ELEVATED MEAN SYSTEMIC FILLING PRESSURE DUE TO INTERMITTENT POSITIVE-PRESSURE VENTILATION

To clarify the effect of intermittent positive-pressure ventilation (IPPV) on systemic circulation, mean systemic filling pressure (P(sf)) and circulating blood volume were measured together with other hemodynamic parameters of capacitance vessel. Change in circulating blood volume was determined by dilution with Cr-51-labeled erythrocytes. Vascular compliance (C(vas)) was measured from the change in P(sf) caused by a bolus injection of blood. These parameters were measured during both spontaneous respiration and IPPV in male Wistar rats anesthetized with pentobarbital sodium. The shift from spontaneous respiration to IPPV reduced cardiac output (CO) by 20.9%. P(sf) increased significantly, from 7.1 +/- 1.2 to 8.6 +/- 1.1 mmHg. Central venous pressure (P(cv)) also increased significantly. The pressure gradient for venous return decreased by 15.6% (from 6.4 to 5.4 mmHg). The resistance to venous return did not change significantly, but there was a significant increase in total peripheral resistance. Neither C(vas) nor circulating blood volume was changed significantly by IPPV. These results indicate that during IPPV the increased P(cv) attenuates the pressure gradient for venous return and decreases CO and that the compensatory increase in P(sf) is caused by a blood shift from unstressed to stressed blood volume.