Extraction of Heart Rate Variability from Smartphone Photoplethysmograms

Table 2

Pearson’s correlation coefficients and linear regression equations between HRV parameters derived from the smartphone and the electrocardiograph.

Parameter	PP	VP	M1D	M2D	TI
AVNN (ms)	1.000 (P < 0.001); y = 1.000x + 0.072	1.000 (P < 0.001); y = 1.000x + 0.019	1.000 (P < 0.001); y = 1.000x − 0.084	1.000 (P < 0.001); y = 1.000x − 0.367	1.000 (P < 0.001); y = 1.000x − 0.097
SDNN (ms)	0.722 (P = 0.000); y = 0.912x + 33.708	0.902 (P = 0.000); y = 0.865x + 26.556	0.933 (P = 0.000); y = 0.891x + 19.641	0.859 (P = 0.000); y = 0.785x + 35.635	0.916 (P = 0.000); y = 0.875x + 20.304
CV (%)	0.703 (P < 0.001); y = 0.756x + 4.519	0.881 (P < 0.001); y = 0.893x + 2.675	0.920 (P < 0.001); y = 0.918x + 1.934	0.826 (P < 0.001); y = 0.827x + 3.561	0.900 (P < 0.001); y = 0.903x + 2.008
RMSSD (ms)	0.596 (P = 0.001); y = 1.034x + 66.019	0.713 (P < 0.001); y = 0.801x + 57.427	0.780 (P < 0.001); y = 0.811x + 44.095	0.629 (P < 0.001); y = 0.677x + 74.746	0.731 (P < 0.001); y = 0.796x + 43.870
SDSD (ms)	0.596 (P = 0.001); y = 1.035x + 66.086	0.713 (P < 0.001); y = 0.801x + 57.497	0.780 (P < 0.001); y = 0.811x + 44.152	0.630 (P < 0.001); y = 0.677x + 74.839	0.732 (P < 0.001); y = 0.796x + 43.924
NN50	0.254 (P = 0.176); y = 0.203x + 90.688	0.285 (P = 0.127); y = 0.184x + 79.417	0.292 (P = 0.118); y = 0.215x + 73.810	0.081 (P = 0.669); y = 0.060x + 96.888	0.391 (P = 0.033); y = 0.306x + 66.480
pNN50 (%)	0.415 (P = 0.022); y = 0.313x + 27.188	0.508 (P = 0.004); y = 0.287x + 23.540	0.513 (P = 0.004); y = 0.309x + 21.844	0.513 (P = 0.004); y = 0.309x + 21.844	0.513 (P = 0.004); y = 0.309x + 21.844
TP (ms2)	1.000 (P < 0.001); y = 1.002x + 20.325	0.999 (P < 0.001); y = 1.001x + 12.614	1.000 (P < 0.001); y = 1.009x + 6.481	1.000 (P < 0.001); y = 0.998x + 4.521	1.000 (P < 0.001); y = 1.006x + 6.888
VLF (ms2)	0.996 (P < 0.001); y = 1.002x + 5.276	0.995 (P < 0.001); y = 0.996x + 9.597	0.998 (P < 0.001); y = 0.999x + 4.785	0.998 (P < 0.001); y = 0.992x + 7.631	0.998 (P < 0.001); y = 1.003x + 2.669
LF (ms2)	0.992 (P < 0.001); y = 1.011x − 8.803	0.989 (P < 0.001); y = 0.993x − 2.426	0.996 (P < 0.001); y = 1.022x − 16.348	0.996 (P < 0.001); y = 0.997x − 3.807	0.996 (P < 0.001); y = 1.009x − 9.753
HF (ms2)	0.993 (P < 0.001); y = 0.982x + 28.252	0.990 (P < 0.001); y = 0.986x + 24.236	0.996 (P < 0.001); y = 1.002x + 17.071	0.997 (P < 0.001); y = 0.981x + 12.937	0.996 (P < 0.001); y = 0.997x + 18.848
LF/HF	0.963 (P < 0.001); y = 0.883x + 0.078	0.967 (P < 0.001); y = 0.850x + 0.111	0.982 (P < 0.001); y = 0.871x + 0.088	0.984 (P < 0.001); y = 0.874x + 0.120	0.981 (P < 0.001); y = 0.882x + 0.075
nLF (%)	0.968 (P < 0.001); y = 0.919x + 2.896	0.967 (P < 0.001); y = 0.812x + 8.941	0.982 (P < 0.001); y = 0.873x + 5.539	0.988 (P < 0.001); y = 0.920x + 3.754	0.981 (P < 0.001); y = 0.872x + 5.673
nHF (%)	0.977 (P < 0.001); y = 0.969x + 2.760	0.985 (P < 0.001); y = 0.889x + 6.224	0.986 (P < 0.001); y = 0.925x + 4.565	0.992 (P < 0.001); y = 0.946x + 3.027	0.988 (P < 0.001); y = 0.926x + 4.509
SD1 (ms)	0.596 (P = 0.001); y = 1.035x + 46.728	0.713 (P < 0.001); y = 0.801x + 40.656	0.780 (P < 0.001); y = 0.811x + 31.219	0.630 (P < 0.001); y = 0.677x + 52.918	0.732 (P < 0.001); y = 0.796x + 31.058
SD2 (ms)	0.920 (P < 0.001); y = 0.922x + 20.291	0.986 (P < 0.001); y = 0.934x + 14.018	0.989 (P < 0.001); y = 0.955x + 9.982	0.978 (P < 0.001); y = 0.898x + 18.234	0.988 (P < 0.001); y = 0.953x + 10.075

: HRV parameters derived from an electrocardiograph and : HRV parameters derived from a smartphone using five different algorithms. PP: peak point; VP: valley point; M1D: maximum first derivative; M2D: maximum second derivative, and TI: tangent intersection. A value <0.05 was considered statistically significant. HRV parameters are explained in Table 1.