## 4 Discussion
In the initial session, the mean blood pressure was recorded at 100.62 \(\pm\) 49.80 mmHg at the right fifth metatarsal and 96.24 \(\pm\) 38.14 mmHg at the right styloid process. In the subsequent session, the mean blood pressure was recorded at 106.14 \(\pm\) 52.60 mmHg at the left fifth metatarsal and 96.93 \(\pm\) 43.94 mmHg at the right styloid process. These values can be explained, first and foremost, in the thickness of the skin at the analyzed points. In their study, [PERSON] et al. measured TcPO2 levels and epidermis thickness in different regions of the body. Their findings demonstrated that, for every micrometer increase in skin thickness, TcPO2 exhibited a decrease of 0.26 mmHg [49]. Given the consideration of the diminished thickness of the skin in the measurement area utilized in this study, the elevated values obtained can be adequately explained. The thickness of the subcutaneous tissue in the malleolus, styloid process, and head of the fifth metatarsal is minimal, and it possesses a thin layer of epidermis. This specific condition would facilitate the diffusion of oxygen through the skin [50]. In the present study, the sensor was positioned directly on the bony prominences. In subsequent research, it would be prudent to affix the sensor around measurement areas to ascertain whether the TcPO2 values diminish and align with the values obtained in other anatomical regions. Second, in the present study, a photo-opticalprobe was utilized, which, in comparison with electrochemical sensors, has been shown to provide higher TcPO2 values. This is because these photo-optical probes do not consume oxygen during the measurement process [16]. With regard to the CCI, the present study is the first to measure TcPO2 in the styloid process of the fifth metatarsal, the head of the fifth metatarsal, and the lateral malleolus. Consequently, no data exist for comparison. A review of the results of ICC evaluated in other test-retest studies, in which TcPO2 measurements were evaluated with different objectives, reveals that results ranging from moderate to excellent were also obtained [21; 22; 23; 24; 26]. Conversely, a recent study sought to ascertain the most efficacious non-invasive measure for diagnosing peripheral arterial disease, with a particular focus on predicting wound healing in revascularized diabetic foot tissues. The investigation revealed that transcutaneous oxygen pressure (TcPO2) and absolute systolic toe pressure emerged as superior indicators of wound healing [44]. These data confirm that measuring TcPO2 is a reliable method for analyzing the skin's physiological response in various conditions, particularly in the presence of foot wounds. As shown in Table 2, the time required to obtain the data exhibited variability according to anatomical location. However, the time required to obtain the data was coincident between anatomical locations on both extremities. The duration of the processes required to obtain TcPO2 exhibited a range of variation, with values ranging from 15.16 \(\pm\) 4.05 min at the right lateral malleolus to 21.40 \(\pm\) 7.79 min at the right fifth metatarsal head. These values are consistent with the 20 min average reported by studies employing TcPO2 at other anatomical locations [20; 21; 22; 24]. While the findings of this study indicate that the utilized equipment offers reliable measurements for the designated anatomical regions, it is imperative to consider the limitations of this study when interpreting the results. First, this study was conducted on healthy volunteers. This condition was deemed necessary in order to serve as an initial point of reference. However, subsequent investigation is required to ascertain the implications of employing the fluorescence-sensitive photo-optical sensor in clinical practice, with these investigations focusing on a population that exhibits a propensity to develop PIs. Conversely, the CCI exhibited variability between equivalent points in each limb.