Implementation of a respiratory drive monitor on a Servo Ventilator

Objective. To design and evaluate a clinical monitor of respiratory drive ( P-0.1) and other respiratory variables in a simple way, using a commercial ventilator. Methods. Nine healthy males were studied as they were breathing spontaneously in a Servo 900C Ventilator, at rest and during light exercis e (50 W). The ventilator was slightly modified to improve its mechanical pe rformance during spontaneous breathing, and was used as a measuring instrum ent. All the relevant information was retrieved, calculated and monitored b y a PC. Respiratory drive was assessed as occlusion pressures from the insp iratory airway pressure signal. The equipment was compared with a two-way n on-rebreathing laboratory system. Furthermore, negative and positive inspir atory pressures were applied from the ventilator, to study respiratory resp onses to mechanical loads. Results. At rest, the ventilator introduced a mi nor influence on inspiratory time and P-0.1, 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 coeff icients of variation. The responses to mechanical loads were easily recorde d and can be used as a simple test of central load-compensating mechanisms. Conclusions. The ventilator, with limitations, may be an alternative to co nventional techniques, especially in clinical studies of the central inspir atory activity with and without respiratory loading.