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.
Highlights
Scuba diving is an increasingly popular activity, especially among older individuals who may be unfit and even under medication
In the group without MTZ, more hydrogen was exhaled one hour before compression by rats force-fed with MNL than those force-fed with water (118 ± 90 ppm versus 3 ± 6 ppm; p = 0.0001)
We have shown in rats that ingesting MNL four hours before a dive—so that peak hydrogen production coincides with decompression—increases the incidence of decompression sickness (DCS) according to both clinical criteria and in terms of reduction of platelet and white blood cell
Summary
Scuba (self contained underwater breathing apparatus) diving is an increasingly popular activity, especially among older individuals who may be unfit and even under medication. Hydrogen-metabolizing microbes (the human colonic archae Methanobrevibacter smithii) were introduced into the large intestines of pigs or rats. Bacterial fermentation of undigested sugars in the large intestine generates hydrogen, some of which diffuses around the body. Bacterial fermentation of undigested sugars in the large intestine generates hydrogen, some of which diffuses around the body14 This endogenous hydrogen could exacerbate DCS even during dives with www.nature.com/scientificreports/. The aim of this study was to assess whether stimulating colonic fermentation in fasting rats by feeding them mannitol (MNL) before the dive would increase the incidence of DCS. Inhibiting this fermentation pathway by administering oral metronidazole (MTZ) was tested. DCS signs and cell counts (platelets, leukocytes) were compared in rats force-fed with MNL and controls, either conditioned with MTZ or not
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