Association between oxygen delivery and digital ulcers in systemic sclerosis

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.

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).

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/m² vs 549 mL/min/m², 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).

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.