***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Acute mountain sickness ( A.M.S. ) and its severe complications , high-altitude pulmonary oedema ( H.A.P.O. ) and cerebral oedema ( C.O. ) , were studied in 278 unacclimatised hikers at 4243 m altitude at Pheriche in the Himalayas of Nepal . The overall incidence of A.M.S. was 53 % , the incidence being increased in the young and in those who flew to 2800 m , climbed fast , and spent fewer nights acclimatising en route . It was unrelated to sex , to previous altitude experience , to the load carried , and to recent respiratory infections . The severity of A.M.S. was inversely related to age ( independent of rate of ascent ) and the highest altitude attained , and was highly ocrrelated with speed of ascent . There were 7 cases of H.A.P.O. and 5 with the more intractable C.O. and , of these 12 , 11 had flown in , 9 had spent only one night at Pheriche , and none were on acetazolamide . 11 required evacuation .  Acetazolamide , compared in a double-blind study with a placebo and also compared with no tablets at all , reduced both the incidence and the severity of A.M.S. in those who flew to 2800 m but not in those who hiked up to that altitude . Prevention consists in slow ascent , rapid recognition of warning signs , and prompt descent to avoid progression Abstract The influence of acetazolamide on  acute mountain sickness  was tested in a double-blind study of forty-three volunteers given acetazolamide or placebo , 250 mg every eight hours , for 32 hours before and 40 hours after abrupt transportation from sea level to 12,800 feet . In response to hypoxia , control subjects hyperventilated and developed mild respiratory alkalosis with increased blood pH and reduced carbon dioxide tension and bicarbonate within eight hours after arrival at altitude . These changes persisted over the five days of the study . Alkalosis was prevented in the acetazolamide-treated group , with a greater increase in ventilation and alveolar oxygen tension and a greater decrease in carbon dioxide tension and bicarbonate than in controls . Significant reductions in frequency and severity of the most prominent symptoms of acute mountain sickness — headache , insomnia and gastrointestinal symptoms — were observed in treated subjects . In control subjects , occurrence and severity of symptoms corr 750 mg per day of acetazolamide in the prevention of  acute mountain sickness ( AMS  ) , as recommended in the meta- analysis published in 2000 in the British Medical Journal , may be excessive and is controversial . To determine if the efficacy of low-dose acetazolamide 125 mg bd ( 250 mg ) , as currently used in the Himalayas , is significantly different from 375 mg bd ( 750 mg ) of acetazolamide in the prevention of AMS , we design ed a prospect i ve , double-blind , r and omized , placebo-controlled trial . The participants were sample d from a diverse population of ( non-Nepali ) trekkers at Namche Bazaar ( 3440 m ) in Nepal on the Everest trekking route as they ascended to study midpoints ( 4280 m/4358 m ) and the endpoint , Lobuje ( 4928 m ) , where data were collected . Participants were r and omly assigned to receive 375 mg bd of  acetazolamide ( 82 participants ) , 125 mg bd of acetazolamide ( 74 participants ) , or a placebo ( 66 participants ) , beginning at 3440 m for up to 6 days as they ascended to 4928 m. The results revealed that composite AMS incidence for 125 mg bd was similar to the incidence for 375 mg bd ( 24 % vs. 21 % , 95 % confidence interval , -12.6 % , 19.8 % ) , in contrast to significantly greater AMS ( 51 % ) observed in the placebo group ( 95 % confidence interval for differences : 8 % , 46 % ; 12 % , 49 % for low and high comparisons , respectively ) . Both doses of acetazolamide  improved oxygenation equally ( 82.9 % for 250 mg daily and 82.8 % for 750 mg daily ) , while placebo endpoint oxygen saturation was significantly less at 80.7 % ( 95 % confidence interval for differences : 0.5 % , 3.9 % and 0.4 % , 3.7 % for low and high comparisons , respectively ) . There was also more paresthesia in the 375-mg bd group ( p < 0.02 ) . We conclude that 125 mg bd of acetazolamide is not significantly different from 375 mg bd in the prevention of AMS ; 125 mg bd should be considered the preferred dosage when indicated for persons ascending to altitudes above 2500 
    Output:
    
On ascent to altitude , several adaptive physiological processes occur ( including hyperventilation , erythropoiesis , and increased cardiac output ) , all of which tend to increase convective oxygen transport to the tissues , a process termed “