Monitoring of Serum Potassium and Calcium Levels in End-Stage Renal Disease Patients by ECG Depolarization Morphology Analysis

Figures

• 

  Figure 1. Diagram of the study protocol. h0 to h48 are the time points (in minutes) for blood sample extraction. Reproduced with permission from Bukhari et al., Computers in Biology and Medicine; published by Elsevier, 2022.

• 

  Figure 2. Flow chart showing the ECG processing steps performed in this study, from the collection of raw ECGs to the estimation of [K+] and [Ca2+].

• 

  Figure 3. Time warping of QRS complexes. Panel (a) shows the reference (blue) and investigated (red) QRS complexes obtained from an ECG segment during HD. Panel (b) shows the warped QRS complexes, which had the same duration whilst keeping the original amplitude. Panel (c) depicts the warped QRS complexes after normalization by their L2-norms. The yellow area in panel (d) represents dw,Qu, which quantified the total amount of warping. The green solid line is the linear regression function γl*(tr) best fitted to γ*(tr).

• 

  Figure 4. Panels (a–f): changes in QRSw, QRSa, dw,Qu, da,Q, dw,QNL and da,QNL during HD stages. Panels (g–i): corresponding variations in [K+], [Ca2+] and RR. In panels (a–i), * denotes p<0.05 and ** denotes p<0.01. In each panel, the central white dot indicates the median. Each dot corresponds to an individual patient. Panel (j): MWQRS (red) of a patient at different HD stages and reference MWQRS (blue). Δ denotes the change in [K+] with respect to the end of HD (h4).

• 

  Figure 5. Pearson correlation coefficients between QRS markers (QRSw, QRSa, dw,Qu, da,Q, dw,QNL and da,QNL) and [K+] (black), [Ca2+] (red) and RR (blue) for all patients at all HD points. The central white dot indicates the median. Each dot corresponds to an individual patient.

• 

  Figure 6. Actual (black) and estimated [K+] and [Ca2+] for a patient using stage-specific (red), patient-specific (green) and global (blue) approaches. Univariable dw,Qu-based estimation is shown in (panel a), dw,Tu-based in (panel b) and multivariable dw,Qu- dw,Tu-based in (panel c).

• 

  Figure 7. Box plots of [K+] and [Ca2+] estimation errors ev during HD stages for all patients using dw,Qu(black), dw,Tu(red) and the combination of dw,Qu and dw,Tu (blue) for stage-specific (top), patient-specific (middle) and global (bottom) approaches. The central line indicates the median, whereas top and bottom edges show the 25th and 75th percentiles.

• 

  Figure 8. QRS and T wave variations at the start (red) and end (blue) of the HD session. Panels (a,b) show the waveforms related to the QRS complex and the T wave, respectively.