An analysis of respiratory drive components during flow-resistive respiratory loading

Inspiratory flow-resistive loading normally causes an additional respiratory drive that limits the resistance-induced decrease in minute ventilation (load compensation). Occlusion pressures (P₁₀₀) were measured during CO₂ rebreathing with and without added inspiratory loads in normal persons and persons with obstructive sleep apnea (OSA). At each point obtained during loaded breathing, the additional drive due to resistive loading was determined by subtracting CO₂-dependent drive (estimated from the nonloaded run) from total drive. In normal subjects, the additional drive correlated with each of four different estimates of load magnitude. In OSA subjects, there was no significant increase in drive due to loading and ventilation decreased markedly during loading. The relationships among ventilation rate, load, and drive, with and without load compensation, were analyzed using a 4-quadrant feedback control diagram. The diagram enables the prediction of ventilation rate for any end-tidal CO₂ in the loaded and nonloaded cases, and the flow decrement that will occur as a result of added inspiratory resistance.