Feedback control of oxygen uptake during stimulated cycle ergometry in subjects with paraplegia

Regulation of exercise intensity is important for aerobic training and exercise testing. Automatic control of oxygen uptake has potential for exercise prescription and in tests to characterise cardiopulmonary status. Here, the feasibility of closed-loop control of oxygen uptake during stimulated leg-cycling exercise in paraplegia is investigated. A new control structure for this purpose is proposed, consisting of a dynamic feedback controller monitoring target and actual oxygen uptake and adjusting an exercise work rate command signal in real time. A further feedback controller automatically adjusts the stimulation intensity to achieve the commanded work rate. The approach was experimentally evaluated in a subject with paraplegia. Empirical parameter estimation results show considerable day-to-day variability in the oxygen uptake response dynamics. Feedback control tests then demonstrate that the proposed controller provided accurate tracking of the oxygen uptake command profile on separate test days, pointing to an underlying robustness of the feedback design approach against day-to-day variability in the subject´s physiological response. The variance of the oxygen uptake response was considerably lower under closed-loop control than in open-loop conditions. The results of the study provide evidence for the feasibility of feedback control of oxygen uptake during stimulated cycle-ergometer exercise in paraplegic subjects.