## 3 Results
### Prototype 2 (Experimental Actuated Resuscitator Machine--ARM)  
The second approach is based on a simpler mechanical design. The mechanism consists of two arms that squeeze the bag-valve resuscitator, which is placed between them. The motion of the arms is driven by a string that is attached to a string role driven by a motor. Once the resuscitator is squeezed, the direction in which the motor is rotating has to be reversed. In the simplest case, this can be achieved uses a microswitch, which marks the end position and relays, which switches the polarity of the voltage applied to a DC motor. A more advanced approach, which we present here, includes using a microcontroller and an H-bridge to invert the motion of a DC motor. Placing two microswitches at the two ends of the arms' travel, in the initial (open) and final positions (closed), enables positional feedback to a microcontroller. By changing the position of the microswitch, which indicates the final (closed) state, the pressure and tidal volume can be tuned. Analogously to the CLAPER case, the tidal volume is determined by the motion range, since this is limited by the positions of the two microswitches. The tidal volume delivered is very precise and repeatable. The use of a  
Figure 2: (**a**) Pressure as a function of time for pivot positions 1 (lighter color) to 5 (darker color). (**b**) Peak pressure from plots in (**a**) as a function of pivot position. (**c**) Flow generated as a function of time for pivot positions 1 (lighter color) to 5 (darker color). (**d**) Peak inspiratory (circles) and expiratory flow (squares) as a function of pivot position. (**e**) Volume pumped as a function of time for pivot positions 1 (lighter color) to 5 (darker color). (**f**) Peak volume pumped for the various pivot positions, the gray boxes show the recommended tidal volumes (6 to 8 mL/kg) for various predicted body weights (ideal weights) calculated from the parameters in Table 1.  
microcontroller enables the control and monitoring of the respiratory rate, inspiration to expiration ratio, and opens the possibility to implement complex feedback-based controls (e.g., PEEP control and triggered inspiration) as well as the implementation of alarms in the case of electrical power fault, disconnections or leaks in the pneumatic system, etc. A render of the prototype is shown in Figure 3.  
Measurements of pressure and flow were also performed on the eARM using the same equipment as for CLAPER as described in the Methods section. An additional tube of approximately 2 m length and 1 cm in diameter was used for connecting the test lung to the bag-valve resuscitator. An additional valve from another bag-valve resuscitator was placed between the tube and the test lung, in order to prevent \"exhaled\" air from residing in the tube and being \"inhaled\" with the next inspiration. The tests measurements were performed at five different positions of the microswitch indicating the final (closed) position in order to control the tidal volume. The breathing rate was set to 20 BPM and the inspiration to expiration ratio to 1:1. The measurement results are shown in Figure 4. In the left part of Figure 4 the time evaluation of pressure, flow, and volume are shown over four breathing cycles for the five positions of the microswitch. The average of the peak pressure, peak volume, and peak inspiratory and expiratory flow for each position of the microswitch are shown in the right part of Figure 4. Since both prototypes rely on a bag valve resuscitator, a similar outcome of the test measurements was expected and also achieved. As a microcontroller is already used for this prototype, an additional pressure sensor was installed. This way we were able to show the potential of such a device to also control the PEEP as well as potential for triggered inspiration (Augmented spontaneous breathing--ASB mode), which means that the system can synchronize its timing to the breathing attempts of the patient.