## 3 Results
### Varied Effects of ETT and SC on PIP in Both Respiratory Systems
#### 3.2.1. Varied Effects of Ventilation Area on \(\triangle\)PIP/PIP% in Both Respiratory Systems  
In the case of obstructive respiratory systems (Figure 3a), it was found that an increase of \(\triangle\)PIP/PIP % levels for endotracheal tubes with larger IDs was lower than for endotracheal tubes with smaller IDs. There was a rise of \(\triangle\)PIP/PIP % levels for 6.5 mm-10 Fr and 7.0 mm-12 Fr which exceeded 50%, but \(\triangle\)PIP/PIP % levels were less than 40% for 7.5 mm-12 Fr and 8.0 mm-14 Fr at the R\({}_{\rm aw}\) 10 cm H\({}_{2}\)O-L\({}^{-1}\)-s. In addition, the change  
Figure 2: Comparison of the change of PIP effects in VC-CMV undergoing closed endotracheal suction: (**a**) Change of airway resistance and (**b**) lung compliance of pulmonary mechanics in various ETTs paired with SCs of CSS. C: control (0.08 L cm H\({}_{2}\)O\({}^{-1}\) of C\({}_{\rm rs}\) and 5 cm H\({}_{2}\)O L\({}^{-1}\)-s of R\({}_{\rm aw}\)) group. VC-CMV: volume control continuous mandatory ventilation, this mode is set to V\({}_{\rm T}\) 0.6 L with peak flow 60 Lpm; PIP: peak inspiratory pressure; R\({}_{\rm aw}\): airway resistance; C\({}_{\rm rs}\): lung compliance; ETT: endotracheal tube; SC: suction catheter; 6.5 mm\(-\)08 Fr: 6.5 mm ETT paired with 08 Fr SC, and so on. The closed suctioning procedure was repeated three times. The error bars represent the standard deviation of 30 breaths in each of the pulmonary mechanic scenarios (five airway resistance levels and six lung compliance levels). The independent samples _t_-test was used to compare with the control group. * \(p\) < 0.05, ** \(p\) < 0.01.  
of \(\bigtriangleup\)PIP/PIP % level in suction catheters with larger ODs was more significant than for suction catheters with smaller ODs when paired with the same endotracheal tube. The change was less noticeable in the case of worse R\({}_{\text{aw}}\). Notably, with the use of 8.0 mm-12 Fr for closed suctioning, the \(\bigtriangleup\)PIP/PIP % level dropped to zero or even below zero when R\({}_{\text{aw}}\) exceeded 20 cm H\({}_{2}\)O-L\({}^{-1}\)-s.  
For restrictive respiratory systems (Figure 3b), the experiment showed that an increase in \(\bigtriangleup\)PIP/PIP % level for endotracheal tubes with smaller IDs was higher than for endotracheal tubes with larger IDs. The \(\bigtriangleup\)PIP/PIP % level rose over 70% for 6.5 mm-10 Fr but only 20% for 8.0 mm-14 Fr at the C\({}_{\text{rs}}\) 0.05 L-cm H\({}_{2}\)O\({}^{-1}\). In addition, the change of \(\bigtriangleup\)PIP/PIP % level for suction catheters with larger ODs was less than for suction catheters with smaller ODs for the same endotracheal tube. Moreover, the change of \(\bigtriangleup\)PIP/PIP % level then dropped to C\({}_{\text{rs}}\) 0.03 L-cm H\({}_{2}\)O\({}^{-1}\). Figure 3: The effect of the ventilation area on \(\bigtriangleup\)PIP/PIP% during VC-CMV: (**a**) Airway resistance of pulmonary mechanics for the obstructive system; (**b**) Lung compliance of pulmonary mechanics for the restrictive system. \(\bigtriangleup\)PIP/PIP% decreased for the larger ventilation area and significantly reduced for severe respiratory systems. \(\bigtriangleup\)PIP: (delta) suctioning peak inspiratory pressure level substrates a baseline peak inspiratory pressure level; \(\bigtriangleup\)PIP/PIP%: percentage of PIP (baseline PIP level) divided by \(\bigtriangleup\)PIP; VC-CMV: volume control continuous mandatory ventilation, this mode is set to VT 0.6 L with peak flow 60 Lpm; R\({}_{\text{aw}}\): airway resistance; C\({}_{\text{rs}}\): lung compliance; ETT: endotracheal tube; SC: suction catheter; VA: ventilation area (ETT cross-section area minus SC cross-section area); 6.5 –08: 6.5 mm ETT paired with 08 Fr SC, and so on. The independent samples \(t\)-test was used to compare with 0.08 L-cm H\({}_{2}\)O\({}^{-1}\) of C\({}_{\text{rs}}\) and 5 cm H\({}_{2}\)O\({}^{-1}\)-s of R\({}_{\text{aw}}\) group. * \(p<0.05\), ** \(p<0.01\).