Respiratory mechanics and morphometric changes during pneumoperitoneum in normal rats.

Pneumoperitoneum may give rise to several respiratory changes; nevertheless, no comprehensive analysis of respiratory mechanics has been performed under this condition. Respiratory mechanics and thoracoabdominal morphometry were evaluated in six sedated, anaesthetized, paralysed, and mechanically-ventilated rats before (control) and during pneumoperitoneum. After airway occlusion at end-inspiration, respiratory system, pulmonary, and chest wall resistive pressures (deltaP1,rs, deltaP1,L and deltaP1,cw, respectively) and viscoelastic/inhomogeneous pressures (deltaP2,rs, deltaP2,L and deltaP2,cw, respectively) were determined. Total pressure changes (deltaPtot) were calculated as the sum of deltaP1 and deltaP2, yielding the values of deltaPtot,rs, deltaPtot,L and deltaPtot,cw, respectively. Respiratory system, lung, and chest wall static (Est,rs, Est,L and Est,cw, respectively), and dynamic elastances (Edyn,rs, Edyn,L and Edyn,cw, respectively), and the corresponding changes in elastance (deltaE) (calculated as Edyn-Est) were also obtained. Chest wall configuration both at functional residual capacity (FRC) and end-inspiration (FRC + tidal volume (VT)) was also evaluated in another four rats. Pneumoperitoneum significantly increased deltaPtot,rs, deltaPtot,cw, deltaP2,rs, deltaP2,cw, deltaErs, deltaEcw, Est,rs, Est,L and Est,cw. Lateral and anteroposterior diameters increased significantly, with the exception of lateral diameters at the level of crista iliaca. Cephalocaudal diameter and FRC decreased. In conclusion, pneumoperitoneum augments elastances and increases the pressure dissipated against viscoelasticity/inhomogeneity of the respiratory system and chest wall. These changes are related to a cephalad displacement of the diaphragm plus changes in thoracoabdominal configuration.