Effect of immediate-release oral morphine (0.1 mg·kg−1 body mass) versus placebo on physiological and perceptual responses at rest, at a standardised submaximal time during constant-load cycle exercise testing (isotime), and at the symptom-limited peak of constant-load cycle exercise testing in adults with advanced COPD and chronic breathlessness syndrome
| Rest | Isotime | Peak | ||||
| Placebo | Morphine | Placebo | Morphine | Placebo | Morphine | |
| Cycle exercise time min | 5.3±4.5 | 5.3±4.5 | 6.2±4.4 | 8.6±6.5* | ||
| Breathlessness intensity Borg units | 0.6±0.9 | 0.4±0.7 | 4.2±2.6 | 3.0±1.6* | 5.9±2.4 | 5.6±2.2 |
| Breathlessness unpleasantness Borg units | 0.5±0.8 | 0.6±1.2 | 4.5±2.6 | 3.1±1.7** | 6.1±2.5 | 5.6±2.0 |
| Leg discomfort Borg units | 0.5±1.1 | 0.4±0.7 | 3.9±3.2 | 3.7±3.2 | 4.9±3.6 | 5.1±3.4 |
| V′O2 mL·kg·min−1 | 4.5±1.1 | 4.4±1.1 | 11.7±2.4 | 11.3±2.5 | 12.5±2.3 | 12.5±2.5 |
| V′CO2 mL·kg·min−1 | 4.3±1.1 | 4.1±1.1 | 11.1±2.6 | 10.8±2.7 | 12.0±2.5 | 12.1±2.5 |
| Heart rate beats·min−1 | 86±13 | 87±14 | 110±21 | 110±21 | 112±21 | 114±21 |
| V′E L·min−1 | 14.6±2.3 | 14.0±1.9 | 28.9±7.4 | 27.6±7.5* | 30.9±7.2 | 30.6±7.8 |
| VT L | 0.89±0.24 | 0.87±0.25 | 1.12±0.28 | 1.16±0.28 | 1.08±0.29 | 1.14±0.26 |
| fR breaths·min−1 | 18.0±6.2 | 18.0±6.2 | 26.9±7.2 | 24.9±7.3* | 30.2±7.7 | 28.1±7.3* |
| VT/Ti | 0.74±0.16 | 0.72±0.17 | 1.48±0.32 | 1.42±0.31 | 1.60±0.34 | 1.58±0.32 |
| Ti/Ttot | 34.0±5.5 | 34.3±5.4 | 32.8±5.0 | 32.9±4.8 | 33.1±5.2 | 32.6±4.6 |
| IC L | 2.03±0.51 | 2.11±0.50 | 1.43±0.33 | 1.51±0.31 | 1.34±0.30 | 1.38±0.28 |
| Δ IC from rest L | -0.61±0.37 | -0.60±0.31 | -0.70±0.31 | -0.73±0.41 | ||
| IRV L | 1.15±0.43 | 1.25±0.49 | 0.31±0.21 | 0.35±0.19 | 0.26±0.19 | 0.25±0.20 |
| V′E/V′CO2 | 49.3±5.6 | 49.6±6.6 | 37.7±6.7 | 36.9±5.6 | 37.3±6.7 | 38.2±5.5 |
| PETCO2 mmHg | 32.6±2.9 | 33.5±3.2** | 37.5±5.7 | 37.9±5.2 | 37.8±6.0 | 38.2±5.5 |
| SpO2 % | 96±2 | 96±2 | 93±4 | 93±4 | 93±4 | 93±4 |
| Gastro-oesophageal balloon-electrode catheter-derived parameters (n=7) | ||||||
| EMGdi,rms µV | 59.5±37.1 | 47.1±26.3 | 134.2±50.3 | 117.2±50.9 | 161.2±63.8 | 149.8±65.8 |
| EMGdi,rms/V′E µV·L·min−1 | 4.3±2.3 | 3.5±2.0 | 5.2±2.9 | 4.8±2.7 | 5.6±2.9 | 5.4±3.2 |
| EMGdi,rms%max | 28±11 | 23±9 | 64±12 | 59±17 | 76±15 | 74±17 |
| Reasons for stopping exercise | ||||||
| Breathlessness n | 11 | 9 | ||||
| Leg discomfort n | 2 | 4 | ||||
| Breathlessness and leg discomfort n | 5 | 2 | ||||
| Other n | 2 | 5 | ||||
Data are presented as mean±sd, unless otherwise stated. V′O2: rate of oxygen uptake; V′CO2: rate of carbon dioxide production; HR: heart rate; V′E: minute ventilation; VT: tidal volume; fR: breathing frequency; VT/Ti: mean tidal inspiratory flow, where Ti represents inspiratory time; Ti/Ttot: inspiratory duty cycle, where Ttot represents total breath duration; IC: inspiratory capacity; Δ: exercise-induced change; IRV: inspiratory reserve volume; V′E/V′CO2: ventilatory equivalent for carbon dioxide; PETCO2: partial pressure of end-tidal carbon dioxide; SpO2: oxygen saturation by pulse oximetry; EMGdi,rms: root mean square of the crural diaphragm electromyogram; EMGdi,rms%max: EMGdi,rms expressed as a percentage of maximum voluntary EMGdi,rms. *: p<0.05 and **: p<0.01 versus placebo.