Reviving the labial thermistor clip.

The labial thermistor clip was first introduced as a physiological measure of female sexual arousal almost 30 years ago (Henson, Rubin, Henson, & Williams, 1977); however, only a few studies have subsequently reported on its use. The development of the clip was based on the idea that surface temperature reflects changes in blood volume such as what causes genital tumescence during physiological sexual arousal. To test this idea, Henson et al. examined the use of labial temperature as an indicator of physiological sexual arousal. For this purpose, they constructed a labial thermistor clip, which was fastened to the labium of 10 volunteers who watched two counterbalanced 10-min films: a nature film and an erotic film. Labial temperature increased for 9 out of the 10 participants during the erotic condition for a mean peak increase of 0.76◦C compared with a mean peak increase of 0.34◦C during the control film. Since this initial publication, the labial thermistor has been compared simultaneously with vaginal blood volume (VBV) and vaginal pulse amplitude (VPA) (Henson & Rubin, 1978; Henson, Rubin, & Henson, 1979a, 1979b, 1982), has been used to compare erotic responses among diabetic women and controls (Slob, Koster, Radder, & van der Werff ten Bosch, 1990), and has also been used to examine the influence of the menstrual cycle on sexual arousal (Hoon, Bruce, & Kinchloe, 1982; Slob, Bax, Hop, Rowland, & van der Werff ten Bosch, 1996; Slob, Ernste, & van der Werff ten Bosch, 1991). Results from these studies indicated the following: (1) VBV, VPA, and labial temperature covaried in most but not all participants; (2) labial temperature was a more consistent measure between sessions; (3) labial temperature yielded higher correlations with subjective ratings of sexual arousal; (4) labial temperature had a slower response rate than VPA; and (5) unlike VBV, labial temperature was unaffected by orgasm. Since 1996, there have been, to our knowledge, no other published studies reporting use of the labial thermistor clip. Possible reasons for this include concerns over the sensitivity of labial temperature to quickly detect a response and the inability of researchers to reliably work with the labial thermistor clip due to lack of information regarding various technical considerations. Through much trial and error, we were able to solve some of these problems and have now successfully tested over 40 premenopausal women (Payne et al., 2006). The following is some useful technical information regarding working with the labial thermistor clip. The clip should be composed of a highly sensitive surface thermistor, such as the Yellow Springs Instruments model 427 probe (www.ysi.com/index.html). This pediatric thermistor consists of a surface probe with a stainless steel disk 4.8 mm in diameter attached to a Tefloncovered flexible wire terminating in a standard 1/4” phone plug. The 427 probe is accurate to within ± .01◦C when recording between 25 and 45◦C. For disinfection, the manufacturer recommends Cidex/glutaraldehyde for low level and Cidex/glutaraldehyde, dilute bleach, 70% isopropyl alcohol for high level. For sterilization, we have used ethylene oxide gas, STERISTM System 10. The thermistor should be glued to one end of a small metal clip. Care should be taken to minimize the amount of adhesive used on the back of the disk itself. Rather, the adhesive can be used on the wire in an effort to minimize thermal mass. A silicone pad is fashioned on the other side of the clip directly perpendicular to the thermistor disk. The pad should be kept small so as to accommodate different sizes of labia minora. Once the clip is made, it can be connected to an amplifier and data acquisition system. We have successfully used BIOPAC systems (www.biopac.com) and accompanying Acqknowledge software along with the MP100 data acquisition unit and SKT100C skin temperature amplifier module. A cable adaptor is also available from BIOPAC to connect the 1/4” thermistor cable into the two-piece lead inserts in the amplifier. The amplifier should be set to DC for absolute temperature measurement at a gain of 1 or 2 V/◦C for a 27–37◦C or 22–43◦C range, respectively. Participants can either be instructed to fasten the labial thermistor clip themselves or it can be fastened for them. They should be told to expect a slight tug while the clip is being placed, but that they will largely be unaware of the clip once it is fastened. Beginning with the clip in the open position (bead slid down), the two ends of the clips should be placed over the widest area of the labium minus. Although it remains to be determined what effect placement of the clip may have on the resulting recording, placing the thermistor facing the inside of the