If there’s one takeaway from Bruno Jaggi’s BMEG 556 at UBC, it’s that the FDA is an amazing resource through the process of medical device development. This has been something I have learnt time and again in a very organic fashion. Once I’ve finished reading all the usual internet links about a certain healthcare device and want to delve deeper, I end up on the FDA’s repositories.

In this case, I started browsing the interwebz to figure out what the best housing for reflectance pulse oximetry was. I started off on an FDA report describing pulseox issues from the perspective of reflection and transmittance. This report talks about the 510k approval process for new pulse oximeters (comparison to an existing approved device with similar specs, for those curious) with a special note on the use of pulse oximeters for over the counter uses.

You see, one of the biggest questions I’ve been asking myself since starting this project was how this device (if marketed), would be classified and if it could ever be “given away” to the intended user without a prescription. A “vital sign” monitor like pulseox, HAS to be classified as a medical device. However, this report refers to nonin finger oximeters for use by high altitude climbers to detect for signs of altitude sickness. Could recreational drug use be one of the exceptions for over the counter use of the MAX30102 sensor? Do I still have to jump through all the regulatory hoops?

 

Additionally, the document gives a great summary of the types of oximeters, reflectance and transmittance in a single paragraph, which I shall reproduce here.

Pulse oximeter sensors may be implemented in either a transmittance or reflectance configuration. In both configurations, light is scattered by blood, which has time dependent characteristics, and bone or other tissue structures which are not time dependent. Transmittance sensors are configured in a manner where the emitter outputs light which travels through tissue (e.g. finger, toe, and ear) and is received on the opposite side by the detector. Reflectance sensors are configured with the emitter and detector in the same plane. Emitted light must reach the detector by reflection off a surface which typically results in smaller signal strengths in comparison to transmittance sensors. Significant differences in the tissue region sampled are a function of emitter/detector geometry. Differences in light propagation between the transmission and reflectance-based system would affect the relative amount of arterial blood sampled, average photon path length, the absorption characteristics of non-blood regions sampled (e.g. dermis, fat, bone, etc.).

• Blood has time dependent light scattering characteristics while bone and other tissue does not
• Reflectance sensors typically have smaller signal strengths as compared to Transmittance
• Critical variables affecting signal
  • Emitter/detector geometry
  • Amount of arterial blood sampled
  • Average photon path length
  • Absorption on non blood regions
• Motion artifacts!!!!!

For approval of applications, they ask for a desaturation study (6 minute walk test, and looking at SpO2) with 200 data points.

The guidance document for 510k submissions on pulseoximeters is a good resource as well. But this one talks more about what needs to part of the 510k for the