***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: BACKGROUND Supplemental oxygen in patients with chronic obstructive pulmonary disease ( COPD ) and exercise hypoxaemia improves exercise capacity and dyspnoea . However , the benefit of oxygen during pulmonary rehabilitation in these patients is still unknown . METHODS Twenty five patients with stable COPD ( mean ( SD ) forced expiratory volume in one second ( FEV1 ) 0.76 ( 0.29 ) l and 30.0 (9.89)% predicted , arterial oxygen tension ( Pao 2 ) 8.46 ( 1.22 ) kPa , arterial carbon dioxide tension ( Paco 2 ) 6.32 ( 1.01 ) kPa ) and significant arterial desaturation on exercise ( 82.0 (10.4)% ) were entered onto a pulmonary rehabilitation programme . Patients were r and omised to train whilst breathing oxygen ( OT ) ( n = 13 ) or air ( AT ) ( n = 12 ) , both at 4 l/min . Assessment s included exercise tolerance and associated dyspnoea using the shuttle walk test ( SWT ) and Borg dyspnoea score , health status , mood state , and performance during daily activities . RESULTS The OT group showed a significant reduction in dyspnoea after rehabilitation compared with the AT group ( Borg mean difference –1.46 ( 95 % CI –2.72 to –0.19 ) ) but there were no differences in other outcome measures : SWT difference –23.6 m ( 95 % CI –70.7 to 23.5 ) , Chronic Respiratory Disease Question naire 3.67 ( 95 % CI –7.70 to 15.1 ) , Hospital Anxiety and Depression Scale 1.73 ( 95 % CI –2.32 to 5.78 ) , and London Chest Activity of Daily Living Scale –2.18 ( 95 % CI –7.15 to 2.79 ) . At baseline oxygen significantly improved SWT ( mean difference 27.3 m ( 95 % CI 14.7 to 39.8 ) and dyspnoea ( –0.68 ( 95 % CI –1.05 to –0.31 ) ) compared with placebo air . CONCLUSIONS This study suggests that supplemental oxygen during training does little to enhance exercise tolerance although there is a small benefit in terms of dyspnoea . Patients with severe disabling dyspnoea may find symptomatic relief with supplemental oxygen Supplemental oxygen improves exercise tolerance of normoxemic and hypoxemic chronic obstructive pulmonary disease ( COPD ) patients . We determined whether nonhypoxemic COPD patients undergoing exercise training while breathing supplemental oxygen  achieve higher intensity and therefore improve exercise capacity more than patients breathing air . A double-blinded trial was performed involving 29 nonhypoxemic patients ( 67 years , exercise SaO2 > 88 % ) with COPD ( FEV1 = 36 % predicted ) . All exercised on cycle ergometers for 45 minutes , 3 times per week for 7 weeks at high-intensity targets . During exercise , they received oxygen ( 3 L/minute ) ( n = 14 ) or compressed air ( 3 L/minute ) ( n = 15 ) . Both groups had a higher exercise tolerance after training and when breathing oxygen . However , the oxygen-trained group increased the training work rate more rapidly than the air-trained group . The mean + /- SD work rate during the last week was 62 + /- 19 W ( oxygen-trained group ) and 52 + /- 22 W ( air-trained group ) ( p < 0.01 ) . After training , endurance in constant work rate tests increased more in the oxygen-trained group ( 14.5 minutes ) than in the air-trained group ( 10.5 minutes ) ( p < 0.05 ) . At isotime , the breathing rate decreased four breaths per minute in the oxygen-trained group and one breath per minute in the air-trained group ( p = 0.001 ) . We conclude that supplemental oxygen provided during high-intensity training yields higher training intensity and evidence of gains in exercise tolerance in laboratory testing STUDY OBJECTIVES The slow oxygen uptake ( VO(2 ) ) kinetics observed in COPD patients is a manifestation of skeletal muscle dysfunction of multifactorial origin . We determined whether oxygen supplementation during exercise makes the dynamic VO(2 ) response faster and reduces transient lactate increase . DESIGN Ten patients with severe COPD ( ie , mean [ + /- SD ] FEV(1 ) , 31 + /- 10 % predicted ) and 7 healthy subjects of similar age performed four repetitions of the transition between rest and 10 min of moderate-intensity , constant-work rate exercise while breathing air or 40 % oxygen in r and om order . Minute ventilation ( VE ) , gas exchange , and heart rate ( HR ) were recorded breath-by-breath , and arterialized venous pH , PCO(2 ) , and lactate levels were measured serially . RESULTS Compared to healthy subjects , the time constants ( tau ) for VO(2 ) , HR , carbon dioxide output ( VCO(2 ) ) , and VE kinetic responses were significantly slower in COPD patients than in healthy subjects ( 70 + /- 8 vs 44 + /- 3 s , 98 + /- 14 vs 44 + /- 8 s , 86 + /- 8 vs 61 + /- 4 s , and 81 + /- 7 vs 62 + /- 4 s , respectively ; p < 0.05 ) . Hyperoxia decreased end-exercise E in the COPD group but not the healthy group . Hyperoxia did not increase the speed of VO(2 ) kinetics but significantly slowed VCO(2 ) and E response dynamics in both groups . Only