COMPARISON OF THE EFFICACY OF A DEMAND OXYGEN DELIVERY SYSTEM WITH CONTINUOUS LOW-FLOW OXYGEN IN SUBJECTS WITH STABLE COPD AND SEVERE OXYGEN DESATURATION ON WALKING

Background - Provision of ambulatory oxygen using an intermittent puls ed flow regulated by a demand oxygen delivery system (DODS) greatly in creases the limited supply time of standard portable gaseous cylinders . The efficacy of such a system has not previously been studied during submaximal exercise in subjects with severe chronic obstructive pulmo nary disease (COPD) in whom desaturation is likely to be great and whe re usage is often most appropriate. Methods - Fifteen subjects with se vere COPD and oxygen desaturation underwent six minute walk tests perf ormed in random order to compare the efficacy of a demand oxygen deliv ery system (DODS) with continuous flow oxygen. Walk distance, breathle ssness, oxygen saturation, resting time, and recovery time (objective and subjective) were recorded and compared for each walk. Results - Br eathing continuous oxygen compared with baseline air breathing improve d mean walk distance (295 m versus 271 m) and recovery time (47 second s versus 112 seconds), whilst the lowest recorded saturation (81% vers us 74%) and time desaturated below 90% (201 seconds versus 299 seconds ) were reduced. When the DODS was compared with air breathing only the walk distance changed (283 m versus 271 m). A comparison of the DODS with continuous oxygen breathing showed the DODS to be less effective at oxygenating subjects with inferior lowest saturation (78% versus 81 %), time spent below 90% (284 seconds versus 201 seconds), time to obj ective recovery (83 seconds versus 47 seconds), and walk distance (283 m versus 295 m). Conclusions - Neither of the delivery systems was ab le to prevent desaturation in these subjects. The use of continuous fl ow oxygen, however, was accompanied by improvements in oxygenation, wa lk distance, and recovery time compared with air breathing. The DODS p roduced only a small increase in walk distance without elevation of ox ygen saturation, but was inferior to continuous flow oxygen in most of the measured variables when compared directly.