Implementation of a respiratory drive monitor on a Servo Ventilator

To design and evaluate a clinical monitor of respiratory drive (P0.1) and other respiratory variables in a simple way, using a commercial ventilator.

Nine healthy males were studied as they were breathing spontaneously in a Servo 900C Ventilator, at rest and during light exercise (50 W). The ventilator was slightly modified to improve its mechanical performance during spontaneous breathing, and was used as a measuring instrument. All the relevant information was retrieved, calculated and monitored by a PC. Respiratory drive was assessed as occlusion pressures from the inspiratory airway pressure signal. The equipment was compared with a two-way non-rebreathing laboratory system. Furthermore, negative and positive inspiratory pressures were applied from the ventilator, to study respiratory responses to mechanical loads.

At rest, the ventilator introduced a minor influence on inspiratory time and P0.1, but not in ventilation, tidal volume, expiratory duration and respiratory frequency. During exercise, the influence was more evident. This effect could also be noticed in the coefficients of variation. The responses to mechanical loads were easily recorded and can be used as a simple test of central load-compensating mechanisms. CONCLUSIONS. The ventilator, with limitations, may be an alternative to conventional techniques, especially in clinical studies of the central inspiratory activity with and without respiratory loading.