Module 5 - Optical methods

Question 1

What components in the blood determine the absorption spectrum?

Answer 1

Oxygenated and de oxygenated hemoglobine.
They have different bindings with oxygen, which determines their absorption

oxy has low molar extinction coefficient around 600-750 nm and higher around infrared, after 800/900 nm

Question 2

How is oxygen saturation measured?

Answer 2

We measure oxygen saturation through the finger (e.g.).

Sensor with LEDs on one side, and a detector on the other side. Transmission / absorption through the finger is measured

Question 3

Draw oxygen saturation setup

DRAW TAB

Answer 3

two leds on top, detector on the bottom. layers skin in between

Question 4

How is NIRS measured?

Answer 4

Does not measure absorption/transmission through the finger, but rather it measures the reflection.

So; emitting diode with detectors. However, detect the scattering of light and the reflections in the detectors. Path through the tissue

Question 5

Explain the difference between NIRS and pulse oximetry

Answer 5

Source and detector are on the other side for pulse oximetry, however for NIRS on the same side.

NIRS measures scattering, pulse oximetry measures absorption/transmission

NIRS pathlength is unknown in scattering

Pulse oximetry is for pulsatile flow and arterial blood and does not indicate if the delivery t tissue is adequate

NIRS has tissue component

Question 6

Draw NIRS setup

DRAW TABLET

Answer 6

input intensity and sensors a bit more to the right