Pilot study to determine whether skin blood flow, oxygenation and skin colour are related in patients with systemic sclerosis

Abstract Background/Aims Improved treatments are needed for Raynaud’s phenomenon. Clinical trials can be difficult since it is challenging to measure Raynaud’s ‘attacks’ outside the laboratory. Ambulatory monitoring would allow testing of new treatments in the patients’ home environment where they usually experience attacks, thus allowing a much more realistic assessment of efficacy. Smartphone technology advancements mean that ambulatory monitoring of, and capture of biomarkers from, patients is now possible and could facilitate clinical trials. The aim of this study was to establish whether smartphone monitoring of skin temperature, an indirect measure of blood flow, and changes in skin colour as compared to laboratory measures of oxygenation could inform outcome measures in future clinical trials. Methods Following acclimatisation in a temperature-controlled room, participants underwent finger occlusion in order to simulate a decrease in perfusion and oxygenation. Simultaneous images were taken of the whole hand at baseline, during occlusion, at release and at 1 and 5 minute(s) post-release. Images of skin temperature (henceforth referred to as blood flow) and skin colour were taken with smartphone thermography (FLIRone) and camera respectively. Oxygenation was measured with multispectral imaging. Blood flow, colour and oxygenation data were extracted from images using automated bespoke software that identified the boundary of the hand and selected regions of interest. Colour data was split into red, green and blue channels. Data were plotted over time at each time point. Results Thirty patients with systemic sclerosis (SSc, median 62 interquartile range [57-69] years of age, 26[87%] female, duration of Raynaud’s phenomenon 20[10-32] years, duration of SSc 17[6-25] years, 6[20%] smokers) and 25 healthy controls (53[40-56] years of age, 23[92%] female, 0[0%] smokers) were recruited into the study. The measures of blood flow, colour (red channel) and oxygenation followed similar trajectories over time for both patients and controls (decreasing during occlusion and increasing post occlusion). Oxygenation data was significantly different between patients and controls for baseline to occlusion (-0.24[-0.30 - -0.14] vs. -0.34[-0.46 - -0.26] arb units, p = 0.004) and occlusion to release (0.42[0.12-0.53] vs. 0.74[0.64-0.82] arb units, p < 0.0001). Grouping all data together (at occlusion to release), correlations were identified between colour (red channel) and blood flow r=-0.36 p = 0.003; colour (red channel) and oxygenation r = 0.31 p = 0.003 and between oxygenation and blood flow r=-0.38 p = 0.003. Conclusion Blood flow, skin colour and oxygenation in both patients with SSc and healthy controls follow similar distributions with time under occlusion and release. Blood flow, skin colour and oxygenation are related suggesting that measuring skin colour (redness) may be an alternative way to assess perfusion and oxygenation. Further larger studies are now required to validate this. Smartphone measures of outcomes offer promise for the future of ambulatory monitoring for clinical trials of Raynaud’s phenomenon. Disclosure G. Dinsdale: None. C. Heal: None. J. Manning: None. S. Wilkinson: None. J. Wilkinson: None. M. Dickinson: None. A. Herrick: None. A. Murray: None.