Functional changes in the diaphragm have been described in patients with GERD, which can impair the stability of the anti-reflux barrier. These include reduced strength of the inspiratory muscles and insufficiently coordinated diaphragmatic contraction. These functional deficits can contribute to the gastroesophageal junction performing its barrier function less effectively.
Inspiratory muscle training addresses this by specifically training the strength and performance of the respiratory muscles, including the diaphragm.
The meta-analysis included three clinical studies with a total of 98 participants. Of these, 91 people suffered from GERD and seven were healthy control subjects. One study was randomized controlled, while two had a non-randomized intervention design.
Inspiratory muscle training was performed using threshold breathing devices, depending on the study over a period of four to eight weeks, once or twice a day and with training intensities between 30 and 60% of maximum inspiratory pressure. The methodological quality of the individual studies was rated as moderate to good overall, but the number of cases was small (n=12–25 depending on the study).
Not all studies examined the same endpoints. Depending on the study, parameters of inspiratory muscle strength, diaphragmatic function, reflux symptoms, and manometric measurements at the gastroesophageal junction were recorded. This heterogeneity limits the comparability of the results.
Two of the three studies examined maximum inspiratory pressure (MIP) as a measure of respiratory muscle strength. In one of these studies, inspiratory muscle training resulted in a significant increase in MIP compared to the control condition, while in the other, no significant difference was detected.
Diaphragmatic excursion was recorded in only one study. In that study, the measured movement of the right and left diaphragms increased significantly after four weeks of training (p < 0.001).
Reflux symptoms were analyzed in two of the included studies. Overall, there were no consistent significant differences between the intervention and control groups.
In one of the studies, a significant difference in GERD-Q score between the groups was found at only one measurement point—in the fourth week of training (1.84 ± 2.17 vs. 3.32 ± 1.49; p = 0.015). There were no significant differences at earlier time points.
Two of the included studies examined the effects on pressure parameters of the lower esophageal sphincter and the esophagogastric junction. In both studies, there were no measurable effects of inspiratory muscle training compared to the control treatment.
This systematic review is the first to systematically summarize the use of inspiratory muscle training in patients with GERD. Overall, the authors consider inspiratory muscle training to be a physiologically plausible approach, but one that has not yet been sufficiently proven.
The review therefore does not allow for a conclusive assessment of the therapeutic benefits, but rather highlights a gap in research: methodologically robust randomized studies with clearly defined clinical endpoints are needed in order to reliably assess the potential value of IMT as a non-pharmacological adjunct in the treatment of GERD.