The dynamics of heart rate, respiratory rate, and arterial blood oxygen saturation level were similar for all animals over the duration of the imaging session, without any statistically significant differences among groups (Student paired t-test). The mean heart and respiratory rates varied between 212–317 BPM (p=0.1076), and 32–49 (p=0.3256) per minute respectively. The mean arterial oxygen saturation ranged between 98–99.9 % (p=0.4574).
The baseline values of HbO2, Hb, HbT, and StO2 revealed no statistical significant differences based on Student paired t-test (p= 0.2138, p=0.3878, p=0.2215, and p=0.3666 respectively) between right and left skin flaps among all animals in all groups. When the cutaneous flaps were compared to adjacent intact skin there were a significant statistical difference in Hb (p=0.0157) and StO2 (p=0.0355) based on one-way ANOVA analysis however there was no significant difference in HbO2 (p=0.8205) and HbT (p=0.8740) as depicted in .
Figure 3 Chromophore plots for left and right side flaps as well as for the region of intact skin that lies between the flaps. There are no statistical differences in HbO2 (a), and HbT (c) but StO2 (d) and Hb (b) show statistically significant differences between (more ...)
Arterio-Venous Occlusion Group
In this group, 12 flaps were created (6 treated with NS and 6 with HHS). By the 4th post-operative day, 8 of them survived while 4 of these flaps failed. SFDI images registered microcirculation changes over the entire time of data acquisition including, baseline, ischemia, and reperfusion periods. depicts quantitative functional images of different parameters at several time points. In this occlusion group, the quantitative images indicate changes chromophore concentration and distribution over time, including the baseline (T= 0), the end ischemia period (T= 2), after 2 hours of reperfusion (T= 4), 24, and 72 hours post-op. SFDI data for the flap that survived indicated that chromophore concentrations recovered (trended toward presurgical baseline values) after blood flow was reestablished. The StO2 and HbO2 concentration values actually overshot baseline values in compensatory fashion whereas these parameters didn’t show any considerable changes in the flap that was compromised and eventually necrotized within 24–48 hours.
Figure 4 These images have been acquired at t= 0 (baseline), 2 (two hours after arterio-venous occlusion), 4 (two hours after blood reperfusion and saline administration), 24 and 72 hours after the pedicle flap was raised in the arterio-venous occlusion group. (more ...)
In order to quantitatively compare data between animals and flaps, the relative percent change of each chromophore value was calculated in three different regions of interest, including control flap, experimental flap and intact skin. The percent change of HbO2 and StO2 depicted in , demonstrated a sharp decline after arterio-venous occlusion when compared to adjacent intact skin. This reduction in HbO2 and StO2 values became statistically different after 4 minutes of vascular occlusion in both survived and compromised flaps groups.
Figure 5 These plots demonstrate the percentage change of each parameter in the arterio-venous occlusion group. We compared the group of flaps that survived to the group of flaps that eventually became necrotic within 24–48 hours post-op and to adjacent (more ...)
In the group of flaps that survived, we observed a gradual increase in HbO2 and StO2 levels which began after 18 minutes of reperfusion. Statistically, the HbO2 and StO2 levels, in the group of flaps that survived, completely recovered after 42 and 46.5 minutes respectively after reperfusion, when compared to the intact skin group. On the other hand, there was no recovery of HbO2 and StO2 levels in the group of flaps that ultimately revealed themselves to be critically compromised. The HbO2 and StO2 variations between critically compromised flaps and those that survived were analyzed using two- way ANOVA but didn’t show any statistically significant difference. On the other hand a Bonferroni post-test analysis showed significant difference at minute 81 after reperfusion.
illustrates a sharp increase in Hb values following complete pedicle occlusion in all flaps, becoming significantly different from adjacent intact skin after 4.5 minutes. The Hb values of the flaps that survived decreased steadily after 42 minutes following reperfusion. However, the flaps that eventually became necrotic displayed no significant changes in Hb for this set of samples. Over the entire duration of the experiment, the HbT level did not fluctuate much, as shown in .
shows the mean value of each parameter after 24, 48, 72, and 96 hours in micromoles per unit liter. The data analysis indicates that there was a statistically significant difference in StO2 concentration when compared the intact skin group and the flaps that survived to those flaps that were critically compromised.
Table 1 shows the mean values of the chormophore concentrations, in micromoles per unit liter, at 24, 48, 72, and 96 hours in the arterio-venous occlusion group. The data is presented as the mean of the absolute value for each parameter ± standard error (more ...)
Selective Venous Occlusion Group
There were 10 flaps (5 animals) in this group (5 treated with NS and 5 with HHS). Four flaps were critcically compromised and six survived. displays the SFDI images at several time points (T=0, 2, 4, 24, and 72 hours). The variations in HbO2, Hb, HbT, and StO2 concentrations during baseline, ischemia, and reperfusion periods reflect changes in microcirculation of the flaps. In particular, during the ischemia period, we observed blood pooling inside the control and experimental flaps, which was indicated by high HbT and Hb concentrations at T=2 hrs, following by complete recovery of the survived flap after 24 –48 hours.
Figure 6 These images were acquired at t= 0 (baseline), 2 (two hours after selective venous occlusion), 4 (two hours after blood reperfusion and saline administration), 24 and 72 hours after the pedicle flap was raised in selective venous occlusion group. The (more ...)
The relative percent change of chromophore concentrations were calculated in the same way as was done for the arterio-venous occlusion experiment. The levels of HbO2 in all the flaps in this group displayed a sharp drop in their values after transient increase following the application of the clamps, as depicted in . The StO2 level dropped dramatically after occlusion () as well, becoming significantly different from the intact skin group after ~4 minutes. and d shows dramatic changes in the Hb and HbT levels after the clamps were applied. All flaps displayed a steep increase in Hb and HbT level within a few minutes after occlusion in comparison to adjacent intact skin group, becoming significantly different at 4.5 and 1.5 minutes after occlusion respectively, based on Bonferroni post-test analysis.
Figure 7 These plots demonstrate the percentage change of each parameter in the selective venous occlusion group. We compared the flaps in the group that survived to the flaps group that eventually became necrotic after 24–48 hours post-op and to adjacent (more ...)
The flaps that survived showed rapid recovery after the clamps were released and the saline solutions were injected. The HbO2 level rebounded, eventually exceeding the baseline values in a compensatory fashion (). Conversely the StO2 level steadily increased, returning to near pre-ischemic level (baseline values). Statistically the StO2 increase was insignificant after 24 minutes based on Bonferroni post-test analysis when compared to intact skin group (). However the HbO2, StO2, Hb, and HbT levels in the critically compromised did not change appreciably after reperfusion. On the other hand, Hb level showed signs of recovery after 24 minutes following reperfusion period when compared to the intact skin group.
shows the mean value of each chromophore after 24, 48, 72, and 96 hours in micromoles per unit liter. The data analysis indicates that there was a statistically significant difference in in StO2 and Hb concentration when compared the intact skin group and the flaps that survived to those flaps that were critically compromised.
Table 2 shows the mean values of the chormophore concentrations, in micromoles per unit liter at 24, 48, 72, and 96 hours in the selective venous occlusion group. The data is presented as the mean of absolute value for each parameter ± standard error (more ...)
Intact Skin Group
As expected, chromophores concentrations in the intact skin did not fluctuate much over the entire duration of experiment. (See and )