Faster oxygen uptake, heart rate, and ventilatory kinetics in stepping compared with cycle ergometry in patients with COPD during moderate-intensity exercise

Abstract

Step tests are a stressful and feasible cost-effective modality to evaluate aerobic performance. However, the eccentric in addition to concentric muscle contractions of the legs on stepping emerge as a potential speeding factor for cardioventilatory and metabolic adjustments towards a steady-state, since eccentric contractions would prompt an earlier and stronger mechanoreceptor activation, as well as higher heart rate/cardiac output adjustments to the same metabolic demand. Moreover, shorter tests are ideal for exercise-limited subjects. Nine subjects with chronic obstructive pulmonary disease were invited to participate in comprehensive lung function tests and constant work tests performed on different days at a 90% gas exchange threshold for 6 min, in single-step tests or cycle ergometry. After careful monoexponential regression modelling, statistically relevant faster phase II time constants for oxygen uptake (45 ± 18 s vs 53 ± 17 s, p = 0.017) and minute ventilation (61 ± 13 s vs 74 ± 17 s, p = 0.027) were observed in the 6-min step tests compared with cycle ergometry, respectively. Despite an absence of heart rate time constant difference (43 ± 20 s vs 69 ± 46 s, p = 0.167), there was a significantly faster rate constant toward a steady state for heart rate (p = 0.02). In addition, 4-min compared with 6-min analysis presented similar results (p > 0.05), providing an appropriate steady-state. We conclude that step tests might elicit faster time constants compared with cycle ergometry, at the same average metabolic level, and 4-min analysis has similar mean errors compared with 6-min analysis within an acceptable range. New studies, comprising mechanisms and detailed physiological backgrounds, are necessary.

Vitamin B12 Supplementation and NT-proBNP Levels in COPD Patients: A Secondary Analysis of a Randomized and Controlled Study in Rehabilitation

“…All subjects were invited to perform an incremental cardiopulmonary exercise testing (CPET) and two equal constant work-rate tests (CWTs, 75% of the maximum incremental CPET load) to calculate time constants ( tau , τ) for V ’O 2 during the rest-to-exercise transition. Detailed CWT methods and oxygen uptake kinetics analysis were previously published ( Paulin et al, 2017 ; Müller et al, 2019 ). Blood samples were collected at rest and T lim during the first CWT, before and after 8 weeks, for NT-proBNP plasmatic level analysis ( Figure 1 ).…”

“…Hence, the faster the rate of adjustment (k) of V’O 2 toward the steady-state during rest-to-exercise constant work-rate exercise transitions, the lower the time constant tau . Thus, we chose to perform Pearson product-moment coefficients for correlations using k , as k generates a more robust Gaussian distribution ( Bland and Altman, 1996 ) and would imply similarly to a plausible physiological significance, as we recently suggested ( Müller et al, 2019 ). The slopes of linear regression for pre- and post-training moments were compared with Univariate ANCOVA.…”