Drive and performance of ventilatory system during rebreathing.

In eight normal subjects, eight patients with asthma, and six patients with chronic obstructive lung disease, the first derivative of occlusion pressure at FRC during rebreathing has been studied. The maximal dP/dt was always lower in patients. Such a behavior may depend on reduced neuronal discharge as well as on reduced effectiveness of the contraction of the respiratory muscles. Though (dP/dt)max. may provide a reliable measure of the sensitivity of the respiratory center only in a homogeneous group, the results of plotting its value against ventilation and end-tidal Pco2 confirm the failure of the thoracomuscular system to convert the output of respiratory centers into increase of pulmonary pressure and ventilation.