Correlation Between Body Plethysmography and Impulse Oscillometry Across Obstructive and Restrictive Lung Diseases: Evidence from an Adult Pilot Study Cohort.

Background/Objectives: Despite the complementary insights provided by body plethysmography and impulse oscillometry, direct comparisons across obstructive and restrictive lung diseases remain limited. The aim of this study was to evaluate correlations between plethysmographic and oscillometric parameters, with a particular focus on hyperinflation and small airway dysfunction. Methods: We retrospectively analyzed 69 adult patients (35 obstructive, 34 restrictive) hospitalized in the Pulmonology Department of Mureș Clinical Hospital. All patients underwent body plethysmography (sRaw, Rtot, FRC, RV, TLC, RV/TLC) and impulse oscillometry (R5, R20, R5-20, X5, Fres, AX). Non-parametric tests were used to compare groups, and associations were assessed using Spearman's correlation. Results: Higher airway resistance (sRaw 124 vs. 62, p < 0.001; R5 0.55 vs. 0.38, p < 0.01) and greater hyperinflation (RV 124 vs. 99, p < 0.001) were observed in patients with obstructed airways. Impulse oscillometry reactance markers (X5, Fres, AX) significantly differentiated obstructive from restrictive pathophysiology (p < 0.02). In the obstructive group, sRaw correlated with R5 (p = 0.01) and R5-20 (r = 0.58, p < 0.001), while AX correlated with RV (r = 0.59, p < 0.001). Restrictive patients revealed negative correlations between AX and static volumes (RV, TLC, RV/TLC; all p < 0.05). DLCO was higher in obstructive patients (75 vs. 62, p = 0.01). Conclusions: Our study demonstrates that body plethysmography and impulse oscillometry provide complementary information on respiratory mechanics and that the results obtained with the two methods correlate significantly, especially in obstructive diseases.