The system consists of:
A- a mechanical pump, based around an Ambu bag. The mechanical parts are largely built from lasercut aluminium sheets.
B- a microcontroller and sensors, controlling the pump & measuring pressures and flow rates. The microcontroller is an Arduino-compatible ATmega2560.
C- Medical tubing and valves to the patient
D- A computer, which plots p-, V-, and Flow-graphs from sensor data and provides a user interface to change settings on the machine.
Code for this was written in C#.
SPECIFICATIONS BETA SERIES 1
POWER
Power-out safety | Yes, machine switches uninterupted between 220V and 24V battery backup | |
| PSU | Maxwell 24V 10A | |
| Battery backup | 2x 7Ah Lead-acid, hot-swappable | |
| Battery autonomy | +1h | |
| Battery state-of-charge monitor | yes | |
| Power-out detection & alarm | yes | |
MOTOR
| Motor | Volvo or DAF windscreen wiper motor, 24V | |
| Motor power | +-40W at shaft | |
| Power usage | 1A@24V average over plunge, 8A peak | |
| Manual actuation of pump possible | yes |
MICROCONTROLLER & SENSORS
| COMPONENT | TYPE / VALUE | REMARK |
| Microcontroller | Atmega2560 | Atmega and pc operate as each others watchdog and will give an alarm when the other half of the system stops responding for 5 seconds. |
| Pressure sensors | Bosch BMP280 andMLP315115A2, , accuracy better than 2 cmH20 | Dual sensors for error checking |
| Flow sensor | SDP-31 | Calibrated in windtunnel against a calibrated sensor |
| Volume measurement | Vt inhaled through integration. Volume delivered to system checked with lookup table, checking plunger position versus volume. | |
| Vt max | 800mL | |
| RRmax | >35 BPM at Ppeak=50cmH20 | Tested without oxygen inflow. |
| Ppeak max | 70cmH20 | |
| Overpressure safety | In-line spring valve, fixed at 80 cmH20 to conform with MHRA requirements | |
| Modes | Pressure control Volume control Pressure assisted mode with pressure-based breathing trigger Pressure assisted mode with flow-based breathing trigger | |
| RAMP | User-configurable control of motor-PID / pressure curve shape | |
| I/E | 1/1 to ⅓, adjustable in steps of 0.1 | |
| PEEP | Manually adjustable PEEP-valve, reference value set in GUI for monitoring offset from desired value | |
ALARMS
| Blockage / no flow alarm | yes | |
| Disconnect / no pressure alarm | yes | |
| Power interrupt alarm | yes, machine switches to battery power | |
| Low battery alarm | yes | |
| PEEP value incorrect or PEEP disconnected | yes | |
| PC disconnect alarm | yes, machine keeps running with current settings | |
| Sensor disconnect alarm | yes, machine goes to conservative operation settings. | |
| Microcontroller failure alarm | yes, PC acts as microcontroller watchdog and gives alarm | |
| Configurable volume threshold | yes | |
| Configurable pressure threshold | yes | |
GUI & CONTROL
| PC running interface | I3 or higher, running Linux, connected over USB | |
| p-, flow- & volume graphs | yes | |
| Data logging | yes, local on pc | |
| Remote control of multiple machines | yes | |
- accurate pressure & volume control
- p-, V- and flow-graphs in a graphical interface
- redundant pressure sensors
- pressure control mode, volume control mode
- full user-configurable pressure curve (Ppeak, Passist, RR, IE, ramp)
- breathing detection & breathing assist mode
- alarms on configurable error ranges for achieved pressures and volumes
- battery backup
- a mature & robust pump design that can be rapidly manufactured from laser-cut aluminium sheets
- a pump design with sufficient power that has no issues achieving the highest pressures, volumes and respiratory rates specified in the MHRA emergency certification requirements.
- an electronics architecture where the main microcontroller and the connected PC each act as each others watchdog and give an alarm when the other one stops working.
- possibility to enable remote monitoring of multiple machines
