SYSTEMIC FILLING PRESSURE IN THE INTACT CIRCULATION DETERMINED WITH ASLOW INFLATION PROCEDURE

In eight mechanically ventilated, anaesthetized pigs weighing 10.3 +/- 0.8 kg(mean +/- SD) we studied the effect of the inflation time of th e lung on the estimation of the mean systemic filling pressure (P-sf) from the changes in venous return and central venous pressure during i nflation of the lung. For this purpose we applied slow inflation proce dures (SIP) to the lung with inflation times of 2.4, 4.8, 7.2, 9.6 and 12 s at tidal volumes (V-T) Of 15 and 30 ml/kg. The data were compare d with the values of P-sf Obtained from inspiratory pause procedures ( IPPs). A linear regression between venous return and central venous pr essure applied during a SIP underestimated P-sf compared with the valu e obtained with IPPs. An exponential fit through the values of P-sf ob tained from the different SIPs predicted an inflation time of about 15 s for an estimation of P-sf that is not different from the P-sf (IPP) . The advantage of the SIP method is that the P-sf can be determined m uch faster than with the method based on IPPs. However, due to the rat her long inflation time needed, the method may be only applicable unde r circumstances where neurohumoral control mechanisms are suppressed a s during intensive care and anaesthesia.