A hypoxia experiment was designed, in order to identify the dynamic component of the hemorheology information in the photoplethysmography (PPG) signal and analyze its characteristics. A total of thirty subjects were measured for PPG signals under normal oxygen volume fraction condition (20%~21%) and low oxygen volume fraction condition (15%~16%), respectively. The signal was analyzed based on the Hilbert-Huang transform (HHT) algorithm. The empirical mode decomposition results show that the dynamic component actually representing the hemorheology information of the PPG signal is intrinsic mode function IMFX. There are two time domain features of IMFX, one is a waveform similar to the arterial systolic relaxation, and the other is a periodic oscillation. The instantaneous frequency and marginal spectrum of IMFX were obtained based on the Hilbert transform algorithm, and the instantaneous frequency was mostly 1.5~2.5 Hz. In the hypoxic environment, the amplitude of the Hilbert marginal spectrum in the above frequency range is significantly smaller than that of the normal oxygen environment (P<0.05), which proves that this feature can be used to determine the hemorheological changes caused by hypoxia.
Lu YU,Long-zhe JIN,Ming-wei XU,Jian-guo LIU. Human hemorheology information evaluation based on Hilbert-Huang transform to decompose photoplethysmography signal. Journal of ZheJiang University (Engineering Science), 2020, 54(2): 340-347.
Fig.6Empirical mode decomposition results of photoplethysmography signal
Fig.7Statistical analysis of intrinsic mode function
Fig.8Hilbert marginal spectrum of IMF
Fig.9Schematic diagram of IMFX marginal spectrum theory process
Fig.10Statistical results of area ratio
编号
φ
全瞬时频率边际谱 振幅/(μV2·Hz?1)
P
1.5~2.5 Hz边际谱 振幅/(μV2·Hz?1)
P
编号
φ
全瞬时频率边际谱 振幅/(μV2·Hz?1)
P
1.5~2.5 Hz边际谱 振幅/(μV2·Hz?1)
P
1)注:边际谱振幅为平均值±标准差,独立样本t检验
1
低
2.4±35.61)
P<0.05
461.1±270.1
P<0.05
16
低
3.9±45.0
P<0.05
390.3±106.0
P<0.05
正
8.3±95.4
1 336.2±405.0
正
4.4±51.0
538.1±537.8
2
低
2.4±24.6
P<0.05
336.5±101.1
P<0.05
17
低
4.9±58.2
P<0.05
722.5±119.7
P<0.05
正
3.9±46.8
545.4±285.9
正
7.8±83.7
955.8±437.8
3
低
2.4±35.4
P<0.05
249.9±250.8
P<0.05
18
低
3.7±46.8
P<0.05
757.7±201.3
P<0.05
正
8.8±91.0
809.4±552.5
正
8.2±79.4
1 063.3±439.0
4
低
4.8±58.1
P<0.05
804.8±301.7
P<0.05
19
低
3.6±34.6
P>0.05
480.5±298.9
P<0.05
正
8.2±93.8
1 156.3±431.3
正
4.8±58.1
656.0±212.2
5
低
3.4±35.3
P>0.05
398.6±240.1
P<0.05
20
低
4.4±45.7
P>0.05
424.0±241.4
P<0.05
正
3.8±55.6
664.7±438.9
正
5.2±95.9
1 020.4±94.3
6
低
7.0±77.2
P>0.05
956.3±372.6
P<0.05
21
低
6.8±66.3
P>0.05
689.4±299.5
P<0.05
正
7.8±100.2
1 430.0±456.7
正
7.5±88.2
1 448.5±98.3
7
低
3.1±39.7
P>0.05
273.8±290.4
P<0.05
22
低
6.3±78.2
P>0.05
947.4±371.8
P<0.05
正
4.3±53.0
443.5±190.7
正
6.9±46.7
1 212.6±200.8
8
低
1.8±23.0
P>0.05
238.0±137.2
P<0.05
23
低
3.1±70.8
P>0.05
653.8±292.4
P<0.05
正
2.6±30.8
415.7±158.5
正
5.7±27.6
920.5±382.2
9
低
2.4±28.1
P<0.05
362.0±77.3
P<0.05
24
低
2.8±50.7
P>0.05
340.5±211.0
P<0.05
正
9.8±128.6
1 378.7±1 205.5
正
3.7±42.1
666.4±622.8
10
低
2.6±35.6
P<0.05
456.1±269.1
P<0.05
25
低
3.6±27.4
P>0.05
346.5±147.8
P<0.05
正
8.6±95.4
1 336.2±405.0
正
5.6±79.6
679.8±902.8
11
低
2.4±25.8
P<0.05
466.7±360.5
P<0.05
26
低
2.8±18.2
P>0.05
667.9±322.2
P<0.05
正
8.6±56.7
828.2±402.5
正
4.8±56.7
1 236.7±980.6
12
低
3.2±38.6
P>0.05
268.7±180.2
P<0.05
27
低
4.7±52.8
P<0.05
713.4±116.9
P<0.05
正
4.3±52.8
420.6±180.5
正
7.6±78.2
985.6±420.8
13
低
2.3±35.9
P<0.05
385.6±270.3
P<0.05
28
低
3.8±34.2
P<0.05
460.4±278.3
P<0.05
正
8.6±94.7
678.2±540.7
正
4.7±52.1
1 042.7±580.5
14
低
7.1±67.3
P>0.05
964.3±342.6
P<0.05
29
低
3.5±34.2
P>0.05
462.0±278.7
P<0.05
正
7.6±102.4
1 328.7±568.9
正
4.7±57.1
667.0±548.3
15
低
2.4±25.7
P<0.05
248.0±168.2
P<0.05
30
低
2.4±28.7
P<0.05
362.0±77.3
P<0.05
正
4.5±55.7
737.6±306.5
正
9.9±100.6
1 378.7±1 202.5
Tab.2IMFX marginal spectrum amplitude statistics for all subjects
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