Respiratory Activity during Exercise: A Feasibility Study on Transition Point Estimation Using Impedance Pneumography

Abstract

The current diagnostic procedures for assessing physiological response to exercise comprise blood lactates measurements, ergospirometry, and electrocardiography. The first is not continuous, the second requires specialized equipment distorting natural breathing, and the last is indirect. Therefore, we decided to perform the feasibility study with impedance pneumography as an alternative technique. We attempted to determine points in respiratory-related signals, acquired during stress test conditions, that suggest a transition similar to the gas exchange threshold. In addition, we analyzed whether or not respiratory activity reaches steady states during graded exercise. Forty-four students (35 females), practicing sports on different levels, performed a graded exercise test until exhaustion on cycloergometer. Eventually, the results from 34 of them were used. The data were acquired with Pneumonitor 2. The signals demonstrated that the steady state phenomenon is not as evident as for heart rate. The results indicated respiratory rate approaches show the transition point at the earliest (more than 6 min before the end of the exercise test on average), and the tidal volume ones at the latest (less than 5 min). A combination gave intermediate findings. The results showed the impedance pneumography appears reasonable for the transition point estimation, but this should be further studied with the reference.

Keywords: elite athletes; exercise; gas exchange threshold; non-invasive respiratory monitoring; respiratory steady-state.

Figure 1

The scheme of the configuration of measurement equipment and devices.

Figure 2

The idea of how the transition point suggesting gas exchange threshold can be searched.

Figure 3

Sample courses of respiratory rate and complex VENT parameter for IP signal acquired for the 34th subject.

Figure 4

Sample figure presenting respiratory-related Poincare-plot equivalent for the respiratory rate case, for the 34th subject. Angle means the tilt of the ellipse fitted and is presented illustratively.

Figure 5

The sample relation of VENT parameter and workload indexed to body mass for the 19th subject (see details in the text) with the linear models providing the estimated transition point. The left one can described by: VENT = 7.46 × WLiBM + 13.73; the right one by: VENT = 24.33 × WLiBM − 22.70, where WLiBM is workload indexed to body mass. The independent variable is linearly distributed, as described in Section 2.4.