Partial Pressure of End-Tidal Oxygen and Blood Lactate During Cardiopulmonary Exercise Testing in Healthy Older Participants and Patients at Risk of Cardiac Disease.

Background: The partial pressure of end-tidal oxygen (PETO₂) and end-tidal oxygen concentration (ETO₂) are among the indices that can be measured by exhaled gas analysis. Several observational studies have shown that skeletal muscle function is impaired in patients with cardiac disease; thus, the assessment of skeletal muscle function is important. Additionally, although it has recently been suggested that the difference in PETO₂ from rest to the ventilatory anaerobic threshold (VAT) reflects oxygen availability in peripheral factors, primarily skeletal muscle, the evidence for this is not well established. Therefore, we hypothesized and investigated whether increased blood lactate (BLa) levels, resulting from decreased skeletal muscle and mitochondrial oxygen availability, and PETO₂ dynamics during cardiopulmonary exercise testing (CPET) would be related.

Methods: All participants performed the symptomatic limited CPET, and their BLa levels were measured. The difference in PETO₂ and ETO₂ from rest to VAT determined by the V-slope method (ΔPETO₂ and ΔETO₂) was calculated and compared with the increase in BLa due to exercise testing.

Results: We recruited 22 healthy older participants (nine males; 69.4 ± 6.8 years) and 11 patients with cardiovascular risk (eight males; 73.0 ± 8.8 years). ΔPETO₂ and ΔETO₂ did not differ between the two groups (P = 0.355 and P = 0.369, respectively), showing no correlation between increase in BLa from rest to VAT, but were significantly correlated with an increase in BLa from rest to the end of exercise (ΔPETO₂, P = 0.030; ΔETO₂, P = 0.029). The correlation was particularly pronounced among those at cardiovascular risk (ΔPETO₂, P = 0.012; ΔETO₂, P = 0.011).

Conclusions: ΔPETO₂ and ΔETO₂ from rest to VAT during CPET may be useful as indices reflecting skeletal muscle oxygen utilization capacity.