Transcutaneous versus arterial oxygen tension during exercise in chronic pulmonary disease. 
Simultaneous transcutaneous (Ptc O2) and arterial (Pa O2) oxygen tension measurements were obtained at rest and during exercise in 15 subjects with known or suspected chronic lung disease.  The overall correlation coefficient between Ptc O2 and Pa O2 was 0 .  74, and the mean difference between the two variables was -1 .  9 kPa (14mmHg).  The correlation coefficient was somewhat, but not significantly, higher during exercise (r = 0 .  86) than at rest (r = 0 .  58).  Large random discrepancies between simultaneous observations of Ptc O2 and Pa O2 as well as between changes in Ptc O2 and changes in Pa O2 in individual subjects were observed.  It is concluded that Ptc O2 cannot be substituted for Pa O2 in exercise testing applied in the diagnosis and assessment of lung disease.