Abstract
Oxygen uptake (VO2) kinetics provide information about the ability to respond to the increased physical load during a constant work rate test (CWRT). Box-Jenkins transfer function (BJ-TF) models can extract kinetic features from the phase II VO2 response during a CWRT, without being affected by unwanted noise contributions (e.g., phase I contribution or measurement noise). CWRT data of 18 COPD patients were used to compare model fits and kinetic feature values between BJ-TF models and three typically applied exponential modelling methods. Autocorrelation tests and normalised root-mean-squared error values (BJ-TF: 2.8 ± 1.3%; exponential methods A, B and C: 10.5 ± 5.8%, 11.3 ± 5.2% and 12.1 ± 7.0%; p < 0.05) showed that BJ-TF models, in contrast to exponential models, could account for the most important noise contributions. This led to more reliable kinetic feature values compared to methods A and B (e.g., mean response time (MRT), BJ-TF: 74 ± 20 s; methods A-B: 100 ± 56 s–88 ± 52 s; p < 0.05). Only exponential modelling method C provided kinetic feature values comparable to BJ-TF features values (e.g., MRT: 75 ± 20 s). Based on theoretical considerations, we recommend using BJ-TF models, rather than exponential models, for reliable determinations of VO2 kinetics.
Highlights
Chronic obstructive pulmonary disease (COPD) is a common lung disease characterised by persistent airflow limitations due to a combination of airway and alveolar abnormalities
The aim of this study was to compare model fits and kinetic feature values between Box-Jenkins transfer function (BJ-TF) models and the three different exponential modelling methods that were identified in COPD literature
constant work rate test (CWRT) time series data were used for the analyses described below
Summary
Chronic obstructive pulmonary disease (COPD) is a common lung disease characterised by persistent airflow limitations due to a combination of airway and alveolar abnormalities. The most important symptom of COPD is dyspnoea during daily activities, but later at rest. Sci. 2019, 9, 1822 physical deconditioning [2]. Physical capacities can be assessed using standard exercise tests like a cardiopulmonary exercise test (CPET, incremental cycling load) or a constant work rate test (CWRT, constant cycling load) [3]. During a CPET, oxygen uptake (VO2 , ml.min−1 ) increases linearly until the maximal or peak VO2 value is reached. This maximal (or peak) VO2 value, the maximal load reached during CPET and the endurance time during CWRT are the most frequently used metrics for evaluating physical capacities. There is additional information, besides these maximal values, that can be extracted from the breath-by-breath VO2 time series that are generated during these tests
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