*3.1. Population with a Non-Pathological Modified Allen's Test*

#### Allen's Test

Here, 100 patients were included. Mean time to arterial refill was 4.12 s (SD = 1.903 s; 95% CI:3.74–4.50 s). The values were not normally distributed (Figure 3).

**Figure 3.** Boxplot diagram of the values obtained from the population with a non-pathological modified Allen's test. **Figure 3.** Boxplot diagram of the values obtained from the population with a non-pathological modified Allen's test.

#### *3.2. Hyperspectral Imaging 3.2. Hyperspectral Imaging*

#### 3.2.1. Tissue Oxygenation (StO2) 3.2.1. Tissue Oxygenation (StO2)

The Shapiro–Wilk test was not able to reject the hypothesis that measured values at every time point were normally distributed. At time point I, mean StO2 was 51.34% (SD = 7.972%; 95% CI:49.76–52.92%). After vessel occlusion (II), mean StO2 decreased to 40.56% (SD = 6.929%; 95% CI: 39.19–41.93%) and after releasing the ulnar artery (III), StO2-values increased again up to 50.42% (SD = 8.117%; 95% CI: 38.81–52.03%) (Figures 4 and 5). Pearson and Spearman test showed a statistically significant correlation between the different time points (each *p* < 0.001). Whereas mean ranks differed significantly between related samples time points I and II as well as between II and III (each *p* < 0.001), the values between time point I and III did not differ significantly (*p* = 0.06). This indicates a strong effect within the compared groups that showed significantly different mean ranks (r each The Shapiro–Wilk test was not able to reject the hypothesis that measured values at every time point were normally distributed. At time point I, mean StO<sup>2</sup> was 51.34% (SD = 7.972%; 95% CI:49.76–52.92%). After vessel occlusion (II), mean StO<sup>2</sup> decreased to 40.56% (SD = 6.929%; 95% CI: 39.19–41.93%) and after releasing the ulnar artery (III), StO2 values increased again up to 50.42% (SD = 8.117%; 95% CI: 38.81–52.03%) (Figures 4 and 5). Pearson and Spearman test showed a statistically significant correlation between the different time points (each *p* < 0.001). Whereas mean ranks differed significantly between related samples time points I and II as well as between II and III (each *p* < 0.001), the values between time point I and III did not differ significantly (*p* = 0.06). This indicates a strong effect within the compared groups that showed significantly different mean ranks (r each >0.5) and a weak effect for group comparison I and III (r = 0.133). *J. Pers. Med.* **2021**, *11*, x FOR PEER REVIEW 7 of 17

**Figure 4.** Boxplot diagrams for return-to-perfusion measurements for StO2, NIR, THI and TWI values obtained from the population with a non-pathological modified Allen's Test. **Figure 4.** Boxplot diagrams for return-to-perfusion measurements for StO<sup>2</sup> , NIR, THI and TWI values obtained from the population with a non-pathological modified Allen's Test.

Whereas a Shapiro–Wilk test could not reject that the measured values of both, per-

Whereas the Shapiro–Wilk test indicated that for both, time points II (both arteries occluded) and III (only radial artery occluded), the normality assumption could not be rejected, this was not the case for the baseline measurement. Mean TWI was 41.28 (SD = 3.690; 95% CI: 40.55–42.01) at rest and increased to 45.68 ± 3.959 (95% CI: 44.89–46.47) when occluding both vessels. After release of the ulnar artery, TWI decreased to 42.01 (SD = 4.162; 95% CI: 41.18–42.84) (Figures 4 and 5). Both Spearman and Pearson correlation test showed statistically significant correlations between all time points (*p* < 0.001). Analyzing the difference in mean ranks, there were statistically significant differences between all groups corresponding to strong effects within the compared groups I and II as well as for II and III (r each > 0.5) and a weak effect for group comparison I with III (r =

