# Texture Analysis is a Useful Tool to Assess the Complexity Profile of Microcirculatory Blood Flow
## 3 Results  
As previously published, during the postural challenge, perfusion decreased significantly on both the test and control feet [4]. The mean and standard deviation (SD) of the entropy parameter (CI) calculated with MSE is presented in Table 1. For the test foot, the CI of the raw PPG signal and all its components decreased significantly during the challenge (Phase II, raw signal: \(p=0.005\); cardiac: \(p=0.012\); respiratory: \(p=0.002\); myogenic: \(p=0.003\); sympathetic: \(p=0.002\); NOd: \(p=0.002\); NOi: \(p=0.002\)). For the control foot, the CI of the raw PPG signal showed an increase without statistical significance. All the components' CI decreased, with the exception of the cardiac, although not so pronounced as in the test foot (respiratory: \(p=0.002\); myogenic: \(p=0.003\); sympathetic: \(p=0.002\); NOd: \(p=0.002\); NOi: \(p=0.002\)). During recovery (Phase III), significant differences were still detected on both feet regarding baseline for the respiratory (test: \(p=0.002\); control: \(p=0.002\)), myogenic (test: \(p=0.008\); control: \(p=0.008\)), sympathetic (test: \(p=0.002\); control: \(p=0.002\)), NOd (test: \(p=0.002\); control: \(p=0.002\)) and NOi (test: \(p=0.002\); control: \(p=0.003\)). The mean and SD of the entropy parameter (TE) calculated for the sine wave and PPG signals with TA is shown in Table 2. For the sine wave  
Figure 4: Time evolution of the PPG signal components’ amplitude ratio for the control (blue) and test (red) feet throughout the protocol (baseline: signal samples 0–60,000; challenge: signal samples 60,000–120,000; recovery: signal samples 120,000–180,000) for a representative subject (20 y.o.). signal scalogram, TE decreased from the cardiac component towards the low frequency components, where it increased again for the NOi. For the test foot PPG scalogram, TE decreased significantly in the cardiac (\(p\) = 0.004), respiratory (\(p\) = 0.013), and myogenic (\(p\) = 0.008) components, increased significantly in the NOd (\(p\) = 0.012) and NOi (\(p\) = 0.010), and showed no change in the sympathetic component. During recovery, all components' TE returned except for the NOd, which showed a significant difference regarding baseline (\(p\) = 0.007). For the control foot PPG scalogram, changes in TE were not so pronounced as in the test foot, with only the cardiac component showing a significant difference regarding baseline (\(p\) = 0.001). During recovery, only the cardiac component showed a significant difference (\(p\) = 0.022) regarding baseline. No significant differences in entropy were found between feet at baseline (Tables 1 and 2) either with CI or TE. During the challenge phase, significant differences were found for the raw signal (\(p\) < 0.001) and all components (p=0.001 for the respiratory; \(p\) < 0.001 for the remaining) with CI. Similarly, TE showed significant differences in all components (cardiac: \(p\) = 0.001; respiratory: \(p\) = 0.045; myogenic: \(p\) = 0.028; NOd: \(p\) = 0.001; NOi: \(p\) = 0.001), except the sympathetic. During recovery, the CI of the sympathetic (\(p\) = 0.012), NOd (\(p\) = 0.002) and NOi (\(p\) < 0.001) were significantly different, while with TE no statistical differences were found.