A new study has found rodents and pigs can use their intestines for respiration, raising the potential of new emergency treatments for human respiratory failure – by keeping the body oxygenated when lungs fail and mechanical ventilation is unavailable or unsuitable.
In the study reported in the journal Med and led by Dr Takanori Takebe, from Tokyo Medical and Dental University and Ohio’s Cincinnati Children’s Hospital Medical Center, researchers reversed symptoms of respiratory failure in mice and pigs by delivering oxygen gas or oxygenated liquid through the rectum.
Dr Takebe commented: ‘Artificial respiratory support plays a vital role in clinical management of respiratory failure due to severe illnesses such as pneumonia or acute respiratory distress syndrome. Although the side effects an safety need to be thoroughly evaluated in humans, our approach may offer new paradigm to support critically ill patients with respiratory failure.’
In the animal kingdom, several aquatic organisms have adapted to survive in low oxygen environments ‘by evolving alternative breathing mechanisms alongside lungs or gills’, noted medicalnewstoday.com.
Loaches, sea cucumbers, some freshwater catfish and stretch spiders all use their lower intestines for respiration. But until now whether mammals have similar capabilities has remained a mystery.
Dr Takebe noted: ‘This is the firs study to show successful repurposing of the distal gut for breathing apparatus inspired by aquatic organisms. We are all surprised the intestinal breathing capacity that loaches have is maintained even in mammalian species such that it is sufficient for rescuing from lethal hypoxia/asphyxia conditions.’
Dr Takabe’s team designed an intestinal gas ventilation system to deliver pure oxygen gas through the rectum of mice in an enema-like procedure. They then exposed the mice to extremely low oxygen conditions.
Without the intestinal ventilation system, none survived to 11 minutes; but administering oxygen gas through the anus increased median survival of the mice to 18 minutes.
However, when researchers made a ‘small abrasion in the intestinal mucous membrane’ – to allow more efficient movement of gas between the intestine and surrounding blood vessels – 75% of those with the abrasion and gas ventilation survived for 50 minutes ‘in conditions that would normally be lethal’.
While an intestinal gas ventilation system requiring damage to the intestinal mucosa is unlikely to prove feasible for clinical use in humans – especially severely ill people – the researchers developed an alternate solution using an oxygenated liquid called perfluorodecalin (POFD) which does not require abrasion of the intestinal mucus layer.
Mice treated with intestinal liquid ventilation ‘could walk significantly farther than those in the control group and more oxygen reached their hearts’.
Similar pumping of repeated cycles of PFD into intestines of pigs found the treated animals had higher oxygen levels than those that did not receive treatment; additionally the treatment ‘reversed the symptoms of skin pallor and coldness that arose from lack of oxygen’.
Dr Takabe summed up: ‘The recent pandemic is overwhelming the clinical need for ventilators and artificial lungs, resulting in a critical shortage of available devices and endangering patients’ lives worldwide.
The level of arterial oxygenation provided by our ventilation system, if scaled for human application, is likely sufficient to eat patients with severe respiratory failure, potentially providing lifesaving oxygenation.’
