The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

THE EFFECT OF ALTERING RISE TIME ON DELIVERED TIDAL VOLUME AND FLOW REQUIRED TO TRIGGER A BREATH WITH THE QUANTUM/PSV VENTILATOR

Randy De Kler, MS. RRT, Jonathan B. Waugh, PhD, RRT, CPFT, Georgia State University, Atlanta, GA

Background: The Quantum/PSV, a recently released ventilator designed for noninvasive ventilatory support, incorporates a new control called "rise time". Rise time controls the time required for set IPAP to be achieved. We examined this device to determine what effect alterations in the rise time setting would have on delivered tidal volume(V_{T}) and the inspiratory flowrate required to trigger a breath. Methods: An carly production model of the Quantum/PSV was used for the study. Data acquisition was made using the Validyne UPC system (Validyne Engineering Corp., Northridge, CA) and a Hans Rudolf pneumotachometer model 3813 (Hans Rudolf, Inc., St. Louis, MO). Calibration of all instruments was completed and all values met ATS (±3%) and ASTM (±2% ) criteria. A Manley test lung (Ohmeda, Madison, WI) served as the lung simulator for the V_{T} measurements with C_{L} 50 ml/cm H_{2}O and R_{AW} 2 cm H_{2}O/L/sec. Quantum/PSV settings were IPAP/EPAP = 20/5, % inspiratory time = 25%, frequency = 10/min. for the V_{} measurements A custom-built, dual chamber lung model was used for the flow trigger measurements. Rise time was changed in 0.1 second increments across most of the range of the parameter (0.2 - 0.9 sec.). Results:

Rise Time

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

V_{T} 404.2 400.5 399.9 398.8 400.1 393.5 391.4 386.9

(S.D.) (0.3) (1.1) (0.4) (0.4) (0.4) (0.2) (0.8) (0.2)

Flow 0.231 0.226 0.235 0.221 0.222 0.203 0.208 0.186

(S.D.)(.001) (.010) (.011) (.005) (.004) (.004) (.002) (.010)

Conclusions: The study data suggest that longer rise time values produce smaller patient V_{t}S at a given IPAP/EPAP setting. This may be due to a lower mean airway pressure associated with more modest flow rates at the longer rise time settings. Changing a patient from a short to a long rise setting may require a slight increase in the pressure boost setting to maintain the previous V_{T} level. The mean flow required to trigger a breath was significantly lower at a rise time of 0.9 seconds than the trigger levels at 0.2, 0.4, and 0.6 second rise time (p < 0.05).

Reference: OF-96-050

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