Background

Near infrared spectroscopy (NIRS) is a technique that uses light in the near infrared (NIR) region of the spectrum (wavelengths between 700nm and 1,300nm) to identify molecules. This is based on analyzing chemical bonds, which vibrate at characteristic frequencies.

NIRS has widespread use in chemistry and biology research, food and agrochemical quality control, as well as medical diagnostics.

The medical applications of NIRS include patient monitoring and non-invasive diagnostics, such as monitoring blood flow and tissue oxygenation status to assess physiologic and metabolic conditions. NIRS is also currently used to study skeletal muscle perfusion and oxygenation, breast tissue tumor detection, and cerebral oxygenation.

Use of NIRS in urology began in 2003 when researchers at the University of British Columbia (UBC) in Vancouver, Canada made an unexpected observation while using NIRS to monitor tissue oxygenation and blood flow in the lower lumbar spinal cord. When the research subject spontaneously voided during the procedure, a significant change was noticed in the continuous NIRS tracings. The researchers concluded that these changes were indicative of changes in bladder physiology. This discovery led to the development and commercialization of two NIRS bladder monitor systems that help physicians in the diagnosis of bladder outlet obstruction (BOO).

How does NIRS work?

The NIRS emitter projects specific wavelengths of near infrared light through the skin, illuminating tissues and organs beneath (such as the detrusor muscle of the bladder). Some of this light is absorbed by chromophores such as hemoglobin (oxygen-carrying blood cells) and cytochromes (membrane-bound proteins involved in energy production) present in blood and muscle. Some of the light is also scattered.

The NIRS sensor detects the amount of light returned and measures changes in the concentrations of these chromophores within the tissues, providing information on oxygen kinetics in the microcirculation.