Bubbles Quantified In vivo by Ultrasound Relates to Amount of Gas Detected Post-mortem in Rabbits Decompressed from High Pressure.

The pathophysiological mechanism of decompression sickness is not fully understood but there is evidence that it can be caused by intravascular and autochthonous bubbles. Doppler ultrasound at a given circulatory location is used to detect and quantify the presence of intravascular gas bubbles as an indicator of decompression stress. In this manuscript we studied the relationship between presence and quantity of gas bubbles by echosonography of the pulmonary artery of anesthetized, air-breathing New Zealand White rabbits that were compressed and decompressed. Mortality rate, presence, quantity, and distribution of gas bubbles elsewhere in the body was examined postmortem. We found a strong positive relationship between high ultrasound bubble grades in the pulmonary artery, sudden death, and high amount of intra and extra vascular gas bubbles widespread throughout the entire organism. In contrast, animals with lower bubble grades survived for 1 h after decompression until sacrificed, and showed no gas bubbles during dissection.

S100B and NSE serum concentrations after simulated diving in rats.

The purpose of this study was to assess whether one could detect S100 calcium-binding protein B (S100B) and neuron-specific enolase (NSE) in serum of rats after a simulated dive breathing air, with the main hypothesis that the serum concentrations of S100B and NSE in rats will increase above pre-exposure levels following severe decompression stress measured as venous gas emboli (VGE). The dive group was exposed to a simulated air dive to 700 kPa for 45 min. Pulmonary artery was monitored for vascular gas bubbles by ultrasound. Pre- and postdive blood samples were analyzed for S100B and NSE using commercially available Elisa kits. There was no increase in serum S100B or NSE after simulated diving and few of the animals were showing high bubble grades after the dives. The present study examined whether the protein biomarkers S100B and NSE could be found in serum from rats after exposure to a simulated dive to 700 kPa for 45 min breathing air. There were no differences in serum concentrations before versus after the dive exposure. This may be explained by the lack of vascular gas bubbles after the dives.

Eccentric exercise 48 h prior to simulated diving has no effect on vascular bubble formation in rats.

PURPOSE: Decompression sickness (DCS) caused by vascular bubble formation is a major risk when diving. Prior studies have shown that physical exercise has a significant impact in both reducing and increasing bubble formation. There is limited knowledge about the mechanisms, but there are indications that exercise-induced muscle injury prior to diving may cause increased bubble formation. The purpose of this study was to investigate the role of exercise-induced muscle injury as a possible mechanism of bubble formation during diving. METHODS: Muscle injury was induced by exposing female Sprague-Dawley rats (n = 30) to a single bout of eccentric exercise, 100 min intermittent, downhill (-16°) treadmill running. Forty-eight hours later, the animals were exposed to a 50-min simulated saturation dive (709 kPa) in a pressure chamber, when the degree of muscle injury and inflammation would be the most pronounced. Bubble formation after the dive was observed by ultrasonic imaging for 4 h. RESULTS: No difference in bubble loads was found between the groups at any time despite evident muscle injury. Maximum bubble loads (bubbles cm(-2) heart cycle(-1)) were not different, exercise: 1.6 ± 3.5 SD vs control: 2.2 ± 4.1 SD, P = 0.90, n = 15 in each group. CONCLUSIONS: Eccentric exercise performed 48 h prior to diving causes skeletal muscle injury but does not increase the amount of vascular bubbles in rats. The prevailing recommendation is that physical activity prior to diving is a risk factor of DCS. However, present and previous studies implicate that pre-dive physical activity does not increase the DCS risk.

Simulated dive in rats lead to acute changes in cerebral blood flow on MRI, but no cerebral injuries to grey or white matter.

