Correspondence

"Correspondence." Journal of Psychosomatic Obstetrics & Gynecology, 27(3), pp. 125–126

Author's reply: I appreciate the “Letter to the Editor” by M.L. Chivers regarding our publication, Psychophysiological and subjective sexual arousal to visual sexual stimuli in new women. Brotto et al. J Psychosom Obstet Gynecol 2005;26(4):229–230. I would like to take this opportunity to reply to the issues raised in that letter.

Chivers most correctly notes that her group's 2005 publication on 11 male-to-female transsexual women was not cited in our paper. At the time of acceptance of our paper into the JPOG, the Lawrence et al. [1] paper was not published nor were the yet unpublished findings known to the authors. This group's publication should certainly be acknowledged as another English-language paper on the sexual psychophysiology of male-to-female transsexual women.

It is interesting to note that unlike our findings, and unlike those of Balsma et al. [2], Lawrence et al. were able to detect a meaningful Vaginal Pulse Amplitude (VPA) trace in their group of women. Although we only included a random sample of four VPA traces in our manuscript to illustrate for the reader the magnitude of artefacts during both the neutral and erotic audiovisual stimulus conditions, we also noted that such artefacts were present in the traces of all 15 participants. In our manuscript we state the following reasons why a meaningful VPA signal may not have been detected in our group. These include: (1) discomfort from the inserted probed leading to shifting while in the laboratory; (2) involuntary muscle contractions from the remaining (male) pelvic muscles—known to be stronger in men than in women, and the fact that the neovagina is created behind these pelvic muscles; (3) influence of the prostate; and (4) the use of voluntary pelvic floor contractions as a method to enhance vasocongestion. Balsma et al. [2] found the same artefacts and also concluded that measurement of VPA in male-to-female transsexuals was difficult.

Our findings (from Canada) and those of Balsma et al. (the Netherlands) are not unique. A British sexual physiologist informed our group that he also found reliable signals in this group impossible to detect based upon a manuscript from another European group of researchers (Levin, personal communication, 2006). He concluded that these movement artefacts were due to strong, spontaneous contractions of the pelvic muscle-bed impacting on the blood flow of the neovagina or creating artefacts by pushing the neovagina onto the photoplethysmograph probe. We do not, therefore, believe that our findings are unique given that they have been replicated by at least two other research groups.

What could account for these differences in ability to detect a VPA signal from the Brotto et al. paper [3] and the Lawrence et al. paper [1]? It is possible that differences in surgical technique account for the differences. All women in our study had penile inversion treatment where scrotal tissue was used to line the vaginal vault. It is possible that this scrotal tissue may have contributed to artefacts in our and in the Balsma [2] paper. Unfortunately details on the surgical technique employed for new women in the Lawrence et al. [1] paper were not provided so a direct comparison cannot be made. It is also not clear from the Lawrence et al. paper [1] whether or not data from all participants were analyzed or if “non-responders” were excluded. In our paper, data from all participants were examined.

Given that our methodology appears to be similar to that of Lawrence et al. from the details provided, we can only conclude the sample differences, relating to the above mentioned factors, may account for the fact that signals were not detected in our nor in Balsma's [2] samples.

We appreciate the important points raised in Chivers' Letter to the Editor, but must respectfully disagree with her conclusion that “… this methodology is, in fact, a reliable and valid measure of sexual response in this population”. Until this effect can be replicated by different research groups using different samples of transsexual women, and until some of these potentially confounding factors can be identified and controlled, it remains unclear if vaginal photoplethysmography is a useful tool in this population. We look forward to continuing research on this important topic.

Lori A. Brotto, Ph.D., R.Psych.

University of British Columbia

Department of Obstetrics and Gynaecology

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