9 Analyzing Pain and Stress from PPG Perfusion Signal Patterns
157
Fig. 9.5 Correlation analysis of ANI during surgical interventions
Table 9.2 Correlation of ANIs and SSI with blood pressure changes
Correlation
Blood pressure
Change
ANI-ECG
ANI-PPG
SSI
Change
Correlation
1
−0.015
0.001
−0.0101
Significance
0.852
0.989
0.221
N
148
148
147
148
ANI-ECG
Correlation
−0.015
1
0.892
−0.016
Significance
0.852
0.000
0.843
N
148
148
147
147
ANI-PPG
Correlation
0.001
0.892
1
0.000
Significance
0.989
0.000
0.996
N
147
147
147
147
SSI
Correlation
−0.101
−0.016
0.000
1
Significance
0.221
0.843
0.996
<0.001
N
148
148
147
148
9.4.2 Surgical Stress Index
Figure 9.6 shows an example sequence of the SSI in the context of selected surgical
events. An increase of the SSI can be clearly seen after skin incision. Hence, the SSI
is a stress index and the ANI is a nociception index. A stress reaction is followed by
an increase in SSI and a decrease in ANI.
The SSI seems to be associated more with changes in heart rate, than with changes
in blood pressure, compared to the ANI. Unfortunately, a direct correlation of the
changes of blood pressure or heart rate with changes of the index is difficult, due to
influence from various physiological conditions.