The return-to-perfusion (RTP) value indicates the difference in percent between the measurements at time point III and time point I. Shapiro–Wilk and Kolmogorov–Smirnov could not reject a normal distribution for StO2-RTP values. The mean difference for StO2 was 1.46% (SD = 8.84%; 95% CI: −0.29–3.21%), for NIR 2.27% (SD = 5.74; 95% CI: 1.13– 3.41%), for THI −10.21% (SD = 21.79%; 95% CI: −14.53– -5.88%) and for TWI −1.82% (SD = 5.63%; 95% CI: −2.93– -0.7%) (Figure 5). Correlation analysis between the MAT and RTP-

occlusion do not seem to follow a normal distribution (*p* = 0.005). Mean THI was 35.39 ± 7.661 (95% CI: 33.87–36.91) while arterial blood flow was present, whereas THI decreased to 20.52 ± 8.973 (95% CI:18.74–22.20) after occlusion of the arteries. After release of the ulnar artery, mean THI increased up to 38.52 ± 9.517 (95% CI: 36.63–40.41) (Figures 4 and 5). Spearman and Pearson test showed statistically a significant correlation between all time points (*p* < 0.001). A significant difference between the mean ranks of the different time points could be shown by the Wilcoxon test. For time points I and II as well as for II and III a strong effect (r > 0.6) and between I and III a moderately strong effect could be

3.2.3. Tissue Hemoglobin Index (THI)

3.2.4. Tissue Water Index (TWI)

3.2.5. Return-to-Perfusion Measurement

shown.

0.231).

>0.5) and a weak effect for group comparison I and III (r = 0.133).

**Figure 5.** Measurements of the hyperspectral analysis over the time course of the experiment. The measured value at time point I symbolizes the baseline measurement, at time point II the values under occlusion of both vessels and at time point III the measured values after opening the ulnar artery. The NIR values (near infrared index/deep perfusion) are shown in pink, the StO2 values (superficial perfusion) in blue, the THI (tissue hemoglobin index) in red and the TWI (tissue water index) in cyan. **Figure 5.** Measurements of the hyperspectral analysis over the time course of the experiment. The measured value at time point I symbolizes the baseline measurement, at time point II the values under occlusion of both vessels and at time point III the measured values after opening the ulnar artery. The NIR values (near infrared index/deep perfusion) are shown in pink, the StO<sup>2</sup> values (superficial perfusion) in blue, the THI (tissue hemoglobin index) in red and the TWI (tissue water index) in cyan.

measurements by Pearson and Spearman test showed no significant correlation between the MAT and RTP-values for StO2 and NIR, whereas there was a statistically significant correlation between the MAT and THI values (*p* < 0.05) in the Spearmen test. On the other

hand correlation analysis did not show a correlation between MAT and TWI.

#### 3.2.2. Near Infrared Perfusion Index (NIR)

*3.3. Cases with Impaired Perfusion*  3.3.1. Allen's Test A total of 14 patients had a MAT with a time to reperfusion of longer than 8 s. In three cases, time to reperfusion was 9 s, in four cases 10 s, in two cases 11 s, in one case 14 s and in four cases, there was no reperfusion detectable after more than 20 s, which is why the test was terminated in such cases (termed as AT max.). 3.3.2. Tissue Oxygenation (StO2) A normal distribution of all time points analyzed within this study was detected. A statistically significant correlation between the different time points could be observed (each *p* < 0.05). Mean ranks differed significantly between the related samples time points Once again, a Shapiro–Wilk test did not significantly contradict that measurements during occlusion and reperfusion were normally distributed (*p* > 0.1). The values measured at time point I (both arteries open), however, do not seem to follow a normal distribution (*p* = 0.031). At time point I, mean NIR was 55.11 (SD = 7.236; 95% CI: 53.67–56.55). After occlusion of both vessels, the perfusion decreased (Mean = 48.14 ± 5.946; 95% CI: 46.96– 49.32) and increased up to 53.88 (SD = 7.876; 95% CI: 52.32–55.44) after release of the ulnar artery (Figures 4 and 5). Both, Pearson and Spearman correlation test showed statistically significant correlations between the different time points (each *p* < 0.001). Using Wilcoxon test, a significant difference between the distribution at the different time points could be demonstrated. Whereas for time points I and II as well as for II and III a strong effect (r > 0.5) was shown, between group I and III merely a weak effect was observed (r = 0.241).

