Comparative analysis of relaxation time interval and integrated relaxation pressure as risk factors for aspiration in patients with oropharyngeal dysphagia

Background/Aims Integrated relaxation pressure (IRP) is an important metric for functional evaluation of the lower esophageal sphincter. However, the effectiveness of IRP for evaluation of upper esophageal sphincter (UES) function has not yet been clarified. Methods High-resolution manometry (HRM) was performed in 180 patients with dysphagia. For comparison, 26 asymptomatic subjects were also recruited. IRP of the UES was defined as means of 0.2, 0.25, or 0.3 seconds (sIRPs) of maximal deglutitive relaxation in a 0.4-second window (a new equation for IRP calculation was developed using MATLAB). Also, the relaxation time interval of the UES, and mesopharyngeal and hypopharyngeal contractility (as a contractile integral) were evaluated using HRM. Results In normal subjects, mean values of 0.2, 0.25, and 0.3 sIRPs differed significantly from each other (P < 0.05). They were not associated with the relaxation time interval of the UES. In contrast, in patients with dysphagia, mean values of 0.2, 0.25, and 0.3 sIRPs were strongly related to relaxation time intervals of the UES (P < 0.05), and mean values of 0.2, 0.25, and 0.3 sIRPs in patients with aspiration were significantly higher than those of patients without aspiration (P < 0.01). However, in multivariate regression analyses, the main risk factor for aspiration was only a shorter relaxation time interval. Conclusions IRP values were significantly higher in patients with dysphagia and aspiration. However, its usefulness as a predictive factor for aspiration was less than the relaxation time interval of the UES.