A single computer-controlled mechanical insufflation allows determination of the pressure-volume relationship of the respiratory system

Objective. To evaluate and further develop a method for determination and m athematical characterisation of the elastic pressure-volume (P-el-V) relati onship in mechanically ventilated human subjects during one single modi ed insufflation with simultaneous determination of resistance of the respirato ry system. Subjects. Eight adult non-smoking human subjects without heart, lung, or thoracic cage disease scheduled for non-thoracic surgery. The stud y was performed in anaesthetised and muscle-relaxed subjects. Measurements and Main Results. The P-el-V curve was determined with a computer-controlle d Servo Ventilator 900C during a modified insufflation with either constant or sinusoidally varying flow. Pressure and flow were measured with the bui lt-in sensors of the ventilator. Tracheal pressure (P-tr) was calculated by subtracting the pressure drop over the tracheal tube. The elastic recoil p ressure in the peripheral lung, P-el, was obtained from the calculated P-tr by subtracting the pressure drop over the airways. P-tr was also directly measured through a catheter. The calculated P-tr gave similar results as th e directly measured P-tr, thus indicating the reliability of the signal ori ginating from the ventilator sensor for computation of downstream pressures . The inflection points of the sigmoidal P-el-V curve and the compliance of the linear segment were determined with high reproducibility. Conclusions. Using one single modified insufflation allows a fast and accurate determin ation of respiratory mechanics. The P-el-V curves were determined with high reproducibility and were adequately described by a three-segment model of the curve incorporating a linear segment between two asymmetrical non-linea r segments.