Colonic Fermentation Promotes Decompression sickness in Rats

Abstract

Massive bubble formation after diving can lead to decompression sickness (DCS). During dives with hydrogen as a diluent for oxygen, decreasing the body’s H2 burden by inoculating hydrogen-metabolizing microbes into the gut reduces the risk of DCS. So we set out to investigate if colonic fermentation leading to endogenous hydrogen production promotes DCS in fasting rats. Four hours before an experimental dive, 93 fasting rats were force-fed, half of them with mannitol and the other half with water. Exhaled hydrogen was measured before and after force-feeding. Following the hyperbaric exposure, we looked for signs of DCS. A higher incidence of DCS was found in rats force-fed with mannitol than in those force-fed with water (80%, [95%CI 56, 94] versus 40%, [95%CI 19, 64], p < 0.01). In rats force-fed with mannitol, metronidazole pretreatment reduced the incidence of DCS (33%, [95%CI 15, 57], p = 0.005) at the same time as it inhibited colonic fermentation (14 ± 35 ppm versus 118 ± 90 ppm, p = 0.0001). Pre-diveingestion of mannitol increased the incidence of DCS in fasting rats when colonic fermentation peaked during the decompression phase. More generally, colonic fermentation in rats on a normal diet could promote DCS through endogenous hydrogen production.

Stimulating fermentation by the prolonged acceleration of gut transit protects against decompression sickness

“…At first glance, the findings reported here might seem to contradict our previous results 9 . In both studies, the aim was to stimulate gut fermentation and H 2 production.…”

“…It seems that insufficient H 2 was generated inside the body to exacerbate the risk of DCS in rats. In fact, the levels of H 2 measured in exhaled air one hour before these dives were significantly reduced compared with those reported previously (35 ppm [10–73] compared with 119 ppm [76–166]; p = 0.0003) 9 . In addition, although we previously stimulated H 2 production by administering a bolus dose of the fermentable mannitol four hours before the dive 9 , we only undertook a medium-term acceleration of bowel transit for a full 7 days before the dive and without a highly fermentable substance in this study.…”

“…DCS cases were generated using the same dive protocol as described in previous studies 4 , 9 , 26 . Globally, DCS manifests as an alteration in physical and behavioural performances accompanied by a deterioration in biological constants.…”

“…It has been shown that the gut microbiota can affect the risk of DCS. In rats and humans diving with air, bacterial fermentation of undigested sugars, which is associated with an increase in hydrogen production at the time of diving, is accompanied by an increase in the incidence of DCS 8 , 9 . Similarly, it has been demonstrated that increased removal of diluent hydrogen by gut microbes can affect the risk of DCS, and both native and supplemental addition of hydrogen-metabolizing microbes help reduce DCS risk 10 – 14 .…”

Thirty-five Day Fluoxetine Treatment Limits Sensory-Motor Deficit and Biochemical Disorders in a Rat Model of Decompression Sickness

“…Like previous studies the dive protocol has indeed caused cases of DCS (Pontier et al, 2008 ; Blatteau et al, 2012 , 2015 ; Vallee et al, 2013 ; De Maistre et al, 2016 ), globally seen as an alteration in physical and behavioral performances accompanied by a deterioration of biological constants, all groups included. However, chronic treatment with fluoxetine modifies the rat performances both significantly and favorably during the physical and behavioral tests, just like their biological and biochemical constants, following exposure to the hazardous protocol.…”