LAUSR

We questioned whether the respiratory muscles of humans contribute to systemic oxidative stress following inspiratory flow resistive breathing, if the amount of oxidative stress is influenced by the level of resistive load, and whether the amount of oxidative stress is related to the degree of diaphragm fatigue incurred. Eight young and healthy participants attended the laboratory for 4 visits on separate days. During the first visit, height, body mass, lung function and maximal inspiratory mouth and transdiaphragmatic pressure (Pdimax) were assessed. During visits 2-4, participants undertook inspiratory flow resistive breathing with either no resistance (Control) or resistive loads equivalent to 50 and 70% of their Pdimax (Pdimax50% and Pdimax70%) for 30 min. Participants undertook 1 resistive load per visit, and the order that they undertook the loads was randomized. Inspiratory muscle pressures were higher (P < 0.05) during the 5th and final min of Pdimax50% and Pdimax70% compared to Control. Plasma F2-isoprostanes increased (P < 0.05) following inspiratory flow resistive breathing at Pdimax70%. There were no increases in plasma protein carbonyls and total antioxidant capacity. Further, although we evidenced small reductions in transdiapragmaic twitch pressures (PdiTW) after inspiratory flow resistive breathing at Pdimax50% and Pdimax70%, this was not related to the increase in plasma F2-isoprostanes. Our novel data suggest that only when sufficiently strenuous, inspiratory flow resistive breathing in humans elicits systemic oxidative stress evidenced by elevated plasma F2-isoprostanes, and based on our data this is not related to a reduction in PdiTW.