Effects of inspiratory muscle training on cardiovascular autonomic control: A systematic review.

PURPOSE: To carry out a systematic review to determine if inspiratory muscle training (IMT) promotes changes in cardiovascular autonomic responses in humans.

METHODS: The methodology followed the PRISMA statement for reporting systematic review analysis. MEDLINE, PEDro, SCOPUS and PubMed electronic databases were searched from the inception to March 2017. The quality assessment was performed using a PEDro scale. The articles were included if: (1) primary objective was related to the effects of IMT on the cardiovascular autonomic nervous system, and (2) randomized clinical trials and quasi-experimental studies. Exclusion criteria were reviews, short communications, letters, case studies, guidelines, theses, dissertations, qualitative studies, scientific conference abstracts, studies on animals, non-English language articles and articles addressing other breathing techniques. Outcomes evaluated were measures of cardiovascular autonomic control, represented by heart rate variability (HRV) and blood pressure variability (BPV) indexes.

RESULTS: The search identified 729 citations and a total of 6 studies were included. The results demonstrated that IMT performed at low intensities can chronically promote an increase in the parasympathetic modulation and/or reduction of sympathetic cardiac modulation in patients with diabetes, hypertension, chronic heart failure and gastroesophageal reflux, when assessed by HRV spectral analysis. However, there was no study which evaluated the effects of IMT on cardiovascular autonomic control assessed by BPV.

CONCLUSIONS: IMT can promote benefits for cardiac autonomic control, however the heterogeneity of populations associated with different protocols, few studies reported in the literature and the lack of randomized controlled trials make the effects of IMT on cardiovascular autonomic control inconclusive.