In this study, the effect of a simulated dive on rat brain was investigated using several magnetic resonance imaging (MRI)-methods and immunohistochemistry. Rats were randomly assigned to a dive- or a control group. The dive group was exposed to a simulated air dive to 600 kPa for 45 min. Pulmonary artery was monitored for vascular gas bubbles by ultrasound. MRI was performed 1 h after decompression and at one and 2 weeks after the dive with a different combination of MRI sequences at each time point. Two weeks after decompression, rats were sacrificed and brains were prepared for histology. Dived rats had a different time-curve for the dynamic contrast-enhanced MRI signal than controls with higher relative signal intensity, a tendency towards longer time to peak and a larger area under the curve for the whole brain on the acute MRI scan. On MRI, 1 and 2 weeks after dive, T2-maps showed no signal abnormalities or morphological changes. However, region of interest based measurements of T2 showed higher T2 in the brain stem among decompressed animals than controls after one and 2 weeks. Microscopical examination including immunohistochemistry did not reveal apparent structural or cellular injuries in any part of the rat brains. These observations indicate that severe decompression does not seem to cause any structural or cellular injury to the brain tissue of the rat, but may cause circulatory changes in the brain perfusion in the acute phase.

Exercise-induced myofibrillar disruption with sarcolemmal integrity prior to simulated diving has no effect on vascular bubble formation in rats.

Decompression sickness is initiated by gas bubbles formed during decompression, and it has been generally accepted that exercise before decompression causes increased bubble formation. There are indications that exercise-induced muscle injury seems to be involved. Trauma-induced skeletal muscle injury and vigorous exercise that could theoretically injure muscle tissues before decompression have each been shown to result in profuse bubble formation. Based on these findings, we hypothesized that exercise-induced skeletal muscle injury prior to decompression from diving would cause increase of vascular bubbles and lower survival rates after decompression. In this study, we examined muscle injury caused by eccentric exercise in rats prior to simulated diving and we observed the resulting bubble formation. Female Sprague-Dawley rats (n = 42) ran downhill (-16º) for 100 min on a treadmill followed by 90 min rest before a 50-min simulated saturation dive (709 kPa) in a pressure chamber. Muscle injury was evaluated by immunohistochemistry and qPCR, and vascular bubbles after diving were detected by ultrasonic imaging. The exercise protocol resulted in increased mRNA expression of markers of muscle injury; αB-crystallin, NF-κB, and TNF-α, and myofibrillar disruption with preserved sarcolemmal integrity. Despite evident myofibrillar disruption after eccentric exercise, no differences in bubble amounts or survival rates were observed in the exercised animals as compared to non-exercised animals after diving, a novel finding that may be applicable to humans.

Doxycycline treatment in a neonatal rat model of hypoxia-ischemia reduces cerebral tissue and white matter injury: a longitudinal magnetic resonance imaging study.

Doxycycline may potentially be a neuroprotective treatment for neonatal hypoxic-ischemic brain injury through its anti-inflammatory effects. The aim of this study was to examine any long-term neuroprotection by doxycycline treatment on cerebral gray and white matter. Hypoxic-ischemic brain injury was induced in 7-day-old rats. Pups were treated with either doxycycline (HI+doxy) or saline (HI+vehicle) by intraperitoneal injection at 1 h after hypoxia-ischemia (HI). At 6 h after HI, MnCl(2) was injected intraperitoneally for later manganese-enhanced magnetic resonance imaging (MRI). MRI was performed with diffusion-weighted imaging on day 1 and T(1) -weighted imaging and diffusion tensor imaging at 7, 21 and 42 days after HI. Animals were killed after MRI on day 42 and histological examinations of the brains were performed. There was a tendency towards lower lesion volumes on diffusion maps among HI+doxy than HI+vehicle rats at 1 day after HI. Volumetric MRI showed increasing differences between groups with time after HI, with less cyst formation and less cerebral tissue loss among HI+doxy than HI+vehicle pups. HI+doxy pups had less manganese enhancement on day 7 after HI, indicating reduced inflammation. HI+doxy pups had higher fractional anisotropy on diffusion tensor imaging in major white matter tracts in the injured hemisphere than HI+vehicle pups, indicating less injury to white matter and better myelination. Histological examinations supported the MRI results. Lesion size on early MRI was highly correlated with final injury measures. In conclusion, a single dose of doxycycline reduced long-term cerebral tissue loss and white matter injury after neonatal HI, with an increasing effect of treatment with time after injury.

