End-Expiratory Occlusion Test During Increase of Vasomotor Tone in a Rabbit Model of Hemorrhage

Figure 1. (A) Percentage of change of aortic flow before and during the end-expiratory hold (AoFEEOT), (B) Percentage of change of stroke volume before and during the end-expiratory hold (SVEEOT), (C) Pulse pressure variation (PPV), and (D) Stroke volume variation (SVV) during basal load (BL), basal load + phenylephrine (BL + PHE), blood withdrawal (BW), blood withdrawal + phenylephrine (BW + PHE) and volume replacement (VOL). The results are given by box representing the 25th to 75th percentile with lines indicating median and the error bars above and below each box represent the 90th and 10th percentiles, respectively. *p < 0.05 vs. BL, BL + PHE, VOL, **p < 0.05 vs. BL, BL + PHE, BW + PHE, VOL, using repeated measures ANOVA analysis.

Figure 2. Absolute values of inferior vena cava flow (IVCF) during the end of expiration (EE) and the mechanical inspiration previous the end-expiratory occlusion test (Pre EEOT) and the difference between both (EE - Pre EEOT), during the different experimental conditions. Basal load (BL), basal load + phenylephrine (BL + PHE), blood withdrawal (BW), blood withdrawal + phenylephrine (BW + PHE), and volume replacement (VOL). The results are given as mean with error bars for SEM. *p < 0.05 vs. BW, **p < 0.05 vs. BL + PHE, using repeated measures ANOVA analysis.

Figure 3. Possible effects of blood withdrawal (BW) and phenylephrine infusion (PHE) on inferior vena cava flow (IVCF) and aortic flow (AoF) curves as from the experimental data. BW would determine a parallel leftward shift of the venous return curve by a decrease of mean circulatory filling pressure (decreasing total and stressed volume without changes in the AoF curve, solid lines). PHE would determine an increase in ventricular afterload, shifting the AoF curve downward and a concomitant increase in venous return resistance (vasoconstriction of large veins and the vena cava) and mean circulatory filling pressure (vasoconstriction of venules and small veins, increasing the relative proportion of stressed volume to unstressed volume) (dash lines). CVP: central venous pressure.

Figure 4. Representative traces of the different hemodynamic variables during mechanical ventilation and end-expiratory occlusion test (EEOT) in the baseline condition. AoF and AoP = aortic flow and pressure, respectively; IVC Flow = inferior vena cava flow; AwP = airway pressure; PPV and SVV = pulse pressure variation and stroke volume variation, respectively.