Characterizing the continuously acquired cardiovascular time series during hemodialysis, using median hybrid filter preprocessing noise reduction

Figures & data

Figure 1 Raw continuous SBP signal across treatment, with signal degradation through noise and outlying impulse (the blow-up shows component heartbeat data points highlighting noise artifact and outliers over a shortened timeframe).

Abbreviation: SBP, systolic blood pressure.

Table 1 Approximate time equivalence of moving average window lengths according to underlying heart rate

MA length (beats)	Heart rate
	50 bpm	70 bpm	90 bpm
13	16 sec	11 sec	9 sec
21	25 sec	18 sec	14 sec
55	1 min	47 sec	37 sec
144	3 min	2 min	2 min
233	5 min	3 min	3 min
377	8 min	5 min	4 min
610	12 min	9 min	7 min

Abbreviation: sec, seconds; min, minutes; Ma, moving average.

Figure 2 Post-MHF product overlain against raw continuous intradialytic SBP data in two patients.

Abbreviations: MHF, median hybrid filter; SBP, systolic blood pressure.

Figure 3 Point plot of conventional intermittent brachial SBP measurement acquired during standard practice.

Abbreviations: NIBP, noninvasive brachial cuff blood pressure; SBP, systolic blood pressure.

Figure 4 Detail of the MHF regression product from continuous SBP monitoring compared with standard intermittent brachial SBP readings.

Abbreviations: MHF, median hybrid filter; NIBP, noninvasive brachial cuff blood pressure; SBP, systolic blood pressure.

Figure 5 Bland–Altman comparison between standard brachial cuff SBP and the post-MHF continuous recording applied to the same patients (n=10).

Abbreviations: MHF, median hybrid filter; SBP, systolic blood pressure; SD, standard deviation.

Table 2 Statistical white noise analysis of the MHF output product after application to the continuous intradialytic SBP trace

Patient	Fisher’s kappa		Bartlett’s Kolmogorov–Smirnov (KS)
	κ	P	KS statistic	P
1	2,691.969	<0.001	0.975	<0.001
2	2,809.109	<0.001	0.972	<0.001
3	1,528.096	<0.001	0.973	<0.001
4	2,037.879	<0.001	0.969	<0.001
5	9,056.110	<0.001	0.989	<0.001
6	1,877.397	<0.001	0.948	<0.001
7	2,464.192	<0.001	0.971	<0.001
8	5,396.599	<0.001	0.966	<0.001
9	4,063.844	<0.001	0.964	<0.001
10	5,180.532	<0.001	0.978	<0.001

Abbreviations: MHF, median hybrid filter; SBP, systolic blood pressure.