Transcutaneous measurement of PO2 and PCO2 in the dermis at the site of the tuberculin reaction in healthy human subjects.

The respiration of the skin at the site of a delayed hypersensitivity reaction in tuberculin skin tests was studied by transcutaneous measurement of dermal oxygen and carbon dioxide tensions in normal individuals who had been immunized with BCG: six reactions were strong positives, four were weak positives, and four without induration were regarded as negative. The tcPO2 fell over the first 2 days of the reaction and remained low for the next 2 days: the severity of the changes was greater in the 'strong' reactions than in the 'weak' reactions. The tcPCO2 showed a reciprocal rise over the first 2 days and, although still high, tended to recover over the fourth day. These results indicate that local hypoxia and hypercapnia are prominent features of the positive tuberculin test, probably as a consequence of the respiration of the infiltrating lymphocytes and monocytes. It is likely that similar respiratory changes occur in those chronic inflammatory diseases where delayed hypersensitivity reactions make a contribution to the pathogenesis of the lesion.