Purpose:

A simple to make, removable, inexpensive stethoscope clip-on attachment to cellular phones to minimize infectious transmission of viruses and bacteria.  The goal here is not to reproduce a commercial electronic stethoscope.  This model has been used to measure heartbeats, pulse sounds, respiratory sounds.  The device is intended to be used by the patient with their personal device in telemedicine or in-office.

Description of Model.

This is a two-part model to enable printing without supports.  Assembly requires glue to attach the bell and clip portions.  4 mm inner diameter IV or vinyl tubing to provide friction fit for cellular phone and improved tube-microphone coupling.  Model is created in OpenSCAD for easy modifiability for each cellular phone.

An open bell design is selected to minimize noise from rubbing.  The diapragm on a closed bell is used with auditory ascultation to attenuate high frequency ambient noises such as speech.  Open bell is often preferred for diagnosis of respiratory noises.  Digital filtering will be used as an alternative to the diaphragm.

The phone does require software to use with this.  iStethoscope on the Apple Store is one possiblity.

App

https://apps.apple.com/az/app/istethoscope-free/id383008092

Do 3D printed parts work for this purpose?

Loubani 2018 3D printed stethoscope may perform as well as a Littman Cardiology III (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0193087)

Uses diaphragm bell (Littman 1966).

Do cell phone microphones work well enough?

Thompson J. design article for a cell phone adapter to a partial stethoscope. (https://www.ncbi.nlm.nih.gov/pubmed/25626549)

Thiyagaraja SR evaluation (https://www.sciencedirect.com/science/article/abs/pii/S1746809418301101)

                Complex due to extra parts needed.

What are the alternatives?

Inexpensive cell phone plugin digital stethoscopes.

StethIO

HeartBuds

Review https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5757962/

 

Design thoughts.

Littman 1966 patent for diaphragm bell (https://patents.google.com/patent/US3276536A/en)

                Mechanically filters out high-frequency noises (not necessary when used with digital filters)

We see a huge variety in open cup designs (potential improvements)

Standard Littman sizes for small bell are 34 mm or less (down to about 1.9 cm)

Bell floor ranges from spherical to square well in Littman lines

Tubing lumen diameter varies

7 mm typical

5 mm for SE