NIRS: Past, Present, and Future in Functional Urology

Abstract

Purpose of Review Near infrared spectroscopy (NIRS) is a non-invasive optical technique that uses near infrared light to detect the oxygenation status and hemodynamics of various organs. This article reviews the use of NIRS for the non-invasive assessment of lower urinary tract dysfunction (LUTD). Applications include assessment of bladder outlet obstruction, overactive and underactive bladder, neurogenic LUTD, pediatric LUTD, interstitial cystitis/bladder pain syndrome, and pelvic floor dysfunction. In addition, the article describes how NIRS is elucidating more about the brain-bladder connection. Technological advancements enabling these applications are also discussed. Recent Findings While evidence exists for the application of NIRS throughout a wide range of LUTD, most of these studies are limited by small sample sizes without matched controls. Investigators have experienced problems with reproducibility and motion artifacts contaminating the data. The literature is also becoming dated with use of older technology. Summary NIRS holds potential for the non-invasive acquisition of urodynamic information over time scales and activities not previously accessible, but it is not yet ready for use in routine clinical practice. Advances in wearable technology will address some of the current limitations of NIRS, but to realize its full potential, larger scale validation studies will be required. Moreover, multidisciplinary collaboration between clinicians, scientists, engineers, and patient advocates will be critical to further optimize these systems.

A wearable optical sensor monitoring bladder urine volume to aid rehabilitation following spinal cord injury

“…While Koven and Herschorn opine that NIRS is "not ready for use in routine clinical practice," stating that advances in wearable technology will address current limitations they identify, their call for "multidisciplinary collaboration between clinicians, scientists and engineers, and patient advocates," is timely, and more importantly the constructive compromise that patients and clinicians alike need to benefit from "the potential NIRS has to offer for the non-invasive acquisition of urodynamic information over time scales and activities not previously accessible." 12 In this context small wireless devices used widely in sports medicine are available commercially that have the required specifications for monitoring the bladder.…”

“…Hence, while movement artifact certainly can compromise the ability to calculate other NIRS data outputs, and particularly quantifiable absolute measures, it is incorrect to imply that all information derived through NIRS is affected comparably. 12 Factors such as the measurement principles employed in NIRS devices also influence the strength and type of artifact induced, with multi-distance measurement methods usually more resilient than single distance measurements, and the algorithms used for calculation of oxygenation and hemodynamic variables from the optical signals obtained can also be relevant. 31 However, specifically designed signal processing solutions increasingly offer additional approaches for effectively addressing movement artifact, and the inclusion of accelerometers in devices is growing as an engineering solution.…”

“…9,10 However, this is an invasive procedure so can only be done in hospital, and is associated with the possibility of complications as catheterization of both the bladder and rectum is required. 11,12 For these reasons, urodynamic evaluations can only be performed at intervals.…”

“…In this context, a recent review by Koven and Herschorn stated "NIRS has opened the door to the non-invasive acquisition of urodynamic information over time scales and activities not previously accessible." 12 The authors also emphasize that "non-invasive, ambulatory bladder volume and pressure assessment would be particularly important in patients with NLUTD who cannot independently sense the fullness of their bladders, providing them with a warning to electively empty or catheterize before accidental incontinence, as well as minimize bladder pressure and risk of renal injury;" and also correctly point to the fact that "the wearable device landscape has exploded in recent years, led by advances in miniaturized hardware, machine learning and data analytics. While this review does cite some of the NIRS research related to patients living with SCI, and references most of the areas where NIRS can contribute unique information in other specific urologic conditions, an important point is omitted.…”

Near infrared spectroscopy of the central nervous system: monitoring oxygenation in the neonatal brain and in the spinal cord following traumatic injury

“…In this context the recent call for "multidisciplinary collaboration between clinicians, scientists engineers and patient advocates to optimize such systems" in the context of application of NIRS in the field of urology is welcome. 62 It is undeniable that a lack of such collaboration in the past compromised the translation of NIRS-related ideas and experimental technologies from bench to bedside that had the potential to benefit both clinicians in this field and their patients. 63 Reluctance to explore the ability of fNIRS to identify neural elements related to bladder sensation and control of voiding also needs to be overcome, so that the unique information related to brain-mediated aspects of urologic disease that can be derived through fNIRS can be gathered from effective research and then used to expand knowledge and improve care.…”