Effect of Resistive Load on the Inspiratory Work and Power of Breathing during Exertion

The resistive work of breathing against an external load during inspiration (WR_I) was measured at the mouth, during sub-maximal exercise in healthy participants. This measure (which excludes the elastic work component) allows the relationship between resistive work and power, ventilation and exercise modality to be explored. A total of 45 adult participants with healthy lung function took part in a series of exercise protocols, in which the relationship between WR_I, power of breathing, PR_I and minute ventilation, were assessed during rest, while treadmill walking or ergometer cycling, over a range of exercise intensities (up to 150 Watts) and ventilation rates (up to 48 L min⁻¹) with applied constant resistive loads of 0.75 and 1.5 kPa.L.sec⁻¹. Resting WR_I was 0.12 JL⁻¹ and PR_I was 0.9 W. At each resistive load, independent of the breathing pattern or exercise mode, the WR_I increased in a linear fashion at 20 mJ per litre of , while PR_I increased exponentially. With increasing resistive load the work and power at any given increased exponentially. Calculation of the power to work ratio during loaded breathing suggests that loads above 1.5 kPa.L.sec⁻¹ make the work of resistive breathing become inhibitive at even a moderate (>30 L sec⁻¹). The relationship between work done and power generated while breathing against resistive loads is independent of the exercise mode (cycling or walking) and that ventilation is limited by the work required to breathe, rather than an inability to maintain or generate power.