Inspiratory muscle training improves autonomic modulation and exercise tolerance in chronic obstructive pulmonary disease subjects: A randomized-controlled trial

https://doi.org/10.1016/j.resp.2019.03.003Get rights and content

Highlights

  • IMT has been used in rehabilitation programs aiming to increase exercise tolerance in COPD subjects.

  • The autonomic imbalance is a risk factor for cardiovascular events and is well established in the COPD population.

  • At this point, no study has studied the effect of IMT on the autonomic modulation of COPD subjects.

  • A low-intensity IMT training improved cardiac autonomic modulation and exercise tolerance in COPD patients.

Abstract

Objectives

We aimed to evaluate the effect a regular inspiratory muscle training program on autonomic modulation measured by heart rate variability, exercise capacity and respiratory function in chronic obstructive pulmonary disease subjects (COPD).

Design

Single-center controlled study, with balanced randomization (1:1 for two arms).

Setting

A COPD reference hospital localized in Sao Luís, Brazil.

Participants

22 COPD subjects joined the study.

Interventions

Three times a week for four weeks inspiratory muscle training (IMT) at 30% of PImax.

Main outcome measures

Pulmonary capacities and inspiratory pressure, total six-minute walk test and, cardiac autonomic modulation.

Results

The intervention group showed improvements in the cardiac autonomic modulation, with increased vagal modulation (total variability and HF [ms2; adjusted p < 0.05]); increased expiratory and inspiratory capacities and, increased distance in the 6-min walk test.

Conclusion

12 weeks of IMT at 30% of the maximal inspiratory pressure increased cardiac autonomic modulation, expiratory and inspiratory and exercise capacity in COPD subjects.

Introduction

Chronic Obstructive Pulmonary Disease (COPD) is one of the leading causes of death worldwide (Halbert et al., 2006; Prince et al., 2015). Recent estimates point out that in 2020, COPD will be the third largest cause of death in the world (Ford et al., 2015). In addition, COPD is directly related to the development of autonomic imbalance, atherosclerosis and other cardiovascular complications (Mazzuco et al., 2015; van Gestel and Steier, 2010). Recent data have shown that cardiovascular diseases can be responsible for the greater number of hospitalizations, as well as 25% mortality in COPD subjects (Choudhury et al., 2014).

Among the variables affected, COPD causes autonomic dysfunction, as well as, reduced forced expiratory volume, decreases in oxygen consumption (VO2), low exercise tolerance and decreased respiratory muscle strength (Lacasse et al., 2005; Leidy et al., 2014). This fact contributes to a marked respiratory muscle desynchrony, accompanied by a fast and superficial respiratory pattern in certain activities such as tying a shoe, teeth brushing, etc (Stjepanovic et al., 2016). Also, the simple sustained elevation of the upper limbs in these subjects may lead to a significant increase in dyspnea sensation (Janaudis-Ferreira et al., 2014; Stjepanovic et al., 2016).

COPD subjects present a increased vagal autonomic modulation, as shown by other studies, mainly during the acute exacerbations (Kabbach et al., 2017). This increased vagal modulation might be one of the mechanisms responsible for the bronchoconstriction, so markedly present in COPD subjects (Audrit et al., 2017; Chong et al., 2017).

Other studies have already demonstrated the beneficial impacts of exercise training, such as running or strength exercises on autonomic modulation and exercise tolerance of COPD subjects (Borghi-Silva et al., 2009; Mohammed et al., 2016). Other exercises, such as inspiratory muscle training (IMT) in COPD subjects have been extensively described for its benefits in respiratory capacity and exercise tolerance (Dellweg et al., 2017; Montemezzo et al., 2014).

In addition, IMT has been shown as an effective strategy to improve cardiac autonomic control in hypertensive subjects and peripheral sympathetic activity in subjects with heart failure, increasing their functional capacity, the overall quality of life and cardiorespiratory fitness (Sin and Paul Man, 2003).

The heart rate variability (HRV) is a clinical tool used to measure the balance between sympathetic and parasympathetic (vagal) modulation through the data collection of the RR intervals. The reduction in the HRV has been associated with increased risk for cardiovascular disease and acute cardiac events, such as myocardial infarction (La Rovere et al., 1998; Thayer et al., 2010).

Since COPD subjects are at a higher risk of developing cardiovascular diseases (Chen et al., 2015; Sin and Paul Man, 2003) and have a marked vagal modulation (Janaudis-Ferreira et al., 2014), efficient strategies for reducing vagal-mediated bronchoconstriction, increasing respiratory capacities and, increasing exercise tolerance in this population are urgent. However, to this date, no study has ever investigated the effect of IMT on autonomic modulation of COPD subjects.

With this insight, the aim of this study was to evaluate the effect of IMT in respiratory function, exercise capacity, and, autonomic function in COPD subjects.

Section snippets

Trial design and study place

This was a single-center, randomized-controlled study, with balanced randomization (1:1 for two groups). The sample was composed of subjects with diagnosed with COPD recruited at the Pulmonary Rehabilitation Program between 2016 and 2017 at the Hospital Universitario Presidente Dutra, a reference center in Sao Luis, Brazil, the capital of Maranhão’state (Fig. 1). The control group received no intervention and was evaluated before and 12 weeks after. The IMT group received an intervention with

Overall characteristics

Table 1 shows the hemodynamic parameters, submaximal exercise capacity, peak oxygen consumption and body mass index (BMI) variables. All subjects were classified GOLD A class with grade I-II airflow obstruction. The subjects had a mean of 1.3 ± 0.4 exacerbations, but all with no hospital admissions in the last month before the protocol.

Respiratory function and Inspiratory muscle strength

No differences were found between control and IMT groups for FVC (liters and % of predicted), FEV1 (liters), FEV1/FVC, and FEF25/75 both in baseline period as

Discussion

This study aimed to evaluate the effect of 12 weeks of IMT at 30% of the maximum inspiratory pressure (PImax) on respiratory function, exercise capacity, and autonomic function in COPD subjects. The main finding of our study shows that a regular protocol of IMT was effective to improve maximal inspiratory and expiratory muscle strength, cardiac autonomic modulation and, functional capacity measured by the 6MWT in COPD subjects. However, the IMT protocol failed in show any improvements in

Conclusion

In conclusion, our study demonstrated that IMT at 30% of PImax for 12 weeks positively affected exercise capacity, PImax, PEmax and, autonomic function in a group of GOLD II COPD subjects.

Conflicts of interest

All authors declare no conflicts of interest.

Acknowledgments

We would like to thank the “Fundação de Amparo à Pesquisa do Estado do Maranhão (FAPEMA)” for its grant support for this research project and, the ‘Hospital Universitário Presidente Dutra’ for their open-mind policy for research. Cristiano Mostarda received grants from CNPq (Universal 442374/2014-3) and FAPEMA (Bolsa Produtividade and Universal 00358/15).

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