Concentration of circulating autoantibodies against HSP 60 is lowered through diving when compared to non-diving rats.

OBJECTIVE: Skin and ear infections, primarily caused by Pseudomonas aeruginosa (P. aeruginosa), are recurrent problems for saturation divers, whereas infections caused by P. aeruginosa are seldom observed in healthy people outside saturation chambers. Cystic fibrosis (CF) patients suffer from pulmonary infections by P. aeruginosa, and it has been demonstrated that CF patients have high levels of autoantibodies against Heat shock protein 60 (HSP60) compared to controls, probably due to cross-reacting antibodies induced by P. aeruginosa. The present study investigated whether rats immunised with P. aeruginosa produced autoantibodies against their own HSP60 and whether diving influenced the level of circulating anti-HSP60 antibodies. METHODS: A total of 24 rats were randomly assigned to one of three groups ('immunised', 'dived' and 'immunised and dived'). The rats in group 1 and 3 were immunised with the bacteria P. aeruginosa, every other week. Groups 2 and 3 were exposed to simulated air dives to 400 kPa (4 ata) with 45 min bottom time, every week for 7 weeks. Immediately after surfacing, the rats were anaesthetised and blood was collected from the saphenous vein. The amount of anti-HSP60 rat antibodies in the serum was analysed by enzyme linked immunosorbent assay. RESULTS: The immunised rats (group 1) showed a significant increase in the level of autoantibodies against HSP60, whereas no autoantibodies were detected in the dived rats (group 2). The rats both immunised and dived (group 3) show no significant increase in circulating autoantibodies against HSP60. A possible explanation may be that HSP60 is expressed during diving and that cross-reacting antibodies are bound.

S100B and its relation to intravascular bubbles following decompression.

INTRODUCTION: When neurological damage occurs in divers, it is considered to be caused by gas bubbles. Entrapment of these bubbles may lead to cellular injury and cerebral oedema. S100B is a protein biomarker that is released in CNS injuries and the concentration is related to the amount of brain damage. METHODS: A total of 27 rats were randomly assigned to one of three groups. Group I served as controls (n = 9). Group II (n = 7) underwent a simulated dive to 400 kPa and Group III to 700 kPa (n = 11). In groups II and III, venous gas bubble scores were evaluated by ultrasound during the first hour after surfacing. The amount of S100B in serum after the dives was tested using a commercial ELISA kit. Bubble grades were compared to S100B protein concentrations. RESULTS: The average level of S100B was significantly higher in rats compressed to 700 kPa compared to the control rats, (P = 0.038) and the rats compressed to 400 kPa, (P = 0.003). There was no difference in S100B concentration between groups I and II. Following the dive to 700 kPa, there were significantly higher bubble grades observed than following the dive to 400 kPa (P = 0.001). CONCLUSION: The correlation between bubble grade and an increase in serum protein level of S100B indicates that this protein may be useful as a biomarker for neurological damage caused by decompression.

The effect of two consecutive dives on bubble formation and endothelial function in rats.

INTRODUCTION: Gas bubble formation during and after decompression is considered to be the main initiator of decompression sickness (DCS). Compressed-air workers have been reported to acclimatise to the working environment and hence have a reduced risk of DCS, but the exact nature of the adaptation is not known. In the present study, we investigated the effect of two consecutive dives, separated by a 24-hour surface interval, on bubble formation and endothelial damage in rats. METHODS: A total of 30 rats were divided into four groups, one control group and three dive groups with different dive profiles, of which two of the groups had two dives. The amount of bubbles in the pulmonary artery was estimated by ultrasound for one hour after surfacing, and tension measurements were performed in vitro on segments of the abdominal aorta following sacrifice of the animals. RESULTS: No significant differences between the groups were found in endothelial function or bubble grade. However, animals that died immediately after the dive, irrespective of grouping order, had lower acetylcholine-induced dilatory responses in the aorta than surviving rats. CONCLUSION: Bubble formation and endothelial function among rats were not significantly affected by exposure to consecutive dives 24 hours apart. An adaptive, protective effect of repeated dives was hence not seen in this animal model.