Influence of expiratory flow-limitation during exercise on systemic oxygen delivery in humans

To determine the effects of exercise with expiratory flow-limitation (EFL) on systemic O-2 delivery, seven normal subjects performed incremental exercise with and without EFL at similar to 0.8 1 s(-1) (imposed by a Starling resistor in the expiratory line) to determine maximal power output under control (W-max,W-c) and EFL (W'(max,e)) conditions. W'max was 62.5% Of W-max,W-e and EFL exercise caused a significant fall in the ventilatory threshold. In a third test, after exercising at Wmax,e without EFL for 4 min, EFL was imposed; exercise continued for 4 more minutes or until exhaustion. 02 consumption (V'(O2),) was measured breath-by-breath for the last 90 s of control, and for the first 90 s of EFL exercise. Assuming that the arterio-mixed venous 02 content remained constant immediately after EFL imposition, we used V'(O2), as a measure of cardiac output (Q'c). Q'(c) was also calculated by the pulse contour method with blood pressure measured continuously by a photo-plethysmographic device. Both sets of data showed a decrease of Q'c due to a decrease in stroke volume by 10% (p < 0.001 for V'(O2)) with EFL and remained decreased for the full 90 s. Concurrently, arterial O-2 saturation decreased by 5%, abdominal, pleural and alveolar pressures increased, and duty cycle decreased by 43%. We conclude that this combination of events led to a decrease in venous return secondary to high expiratory pressures, and a decreased duty cycle which decreased O-2 delivery to working muscles by similar to 15%.