Dose-response effect of oxygen on hyperinflation and exercise endurance innonhypoxaemic COPD patients

Dynamic hyperinflation contributes to exertional breathlessness and reduced exercise tolerance in chronic obstructive pulmonary disease (COPD) patient s. This study examined whether oxygen supplementation results in a dose-dep endent decrease in hyperinflation associated with functional and symptomati c improvement. Ten severe COPD patients without clinically significant oxygen (O-2) desatu ration during exercise, and seven healthy subjects, performed five exercise tests at 75%, of maximally tolerated work rate. Inspired oxygen fraction ( FI.O-2) was varied (0.21, 0.3, 0.5, 0.75 and 1.0) among tests in a randomiz ed order. Ventilation (V 'E) was measured, and end-inspiratory (EILV) and e nd-expiratory (EELV) lung volume changes were assessed from inspiratory cap acity manoeuvres. In the patients, compared to room air, endurance time increased with FI.O-2 =0.3 (mean +/- SEM 92 +/- 20%) and increased further with FI.O-2=0.5 (157 /- 30%). At isotime, compared to room air, there were significant reduction s in dyspnoea score, EELV, EILV, V 'E and respiratory frequency (fR) with F I.O-2=0.3. Improved endurance time negatively correlated with; change in EE LV (r=0.48, p=0.002) and EILV (r=043, p=0.005). The dyspnoea rating decreas e correlated with fR decrease. In healthy subjects, smaller V 'E and fR dec reases were observed at FI.O-2=0.5, accompanied by more modestly increased endurance. Oxygen supplementation during exercise induced dose-dependent improvement i n endurance and symptom perception in nonhypoxaemic chronic obstructive pul monary disease patients, which may be partly related to decreased hyperinfl ation and slower breathing pattern. This effect is maximized at an inspired oxygen fraction of 0.5.