Changes in transcutaneous oxygen tension during exercise in pulmonary emphysema

Abstract

Continuous measurements of transcutaneous oxygen tension (tcPO2) were made in 23 patients with radiological evidence of emphysema, at rest and during a maximal progressive exercise test. tcPO2 during the final phase of exercise was compared with tcPO2 at rest; the mean change (exercising minus resting value) in tcPO2 (ΔtcPO2) was -0.8 mm Hg (SD 10.5, range - 18 to +25) (-0.1 kPa (SD 1.4, range -2.4 to +3.3)). ΔtcPO2 was correlated with: resting arterial oxygen tension (PaO2) (r = 0.606, p < 0.005); resting arterial carbon dioxide tension (PaCO2) (r = -0.691, p < 0.001); FEV1 % predicted (r = 0.688, p < 0.001); vital capacity % predicted (r = 0.543, p < 0.01); and transfer factor (TLCO) % predicted (r = 0.604, p < 0.005). There was no significant difference between the ΔtcPO2 of 10 patients who regularly produced sputum and of 13 patients with no sputum. ΔtcPO2 appears to be more closely related to the severity of emphysema than to the presence or absence of chronic bronchitis. Pretreatment with fenoterol aerosol resulted in an increased work load in three out of 10 patients. Overall there was no change in ΔtcPO2. In all except one patient there was a rise in tcPO2 after the end of exercise. In the 11 patients whose tcPO2 fell during exercise, tcPO2 returned to the resting value within two minutes of the cessation of exercise; this was followed by a further rise beyond the resting value, and a single postexercise arterial sample is therefore a poor indicator of the response of PaO2 to exercise. Measurement of tcPO2 is of value in following rapid changes in PaO2 during and after exercise and avoids the necessity for an indwelling arterial cannula.