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 (K2HP–RM), the unconditioned TE from RM to HP (TERM→HP) and the TE from RM to HP conditioned on SAP (TERM→HP| SAP). In PRE condition we found that STAND led to a decrease of TERM→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. TERM→HP and K2HP–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.

Highlights

  • In the field of the analysis of spontaneous fluctuations of heart period (HP) with the term cardiorespiratory coupling (CRC) is intended the set of mechanisms responsible for a variable quote of HP variability (HPV) driven by respiration

  • The effect of STAND was significant over μHP regardless of the training status (i.e. before weeks of IMT (PRE) and after weeks of IMT (POST)) and type of training (i.e. sham IMT (SHAM), MIP60, and critical inspiratory pressure (CIP))

  • SHAM and MIP60 trainings lengthened μHP at rest in supine condition (REST) respectively, while CIP training shortened μHP during STAND. σ2HP and μSAP were not influenced by experimental condition and training status

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Summary

Introduction

In the field of the analysis of spontaneous fluctuations of heart period (HP) with the term cardiorespiratory coupling (CRC) is intended the set of mechanisms responsible for a variable quote of HP variability (HPV) driven by respiration. Improving CRCS might be advisable because it Abbreviations: μ, mean; σ2, variance; BRS, baroreflex sensitivity; CIP, IMT at the critical inspiratory pressure; CRC, cardiorespiratory coupling; CRCS, CRC strength; ECG, electrocardiogram; HP, heart period; HPV, HP variability; IMT, inspiratory muscle training; K2, squared coherence function; MEP, maximal expiratory pressure; MIP, maximal inspiratory pressure; MIP60, IMT against a respiratory resistance set to 60% of MIP; POST, after 11 weeks of IMT; PRE, before 11 weeks of IMT; REST, at rest in supine position; RF, respiratory frequency; RM, respiratory movement signal; RSA, respiratory sinus arrhythmia; SAP, systolic arterial pressure; SEQ%, percentage of HP-SAP pattern of baroreflex origin; SHAM, IMT against an inspiratory resistance of 6 cmH2O; STAND, active standing; TE, transfer entropy; VO2, oxygen uptake

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