Figure 1.
Ten animals were studied during volume-controlled ventilation during ventilation with 5 ml/kg (baseline) and 10 ml/kg tidal volume (VT) (measurement time point 1) in the normal lung (NL) as well as after induction of acute lung injury (ALI) (time point 2) at inspired fractions of oxygen of 0.5 and 1.0, respectively. Then a constant low-flow inflation maneuver (pressure-volume (PV) maneuver) was performed and positive end-expiratory pressure (PEEP) was set 2 cm H2O above the lower inflection point (LIP) identified in the PV curve. Using a crossover design, further measurements were performed 5 and 30 min after ventilation with low VT and active interventional lung assist (ILA) and after another 5 and 30 min with high VT and inactive ILA (no ILA) (time points 3–6). Five animals were randomly ventilated in the reversed chronological order. Ventilator settings of VT and PEEP at each measurement time point are shown in the lower part of the Figure. *, time elapsed after the change in ventilator and ILA settings.
Figure 2.
Regional ventilation distribution.
Examples of functional EIT scans of regional lung ventilation in animal 2 during all measurement time points (see Figure 1 for explanation). The orientation of the scans is indicated (ant., anterior; post., posterior). Panel A: Ventilated areas within the chest cross-section exhibit higher values of relative impedance change and are shown in red tones. In normal lungs (NL), symmetrical ventilation distribution between the right and left lung regions was found. With induction of acute lung injury (ALI), higher ventilation in the right lung region with pronounced ventilation in its ventral part and reduced left lung ventilation especially in its dorsal part were found. After PEEP was set 2 cm H2O above the lower inflection point (LIP) according to the pressure-volume curve, a shift in ventilation toward the dependent (dorsal) lung regions was observed. No obvious difference between ventilation with 10 ml/kg VT and inactive interventional lung assist (ILA) (high VT, no ILA) and ventilation with 5 ml/kg VT and active ILA (low VT, ILA) was detected. Panel B: Ventilation difference scans of the same animal. Red color indicates increase in regional ventilation, blue color shows the decrease in ventilation compared with baseline.
Figure 3.
Regional ventilation and respiratory system compliance.
Ventrodorsal profiles of regional tidal volume (VT) (A), regional respiratory system compliance (CRS) (C) and differences in regional VT (ΔVT) (B) and regional CRS (ΔCRS) (D) with respect to baseline (mean values ±SD in 10 animals). Panel A (VT [%]) shows the relative distribution of VT in 32 horizontal layers in% of overall VT in the chest cross-section. Panel B (ΔVT [%]) indicates the respective differences in regional VT compared with baseline. It shows a shift in ventilation toward the dorsal regions already with higher VT at time point 1 in normal lung and more pronounced shifts at points 3 through 6 with a PEEP set 2 cm H2O above the lower inflection point in acute lung injury (ALI). Panel C (CRS [ml/kg H2O]) shows regional CRS in the same 32 layers with the respective differences to baseline provided in panel D (ΔCRS [ml/kg H2O]). The differences in regional CRS indicate slightly lower and higher CRS in the ventral and dorsal regions at time point 1. Significantly lower values were found in layers 7 to 12 and significantly higher ones in layers 16 to 25 (layers counting from 1 to 32 in the ventrodorsal direction). ALI (time point 2) resulted in significant decrease in CRS in all layers. A small increase in CRS in the dorsal regions (significant in layers 23 and 24) with the decreased CRS in the ventral regions (significant in layers 1 to 17 and 27 and 28) at time point 3/5. At all other three time points, the findings were comparable. High VT, ventilation with 10 ml/kg BW, low VT, ventilation with 5 ml/kg BW.
Table 1.
Respiratory and hemodynamic data.
Figure 4.
Ventilation distribution during individual measurement time points represented by the geometrical center of ventilation. The center of ventilation is given in percent of the anteroposterior chest diameter. Values above 50 indicate a location in the dorsal half of the chest cross-section. The median, the 25th and the 75th percentile, minimum and maximum values of ten animals are shown. The gray areas in the diagram show the positive end-expiratory pressure (PEEP) values during the individual measurement time points. Significant differences between corresponding high VT and low VT are indicated. Every group with ALI and high PEEP is significantly different from normal lung and ALI with PEEP 10 cm H2O (Time point 2). Left Y axis: center of ventilation, right Y axis: PEEP. High VT, ventilation with 10 ml/kg BW, low VT, ventilation with 5 ml/kg BW.
Figure 5.
Changes in end-expiratory lung volume (ΔEELV) at individual measurement time points in comparison to baseline. The median, the 25th and the 75th percentile, minimum and maximum values of ten animals are shown. The gray areas in the diagram show the positive end-expiratory pressure (PEEP) values during the individual time points. Significant differences between the measurements are indicated. Left Y axis: ΔEELV, right Y axis: PEEP. High VT, ventilation with 10 ml/kg BW, low VT, ventilation with 5 ml/kg BW.
Table 2.
Gas exchange data.
Figure 6.
Regional differences in respiratory system compliance.
Differences in regional respiratory system compliance (ΔCRS) in 32 regions of interest in the chest cross-section in five patients with ARDS between ventilation at high and low tidal volume (VT) at three levels of positive end-expiratory pressure set according to the lower inflection point (LIP) of the quasistatic pressure-volume curve. ΔCRS are presented as ventrodorsal profiles. Values are means ±SD.
Table 3.
Respiratory and hemodynamic data of the studied patients.