The successful measurement of clitoral pulse amplitude using a new clitoral plethysmograph

Background: Although the clitoris is more sensitive to stimulation than the vagina, and its innervation more conducive to sensory feedback, the field of sexual psychophysiology relies heavily on the measurement of vaginal pulse amplitude (VPA). This is most likely due to the availability of an instrument, the vaginal photoplethysmograph, that is easy to place and that allows for relatively stable measurement. Recently, two studies (Gerritsen et al., 2009; Suschinsky et al., 2015) have used clitoral photoplethysmography to assess blood flow in the clitoris. However, only clitoral blood volume (CBV), thought to represent general clitoral vasocongestion, was reported rather than clitoral pulse amplitude (CPA). In the current study, we developed and tested a new clitoral photoplethysmograph for the measurement of CPA. Methods: After several design iterations, we selected two different versions of the new device, which differed in their orientation of the sensor and light source (i.e. parallel and angled). We tested the two newly developed clitoral sensors in 15 premenopausal, sexually functional women (mean age = 26.6, SD = 4.7). Vaginal pulse amplitude (VPA) was assessed simultaneously using a standard vaginal photoplethysmograph. Women wore elastic spandex shorts to enable stable placement of the instruments. The women viewed a three-minute erotic and an anxiety-inducing film segment with each clitoral sensor, and were presented with neutral video excerpts prior to the first and after each subsequent video. In addition, they were asked to use a lever to indicate their subjective level of sexual arousal during the erotic video presentations. Results: Due to technical problems, the data of three women could not be used. For the remaining participants we obtained satisfactory signals, especially when using the non-parallel clitoral device, which detected clear pulse waves in all women. Less than 2% of the clitoral and vaginal device data were impacted by artifacts. Main effects of Film and the interaction between Film and Epoch were stronger, in terms of effect size, for the clitoral than for the vaginal device. Furthermore, CPA followed more closely the changes in intensity of the sexual films than VPA: The clitoral pulse signal grew more steadily throughout the three-minute erotic video sequence, showing a substantial increase during the third minute, when vaginal intercourse was depicted. The vaginal pulse wave, on the other hand, showed the fastest and strongest increase during early parts of the erotic video (depicting petting and oral sex). Both within- and between-subject correlations between genital response and subjective sexual arousal were higher for the clitoral than for the vaginal device. Key Words: clitoral pulse amplitude, clitoral photoplethysmography, sexual arousal, vaginal pulse amplitudestatus: accepte