 The Tetra-NIRS unit uses near infrared light at 3 different wavelengths to measure changes in haemoglobin and cytochrome from the detrusor muscle from the human bladder wall. This process is similar to what is used for cerebral and muscle oxygenation monitoring e.g., pulse oximetry. Previous clinical feasibility studies have identified the correlation between the changes in haemoglobin and cytochrome of the bladder, and bladder pressure values obtained during urodynamics procedures and uroflow procedures. 