[The rate of isometric inspiratory pressure change as a measure for the CO2 sensitivity of the respiratory center in patients with obstructive lung disease].

In healthy persons with and without loaded breathing, in asthmatics, and in patients with chronic obstructive lung disease (COLD) the rate of isometric inspiratory pressure development ([dp/dt]max) has been measured in order to assess the clinical significance of (dp/dt)max as an index of the motor output of the respiratory center in response to increased levels of carbon dioxide. During unloaded breathing normal subjects showed an excellent correlation between the ventilatory and the (dp/dt)max responses to CO2. Normal persons breathing through an external expiratory flow resistance, the asthmatics, and the patients with COLD had not only a blunted ventilatory response, but also a reduced (dp/dt)max response. The parallel changes observed in both variables indicate that under conditions of mechanical loading the (dp/dt)max does not exclusively reflect the motor output of the respiratory center, but is influenced by other factors such as the work of breathing and the mechanical efficiency of the respiratory pump. Accordingly, measurements of (dp/dt)max are of little help in deciding whether the development of CO2 retention in patients with obstructive airway disease is primarily due to increased mechanical load or to decreased sensitivity of the respiratory center.