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Related Experiment Video

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Estimation of the second ventilatory threshold through ventricular repolarization profile analysis.

Javier Milagro1,2, Adrián Hernández-Vicente3,4, David Hernando1,2

  • 1Biomedical Signal Interpretation and Computational Simulation Group, Aragón Institute of Engineering Research, University of Zaragoza, Zaragoza, Spain.

Scandinavian Journal of Medicine & Science in Sports
|October 10, 2020
PubMed
Summary

This study introduces a new electrocardiogram (ECG) method to estimate the second ventilatory threshold (VT2) non-invasively. The approach analyzes T-wave changes during exercise, potentially reflecting autonomic control shifts at VT2.

Keywords:
autonomic nervous systemexercise testventilatory thresholdventricular repolarization

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Area of Science:

  • Exercise Physiology
  • Cardiovascular Physiology
  • Biomedical Engineering

Background:

  • The second ventilatory threshold (VT2) marks a significant physiological transition during incremental exercise.
  • Autonomic nervous system (ANS) control of cardiac function, particularly ventricular repolarization, may alter at VT2.
  • Current VT2 estimation methods often rely on invasive or complex gas exchange analysis.

Purpose of the Study:

  • To propose and validate a novel, non-invasive method for estimating VT2 using electrocardiogram (ECG) T-wave analysis.
  • To investigate potential changes in ventricular repolarization dynamics and their relation to ANS activity around VT2.
  • To explore the physiological mechanisms linking T-wave characteristics to VT2 during exercise.

Main Methods:

  • 25 healthy volunteers performed incremental cycle ergometer tests with simultaneous respiratory gas exchange and multi-lead ECG monitoring.
  • VT2 was determined using standard gas exchange criteria as the reference.
  • ECG T-wave instability index (dT) and its low-frequency oscillations (LFdT) were computed to derive VT2 estimates (VT2dT and VT2LFdT).

Main Results:

  • VT2dT estimation yielded a mean error of -4.7 ± 25.2 W, with 68% of subjects within 25 W and 89.5% within 50 W of the reference VT2.
  • VT2LFdT estimation resulted in a mean error of 15.3 ± 32.4 W.
  • Consistent patterns in dT and LFdT profiles across subjects suggest altered autonomic control of ventricular repolarization around VT2.

Conclusions:

  • Non-invasive ECG T-wave analysis provides a feasible method for estimating VT2 during incremental exercise.
  • Observed changes in ventricular repolarization dynamics may reflect shifts in sympathetic modulation of the heart at VT2.
  • This ECG-based approach offers a promising alternative for VT2 assessment, potentially linked to autonomic nervous system regulation.