Respiratory bi-directional pressure and flow data collection device with auxiliary thoracic and abdominal circumferential monitoring.

Published: 31 March 2022| Version 1 | DOI: 10.17632/wfw7nyctcy.1
Ella Guy


The venturi flow meter is adapted from a basic 3D printed design [1], to monitor differential pressure in both directions, which can be combined to generate complete breath profiles. The venturi is designed to be integrated in series with respiratory circuitry, combined 22m cone and 15 mm socket (22 M/15F) connections. In its current application one end is connected to a CPAP device using its accompanying circuitry, and the other end is connected to Heat and Moisture Exchanger Pleated Mechanical (HEPA) Filter (002874, Smiths Medical, MN, USA), subsequently leading to a Bi-level CPAP System Hospital Mask (RT041S, Fisher and Paykel Healthcare, Auckland, New Zealand). Auxiliary measurements of thoracic and abdominal circumferences provide external non-invasive data, which can be correlated to change in lung volume. Thus, measurement of change in circumference can be used to validate models of patient specific lung mechanics applied to the venturi pressure and flow dataset. Circumference is measured by a flexible fiberglass dressmakers tape spooled onto spring loaded barrel which is connected to a rotary encoder. The rotary encoder counts are subsequently translated into change in unspooled tape length in data processing. Ultimately the device is designed for respiratory research, specifically the application and validation of models designed to ascertain patient-specific respiratory condition using simple non-invasive measurements. The outlined device provides researchers with: - A low-cost alternative to commercial sensor systems - Non-invasive data collection - Built in validation for respiratory models - High customisability


Steps to reproduce

- The PCBs were ordered from LCSC, populated in the SMT lab at the University of Canterbury using a pick and place machine, and reflow soldered in a reflow oven. - Pin headers, pressure sensors, and rotary encoder leads were hand-soldered on the PCBs. Arduino and Teensy microcontrollers were subsequently connected, and code was uploaded to these boards. - The venturi tube, middle barb, and two end barbs were 3D printed. Remaining filament fibers in interior of the barbs and venturi were removed using a pipe cleaner and needle. The barbs were then inserted into the venturi tube and superglued in place. - The tape measure housing and coupler were 3D printed. A basic metal tape measure was disassembled to retrieve the barrel with inbuilt torsional spring. The tape coupler was press fit into top of the torsional spring barrel. The metal tape measure was removed and replaced by a dress-makers fiberglass tape measure. The end of the fiberglass tape measure was adhered to the barrel using epoxy. After the glue was cured the tape was wound around the barrel and the barrel was inserted into the base of the tape measure housing using the central ratcheting mechanism. - The Pin Cap and Pin are 3D printed. The tape measure is wrapped and glued around the pin which was then inserted into the cap. The length wrapped around is set to ensure the tape reads the 108mm offset circumference when fully spooled. - The rotary encoders were attached to the lids of the tape measure housings using M2 8mm Button Socket Screws and nylock nuts. The coupler was fit onto the top of the barrel, the lid was attached. Finally, the grub screw was tightened to fix the shaft to the rotary encoder. - The venturi stand was 3D printed. The three pressure breakout boards and the control board were attached to the stand using M3 10, 12, and 16mm Socket Cap Screws, plastic spacers, and nylock nuts. - Pressure tubing and tees were connected between barbs and sensors. - A basic test frame was laser cut from Perspex. The venturi stand was attached to the frame by M4 10mm Socket Cap Screws and nylock nuts and the rotary encoder breakout board was attached by M3 10mm Socket Cap Screws and nylock nuts. - The rotary encoder breakout board is connected to the control board by a 300mm connector lead, and a jumper added to allow the nano to power the breakout board. Pressure sensor breakout boards are attached to the control board using 100 and 150mm connector leads. Rotary encoder breakout board leads are fed through the hole in the frame and attached to the rotary encoder tape devices. - Data collection code for the collective device outlined was written in MATLAB. The computer collecting data is first connected to the Arduino nano. The computer should be connected while the tape measures are fully wound up with the end slotted into the housing, as this is the initial circumference they are calibrated for.


University of Canterbury


Biomedical Research