When you sit there and read these words, you are probably breathing. The air flows into your lungs through the upper airways, which include your mouth and nose. After releasing the precious oxygen payload, it comes out again in the same way.
We assume that is how most mammals breathe – but maybe it’s not the full picture. Recent research suggests that rodents and pigs can also breathe through their butts.
Technically, the delivery of oxygen through the rectal intestine suggests a new enema-like means of ventilating patients who are short of breath – if the same strange ability can be demonstrated in humans.
Intestinal breathing sounds extremely strange, but has been known for some time – at least with fish. In oxygen depleted or hypoxic emergencies, some aquatic animals, such as sea cucumbers, freshwater catfish, and freshwater loach, can maximize their oxygen uptake by breathing through their intestines.
This, of course, raised the intriguing question of whether other animals – including mammals – can do the same. Though it seemed unlikely, a team of Japanese and American scientists led by Kyoto University thoracic surgeon Ryo Okabe decided to find out in hopes of determining the feasibility of rectal ventilators for human patients.
“Artificial respiratory assistance plays an important role in the clinical management of respiratory failure due to serious illnesses such as pneumonia or acute respiratory distress syndrome,” said gastroenterologist Takanori Takebe of Tokyo Medical and Dental University and Cincinnati Children’s Hospital Medical Center.
“While the side effects and safety in humans require careful study, our approach may offer a new paradigm for supporting critically ill patients who have stopped breathing.”
As the team points out, standard medical options for patients with respiratory failure are based on mechanical ventilation or artificial lung systems. However, the current pandemic has created a critical shortage of such devices and a safe alternative method could provide additional life-saving support to patients in emergency situations.
This next part is not for the squeamish, however.
Initially, her research topics were mice, which were thankfully stunned for the next part. The researchers developed an oxygen ventilation system that can be inserted anally. They induced hypoxia through tracheal intubation and compared intestinally ventilated mice with control mice that received no ventilation.
None of the control mice survived longer than 11 minutes. This was in marked contrast to the mice that received intestinal oxygen, of which 75 percent survived 50 minutes.
This is a fascinating result, but it required abrasion of the intestinal lining in order to achieve the most efficient oxygen supply to the intestinal lumen. The group of mice that received intestinal ventilation without abrasion had a mean survival time of only 18 minutes.
It is unlikely that intestinal abrasion will be possible for human patients – especially human patients who are sick enough to question intestinal ventilation. So the team looked for alternatives.
They turned to liquid perfluorochemicals, a class of chemicals in which the hydrogen atoms were replaced with fluorine.
These have several properties that make them a good prospect for ventilation, including their high gas solubility as well as their physical properties. In the past, patients with shortness of breath have been treated with liquid perfluorochemicals by partially filling their lungs to facilitate oxygen transfer with varying degrees of success. Perfluorochemicals have been classified as clinically safe for this purpose.
The team therefore tried to oxygenate a perfluorocarbon and use it to treat mice, rats and pigs.
The mice were placed in an oxygen depleted chamber; Those treated with perfluorocarbon ventilation could walk longer than untreated mice, and more oxygen reached their hearts. The rats were also treated to assess whether their body absorbed the perfluorochemical to determine their safety.
Finally, using perfluorochemical intestinal ventilation, dyspnoea was reduced in anesthetized pigs under non-lethal hypoxic conditions. During the treatment, her skin became warm and reddened, and her oxygen levels increased with no apparent side effects.
It’s unclear if a similar approach would work for humans, but the team is optimistic.
“The level of arterial oxygen delivery from our ventilation system, when scaled for human use, is likely to be sufficient to treat patients with severe respiratory failure and potentially provide a life-saving oxygen supply,” Takebe said.
The research was published in Med.