small increases in lactate occurred with exercise , and this increase did not correlate with the tau for VO(2 ) . CONCLUSION In nonhypoxemic COPD patients performing moderate exercise , the lower ventilatory requirement induced by oxygen supplementation is not related to improved muscle function but likely stems from direct chemoreceptor inhibition A r and omized , controlled , single-blind study was performed on 20 patients with chronic obstructive pulmonary disease and exercise-induced hypoxaemia . Ten patients each were r and omly assigned to one of two groups , one training with air and the other training with oxygen . There were no significant differences between the groups regarding values measured prior to the study . The patients trained 3 times per week for 30 minutes each time for a duration of 8 weeks . The training consisted of interval walking on a treadmill ( intensity set according to Borg ratings ) with either air or oxygen administered through a nasal cannula at a rate of 5 l/min . Training significantly improved the 6-minute walking distance by 20 % and 14 % in the air and oxygen group , respectively , when the patients were tested on air . In the same test the air group significantly decreased Borg ratings for perceived exertion . Borg ratings for dyspnoea and perceived exertion significantly decreased in the oxygen group when they were tested on oxygen . It was concluded that oxygen supplementation did not further improve the training effect , compared with training with air , in patients with chronic obstructive pulmonary disease and exercise-induced hypoxaemia Supplemental oxygen has acute beneficial effects on exercise performance in patients with chronic obstructive pulmonary disease ( COPD ) . The purpose of this study was to investigate whether oxygen-supplemented training enhances the effects of training while breathing room air in patients with severe COPD . A r and omized controlled trial was performed in 24 patients with severe COPD who developed hypoxaemia during incremental cycle exercise ( arterial oxygen saturation ( Sa , O2 ) < 90 % at peak exercise ) . All patients participated in an in-patient pulmonary rehabilitation programme of 10 weeks duration . They were assigned either to general exercise training while breathing room air ( GET/RA group : forced expiratory volume in one second ( FEV1 ) 38 % of predicted ; arterial oxygen tension ( Pa , O2 ) 10.5 kPa at rest ; Pa , O2 7.3 kPa at peak exercise ) , or to GET while breathing supplemental oxygen ( GET/O2 group : FEV1 29 % pred ; Pa , O2 10.2 kPa at rest ; Pa , O2 7.2 kPa at peak exercise ) . Sa , O2 was not allowed to fall below 90 % during the training . The effects on exercise performance while breathing air and oxygen , and on quality of life were compared . Maximum workload ( Wmax ) significantly increased in the GET/RA group ( mean ( SD ) 17 ( 15 ) W , p<0.01 ) , but not in the GET/O2 group ( 7 ( 25 ) W ) . Six minute walking distance ( 6MWD ) , stair-climbing , weight-lifting exercise ( all while breathing room air ) and quality of life significantly increased in both groups . Acute administration of oxygen improved exercise performance before and after training . Training significantly increased Wmax , peak carbon dioxide production ( V'CO2 ) and 6MWD while breathing oxygen in both groups . Differences between groups were not significant . Pulmonary rehabilitation improved exercise performance and quality of life in both groups . Supplementation of oxygen during the training did not add to the effects of training on room air Dynamic hyperinflation contributes to exertional breathlessness and reduced exercise tolerance in chronic obstructive pulmonary disease ( COPD ) patients . This study examined whether oxygen supplementation results in a dose-dependent decrease in hyperinflation associated with functional and symptomatic improvement . Ten severe COPD patients without clinical ly significant oxygen ( O2 ) desaturation during exercise , and seven healthy subjects , performed five exercise tests at 75 % of maximally tolerated work rate . Inspired oxygen fraction ( FI , O2 ) was varied ( 0.21 , 0.3 , 0.5 , 0.75 and 1.0 ) among tests in a r and omized order . Ventilation ( V'E ) was measured , and end-inspiratory ( EILV ) and end-expiratory ( EELV ) lung volume changes were assessed from inspiratory capacity manoeuvres . In the patients , compared to room air , endurance time increased with FI , O2=0.3 ( mean+/-SEM 92+/-20 % ) and increased further with FI , O2=0.5 ( 157+/-30 % ) . At isotime , compared to room air , there were significant reductions in dyspnoea score , EELV , EILV , V'E and respiratory frequency ( fR ) with FI , O2=0.3 . Improved endurance time negatively correlated with change in EELV ( r=0.48 , p=0.002 ) and EILV ( r=0.43 , p=0.005 ) . The dyspnoea rating decrease correlated with fR decrease . In healthy subjects , smaller V'E and fR decreases were observed at FI , O2=0.5 , accompanied by more modestly increased endurance .  