Age-related variation in distal esophageal mean nocturnal baseline impedance: a hierarchical analysis of reflux burden and clearance

Mean nocturnal baseline impedance (MNBI) indicates esophageal mucosal integrity in impedance–pH monitoring. Although aging has been associated with impaired esophageal clearance and increased reflux burden, the extent to which age-related differences in MNBI persist remains uncertain. We investigated how the association between age and distal MNBI changed after sequential inclusion of acid exposure and post-reflux chemical clearance, and explored the incremental contribution of esophageal peristaltic vigor. This study included 184 patients with heartburn and/or regurgitation symptoms and acid exposure time (AET) ≥ 4% in 24-hour multichannel intraluminal impedance–pH monitoring. Distal MNBI was measured 5 cm above the lower esophageal sphincter. Among them, 155 had available high-resolution manometry data. Comparisons by age, Spearman correlation analyses, and hierarchical multivariable linear regression analyses were performed. Distal contractile integral (DCI) was subsequently evaluated in the manometry subgroup. Compared with patients aged < 65 years, those aged ≥ 65 years had higher total AET (9.3% vs. 6.9%, P = 0.018), higher supine AET (5.9% vs. 3.7%, P = 0.020), and a lower post-reflux swallow-induced peristaltic wave (PSPW) index (20.2% vs. 27.3%, P = 0.020). Age correlated positively with AET ( r s = 0.201) and inversely with distal MNBI ( r s = -0.154), whereas PSPW index correlated positively with distal MNBI ( r s = 0.327). After AET was added to the regression model, R² increased from 0.047 to 0.236, and the association of age was attenuated ( P = 0.084). In the adjusted model, AET remained negatively associated with distal MNBI (B = − 27.02, P < 0.001), whereas PSPW index was positively associated with distal MNBI (B = 8.15, P = 0.009); the age coefficient remained negative but was further attenuated (B = − 4.93, 95% CI (− 10.98, 1.12), P = 0.110). Among patients with available HRM data, addition of DCI increased the explained variance by 1.7%, but this increment was not statistically significant ( P = 0.064). Age was inversely associated with distal MNBI after adjustment for sex and BMI, but this association was attenuated after inclusion of AET and PSPW index. A modest residual age-related association cannot be excluded. In the HRM subgroup, addition of DCI produced a small increase in explained variance that did not reach statistical significance.