# Web Applications for Teaching the Respiratory System: Content Validation
## 4 Discussion
### Work of Breathing Indexes Model  
#### 4.2.1 Statistical Analysis  
The main objective of MV is to increase the gas exchange and reduce the respiratory effort, or the respiratory muscles' load, produced by variations in R or C due to restrictive or obstructive pathologies [43]. This load can be measured by indexes related to weaning success, such as RSBI, WOB, and PI\({}_{\text{max}}\).  
Population Analysis  
The relation between changes in the MV setting and the RSBI, WOB and, PI\({}_{\text{max}}\) indexes was depicted in Figure 7. The changes assessed were PEEP and PS increments, so as to know the response to changes in respiratory muscles' loads in a population of healthy men and the response of the predictive model.  
PEEP is defined as the positive end-expiratory pressure, and it is detected as an offset in the pressure measured in the mouth. In physiological terms, PEEP is used for alveolar recruitment, raising C and lung capacity [44]. Increases in PEEP improve the gas exchange because they make more alveolar units available [45]. [PERSON] et al. [46] analyzed changes in C and the level of oxygenation of healthy and obese subjects under PEEP stimuli of 0 cmH\({}_{2}\)O and 10 cmH\({}_{2}\)O. They found considerable oxygenation improvements and C increments only in PEEP of 10 cmH\({}_{2}\)O and pathological situations, concluding that PEEPdoes not have a relevant effect when it comes to subjects without obstructive, restrictive, or cardiopulmonary problems. Therefore, both the experimental and predicted RSBI and WOB values (Figure 7(I),(II), respectively) do not present a marked effect as pressure increases.  
PS can be remarkably effective in reducing patient effort, avoiding respiratory distress, and can offer a comfortable ventilator support to many patients [47]. Studies with healthy subjects have shown the PS effect for WOB [48] and RSBI decreases [49], just as the results for the predicted and experimental data in Figure 7(IV),(V) suggest.  
The PI\({}_{\text{max}}\) increases proportionally under PEEP (Figure 7(III)) and PS (Figure 7(VI)) stimuli, although it does not exceed the muscular overexertion threshold product of the healthy condition of the subjects. In both cases, the increases in each group of data are equivalent to the added pressure value with respect to to the basal state (PEEP and PS = 0 cmH\({}_{2}\)O), due to the fact that the mechanical ventilator applies both pressures, increasing pressure at the mouth (P\({}_{\text{ao}}\)) and consequently increasing airway pressure [24; 50; 51].  
Individual Analysis  
The similarities in both the experimental and predicted distribution data of Figure 8, the non-existence of statistically significant differences between both values, and the low percentage of error shown in Table 7 (less than 23%) prove the good level of prediction by the models involved, including the non-dependence on input parameters as long as they are consistent at a physiological level.  
The index with the highest error percentage was the PI\({}_{\text{max}}\), which may be a product of the difficulty in the measurement reported by the ATS/ERS and confirmed by some studies [24; 52]. There is a dependence on the participants' complete collaboration.