DO TURBINES WITH SERVO-CONTROLLED SPEED IMPROVE CONTINUOUS POSITIVE AIRWAY PRESSURE GENERATION

Nasal continuous positive airway pressure (CPAP) devices with a servo- mechanism to control pressure have recently been developed. We evaluat ed sir such devices and three conventional systems in terms of effecti veness in maintaining constant pressure. Machines were tested with pre ssure levels of 5, 10 and 15 cmH(2)O. Dynamic behaviour was evaluated: 1) by calculating the imposed work of breathing during simulated brea th generated by a sinusoidal pump; and 2) by following the fall in pre ssure after a transient flow of 1 l.s(-1). Quasi-static behaviour was evaluated by simulating a predetermined air leak. Under dynamic condit ions, work of breathing was lowest with one conventional nasal CPAP de vice and three servo-controlled nasal CPAP devices; whereas, the highe st levels of work of breathing were recorded with two servo-controlled nasal CPAP devices. The pressure-time response to a transient flow yi elded similar results, with a significant inverse correlation between pressure values observed after 300 ms and imposed work of breathing du ring simulated breathing (r = -0.91). Under quasi-static conditions, m icroprocessor servo-controlled devices exhibited the best performance. These results suggest that microprocessor servo-controlled nasal CPAP devices are not always the best systems for maintaining constant airw ay pressure in dynamic situations. However, they are more effective in ensuring maintenance of the desired pressure in the event of an air l eak at the mask.