POSITIVE PRESSURE INSPIRATION DIFFERENTIALLY AFFECTS RIGHT AND LEFT-VENTRICULAR OUTPUTS IN POSTOPERATIVE CARDIAC-SURGERY PATIENTS

Purpose: The purpose of this study was to determine the dynamic change s in right ventricular (RV) and left ventricular (LV) output during po sitive airway pressure inspiratory hold maneuvers so as to characteriz e the interaction of processes in creating steady-state cardiac output during positive pressure ventilation. Materials and Methods: We exami ned the disparity of RV and LV outputs at 5 seconds (early) and 20 sec onds (late) into a 25-second inspiratory hold maneuver in 14 subjects in the intensive care unit immediately following coronary artery bypas s surgery. RV output was measured by the thermodilution technique, whe reas LV output was measured by the arterial pulse contour method. RV a nd LV volumes were also measured by thermal and radionuclide ejection fraction techniques, respectively. Results: As P-aw was progressively increased from 0 to 20 cm H2O in sequential inspiratory hold maneuvers , both RV and LV outputs changed differently both at 5 seconds and 20 seconds into the inspiratory hold maneuvers. When expressed as change in cardiac output (L/min) for every cm H2O P-aw increase relative to e nd-expiratory values, RV output increased at 5 seconds (0.05 +/- 0.15 L/min) then decreased at 20 seconds (-0.08 +/- 0.21, P < .05), LV outp ut decreased slightly at 5 seconds (-0.14 +/- 0.22) and did not change from this minimal depressed level at 20 seconds (P < .05). Changes in RV and LV output were paralleled by changes in RV and LV end-diastoli c volumes, respectively. Conclusion: Positive pressure inspiration ind uces time-dependent changes in central hemodynamics, which are dissimi lar between RV and LV function. Initially, inspiration increases RV ou tput but decreases LV output, such that intrathoracic blood volume inc reases. However, sustained inspiratory pressures induce proportionally similar decreases in both RV and LV outputs. Thus, the hemodynamic ef fects of positive pressure ventilation will depend on the degree of lu ng inflation, the inspiratory time, and when measurements are made wit hin the ventilatory cycle. These data also suggest that positive press ure ventilation with up to 20 cm H2O P-aw does not significantly impai r ventricular performance in humans. Copyright (C) 1997 by W.B. Saunde rs Company.