## 4 Discussion  
The primary objective of this study was to assess the reliability and repeatability of a fluorescence-sensitive photo-optical sensor in measuring TcPO2 at sites prone to PIs in the foot. For the right styloid process and the left fifth metatarsal, the ICCs exhibited moderate reliability, with an excellent value for the left styloid process and a satisfactory value for the remaining anatomical regions. The measurement of PO2 by fluorescence in the field of biology is not a novel concept [35; 36]; however, the application of a photo-optical sensor that is sensitive to fluores  
Figure 6: Relationship between TCPO2 for each anatomical point, with a distinction between right and left legs. The small circles are the TcPO2 (mmHg), the central line is the graph of the Pearson correlation model, and the blue dashed lines are the 95% confidence interval of the model provided by the IBM SPPS® statistical package. cence for the measurement of TcPO2 in the clinic is a relatively recent development. The first relevant reference we found is the study carried out by [PERSON] et al. in 2015 [PERSON] _et al._ (2015). This study examined the concordance between photo-optical and electrochemical TcPO2, at rest and during exercise, in patients with claudication. Subsequently, the research group led by [PERSON] published three studies using photo-optical TcPO2 to predict the duration of diabetic foot ulcers [15], in order to study the application in measurements of revascularization patients [38], and for real-time measurements during activity in patients with peripheral arterial disease compared to an electrochemical sensor [16]. All of the articles referenced employed the same photo-optical sensor that has been marketed by MediCap(r), which was also utilized in this study. Despite the evident dissimilarity in objectives and rationales underlying the aforementioned studies and the present one, it is noteworthy that two of the studies used a control probe in the subalcivicular region when conducting measurements on the lower extremities [16; 38]. The feasibility of this endeavor was enabled by the utilization of a MediCap(r) 8008 multichannel model in both studies. In our specific case, the MediCap(r) 8001 single-channel model was employed; it lacks the capacity for simultaneous monitoring. Nevertheless, the application of the control probe is constrained to the diagnosis of lower limb arterial disease and remains inadequately substantiated by the extant literature [11]. A review of the extant literature reveals a paucity of studies measuring TcPO2 in the context of PIs. Most of these studies focus on performing assessments of the sacrum, trochanter, and calcaneus [39; 40; 41; 42; 43], but we did not find any reference to the points evaluated in our study. In an effort to locate more comprehensive studies of the foot, a search was conducted within the domain of diabetic foot research, where there is substantial expertise in the assessment of TcPO2 [17; 44; 45; 46; 47; 48]. Indeed, the measurement of TcP02 was shown to be an effective predictor of the healing of diabetic foot ulcers, with a threshold of 25 mmHg. Higher values were associated with an increased probability of healing, while lower values were linked to a higher probability of major amputation [45]. It is important to reiterate the absence of coincidences in the positioning of the sensors. In diabetic feet, sensors are applied on both the dorsal aspect of the foot, between the first and second metatarsal bones, and on the plantar surface, between the navicular bone and the medial malleolus, with consideration given to the angiosome pattern [17; 47]. A preliminary analysis of the study outcomes reveals that the documented values exceed the established benchmarks for healthy skin beneath the knee, which are typically close to 70 mmHg[43; 49]. In comparison, the following results were obtained.