Ultrasound breakthrough could help humans venture into deep space

A future where humans are placed in hibernation to travel into space is a step closer after scientists proved they can put mammals into a sleep-state using ultrasound.

Many animals and birds are able to enter a torpor-like state in which they suppress their metabolism and reduce body temperature to conserve energy and heat during periods of extreme cold or lack of food.

Since the 1960s, scientists have proposed that inducing a similar state in humans could help protect patients with life-threatening conditions and allow astronauts to embark on long-distance interstellar flights with fewer supplies.

The concept of travelling through space in suspended animation has been at the heart of several science fiction films including Passengers, 2001: A Space Odyssey, and Interstellar.

Now, a team at Washington University in St. Louis has shown they can send rodents into a state of reversible hibernation by firing ultrasound pulses at their heads, stimulating the hypothalamus preoptic area in the brain, and causing their heart rates to halve and their temperature to drop.

Ultrasound-induced hypothermia and hypometabolism

They have called the phenomenon UIH - Ultrasound-induced hypothermia and hypometabolism.

Hong Chen, an associate professor at Washington University, said: “Ultrasound-induced hypothermia and hypometabolism has the potential to address the long sought-after goal of achieving non-invasive and safe induction of the torpor-like state, which has been pursued by the scientific community at least since the 1960s.

“Ultrasound stimulation possesses a unique capability to noninvasively reach deep brain regions with high spatial and temporal precision in animal and human brains.”

When animals enter a short period of reduced metabolic rate it is known as torpor, while long term or seasonal slumbers are known as hibernation.

To induce torpor, the team created a wearable ultrasound device that can be mounted on the head of rats and mice to stimulate the hypothalamus preoptic brain region, which is known to regulate hibernation.

When the ultrasound was turned on, the rodents showed a drop in body temperature of about 3C for roughly an hour. The mice’s metabolism also altered from using both carbohydrates and fat for energy to only fat – a key feature in hibernation – and their heart rates fell by about 47 per cent. They also breathed less oxygen.

When the scientists dug into what was causing the effect, they found that the ultrasound activated an ion channel linked to metabolism and temperature.

Although mice can enter torpor naturally, the team showed the same process works on rats, an animal that does not hibernate.

The researchers said the rat experiments demonstrated that the brain regions regulating hibernation may also be present in non-hibernating mammals and gave hope that the technique could be used in humans.

Writing in the journal Nature Metabolism, the authors concluded: “We showed that ultrasound stimulation-induced hypothermia in rats, which do not naturally enter torpor, suggesting the possibility that similar effects could be induced in humans.

“UIH may unlock applications ranging from new medical treatments to long-duration human spaceflight.”

'Huge breakthrough'

Writing in a linked commentary, Martin Jastroch, professor of mammalian molecular physiology at Stockholm University, said the study represented a “huge breakthrough”.

He said: “Putting human metabolism ‘on ice’ could have multiple benefits, as it would preserve organs for transplantation or surgery or in patients in intensive care, reduce cellular damage during cardiac arrest and stroke, and potentially enable human hibernation for long-distance space expeditions, where travel times of 7–8 months are forecasted to be needed to reach our closest neighbour planet, Mars.

“What may seem like one small step for this one research group promises to be a giant leap for mankind to exploit torpor-like states in medicine and possibly for deep-space travel.”