Higher skeletal muscular metabolic reserve capacity in COPD patients than healthy subjects.

We investigated the interaction between skeletal muscle exercise capacity and central restrictions using exercise modalities, which recruit differing levels of muscle mass in eight patients chronic obstructive lung disease (COPD) (FEV(1)% of predicted; 35 [SE 4%]) and eight healthy controls. Subjects performed conventional bicycling, two-leg knee extensor (2-KE) and single-leg knee extensor (1-KE) exercises. Maximal values for pulmonary VO(2) (VO(2max)), power output, blood lactate, heart rate, blood pressure, and arterial oxygen saturation of hemoglobin were registered. VO(2max) in controls was 2453 (210), 1468 (124), and 976 (76) mL/min during bicycling, 2-KE and 1-KE, respectively. The COPD patients achieved 48% (P<0.05), 62% (P<0.05), and 81% (P=0.10) of the control values. The mass-specific VO(2max) (VO(2max)/exercising muscle mass) during 1-KE was 345 (25) and 263 (30) mL/kg/min (P<0.05) in controls and COPD patients, respectively. During 2-KE the controls and COPD patients achieved 85% (4%) and 67% (5%) (P=0.06) of the mass-specific VO(2) during 1-KE, while during bicycling they achieved 31% (2%) and 17% (1%) (P<0.05), respectively. The COPD patients have central restrictions when exercising with a relatively small muscle mass (2-KE) and have a higher muscular metabolic reserve capacity than controls during whole body exercise.

Hypoxaemia in chronic obstructive pulmonary disease patients during a commercial flight.

The aim of the study was to investigate hypoxaemia in chronic obstructive pulmonary disease patients during a commercial flight. The effect of a commercial flight, lasting 5 h 40 min, on arterial blood gas levels and symptoms in 18 chronic obstructive pulmonary disease patients with a pre-flight percutaneous oxygen saturation of 94% and self-reported ability to walk 50 m without severe dyspnoea was studied. The arterial oxygen tension (Pa,O2) decreased from sea level to cruising altitude (10.3+/-1.2 versus 8.6+/-0.8 kPa), but, thereafter, except for one patient, remained stable throughout the flight. During light exercise, however, there was further desaturation (percutaneous oxygen saturation 90+/-4 versus 87+/-4%). After 4 h, a decrease in arterial carbon dioxide tension (5.0+/-0.4 versus 4.8+/-0.4 kPa) and an increase in cardiac frequency (87+/-13 versus 95+/-13 beats x min(-1)) were observed. A pre-flight Pa,O2 of >9.3 kPa did not secure an acceptable in-flight Pa,O2. Aerobic capacity showed the strongest correlation with in-flight Pa,O2. In conclusion, following an initial decrease in arterial oxygen tension, chronic obstructive pulmonary disease patients in a stable state of their disease seem to maintain a stable arterial oxygen tension throughout a flight of intermediate duration, except when walking along the aisle. However, a decrease in arterial carbon dioxide tension, indicating compensatory hyperventilation, could imply a risk of respiratory fatigue during longer flights.

Relationship between exercise desaturation and pulmonary haemodynamics in COPD patients.

Pulmonary hypertension (PH) in patients with chronic obstructive pulmonary disease (COPD) has traditionally been explained as an effect of hypoxaemia. Recently, other mechanisms, such as arterial remodelling caused by inflammation, have been suggested. The aim of this study was to investigate whether exercise-induced PH (EIPH) could occur without concurrent hypoxaemia, and whether exercise-induced hypoxaemia (EIH) was regularly accompanied by increased pulmonary artery pressure or pulmonary vascular resistance index (PVRI). Pulmonary haemodynamics in 17 patients with COPD of varying severity, but with no or mild hypoxaemia at rest, were examined during exercise equivalent to the activities of daily living (ADL) and exhaustion. EIPH occurred in 65% of the patients during ADL exercise. Pulmonary arterial pressure during exercise was negatively correlated with arterial oxygen tension, but EIPH was not invariably accompanied by hypoxaemia. Conversely, EIPH was not found in all patients with EIH. The resting PVRI was negatively correlated with arterial oxygen tension during ADL exercise, but an elevated PVRI without EIH occurred in 35% of the patients. In conclusion, exercise-induced pulmonary hypertension occurred during exercise equivalent to the activities of daily living in chronic obstructive pulmonary disease patients with no or mild hypoxaemia at rest. Although pulmonary artery pressure and arterial oxygen tension were negatively correlated during exercise, a consistent relationship between hypoxaemia and pulmonary hypertension could not be demonstrated. This may indicate that mechanisms other than hypoxaemia contribute significantly in the development of pulmonary hypertension in these patients.

Effect of exercise mode on oxygen uptake and blood gases in COPD patients.

Patients with chronic obstructive pulmonary disease (COPD) are characterised by decreased exercise tolerance, and, more variably, exercise induced hypoxaemia (EIH). Evaluation of physical work capacity and physiological responses to exercise may be performed by various procedures, but there are diverging opinions as to which exercise test should be preferred. In the current study, oxygen uptake and arterial blood gases in COPD patients have been compared during submaximal and maximal exercise on treadmill and ergometer bicycle. Treadmill exercise resulted in higher peak oxygen uptake than bicycle exercise (1111+/-235 vs. 987+/-167 ml min(-1), P<0.02), while the plasma lactate levels were higher during cycling (1.8+/-0.8 vs. 3.8+/-1.7 mmol l(-1), P<0.001). Neither carbon dioxide output, ventilation, nor rate of perceived exertion (Borg RPE scale) showed significant differences between the two modes of exercise. The EIH during both maximal (delta Sa,O2 = -5.6+/-4.2 vs. -3.4+/-5.1%) and sub-maximal exercise was more pronounced during treadmill walking than during cycling. The present study indicates that the VO2peak in COPD patients is higher, the maximal lactate concentrations lower and the development of EIH more pronounced when exercise testing is performed on a treadmill than on a bicycle ergometer.