Kinetic analyses as a tool to examine physiological exercise responses in a large sample of patients with COPD

Kinetic features such as oxygen uptake (V̇o₂) mean response time (MRT), and gains of V̇o₂, carbon dioxide output (V̇co₂), and minute ventilation (V̇e) can describe physiological exercise responses during a constant work rate test of patients with chronic obstructive pulmonary disease (COPD). This study aimed to establish simple guidelines that can identify COPD patients for whom kinetic analyses are (un)likely to be reliable and examined whether slow V̇o₂ responses and gains of V̇o₂, V̇co₂, and V̇e are associated with ventilatory, cardiovascular, and/or physical impairments. Kinetic features were examined for 265 COPD patients [forced expiratory volume in 1 s (FEV₁): 54 ± 19%predicted] who performed a constant work rate test (duration > 180 s) with breath-by-breath measurements of V̇o₂, V̇co₂, and V̇e. Negative/positive predictive values were used to define cutoff values of relevant clinical variables below/above which kinetic analyses are (un)likely to be reliable. Kinetic feature values were unreliable for 21% (= 56/265) of the patients and for 79% (= 19/24) of the patients with a peak work rate (WR_peak)< 45 W. Kinetic feature values were considered reliable for 94% (= 133/142) of the patients with an FEV₁ > 1.3 L. For patients exhibiting reliable kinetic feature values, V̇o₂ MRT was associated with ventilatory (e.g., FEV₁ %predicted: P < 0.001; r = -0.35) and physical (e.g., V̇o_2peak %predicted: P = 0.009; r = -0.18) impairments. Gains were mainly associated with cardiac function and ventilatory constraints, representing both response efficiency and limitation. Kinetic analyses are likely to be unreliable for patients with a WR_peak < 45 W. Whereas gains enrich analyses of physiological exercise responses, V̇o₂ MRT shows potential to serve as a motivation-independent, physiological indicator of physical performance.NEW & NOTEWORTHY A constant work rate test that is standardly performed during a prerehabilitation assessment is unable to provide reliable kinetic feature values for chronic obstructive pulmonary disease (COPD) patients with a peak work rate below 45 W. For patients suffering from less severe impairments, kinetic analyses are a powerful tool to examine physiological exercise responses. Especially oxygen uptake mean response time can serve as a motivation-independent, physiological indicator of physical performance in patients with COPD.