably be detected using ECG-derived RR and TV algorithms. These results support the concept that our algorithms can be utilized to detect SA in conjunction with ECG monitoring.

Fig 1

(A) The Smart-Phone based ECG acquisition system, cvrPhone. Flow-diagram of the 12-lead ECG signals from the torso to Smart-Phone. Ten electrodes are placed on the torso for the recording of 8 ECG leads (Leads I and II and six precordial leads) and the real-time display of selected three ECG signals on the smartphone screen. (Modified from [17] under a CC BY license, with permission from the authors, original copyright 2017). (B) Lay-out of the algorithms to estimate the RR and TV. (C) Estimation of the tidal-volume (TV) at 250 to 0 to 750 to 0 to 500 to 0 to 750 ml (marked by the red lines), at RR of 6 breaths/min (upper panel) and 14 breaths/min (lower panel) set by adjusting the mechanical ventilator and using the value indicated by the capnogragh monitor as the gold standard.

Fig 2

Tidal volume estimations (A) and the estimation errors (B), in the order of the tidal volume setting. The tidal volume setting of the mechanical ventilator was changed from 250 to 0 to 750 to 0 to 500 to 0 to 750 ml, as marked by the red thick lines on (A). The respiration rate was 6 breaths/min for the upper two panels and 14 breaths/min for the lower two panels. There were 9 records from 9 animals in case of 6 breaths/min, and 8 records from 8 animals in case of 14 breaths/min. Each bar plot represents 90, 75, 50, 25 & 10% of all estimated values (A) or of all estimation errors (B). There was difference in the estimated TV errors between any two apneic events or between the two 750 ml settings. On the other hand, the TV estimation error was between 0 and 250 ml (p = 0.34, p = 0.23 & p = 0.29 at 6 breaths/min, and p<0.05, p = 0.66 & p<0.05 at 14 breaths/min), 250 and 500 ml (p = 0.54 at 6 breaths/min, and p<0.05 at 14 breaths/min), and 500 and 750 ml (p = 0.15 & p = 0.62 at 6 breaths/min, and p<0.05 & p = 0.16 at 14 breaths/min).

Fig 3

Tidal volume (TV) estimations (A) and TV estimation errors (B), in the order of increasing TV. The tidal volume setting of the mechanical ventilator was changed from 250 to 0 to 750 to 0 to 500 to 0 to 750 ml during tests, and rearranged in the order of increasing TV in the plots. The TV setting values are marked by the red thick lines on the left panels. The respiration rate was 6 breaths/min for the upper two panels and 14 breaths/min for the lower two panels. There were 9 records from 9 animals in case of 6 breaths/min, and 8 records from 8 animals in case of 14 breaths/min. Each bar plot represents 90, 75, 50, 25 & 10% of all estimated values (A) or estimation errors (B). All pairs of adjacent TVs in (A) are different with 0 vs 250 ml (p<0.001), 250 vs 500 ml (p<0.001) and 500 vs 750 ml (p<0.001) for 6 breaths/min and 0 vs 250 ml (p< = 0.001), 250 vs 500 ml (p<0.001) and 500 vs 750 ml (p<0.001) for 14 breaths/min. In (B), the TV estimation errors increase with incremental TV values, and the magnitude of these errors at 6 breaths/min is larger (p = 0.61, p = 0.89 & p = 0.07 at 250, 500 & 750 ml, respectively) than the errors at 14 breaths/min during non-apnea events.

Fig 4

Respiratory rate (RR) estimations (A) and the associated estimation errors (B). The respiration rate was set to 6 or 14 breaths/min as marked by the thick red lines on (A). There were 9 records from 9 animals in case of 6 breaths/min, and 8 records from 8 animals in case of 14 breaths/min. In (A), the RR distributions between 0, 250, 500 and 750 ml (either at 6 or 14 breaths/min) were significantly different (p<0.001). There was statistical difference in the estimated RR distributions between any two 6 breaths/min (p<0.001, p<0.001, p = 0.112) or 14 breaths/min (p<0.056, p<0.05, and p<0.001), for any two TV settings. Each bar plot represents 90, 75, 50, 25 & 10% of all estimated values (A) or estimation errors (B).