# Web Applications for Teaching the Respiratory System: Content Validation
## 2 Materials and Methods
### Validation Process
#### 2.2.2 Work of Breathing Indexes Module  
Description of the Database  
A proprietary database comprising 35 healthy men (age 26.60 \(\pm\) 5.40, weight 73.12 \(\pm\) 9.15 kg, size 1.72 \(\pm\) 0.05 m, and BMI 24.58 \(\pm\) 2.76 kg/m\({}^{2}\)) was used to validate the models involved in the \"Work of Breathing Indexes\" module. Volunteers were involved in two trials of PEEP and PS variations during non-invasive spontaneous ventilation. In Test D, the PEEP was changed from 0 to 10 cmH\({}_{2}\)O, with increments of 2 cmH\({}_{2}\)O every 3 minutes, while the PS was kept at 0 cmH\({}_{2}\)O. In Test E, the PS was varied from 0 to 10 cmH\({}_{2}\)O with increments of 2 cmH\({}_{2}\)O every 3 min, while the PEEP was preserved at 0 cmH\({}_{2}\)O. Each trial consisted of 210 records, 6 per subject. Table 2 summarizes the ventilatory mechanics and MV parameters of both tests. The registration protocol, inclusion criteria, and ethical approval are detailed in the work carried out by the GIBIC research group in [4]. \begin{table}
\begin{tabular}{c c} \hline
**Ventilatory Mechanics** & **Values** \\ \hline R (cmH\({}_{2}\)O/L/s) & 13.86 (9.06–21.33) \\ C (mL/cmH\({}_{2}\)O) & 73.26 (57.62–88.33) \\ P\({}_{\rm musc}\) (cmH\({}_{2}\)O) & 15.78 (12.45–21.81) \\ RR (bpm) & 13.58 (10.50–17.38) \\ \hline \end{tabular}
\end{table} 
Table 1: Median and interquartile ranges of ventilatory mechanics data for obstructive DB. \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **Test D** & **Test E** \\ \hline PEEP (cmH\({}_{2}\)O) & 0, 2, 4, 6, 8, 10 & 0 \\ PS (cmH\({}_{2}\)O) & 0 & 0, 2, 4, 6, 8, 10 \\ LE & 1 : 0.83 (0.73–0.92) & 1 : 0.83 (0.75–0.93) \\ R (cmH\({}_{2}\)O/L/s) & 9.67 (7.62–12.57) & 12.27 (9.11–15.01) \\ C (mL/cmH\({}_{2}\)O) & 99.68 (80.00–139.42) & 74.99 (61.20–89.97) \\ P\({}_{\rm musc}\) (cmH\({}_{2}\)O) & 12.32 (9.07–16.12) & 11.58 (8.65–15.48) \\ RR (bpm) & 15.28 (12.17–17.40) & 15.98 (13.26–19.24) \\ \hline \end{tabular}
\end{table} 
Table 2: The median and interquartile range of the MV parameters and ventilatory mechanics of the subjects in Test D and E in DB PS/PEEP. Analysis  
For both the population analysis and the individual analysis (see Figure 4), the WOB, RSBI, and PI\({}_{\text{max}}\) indexes were compared. They were calculated from information extracted from the DBs, following the expressions in Equations (3)-(5), and averaging their values for at least five respiratory cycles. The WOB was calculated as the area under the Campbell diagram curve, which relates the pressure exerted through the respiratory system with the resulting changes in volume [23]. For this, Equation (3) was used for a respiratory cycle:  
\[WOB=\frac{1}{V_{T}}\int_{t_{0}}^{t}Pmusc(t)*\hat{V}(t)dt. \tag{3}\]  
The RSBI was calculated by Equation (4), according to [PERSON] and [PERSON]'s proposal [6]:  
\[RSBI=\frac{RR}{V_{T}}. \tag{4}\]  
The PI\({}_{\text{max}}\) was calculated according to the American Thoracic Society/European Respiratory Society, ATS/ERS [24], as the maximum pressure that a subject can generate in the mouth during inspiration, as shown in Equation (5), where t\({}_{0}\) and t correspond to the onset and final inspiration times:  
\[PI_{max}=max\Big{\{}\,P_{aw}(t)|_{t_{0}}^{t}\Big{\}}. \tag{5}\]  
For the population analysis, the trend and the behavior of the indexes predicted by the models were compared to the data obtained from subjects in the DBs and analyzed. The experimental data were grouped according to their PEEP and PS levels for Tests D and E, respectively. To obtain the predicted data (WOB, RSBI, and PI\({}_{\text{max}}\)), the median values of the muscular effort (RR and P\({}_{\text{musc}}\)), ventilatory mechanics (R and C), and I:E variables were used as the input parameters for the models, according to Table 2. Corresponding PEEP and PS values were used for each level. Regarding the individual analysis, predicted values of the WOB, RSBI, and PI\({}_{\text{max}}\) were obtained using experimental values of RR, P\({}_{\text{musc}}\), R, C, and I:E of each subject as the module's inputs.