Lily-Anne Kalderen
Last four months, I lived in Stockholm, Sweden, to complete my undergraduate degree in Applied Physics and do my thesis there. I was part of a research group at Stockholm University of Technology (KTH).
My project focused on measuring differences in blood oxygen saturation by using Near-Infrared Spectroscopy (NIRS). This method looks at how the absorption of oxygenated and deoxygenated haemoglobin changes during exercise to determine changes in blood oxygen saturation.
Measuring with light
This illustration shows how NIRS works: light of two different wavelengths is sent into the arm and part is reflected back to the detector. Using the Modified Beer Lambert Law and the ratio of light passed through the arm and detected again at each wavelength, we can measure how the concentration of blood with and without oxygen changes, and therefore see how a muscle uses oxygen. The measurement starts with a person holding a neutral resting position, performing an exercise to tighten the muscles, and then resting again. This is repeated one more time during a measurement.
How does Near-Infrared Spectroscopy (NIRS) work?
NIRS uses the absorption spectrum of haemoglobin and uses light between 650 and 950 nanometres. Light between these wavelengths were used because here the least light is lost to water, melanin and fat, and there is still absorption from haemoglobin - but not so much that all the light is immediately absorbed. Light is scattered forward through the various layers of skin, with some light lost to absorption and scattering. The light reaches the muscles, where it is partly absorbed by the haemoglobin and partly reflected, after which the detector captures the light. By measuring how much of both wavelengths returns, combined with the absorption spectrum and the Modified Beer Lambert Law, we can see how the concentration of oxygen changes during exercise and recovery.
Since every person is different, light also behaves slightly differently for each person, which can affect the quality of results. I investigated how different
factors from a person's daily life (such as exercise) has on results. I also looked at factors that needed to be adjusted for each person in the experiment (e.g. the amount of light I had to use to get a signal without saturating the detectors).
Challenges and what did I learn
During my project, I had only 11 participants, so the results were limited and it was not possible to draw a concrete conclusion. However, I was able to make suggestions for future research.
During this experiment, I learned a lot about the equipment, how to work in a laboratory, and also a lot about processing results and setting up an experiment. I had a lot of contact with others in the research group, which also allowed me to learn a lot from them. Because everyone was also working on their own research, I learned about different topics within physics and became further interested in these different physics subjects. In addition, I learned more about Swedish culture and improved my Swedish.