Oxygen supplementation during exercise induced dose-dependent improvement in endurance and symptom perception in nonhypoxaemic chronic obstructive pulmonary disease patients , which may be partly related to decreased hyperinflation and slower breathing pattern . This effect is maximized at an inspired oxygen fraction of 0.5 The effect of oxygen on breathlessness and exercise tolerance was examined in " pink and puffing " patients with fixed airways obstruction . When breathing oxygen , patients were less breathless and walked further . This was true whether the cylinder was carried by the patient or by an assistant . It was not possible to identify those patients who would benefit most . The best method of assessing improvement was by comparing breathlessness on a st and ardised progressive exercise test on a treadmill .  Four patients had a greater than 30 % reduction in breathlessness on submaximum exercise when breathing oxygen . Breathing oxygen for five or fifteen minutes before exercise but not during exercise ( predose ) result ed in a similar improvement in exercise tolerance . For short periods of exercise predosing with oxygen provides a convenient alternative to continuous oxygen . For longer periods of exercise the benefits of portable oxygen in selected patients have been previously underestimated It is unclear whether short-term benefits from supplemental oxygen translate into improved quality of life in patients with severe COPD . In a 12 wk double-blind r and omized crossover study , we assessed the effects of supplemental air and oxygen on exercise performance ( step tests and 6 min walking distance [ 6MWD ] ) initially and after two 6 wk periods at home using exertional cylinder air or oxygen . We measured quality of life at baseline and after the two 6 wk domiciliary periods . The 26 patients ( 24 males ) had a mean age of 73 + /- 6 yr ; mean FEV1 , 0.9 + /- 0.4 L ; mean DLCO , 10.6 + /- 2.4 ml/min/mm Hg ; mean resting PO2 , 69 + /- 8.5 ( range 58 to 82 ) mm Hg ; mean PCO2 , 41 + /- 3.3 mm Hg ; and mean resting SaO2 , 94 + /- 2.1 ( mean + /- SD ) . Laboratory tests were performed breathing intranasal air or oxygen at 4 L/min , and measurements were made of SaO2 and Borg dysnea scores .  Supplemental oxygen increased 6MWD and steps by small , statistically significant increments acutely at baseline and after 6 and 12 wk , without corresponding falls in Borg score . Degree of desaturation at baseline did not correlate with increase in 6MWD or steps achieved at baseline or at 6 or 12 wk , nor with the domiciliary gas used . There was no 
    Output:
    
Long term oxygen therapy ( LTOT ) in resting hypoxaemic COPD patients has physiological benefits ( for example , reversal of polycythemia , improved exercise performance , improved neurological status , reduced pulmonary hypertension ) and together with pulmonary rehabilitation may improve health related quality of life (HRQL).2 - 8 Furthermore only LTOT and smoking cessation have been shown to improve survival in patients with COPD .2'3 In a survey of patients with severe COPD treated with LTOT , 50 % did not leave the house ( MRC dyspnoea grade 5 ) and 78 % were breathless while walking around at home and perforning activities of daily living (ADL).9 In advanced COPD , hypoxaemia usually worsens during exercise and induces a transient but marked elevation of pulmonary artery pressure ( PAP ) .
Breathing oxygen during exercise produces a small but significant fall of PAP and pulmonary vascular resistance .
An attempt to evaluate the efficacy of long term ambulatory oxygen therapy in patients with chronic lung disease on exercise capacity , symptom perception and other relevant measurements of improvement was recently made by a systematic review .11 In this review , 90 abstract s and 17 full text papers were examined but only two trials20'21 investigating the effects of ambulatory oxygen therapy in COPD met the inclusion criteria " 1 and indicated that the treatment of COPD patients with ambulatory domiciliary oxygen therapy failed to show any consistent benefit .
There was no clear effect of oxygen therapy on exercise capacity , dyspnoea , HRQL or lung function .
One study 20 reported significant improvements in minute ventilation and PaO2 that was not reported by the other.2 ' McDonald et al. 21 concluded that although oxygen supplementation induced some acute increments in exercise performance , such improvements had little impact on patients ' ADL .
However their patients did not suffer from severe hypoxaemia and would not have met the criteria for LTOT , unlike the patients of Lilker et al. 20 who concluded that ambulatory oxygen therapy was of more value than placebo in a selected group of COPD patients with cor pulmonale and resting hypoxaemia .