In the present study, we aimed to compare lower extremity tissue oxygen saturations in DM patients and healthy individuals. The study involved 22 patients with diabetes mellitus and 20 healthy subjects. StO 2 of all participants was measured with near-infrared spectroscopy on the dorsal side of the foot. First, stO 2 values between groups were compared, and then the DM group was divided into subgroups for further analysis. Median (IQR: 75th percentile-25th percentile) StO 2 levels were 83.6% (84.2-83.0) in the patient group, while this was 81.3% (82.4-80.4) in the control group. In the comparison between groups, the patient group had significantly higher StO 2 levels (p <0.0001). In the subgroup analysis of the DM group, patients with neuropathy, nephropathy, or coronary artery disease have significantly higher StO 2 levels than patients without these complications or diseases. Our result showed that StO 2 values in DM patients were higher than in healthy subjects, and in the presence of some complications, this elevation was even more pronounced. We attribute this situation to the inability of the cells to sufficiently utilize the oxygen due to metabolic dysregulation, and thus the oxygen saturation in the veins returning from the tissue remains high. We may call this pathophysiological capillary shunting, which became more pronounced in the presence of DM complications.

Background: Photoplethysmography flow-mediated dilatation (PPG-FMD) is an endothelial function measurement tool, and its use is increasing as it is easy to apply and relatively inexpensive. The analysis protocol of PPG-FMD has not yet been standardized. This study aimed to define the continuous correction method in PPG-FMD analysis and interpret the results obtained from a healthy population.Methods: The study population consisted of 30 healthy persons. Endothelial function measurement was done with the PPG-FMD method. In the correction process of the PPG signal, a continuous (element-wise) correction approach was defined and applied. PPG-dilation indexes (PPG-DI) were calculated for each subject, and its correlation with demographic and anthropometric data were analyzed. Finally, the study group was divided into subgroups, and endothelial function results were compared.Results: The median PPG-DI (IQR) value of the whole study group was 112% (60). The Pearson correlation coefficients (r) obtained in the analysis were as follows; r=-0.6278 for age, r=-0.4635 for BMI, r=-0.4628 for waist circumference, r=-0.4207 for systolic blood pressure, r=-0.2804 for diastolic blood pressure. In the subgroup analysis, groups with older age, high BMI, male sex, smoker, and high waist circumference had lower PPG-DI results.Conclusions: PPG-FMD could be a good alternative in the endothelial function measurement, with its operator-independent and easily applicable nature. Although the measurement protocol is similar to USG-FMD, PPG-FMD contains much more technical details during the analysis process. We introduced a novel signal correction method, and we believe that this will be a basis for future studies on this subject.

BACKGROUND: Venous oxygen saturation reflects venous oxygenation status and can be used to assess treatment and prognosis in critically ill patients. A novel method that can measure central venous oxygen saturation (ScvO2) non-invasively may be beneficial and has the potential to change the management routine of critically ill patients. OBJECTIVE: The study aims to evaluate the potential of sublingual venous oxygen saturation (SsvO2) to be used in the estimation of ScvO2. METHODS: We have developed two different approaches to calculate SsvO2. In the first one, near-infrared spectroscopy (NIRS) measurements were performed directly on the sublingual veins. In the second approach, NIRS spectra were acquired from the sublingual tissue apart from the sublingual veins, and arterial oxygen saturation was measured using a pulse oximeter on the fingertip. RESULTS: Twenty-six healthy subjects were included in the study. In the first and second approaches, average SsvO2 values were 75.0% ± 1.8 and 75.8% ± 2.1, respectively. The results of the two different approaches were close to each other and similar to ScvO2 of healthy persons (> 70%). CONCLUSION: Oxygen saturation of sublingual veins has the potential to be used in intensive care units, non-invasively and in real-time, to estimate ScvO2.