Sleep apnea syndrome (SAS) is a common comorbidity of type 1 and type 2 diabetes. A low transcutaneous oxygen tension (PtcO2) measured on the foot is pejorative prognostic factor for the healing of a diabetic foot wound. SAS causes intermittent nocturnal hypoxia and sympathetic overactivity. The investigators hypothesized that SAS could be a factor reducing the PtcO2.Therefore, the main objective of this study is to assess the variation in PtcO2 between the end of the night and midday in patients with -or at risk of- diabetic foot wound according to the presence or not of sleep apnea syndrome.The secondary objective is to address the microvascularisation of diabetic patients having foot wounds according to their status regarding sleep apnea syndrome.