Detection of disturbances in pulmonary gas exchanges during exercise from arterialized earlobe PO2PO2

Blood sampling from the arterialized earlobe is widely used in clinical exercise testing but Fajac et al. (1998) (Eur. Respir. J. 11, 712–715) have shown that arterialized PO2(PcCO2)PO2(PcCO2) is not a valid surrogate for PaO2PaO2. In the present study, in order to detect disturbances in pulmonary gas exchanges during clinical exercise testing from the alveolar-arterial gradient of PO2PO2 (P[Ai­a]O2P[Ai­a]O2), a correction factor for PcO2PcO2 was validated from data on a large cohort (107 patients at one or two levels of exercise: 172 pairs of samples). Pulmonary gas exchanges and pH, PO2PO2, PCO2PCO2, PAiO2PAiO2 and P(Ai­a)O2P(Ai­a)O2 from arterial and arterialized blood were measured or computed. Arterial and arterialized pH and PCO2PCO2 (and thus PAiO2PAiO2) were similar but PcO2PcO2 was lower than arterial PO2 (PaO2)PO2 (PaO2). However, when corrected for the systematic bias between PaO2PaO2 and PcO2PcO2, which increased with PcO2PcO2, PcO2PcO2 adequately detected disturbances in pulmonary gas exchanges with a very high sensibility and specificity (predictive values of a negative or positive test ∼95%).