Respiratory Muscle Trainer (RMT)

Respiratory Muscle Trainers (RMTs) are proven to be useful in improving the condition of patients after breathing-related conditions like COVID-19 or COPD. These RMT devices are neither well-available nor affordable in most Low- and Middle-Income Countries. 

This design was developed to address this need. Most important requirement was to have a calibrated, adjustable expiratory pressure range of 0 to 80 cmH2O in 10 cmH2O increments. Details about the spring size and design calculations to adjust the design for deviating spring sizes can be found in the technical article mentioned below.

Three RMT devices were produced using a 3D printer in Nepal, and successfully assembled and tested on functionality. Material cost of the final design was USD 1.30 per device.  Two different institutes were able to successfully print the model after minor printer-specific adaptations. The design allows for easy production in LMIC hospitals. 

Future research is required to further validate the clinical effectiveness of the novel device.

Clinical case report on RMT use published here: https://pubmed.ncbi.nlm.nih.gov/39257640/

Technical article on RMT design published here: https://www.best-lmic.org/bl/article/view/3

For deviating spring sizes the model might need to be adapted. SolidWorks files supplied for doing so. 

Some key technical remarks on printing and on making adjustments:

• Different printer build accuracy and precision or filament properties might cause bad fits. Tune the model accordingly.

• Adapting certain dimensions might lead to changed performance. Known effects so far are: 

  • Reducing the diameter of the stem of the valve plunger (or increasing the diameter of the hole in the corresponding counter part) might lead to the plunger guidance being less stable, allowing the plunger to tilt when operated horizontally and getting stuck as a result, especially for low-pressure setpoints.

  • Reducing the inserted length of valve plunger stem into the counter hole might lead to the plunger guidance being less stable, allowing the plunger to tilt when operated horizontally and getting stuck as a result, especially for low-pressure setpoints.

  • Different spring properties will lead to a different pressure range. Please validate minimum and maximum pressure that can be reached by the device.

  • Changing the sealing valve plunger diameter or valve orifice diameter will lead to a different pressure range. Please validate minimum and maximum pressure that can be reached by the device.

• When the PEI sheet/build plate is too rough, the hard valve seat might not seal well. Patiently polishing the sealing surface might resolve, or improving the smoothness of the PEI sheet/build plate. 

• Some corners around the arrows that indicate air flow direction can be tricky to print for some printers. This can result in some air leakage, reducing pressure buildup. Change printing resolution settings or apply post-processing to close such tiny gaps.