Response to ventilatory obstruction during steady-state exercise

Five normal male subjects, 27–37 years of age, were studied during steady-state treadmill exercise to observe the effects of varying expiratory airway obstruction on minute volume, oxygen consumption and carbon dioxide elimination. A 5-mm-diameter resistance produced significant depressions in minute volume for the duration of the obstructed period. Carbon dioxide elimination showed significant reductions during the first 6 minutes of breathing against resistance. Oxygen uptake, however, was reduced significantly only during the 1st minute of obstructed breathing, but the reduction was great enough so that, despite subsequent rises in oxygen uptake, an ‘oxygen debt’ had already been incurred for the total period of obstruction. Following removal of the resistance, all these values rebounded to levels above those of the original steady state. The physiological mechanisms possibly effecting the response to obstruction are discussed.