Dutch scientists have been investigating what happens when you gradually increase the pressure inside someone's vagina. As it turns out, it might make watching porn a lot more enjoyable.

There is a resounding lack of research on the physiology of female sexuality. This knowledge gap feeds into the idea that women's bodies are somehow inherently mysterious and hard to understand. Now scientists in the Netherlands report a happy accident in a study in the Journal of Sex & Marital Therapy: the discovery that applying pressure inside the vagina with a newly invented instrument heightens women's arousal while watching erotic films.

It all came about because there weren't any instruments scientists could use to study genital pain – a condition where women experience severe discomfort during sex – in a reliable way. Previous studies had used simple balloons that were gradually inflated, but those had an annoying habit of sliding out of the vagina partway through an experiment.

"It was just to examine how women do experience vagina pressures because we didn't know anything about it," study author Reinhilde Melles of Maastricht University in the Netherlands told IBTimes UK.

Hence, the Vaginal Pressure Inducer. It's a hi-tech, remote-controlled balloon that is gradually filled with water at 37C, secured with something a bit like a pair of pants crossed with a Velcro harness.

While scientists in another room could control how much the balloon inflated, the women wearing it could stop it at any time by pressing a button. Each woman used a fresh balloon and the instrument was sterilised with alcohol between sessions.

The group at Maastricht, led by Reinhilde Melles, tested the Vaginal Pressure Inducer on a group of 42 healthy women who had never experienced sexual problems or genital pain. The women watched several films each about 7 minutes long. The first was a neutral film to get used to the surroundings. Then they watched a film showing manual, oral and penetrative sex, one showing fully clothed people doing a bit of petting and kissing, and another neutral film for comparison.

To figure out whether emotional rather than sexual arousal might affect the results, they also showed women non-sexual scenes from The Eighth Day, Life is Beautiful and Forrest Gump. Yes, that's right, women had to watch Forrest Gump while a balloon slowly inflated inside their vaginas – all in the name of science.

Interestingly, the sexier the film, the more pressure women would tolerate before pressing the button to end the experiment. The women had the least tolerance for pressure while watching the non-sexual film scenes.

Vaginal Pressure Inducer
The Vaginal Pressure Inducer while uninflated. Melles et al / Journal of Sex and Marital Therapy

It wasn't just that the women would put up with more pressure during the sexual films – they reported "significantly higher" levels of arousal when watching them with the added pressure than watching them without it.

"Vaginal pressure may heighten subjective sexual arousal during high-arousal sexual films, which may implicate that vaginal pressure can potentiate sexual arousal in sexually functional women," the authors concluded.

But what were the women's verdicts? Many reported having a reasonably good time during the experiment, but some were left feeling a little perplexed.

"Exit interviews revealed mainly positive reactions of women concerning the experiment varying from 'a bit weird', to 'stimulating', 'interesting'," the authors write. "With respect to the vaginal pressure, reactions ranged from 'not very pleasant' to 'doable'."

All in all, it looks like the VPI will probably work for its intended purposes of helping to understand the condition of genital pain in women, and help pave the way for evidence-based treatments.

"We work a lot with genital pain patients and it would be very helpful to see how they experience vaginal pressure and assess the difference between them and healthy controls," Melles said.

And as well as its potential therapeutic benefits, it's another happy, if unintentional, step towards demystifying female sexuality. Melles and her colleagues also have plans to commercialise the instrument for potential use as a sex toy.

"It would be also possible to use it to increase the pleasurableness of sex. And maybe also to learn how women can have an orgasm during penetrative sex. About a third of women are able to have an orgasm during sex, but many more would like it.

"With this instrument it could be possible to learn to associate vaginal pressure with pleasureableness."

Vaginal Pressure Inducer
The Vaginal Pressure Inducer inflated to exert pressure inside the vagina. Melles et al / Journal of Sex and Marital Therapy