October Clinical and Technical Insight

Oct 29, 2015
2 min read

Here are a few summarizations of clinical and technical insight provided by different clinicians and reseachers affiliated with Johns Hopkins. Meetings with these clinical experts have helped us understand key design specifications. Meetings with various researchers has helped us determine different technologies that could be used to monitor cardiac output.

Muyinatu Bell, PhD – CISST Engineering/Imaging Techniques

Photoacoustics can probably penetrate a maximum of 2 cm.
First challenge will come with getting the light to the target area.
Second challenge will involved actually getting the sound.
Will require a nice ultrasound probe that will prevent interference from ribs and bones.
Phase delay probes
Through beam formers, we can develop a stronger SNR.
Typically, ultrasounds have an array of piezoelectric sensors. This increases the signal to noise ratio.
Given our budget, we may only be able to build a device with one piezoelectric sensor.
For the light source, we will need a laser with a wavelength that is close to the peak of oxygenated hemoglobin. (higher wavelength = more absorption)
Look into pulse laser which is on the order of nanoseconds. We will need something like this to create the photoacoustic effect.
Pulse laser diodes are cheap but low in energy so they will not work with just one piezoelectric sensor.
A minimally invasive device is more feasible given our time and budget.
Use of intubation tube seems promising.
Phantoms are gelatin based testing devices that would allow us to look at optical and acoustic scattering.
Could use chicken breast, liver, etc to create a model for testing.
Could use a heart of a pig embedded in gelatin.

Viachaslau Barodka, MD – Division of Cardiac Anesthesia

Swan Ganz has an intrinsic error of 20% so if our device is more accurate than 20% that in itself is pretty good.
CO is the meat of the cardiac system.
Pulse oximetry had no scientific trial showing that it was useful. It makes doctors more comfortable, similar to our project.
TEE has delays by several minutes. It cannot be used in non-intubated patients.
Could potentially create a device with 2 parts, where one part measures mixed venous oxygen saturation using a minimally invasive intubation tube while the other part noninvasively takes a measurement for central venous oxygen saturation through the carotid artery.
Need to balance out accuracy and invasiveness.
The depth that must be met to obtain central venous oxygen saturation is approximately 1-2cm, but for fatter patients could be up to 1 inch.