A hypotensive protocol of inspiratory muscle strength training: Systematic review and meta-analysis with trial sequential analysis

Abstract

The aim of this study was to evaluate the hypotensive effect and optimal protocol of inspiratory muscle resistance training (IMST). Randomized controlled trials using IMST to lower blood pressure (BP) were retrieved from 12 databases as of July 2022. A meta-analysis of BP and heart rate variability (HRV) was performed and a trial sequence analysis was performed using trial sequential analysis (TSA) software. Twelve articles (n = 386 participants) from five countries were included, with a mean quality score of 5.83. IMST achieved significant results in reducing systolic, diastolic, and mean arterial pressure (-7.93 [-12.08, -3.78]; -3.80 [-6.08, -1.53]; -4.90 [-13.76, 3.96]). Furthermore, TSA has shown that the findings for systolic and diastolic BP are conclusive. Finally, considerable variation remained between studies when analyzing HRV. The overall hypotensive effect of IMST was demonstrated by the TSA and was well tolerated in different populations. Of these, two interventions, high resistance or low resistance combined with slow breathing, showed the best efficacy under an 8-week exercise intervention. In addition, the process of lowering BP by modulating sympathetic vagal activity has not been further confirmed in this study. Future long-term interventions, especially those over 3 months, are needed to observe the prolonged antihypertensive effects and modulatory mechanisms; controlling for variables such as respiratory rate and executing more rigorous studies to further explore antihypertensive options.

Keywords: exercise protocol; hypertension; inspiratory muscle strength training; mechanism; meta-analysis.

FIGURE 1

Database search and selection process using PRISMA.

FIGURE 2

Meta‐analysis of systolic blood pressure after IMST intervention total effect (A) and subgroup analysis by duration (B).

FIGURE 3

Antihypertensive effect of IMST under inspiratory resistance subgroup analysis.

FIGURE 4

Antihypertensive effect of IMST under population subgroup analysis.

FIGURE 5

Trial sequential analysis on the efficacy of IMST in reducing systolic (A) and diastolic blood pressure (B). The solid blue line shows the cumulative Z curve after the random‐effects cumulative meta‐analysis, the red horizontal dashed lines represent the conventional alpha boundaries, the red vertical line represents the desired sample size, and the red diagonal lines represent TSA boundaries.