The HDVent has been designed for the treatment of COVID-19 patients but fullfills very general ventilation functions. The HDVent can be run in three different modes:
Open loop continuous mandatory ventilation (OL-CMV):
In the OL-CMV mode the insipiration timer is triggered, the length of the inspiration can be changed and the stepper is moved at a constant speed.
Pressure controlled continuous mandatory ventilation (PC-CMV):
In the PC-CMV mode the pressure of the ventilation is controlled and follows a trapezoidal setpoint ramp while the length of the inspiration is fixed. The stepper is moved accordingly.
Volume controlled continuous mandatory ventilation (VC-CMV):
In the VC-CMV mode the flow of the ventilation is controlled and follows a trapezoidal setpoint ramp while also here the inspiration time is fixed. Also here the stepper is moved accordingly such that the flow follows the set curve.
Overall the HDvent can access the following range of common ventilation variables:
The full HDVent system was tested using a commercial available test lung (Dräger SelfTestLung, Vmax=1000ml) which models resistance and compliance of an average adult lung. The measured volume flow was calibrated to an estimated accurac of 2% by focing calibrated volumes of air through the spirometry tube.
The figure above shows a measurement of tidal volume (red) and peak pressure (blue) versus the percentage of maximal displacement of the moving arm in OL-CMV mode. The red line indicates a linear dependence of the tidal volume on the arm movement. The attained peak pressure reflects the compliance of the text lung.
The above figure shows Volume V (red), pressure p (blue), and flow (orange) versus time in PC-CMV mode for three different set pressures of 25 mbar (dark blue), 20 mbar (light blue), and 15 mbar (bright blue) shown as dashed lines. Panel c) shows ventilation in VC-CMV mode for three different set flows of 30 l min−1 (dark orange), 24 l min−1 (light orange), and 18 l min−1 (bright orange) shown as dashed lines. For b) and c) a PEEP of 7 mbar was set and BPM was 10.
We performed a long-term stability measurement in OL-CMV. Over 3 days (43k cycles), the tidal volume and pressure profiles remained constant to ±0.5 %, while the device showed no signs of wear. The most limiting component in terms of longevity is the Ambubag, which we estimate should be replaced every 5 days for safety.