Abstract Introduction Penile tumescence is a major concern following Radical Prostatectomy (RP). We have reported on the use of electrical stimulation of the S2-S4 nerve roots as a method to elicit tumescence during RP. Associated with tumescence is an increase in penile temperature. With the development of intraoperative neuromonitoring (IONM) during RP, the adjunct use of temperature monitoring is proposed as a measure of penile tumescence. Objective To compare the reliability and sensitivity of fNIRS vs penile temperature as a measure of tumescence in normal subjects. Methods fNIRS and penile temperatures were recorded continuously from 6 sexually normal volunteers (age 28-32 yo) prior to, during, and following Visual Sexual Stimulation (VSS). Once a physical erection started VSS was stopped. fNIRS was recorded from the deep Cavernosal arteries. Temperature, in Centigrade, was recorded using sensors (Physitemp Instruments, Clifton, NJ) placed over the dorsal artery at the base of the penis, at the External Hallucis Longus (EHL), and ambient (room). Results Reliable fNIRS and temperature data were recorded from all subjects. Table 1 depicts results for both procedures. Event Baseline Peak Tumescence Detumescence (Return to baseline) Penile Temp 33.2-33.4 34.4 – 34.6 33.2-33.4 EHL 32.3-33.4 32.3-33.5 32.0-32.1 Ambient (room) 25 25 25 fNIRS – Hb0 (-0.015)-(-0.040) (-0.023)-(-0.060) (-0.015)-(-0.030) fNIRS - Hbr 0.00 – 0.015 0.025-0.030 0.01 – 0.02 Table 1. Mean +/- 2 SD of temperature and fNIRS as a function of state. During the tumescent cycle (i.e., from and return to baseline) temperature increased from 1.2 – 1.4 degrees; control increased 0.1 degree, and ambient showed no change. The range of fNIRS – Hb0 and fNIRS – Hbr demonstrated appropriate increases. This indicates changes in penile temperature and fNIRS were due to VSS. The duration of the tumescent cycle for fNIRS /= 120 seconds and for temperature 600-800 seconds. Conclusions VSS produced reliable changes in penile temperature and blood flow in all subjects. The tumescent cycle was shorter for fNIRS than for penile temperature, which indicates an increase in penile tissue temperature. Relative to intraoperative monitoring, eliciting a complete tumescent cycle is not necessary. If electrical elicitation of the S2-S4 nerve roots was stopped with the onset of increased penile temperature, the tumescent cycle would be significantly reduced with a concomitant reduction in the duration of temperature increase. By reducing this duration, testing would become more sensitive to the onset of irritation of the erectile neuroplexus. Disclosure Yes, this is sponsored by industry/sponsor: Neurovascular Research & Design Clarification: Industry initiated, executed and funded study Any of the authors act as a consultant, employee or shareholder of an industry for: Neurovascular Research & Design
J Owen (2026) studied this question.