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Objective: Tissue hypoxia due to microvasculopathy is the main cause of digital ulcers (DUs) in systemic sclerosis (SSc). Reduced oxygen delivery (DO2) to the tissues may also contribute to the development of DU. This study was conducted to investigate the association between DO2 and DUs in patients with SSc., Methods: In all, 111 patients and 30 healthy controls were enrolled. DO2 was calculated by using the formula; DO2 = Cardiac output × arterial oxygen saturation (SpO2) × serum haemoglobin level × 1.39 × 10. Both right index finger SpO2 measurements (index-SpO2) and highest value of SpO2 (maximum SpO2) obtained among the fingers of the subjects were used for the calculations and DO2 results were adjusted both for weight and body surface area (BSA)., Results: Mean DO2 was lower in SSc patients as compared to controls in all 4 different calculations but the difference was only statistically significant when using index-SpO2 and adjusting for BSA (498 mL/min/m 2 vs 549 mL/min/m 2 , p = 0.03). There was a strong positive correlation between cardiac output and DO2 calculated by using the index-SpO2 (r = 0.903; p < 0.001). Of the SSc patients, 46 (41.4 %) had DUs within the last 12 months. Patients with DUs had higher mean mRSS, lover mean FVC and more frequently diffuse disease, interstitial lung disease, anti-SCL70 antibody positivity (p < 0.05 for all). No difference was observed in DO2 among DU positive or DU negative groups by any calculation (p > 0.05 for all)., Conclusions: DO2 in SSc patients seems to be lower than healthy controls. However, DO2 is similar between the patients with and without DUs. Our results suggest that the contribution of DO2 is negligible to the development of DU and support the major role of microvasculopathy in SSc patients with DUs., Competing Interests: Declaration of competing interest The authors have no competing interests to declare, (Copyright © 2022 Elsevier Inc. All rights reserved.)

Nailfold capillaroscopy is a simple method for determining microvascular damage in systemic sclerosis (SSc). The pulse oximeter is a noninvasive tool that is used to estimate a patient's arterial blood oxygen saturation. The aim of this study was to investigate the effect of capillaroscopic patterns on pulse oximetry measurements in SSc patients. The nailfolds from 2nd to 5th fingers in both hands were examined in all subjects by using capillaroscopy. Patients were categorized according to their capillaroscopy findings in 3 groups as having early, active or late patterns. Oxygen saturation (SpO2) measurements were performed from 2nd to 5th fingers in both hands with a finger probe. We studied 53 SSc patients (F/M: 48/5). According to capillaroscopy findings 18 patients were classified as having early pattern (34.0%), 19 active pattern (35.8%), and 15 late pattern (28.3%). Only 1 (1.9%) patient had normal capillaroscopy findings. SpO2 could not be measured in 47 (11.0%) fingers and in 20 (37.7%) SSc patients. There were 20 (37.7%) patients with a ≥4% difference between the minimum and maximum SpO2 measurements among fingers. There were no difference between the groups of SSc patients defined by capillaroscopy findings in terms of mean maximal SpO2 or mean minimal SpO2 measured from fingers (p NS, for all). Assessment of SpO2 values in patients with SSc is challenging. We did not detect any effect of capillaroscopic patterns on mean SpO2 values. On the other hand ≥4% difference between minimum and maximum SpO2 values measured from fingers of a patient may be considered as an indirect sign of microvascular damage. Assessment of the highest measured SpO2 values among the fingers of a patient may be more suitable in practice., (Copyright © 2014 Elsevier Inc. All rights reserved.)