Tracking Tidal Volume From Holter and Wearable Armband Electrocardiogram Monitoring

Abstract

A novel method for tracking the tidal volume (TV) from electrocardiogram (ECG) is presented. The method is based on the amplitude of ECG-derived respiration (EDR) signals. Three different morphology-based EDR signals and three different amplitude estimation methods have been studied, leading to a total of 9 amplitude-EDR (AEDR) signals per ECG channel. The potential of these AEDR signals to track the changes in TV was analyzed. These methods do not need a calibration process. In addition, a personalized-calibration approach for TV estimation is proposed, based on a linear model that uses all AEDR signals from a device. All methods have been validated with two different ECG devices: a commercial Holter monitor, and a custom-made wearable armband. The lowest errors for the personalized-calibration methods, compared to a reference TV, were -3.48% [-17.41% / 12.93%] (median [first quartile / third quartile]) for the Holter monitor, and 0.28% [-10.90% / 17.15%] for the armband. On the other hand, medians of correlations to the reference TV were higher than 0.8 for uncalibrated methods, while they were higher than 0.9 for personal-calibrated methods. These results suggest that TV changes can be tracked from ECG using either a conventional (Holter) setup, or our custom-made wearable armband. These results also suggest that the methods are not as reliable in applications that induce small changes in TV, but they can be potentially useful for detecting large changes in TV, such as sleep apnea/hypopnea and/or exacerbations of a chronic respiratory disease.

Fig. 1.

(a) Example of registered respiration during the experiment involving dynamic changes in TV. Panel (b) shows the reference TV, obtained by the peak-to-peak amplitude-EDR (AEDR) estimation algorithm applied to the volume signal obtained from the spirometer shown in (a). Panel (c) shows slope-range-based EDR signal obtained from the PCA channel. Below, its estimated AEDR obtained by the three estimation algorithms are shown: peak-to-peak (d), RMS (e), and analytic (f).

Fig. 2.

Scheme of the 9 different AEDR signals obtained per ECG channel.

Fig. 3.

Bland-Altman plots of the intrasubject mean of estimated TV $(\overline{y_{\mathrm{M}}^{\mathrm{P}}\left(n\right)},\text{M}\in \{\text{PEAK},\text{RMS},\text{ANA}\}$) and intrasubject mean of reference TV ($\overline{y_{\mathrm{R}}\left(n\right)}$), for both devices Holter (top row) and armband (bottom row) when including the PCA channel. Note that different axis limits are used for the armband in cases of RMS and ANA in order to show an outlier.