#### I and II (*p* < 0.001) as well as between I and III (*p* = 0.048), whereas the values between time point II and III did not differ significantly (*p* = 0.076). This corresponded to a strong effect 3.2.3. Tissue Hemoglobin Index (THI)

within the compared groups I and II (r = 0.6) and a moderately strong effect for group comparison I and III and II and III (r > 0.3). 3.3.3. Near Infrared Perfusion Index (NIR) A normal distribution for the measured values of all time points was seen. A statistically significant correlation between the different time points could be shown by Pearson and Spearman test with *p* < 0.01. There were significant differences in mean ranks between the related samples time points I and II as well as I and III (*p* = 0.002), whereas the values between time point II and III did not differ significantly (*p* = 0.213). This corresponded to a strong effect between the compred groups that showed significantly different mean Whereas a Shapiro–Wilk test could not reject that the measured values of both, perfusion and reperfusion were normally distributed (*p* > 0.05), the values obtained during occlusion do not seem to follow a normal distribution (*p* = 0.005). Mean THI was 35.39 ± 7.661 (95% CI: 33.87–36.91) while arterial blood flow was present, whereas THI decreased to 20.52 ± 8.973 (95% CI:18.74–22.20) after occlusion of the arteries. After release of the ulnar artery, mean THI increased up to 38.52 ± 9.517 (95% CI: 36.63–40.41) (Figures 4 and 5). Spearman and Pearson test showed statistically a significant correlation between all time points (*p* < 0.001). A significant difference between the mean ranks of the different time points could be shown by the Wilcoxon test. For time points I and II as well as for II and III a strong effect (r > 0.6) and between I and III a moderately strong effect could be shown.

#### ranks (r each > 0.5), whereas for group II and III only a weak effect could be shown (r = 3.2.4. Tissue Water Index (TWI)

0.235). Whereas the Shapiro–Wilk test indicated that for both, time points II (both arteries occluded) and III (only radial artery occluded), the normality assumption could not be rejected, this was not the case for the baseline measurement. Mean TWI was 41.28 (SD = 3.690; 95% CI: 40.55–42.01) at rest and increased to 45.68 ± 3.959 (95% CI: 44.89–46.47) when occluding both vessels. After release of the ulnar artery, TWI decreased to 42.01 (SD = 4.162; 95% CI: 41.18–42.84) (Figures 4 and 5). Both Spearman and Pearson correlation test showed statistically significant correlations between all time points (*p* < 0.001). Analyzing the

difference in mean ranks, there were statistically significant differences between all groups corresponding to strong effects within the compared groups I and II as well as for II and III (r each > 0.5) and a weak effect for group comparison I with III (r = 0.231).

#### 3.2.5. Return-to-Perfusion Measurement

The return-to-perfusion (RTP) value indicates the difference in percent between the measurements at time point III and time point I. Shapiro–Wilk and Kolmogorov–Smirnov could not reject a normal distribution for StO2-RTP values. The mean difference for StO<sup>2</sup> was 1.46% (SD = 8.84%; 95% CI: −0.29–3.21%), for NIR 2.27% (SD = 5.74; 95% CI: 1.13– 3.41%), for THI −10.21% (SD = 21.79%; 95% CI: −14.53– -5.88%) and for TWI −1.82% (SD = 5.63%; 95% CI: −2.93– -0.7%) (Figure 5). Correlation analysis between the MAT and RTP-measurements by Pearson and Spearman test showed no significant correlation between the MAT and RTP-values for StO<sup>2</sup> and NIR, whereas there was a statistically significant correlation between the MAT and THI values (*p* < 0.05) in the Spearmen test. On the other hand correlation analysis did not show a correlation between MAT and TWI.

#### *3.3. Cases with Impaired Perfusion*

### 3.3.1. Allen's Test

A total of 14 patients had a MAT with a time to reperfusion of longer than 8 s. In three cases, time to reperfusion was 9 s, in four cases 10 s, in two cases 11 s, in one case 14 s and in four cases, there was no reperfusion detectable after more than 20 s, which is why the test was terminated in such cases (termed as AT max.).
