PURPOSEFlutter therapy uses a handheld instrument that consists of a pipe-like device with a ball in the central core that oscillates during exhalation, providing oscillating positive expiratory pressure. The purpose of this study was to determine the effect of airflow and the incline of the device at the mouth on expiratory pressure and oscillation frequency.METHODSA Flutter device was attached to a circuit that consisted of a pneumotachograph and a ventilator. The ventilator generated different flows and expiratory pressure was measured with a pressure transducer. The angles considered were +40° to −40° in increments of 10°, with the reference for incline being the horizontal line. Expiratory pressure, airflow, angle of incline, and oscillation frequency were measured.RESULTSThere was a strong and significant correlation between flow and expiratory pressure at each level of incline (P≤ .006; r > 0.93). There also was a significant and strong correlation between expiratory pressure and oscillation frequency (P<.05; r = 0.81–0.97). There was a significant reduction in expiratory pressure at a negative incline of −40°.CONCLUSIONSThe results of this study indicate that a positive incline and a large airflow result in an increase in expiratory pressure. This information will assist clinicians to better understand the effects of the Flutter device.