Review of 'Time‐Efficient Inspiratory Muscle Strength Training Lowers Blood Pressure and Improves Endothelial Function, NO Bioavailability, and Oxidative Stress in Midlife/Older Adults With Above‐Normal Blood Pressure'

To the Editor:

We read with great interest this article detailing the randomized, double-blind, sham-controlled trial performed by Craighead et al. (1). In this article, the authors investigated the safety, adherence, and efficacy of high-resistance inspiratory muscle strength training (IMST) for lowering systolic blood pressure (SBP) and improving vascular function. We would like to comment on some concerns.

First, despite the fact that the mean 24-hour SBP did not change after 6 weeks of IMST, the conclusion states that IMST lowers the 24-hour SBP compared with sham training. As the authors mentioned that the “Twenty-four-hour daytime and nighttime SBP were lower in the IMST group compared with sham group at end-intervention attributable to a trend for reductions in SBP with IMST concomitant with modest increases in the sham control group.”(1), the significant difference in 24-hour SBP at end-intervention between the IMST and sham groups was due to SBP increases in the sham control group. This result does not support the conclusion that IMST improves the 24-hour blood pressure.

Second, the safety of high-resistance IMST should be carefully assessed. Several studies have reported adverse events caused by IMST, such as cephalalgia, dyspnea, hypertension, headache, and arrhythmias (2,3). Notably, in a previous study, 33% of elderly patients experienced cardiac arrhythmias (3). Because asymptomatic patients with arrhythmias could not be recognized without electrocardiogram monitoring, the safety of IMST in potentially high-risk patients requires further investigation. In the next confirmatory trial, it may be useful to use a smart watch to monitor arrhythmia during IMST at home.

Third, in the present study, 25% (16/64 participants) of the patients did not meet the inclusion criteria, and over 40% of the patients (26/64 participants) were either excluded or withdrew before study randomization. However, a description of the reasons for exclusion was lacking. We would like to know the reasons for exclusion in order to discuss the application of IMST in clinical practice (4).

Finally, we respect the authors for their excellent work, and we hope that our comments will help in conducting future research.

References

1. Craighead DH, Heinbockel TC, Freeberg KA, Rossman MJ, Jackman RA, Jankowski LR, Hamilton MN, Ziemba BP, Reisz JA, D'Alessandro A, Brewster LM, DeSouza CA, You Z, Chonchol M, Bailey EF, Seals DR. Time-efficient inspiratory muscle strength training lowers blood pressure and improves endothelial function, NO bioavailability, and oxidative stress in midlife/older adults with above-normal blood pressure. J Am Heart Assoc. 2021 Jun 29:e020980. doi:10.1161/JAHA.121.020980.
2. Ramos PS, Da Costa Da Silva B, Gomes Da Silva LO, Araújo CG. Acute hemodynamic and electrocardiographic responses to a session of inspiratory muscle training in cardiopulmonary rehabilitation. Eur J Phys Rehabil Med.2015;51:773-779.
3. Nepomuceno BRV Jr, Barreto MS, Almeida NC, Guerreiro CF, Xavier-Souza E, Neto MG. Safety and efficacy of inspiratory muscle training for preventing adverse outcomes in patients at risk of prolonged hospitalisation. Trials. 2017;18:626.
4. Schulz KF, Altman DG, Moher D; CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ. 2010;340:c332.