Box-Jenkins Transfer Function Modelling for Reliable Determination of VO2 Kinetics in Patients with COPD

Abstract

Oxygen uptake (VO 2 ) 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 VO 2 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 VO 2 kinetics.

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

“…Breath-by-breath data during CWRT were pre-processed and resampled to a 1 Hz time series as explained by Buekers and colleagues (6). A Box-Jenkins transfer function with a first order system model and a second order noise model was fitted to the V O 2 time series from 30 s before the increase in WR until 180 s after this step increase in WR to calculate V O 2 MRT (= time delay + time constant; Figure 1) (6).…”

“…An additional slow component, superimposed on the primary component of the response (Figure 1), can delay or prevent reaching this steady state (35,37). Kinetic features such as mean response time (MRT) and gain describe the primary component of the V O 2 response (6). V O 2 mean response time (MRT) indicates the rate of the V O 2 increase above unloaded cycling.…”

“…These slow V O 2 responses in patients with COPD have been attributed to slow muscle O 2 utilization (22,23,32) and/or ventilatory and cardiovascular restrictions that reduce oxygen delivery to the working muscles (5,9,10,12,15,19). When a V O 2 response is severely slowed, the V O 2 increase is rather linear in nature, making MRT calculations unreliable (6). Low response amplitudes during CWRT can additionally lead to unreliable kinetic feature values for patients with COPD (8).…”

Special Issue on “Human Health Engineering”

“…Contributions can focus on sensors, wearable hardware, algorithms, or integrated monitoring systems. We organized the different papers according to their contributions to the main parts of the monitoring and control engineering scheme applied to human health applications, namely papers focusing on measuring/sensing of physiological variables [24][25][26][27][28][29][30][31], contributions describing research on the modelling of biological signals [32][33][34][35][36][37][38], papers highlighting health monitoring applications [39][40][41][42], and finally examples of control applications for human health [43][44][45][46][47][48]. In comparison to biomedical engineering, we envision that the field of human health engineering also covers applications on healthy humans (e.g., sports, sleep, and stress) and thus not only contributes to develop technology for curing patients or supporting chronically ill people, but also for disease prevention and optimizing human well-being more generally.…”

“…Buekers et al [36] applied a dynamic Box-Jenkins transfer function modelling approach for quantifying the VO 2 kinetics in patients with COPD performing a constant working rate test (CWRT). The added value of this work is that it contributes in optimizing clinical tests for objectively quantifying the physical capacity of patients.…”