A Transfer Entropy Approach for the Assessment of the Impact of Inspiratory Muscle Training on the Cardiorespiratory Coupling of Amateur Cyclists

Raphael Martins de Abreu; Aparecida Maria Catai; Beatrice Cairo; Patricia Rehder-Santos; Claudio Donisete da Silva; Étore De Favari Signini; Camila Akemi Sakaguchi; Alberto Porta

doi:10.3389/fphys.2020.00134

A Transfer Entropy Approach for the Assessment of the Impact of Inspiratory Muscle Training on the Cardiorespiratory Coupling of Amateur Cyclists

Front Physiol. 2020 Feb 25:11:134. doi: 10.3389/fphys.2020.00134. eCollection 2020.

Authors

Raphael Martins de Abreu¹, Aparecida Maria Catai¹, Beatrice Cairo², Patricia Rehder-Santos¹, Claudio Donisete da Silva¹, Étore De Favari Signini¹, Camila Akemi Sakaguchi¹, Alberto Porta^{2

3}

Affiliations

¹ Department of Physical Therapy, Federal University of São Carlos, São Carlos, Brazil.
² Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.
³ Department of Cardiothoracic - Vascular Anesthesia and Intensive Care, IRCCS Policlinico San Donato, Milan, Italy.

Abstract

The strength of cardiorespiratory interactions diminishes with age. Physical exercise can reduce the rate of this trend. Inspiratory muscle training (IMT) is a technique capable of improving cardiorespiratory interactions. This study evaluates the effect of IMT on cardiorespiratory coupling in amateur cyclists. Thirty male young healthy cyclists underwent a sham IMT of very low intensity (SHAM, n = 9), an IMT of moderate intensity at 60% of the maximal inspiratory pressure (MIP60, n = 10) and an IMT of high intensity at the critical inspiratory pressure (CIP, n = 11). Electrocardiogram, non-invasive arterial pressure, and thoracic respiratory movement (RM) were recorded before (PRE) and after (POST) training at rest in supine position (REST) and during active standing (STAND). The beat-to-beat series of heart period (HP) and systolic arterial pressure (SAP) were analyzed with the RM signal via a traditional non-causal approach, such as squared coherence function, and via a causal model-based transfer entropy (TE) approach. Cardiorespiratory coupling was quantified via the HP-RM squared coherence at the respiratory rate (K ² _HP-R _M), the unconditioned TE from RM to HP (TE_R _M _→ _HP) and the TE from RM to HP conditioned on SAP (TE_R _M _→ _{HP| SAP}). In PRE condition we found that STAND led to a decrease of TE_R _M _→ _{HP| SAP}. After SHAM and CIP training this tendency was confirmed, while MIP60 inverted it by empowering cardiorespiratory coupling. This behavior was observed in presence of unvaried SAP mean and with usual responses of the baroreflex control and HP mean to STAND. TE_R _M _→ _HP and K ² _HP- _RM were not able to detect the post-training increase of cardiorespiratory coupling strength during STAND, thus suggesting that conditioning out SAP is important for the assessment of cardiorespiratory interactions. Since the usual response of HP mean, SAP mean and baroreflex sensitivity to postural stressor were observed after MIP60 training, we conclude that the post-training increase of cardiorespiratory coupling during STAND in MIP60 group might be the genuine effect of some rearrangements at the level of central respiratory network and its interactions with sympathetic drive and vagal activity.

Keywords: autonomic nervous system; baroreflex; breathing exercise; cardiac control; complexity; heart rate variability; multivariate linear regression model; sport medicine.