Why is hypoxia a feature of rheumatoid arthritis?
Tissue hypoxia results from an inadequate supply of oxygen, with resultant effects on biological functions. Within the context of tumours, hypoxia is a well described phenomenon, arising from a hyperplastic response by the tumour cells that leads to an increased distance from pre-existing blood vessels. Because arthritic synovium is also characterized by an altered proliferative response, it is not surprising that hypoxia is also thought to contribute to RA development. At this point, it is worth noting that there is little agreement about what constitutes ‘hypoxia’. Oxygen tensions under physiological conditions range from arterial blood levels to much lower tissue levels. Many studies ex vivo consider oxygen tension in relation to atmospheric oxygen levels, namely 20% to 21% oxygen, which is higher than in vivo oxygen levels. Moreover, some authors’ definition of ‘hypoxia’ may actually be more analogous to physiological ‘normoxia’, with studies performed at 5% to 7% oxygen. The studi
