Current Insights of Inspiratory Muscle Training on the Cardiovascular System: An Update of the Systematic Review with Meta-Analysis

What is it about?

Background: Cardiorespiratory limitation is a common hallmark of cardiovascular disease which is a key component of pharmacological and exercise treatments. More recently, inspiratory muscle training (IMT) has become an effective complementary treatment with positive effects on muscle strength and exercise capacity. Aim: We assessed the effectiveness of IMT on the cardiovascular system through autonomic function modulation via heart rate variability and arterial blood pressure. Methods: Randomized controlled trials (RCTs) were identified from searches of The Cochrane Library, MEDLINE, and EMBASE to November 2023. We included studies examining a program of IMT (≥ one-week treatment) offered as a sole intervention or as an adjuvant to another form of exercise. Citations, conference proceedings, and previous reviews were included without population restriction, comparing IMT intervention to no treatment, placebo, or active control. Results: We identified 20 RCTs involving 521 subjects (mean age range 21–71 years). IMT programs targeted maximum inspiratory pressure (MIP) and cardiovascular outcomes, using low (n=11) and moderate to high intensity (n=9) protocols, but the protocols varied considerably (duration: 1–12 weeks, frequency: 3–14 times/week, time: 10–30 mins). An overall increase of the MIP (cmH2O) was observed (23.66 95% CI 15.95 to 31.37, I2=77%), according to weighted mean difference (95%CI) and was accompanied by a reduction of the low to high-frequency ratio (-0.70 95% CI -1.34 to -0.05, I2=42%). In a subgroup analysis, low- and moderate-intensity IMT treatment was associated with a reduction of the systolic blood pressure (SBP) (-5.08 95% CI -9.11 to -1.06 mmHg, I2=0%), heart rate (HR) (−3.58 95% CI -5.94 to -1.21 bpm, I2=63.4%) and diastolic blood pressure (DBP) (−11.25 95% CI -16.46 to -6.05 mmHg, I2=0%), respectively. Conclusion: IMT is an effective treatment for inspiratory muscle weakness in several populations and could be considered a complementary treatment to improve the cardiovascular system, mainly SBP, HR, and DBP. Further research is required to understand the above findings better. More studies are needed to better understand the role of IMT as a component or alternative to regular exercise protocols for treating individuals with increased blood pressure response.

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Why is it important?

More recently, IMT has been evaluated as an adjunct therapy to improve autonomic modulation due to the recognized respiratory effects. According to several studies, IMT may reduce sympathetic activity [9,11] through respiratory muscle metaboreflex attenuation [12], improving functional capacity and physical performance [12-15]. Therefore, the purpose of this study was to systematically review the effects of the IMT on global cardiovascular function through autonomic function modulation of heart rate variability and arterial blood pressure.