Aerobic endurance training reduces bubble formation and increases survivalin rats exposed to hyperbaric pressure

1. The formation of bubbles is the basis for injury to divers after decompr ession, a condition known ass decompression illness. In the present study w e investigated the effect of endurance training in the rat on decompression -induced bubble formation. 2. A total of 52 adult, female Sprague-Dawley rats (300-370 g) were randoml y assigned to one of two experimental groups: training or sedentary control . Trained rats exercised on a treadmill for 1.5 h per day for 1 day, or for 2 or 6 weeks (5 days per week) at exercise intervals that alternated betwe en 8 min at 85-90% of maximal oxygen uptake ((V) over dot (o2,max)) and 2 m in at, 50-60% Of Rats were compressed (simulated dive) in a decompression c hamber in pairs, one sedentary and one trained, at a rate of 200 kPa min(-1 ) to a pressure of 700 kPa, and maintained for 45 min breathing air. At the end of the exposure period, rats were decompressed linearly to the 'surfac e' (100 kPa) at a rate of 50 kPa min(-1). Immediately after reaching the 's urface' (100 kPa) the animals were anaesthetized and the right ventricle wa s insonated using Doppler ultrasound. 3. Intensity-controlled interval training significantly increased (V) over dot(o2,max) by 12 and 60% after 2 and 6 weeks, respectively. At 6 weeks, le ft and right ventricular weights were 14 and 17% higher, respectively, in t rained compared to control rats. No effect of training was observed on skel etal muscle weight. Bubble formation was significantly reduced in trained r ats after both 2 and 6 weeks. However, the same effect was seen after a sin gle bout of aerobic exercise lasting 1.5 h on the day prior to decompressio n. All of the rats that exercised for 1.5 h and 2 weeks, and most of those that trained for 6 weeks, survived the protocol, whereas most sedentary rat s died within 60 min post-decompression. 4. This study shows that aerobic exercise protects rats from severe decompr ession and death. This may be a result of less bubbling in the trained anim als. The data showed that the increase in aerobic capacity per se was not t he main mechanism, but rather an acute effect that was most notable 20 h af ter a single, or the last, exercise bout, with less effect after 48 h.