Fig. 6

Radar chart of National Aeronautics and Space Administration—Task Load Index for each ventilator. The radar chart of the NASA-TLX indicates both the overall mental workload evaluation (TLX value) and the different dimensions that are evaluated. Three dimensions are dependent on user perception of the task (mental workload, temporal workload and physical workload) and three dimensions dependent on the interaction between the subject and the task itself, which may be mostly related to the interface (effort, performance and frustration). The larger the area of the radar chart, the higher the TLX and thus the mental workload, and the lower the ergonomics. Values of the TLX score are indicated for each ventilator, our reference value being depicted in the upper left. Our reference value (Avea, in orange) had the lowest mental workload value (TLX = 41.6), thus depicting the potential influence of experience on mental workload. For this reason, it is strictly mandatory to compare measurements performed on naïve subjects. R860 had the lowest TLX value, and V680 had the highest (*p = 0.049). Dimensions of the mental workload that seemed to require the most important improvements were performance and efforts