We measured respiratory mechanics in six anesthetized, mechanically ventilated, paralyzed rats by the end-inflation occlusion method. The respiratory system was inflated with a constant flow (F=4 ml/sec), and the flow suddenly interrupted after a volume of 3 ml (VT) was delivered.

From tracings of tracheal pressure, the static elastic pressure (Pel,rs), the ohmic resistive pressure needed to overcome airflow and respiratory system tissues resistance to the movement (Pmin,rs), and the pressure dissipation due to pendelluft and stress-relaxation (Pvisc,rs) were measured.

The method models the respiratory system as a two compartment model, allowing the calculation of the static elastance (Est,rs=Pel,rs/VT), of the ohmic resistance (Rmin,rs=Pmin,rs/F), and of the resistance due to the effects of pendelluft and stress-relaxation (Rvisc,rs=Pvisc,rs/F). The overall resistive pressure dissipation allows the calculation of Rmax,rs=Rmin,rs + Rvisc,rs.

The measurements were repeated three times at 10 minutes intervals.

Results were: 

a) the mean values of Est,rs (1.85 ± 0.24cmH2O/ml), Rmin,rs, Rvisc,rs, and Rmax,rs (0.06 ± 0.01, 0.43 ± 0.04, 0.49 ± 0.05 cmH2O/ml sec-1) are in the range of those reported for normal rats.

b) we did not observe any significant change of respiratory system mechanics with time.

We conclude that our experimental technique is suitable for respiratory system mechanics measurements, and that the experimental preparation is stable in time for at least 30 minutes.