| A sudden or excessively rapid reduction in ambient environmental pressure, such as during escape from a disabled submarine or the ascent from an aborted underwater dive, or even in high-altitude flight, can entail a very serious risk of decompression sickness (DCS). It is widely accepted that DCS is caused by the formation of gas bubbles in body tissues during decompression. The severity of the symptoms of DCS depends on the size of the bubbles and their location in the body. The most common symptom of DCS is joint pain, which causes a distorted gait known as"the bends."Bubbles in the brain can cause loss of consciousness and even death, bubbles in the lungs can cause breathing abnormalities, and bubbles in the spinal cord can result in paralysis which known as DCS Type II. Treatment of DCS Type II is becoming the core of the underwater security operations.Attenuation of DCS symptoms using an alternative method when hyperbaric treatment is delayed or unavailable has long been sought in the diving and aviation community. Since Clark first demonstrated the enhanced oxygen carrying capacity of neat Perfluorocarbons (PFCs) in 1966, PFCs have already found many biological applications. PFCs are chemically and biologically inert compounds made up of polyfluorinated carbon chains first for industrial use and then developed as intravenous agents for medicine. Emulsified fluorocarbons could dissolve and transport large amounts of non-polar gases, including O2 and N2, and therefore improve tissue oxygenation and result in faster inert gas elimination. According to the oxygen delivery, gas eliminating, and surfactant properties of PFCs, it is attractive to hypothesize that intravenous PFC emulsion with or without oxygen breathing may serve as ideal candidates for DCS therapeutic agents.The objective of our study is to investigate the treatment effect of intravenous PFC emulsion with or without oxygen breathing on DCS, especially DCS Type II. The study is divided into two parts.The first part is to investigate the effects of intravenous PFC emulsion on DCS in rats. Adult Sprague-Dawley rats were treated with"700 kPa-60 min hyperbaric air exposure and 3 min decompression"profile and were given PFC emulsion (7 ml/kg) intravenously before compression (n=20) or after decompression (n=23). The morbidity, mortality of DCS and some other symptomatic and pathologic index (lung, brain and spinal cord) were studied. Saline after exposure (n=20) or only sham operation (n=21) were given to the control groups. The morbidity of the animals treated with PFC emulsion (21.74%) were significant lower than those of the saline (60.00%, P<0.05) or sham operation (66.67%, P<0.01) groups. Compared with sham operation group (42.86%), the mortality of PFC emulsion animals (13.04%) were significant lower (P<0.05). Most of symptomatic and pathologic parameters were improved notablely (P<0.05). The morbidity and mortality of the animals treated with PFC emulsion before compression (80.00%, 45.00%) didn't change significantly when compared to the control groups (P>0.05). It can be concluded from the first study that the therapeutic effect of intravenous PFC emulsion were excellent on acute DCS.The second part is to investigate the effectiveness of intravenous PFC emulsion with oxygen breathing on spinal cord function after decompression. Somatosensory evoked potentials (SSEPs) and histologic examination were chosen to serve as measures. After fast decompression (203 kPa/min) from 709 kPa (for 60 min), male Sprague-Dawley rats were randomly received: 1) air and saline, 2) O2 and saline, 3) O2 and PFC emulsion. The incidence and average number of abnormal SSEP waves in survival animals received O2 and PFC emulsion were significantly reduced (P<0.05). Foci of demyelination, necrosis and round nonstaining defects in white matter regions of the spinal cord could be found in severe DCS rats. We concluded that administration of PFC emulsion combined with oxygen breathing was beneficial for DCS spinal conductive disfunction in rats.In conclusion, PFC emulsion with or without oxygen treatment may be a valuable adjunct therapy during the first aid treatment of DCS Type II.
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