Comparison between Pulmonary Resistance and Penh in Anaesthetised Rats with Tracheal Diameter Reduction and after Carbachol Inhalation

Introduction: Single-chambered barometric whole-body plethysmography is frequently used as a noninvasive lung function test. However, the validity of the enhanced Pause (Penh), an index of airflow limitation, remains controversial. We compared Penh with pulmonary resistance (R(L)) to test whether Penh detects tracheal subobstruction and carbachol-induced airflow limitation in spontaneously breathing, anaesthetised rats. Methods: Fourteen male Sprague-Dawley rats underwent tracheal catheterisation, followed by measurements of R(L) and Penh. Six rats underwent tracheal subobstruction by the consecutive insertion into the lumen of the tracheal tube of two catheters of decreasing diameter. Eight rats received an inhaled saline challenge, followed by two noncumulative nebulizations of carbachol (1.25 mg/mL, 1 min). Results: In rats with tracheal calibre reductions, R(L) significantly increased at each reduction (0.218+/-0.052 vs. 0.417+/-0.058 vs. 0.820+/-0.258 cm H(2)O/mL s, p<0.05), whereas Penh only increased after the last reduction (1.88+/-0.25 vs. 2.47+/-0.26, p<0.05). Increases (Delta) of R(L) and Penh were not correlated. In comparison to postsaline values, carbachol induced a significant increase of Penh (1.93+/-0.44 vs. 4.05+/-1.45, p<0.005) and R(L) (0.137+/-0.04 vs. 0.284+/-0.084 cm H(2)O/mL.s, p<0.005). DeltaPenh and DeltaR(L) were significantly correlated (r=0.80, p<0.05). Discussion: This study showed, by comparing Penh with R(L), that single-chambered plethysmography measuring Penh allows to detect carbachol-induced airflow limitation in spontaneously breathing, anaesthetised Sprague-Dawley rats, but poorly detects an increase in R(L) due to tracheal calibre reductions. These findings suggest that Penh might be only be used as an index of airflow limitation under well-defined experimental conditions.