Silicon Valley entrepreneur Bryan Johnson’s girlfriend is tracking her nighttime ‘female erections’ using a £12,000 ‘techno tampon’.

Kate Tolo, who is dating the millionaire biohacker and works with him on his anti-ageing mission, is attempting to unlock new clues about women’s health and longevity.

The 31-year-old is inserting a research-grade device into her vagina every night to detect surges in blood flow to vaginal tissue during sleep.

Johnson, 49, also tracks his nighttime erections, using a much cheaper device that costs around $275 (£205), which connects to his smartphone.

He believes the data offers a useful insight into his vascular health, with erectile function in men sometimes considered a potential indicator of cardiovascular problems.

Tolo argues that women could benefit from similar monitoring, despite having no penis to track.

Women also experience changes in blood flow to erectile tissue during sleep, with the clitoris swelling as blood flow increases. The clitoris and penis develop from the same embryonic tissue during the early stages of pregnancy.

Research dating back decades has examined these nighttime changes, but Tolo says the technology used to measure them has barely advanced.

‘The tech was invented in 1975 and hasn’t changed in 50 years,’ she told The New York Post.

Explaining how the probe works, she continued: ‘I insert the 5cm probe [and] tape a wire to my leg that is plugged into a machine and a laptop.

‘The laptop can’t fall asleep or we lose the data. I sadly learned that through experience.’

A study published in 1985 found that vaginal blood flow varied with sleep stages, increasing during REM sleep.

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Researchers also recorded nighttime changes in all the women studied, regardless of how easily they said they became sexually aroused.

Tolo believes the findings could eventually help doctors distinguish between physical and psychological causes of female sexual dysfunction.

Dr Hillary Seger, a member of Tolo’s care team, said: ‘In men, the reasoning behind nocturnal tumescence testing has been that if erections still happen during sleep, the vascular and neurological machinery is intact — though even in men the test is more limited than people assume.

‘For women, there is no validated clinical equivalent. Kate’s recordings are the first look I’ve had at how this signal behaves across a full menstrual cycle.’

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