Affiliations: Department of Urology and Near Infrared Study Group, University of British Columbia, Vancouver, BC, Canada | Stellenbosch Institute for Advanced Study, Wallenberg Research Centre, Stellenbosch, South Africa
Note:  Corresponding author: Dr. Andrew Macnab, Department of Urology and Near Infrared Study Group, University of British Columbia (UBC), UBC Hospital Bladder Care Centre, Unit 1B – Room F329, 221 Wesbrook Mall, Vancouver, BC, Canada V6T 2B5. Tel.: +1 604 822 7616; Fax: +1 604 822 7591; E-mail: [email protected]
Abstract: Transcutaneous near infrared spectroscopy (NIRS) is a recognized means of non-invasively monitoring changes in the concentration of oxygenated and deoxygenated hemoglobin in tissue. However in applications of this technique to the bladder, because the combined thickness of the detrusor muscle and the wall of the organ is only a few millimeters, the question arises whether the trends and variations in hemoglobin concentration detected transcutaneously reflect physiologic changes occurring in the detrusor or are influenced by the effect of overlying tissue on the NIRS signal. In this study a rabbit model was used so that NIRS data could be collected transcutaneously and then with the optical probe applied directly the anterior bladder wall after surgical exposure of the organ, and the data compared. Studies were done with an Oxymon dual channel spectrometer on 6 anaesthetized New Zealand white rabbits using interoptode distances adjusted for the two measurement sites, a consistent bladder filling and emptying protocol, and exposure to a brief period of controlled hypoxia (oxygen saturation decrease to 80%). Consistent data were obtained from transcutaneous and direct bladder wall measurements which confirms that transcutaneous NIRS monitoring does reflect changes occurring within the detrusor muscle in the anterior bladder wall. Hence, transcutaneous monitoring in humans using appropriate methodology and inter-optode spacing can be expected to avoid any potentially confounding signals from tissues in the abdominal wall overlying the bladder.