Cardiopulmonary exercise testing: does measured peak O₂ reflect a valid peak O₂ in patients with hemiparetic stroke?

The relationships between cardiopulmonary exercise testing(CPET) variables at submaximal and peak efforts across severities of mobility and hemiparesis in patients with stroke are crucial for interpretation but unexplored.

We hypothesized that patients with more severe neurological deficits are likely to exhibit a lower peak respiratory exchange ratio(pRER). Moreover, individuals with lower pRER experience greater limitations at peak performance compared to those with higher pRER, while their submaximal performance remains relatively unaffected.

This retrospective study involved 153 patients with hemiparetic stroke who underwent CPET between 2012 and 2023. Participants with pRER ≤1.05(n = 26), between 1.05-1.15(n = 48), and ≥1.15(n = 79) were selected for further analysis. Five established norms were used to evaluate peak $\dot{V}$O₂, ventilatory anaerobic threshold(VAT), and the lowest value of ventilatory equivalents for carbon dioxide($\dot{V}$_E/$\dot{V}$CO₂ nadir).

Consistent with our hypothesis, patients with lower pRER showed decreased manual muscle strength on the paretic side and lower scores for transfers, mobility on level surfaces, and stair climbing. However, the ratio of VAT to peak $\dot{V}$O₂ remained consistent across different pRER values. Significant linear correlations were observed between the ratio of measured-to-predicted values of peak $\dot{V}$O₂ versus VAT, and peak $\dot{V}$O₂ versus $\dot{V}$_E/$\dot{V}$CO₂ nadir in all pRER groups(≥ 1.15, 1.05-1.15, and ≤1.05) utilizing different norms.

More severe hemiparesis and mobility impairments are associated with a lower pRER during CPET using cycle ergometry. Nevertheless, the measured peak $\dot{V}$O₂ still seems to represent a valid peak $\dot{V}$O₂. These findings aid in interpreting CPET results in patients with hemiparetic stroke.