Arterial oxygen desaturation during treadmill and bicycle exercise in patients with chronic obstructive airways disease

Abstract

Nine men with severe chronic obstructive airways disease (COAD), known to desaturate on exercise, performed a 6 min self-paced walk on a treadmill, followed by a bicycle exercise with workloads adjusted to mimic the oxygen consumption achieved on the treadmill. During both exercises ventilation, O2 consumption, CO2 production, PaO2 [partial arterial pressure O2], PaCO2, pH and arterial lactate were measured and subjective breathlessness recorded. A reasonable match of O2 consumption between the 2 exercises was achieved. In all subjects PaCO2 fell to a lower level during treadmill compared with bicycle exercise. Ventilation, CO2 production and arterial lactate were higher during bicycle exercise. Subjective breathlessness was greater during bicycle exercise, in proportion to the higher ventilation on the bicycle. The greater anaerobiosis occurring on the bicycle led to acidosis and an increased ventilation, minimizing the exercise fall in PaCO2. Bicycle testing may seriously underestimate exercise desaturation occurring during level walking in patients with severe COAD.