Near-infrared spectroscopy (NIRS) is a non-invasive optical method used to continuously measure tissue oxygenation and hemodynamics in the brain and muscle. It works by emitting light in the red and near-infrared region of the spectrum into the tissue, where it scatters due to refraction inside cells. Oxygenated and deoxygenated hemoglobin have different absorbance spectra in this region, allowing their concentrations to be measured. For muscle oxygen saturation (SmO2), light is emitted and detected at different distances from the emitter, and the ratio of oxygenated to total hemoglobin is reported as a percentage of SmO2. NIRS is useful for measuring oxygen supply and demand

1. Near Infared
Spectroscopy

2. NIRS
(Near Infrared Spectroscopy)
A non-invasive optical method for continuous
measurement of tissue oxygenation and
hemodynamics
The brain Muscle
Common Tissues measured

3. How does it work?
- Light travels through tissue especially in the Red and Near-Infrared region
of the spectrum.
- In tissues, light scatters due to factors inside cells causing refraction.
- If you know the refraction index of a specific protein or compound, it can
be measured
- Oxygenated and deoxygenated hemoglobin have different absorbance
spectra in this region

4. How does it work?
- For HgB, NIRS utilizes four
separate light sources that
cover the wavelength range
from 630 to 850 nm
- Oxy-HgB and Deoxy-HgB are
chromophores (atoms absorb
light at different
wavelengths)

5. - Light is emitted into the
tissue at one location and
then is detected at two
locations, 12.5 and 25 mm
from the emitter.
- Oxy-HgB conc. to the total
HgB conc. in the muscle is
reported as a % = SmO2
How does it work?

6. SmO2 – O2 muscle saturation
- The measurement of SmO2 takes place in the capillaries
of the muscle, where O2 is being consumed.
- SmO2 is a good measure of O2 supply v demands in
muscle.
Intense exercise
O2-HgB dissociation
curve changes
Factors that effect SmO2
Other chemical or
neurological changes

8. Negatives of NIRS
- You must control for external light sources
- You must know the absorbance of substances you are
measuring

9. Brain NIRS
- You must control or external light sources
- You must know the absorbance of substances you are
measuring