The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

LABORATORY EVALUATION OF C-FLEX AS AN ADJUNCT TO CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP).

Dean R. Hess, PhD, RRT, FAARC, William H. Hardy, MPM, RRT. Massachusetts General Hospital and Harvard Medical School, Boston MA; Respironics, Inc, Murrysville, PA.

Background: An issue associated with the use of CPAP for the treatment of obstructive sleep apnea is patient compliance. Several technical features have been introduced to address this issue (e.g., ramp). The purpose of this study was to evaluate the performance of a new CPAP embellishment called C-Flex, which allows a small amount of pressure relief at the beginning of exhalation.

Hypothesis: Use of C-flex provides an adjustable pressure relief at the initiation of the expiratory phase during CPAP.

Methods: A 2chambered lung model was used to simulate spontaneous breathing. The model was set for a compliance of 0.1 L/cm H2O, resistance of 5 cm H2O/L/s, rate 15/min, inspiratory time of 1 s. Pressure and flow were measured immediately proximal to the resistor (Ventrak, Novametrix, Wallingford, CT). CPAP settings of 5, 10, and 15 cm H2O were used with 3 levels of C-Flex (0 = no pressure relief, 3 = maximal pressure relief). For each combination of settings, the following exhalation parameters were measured: time for pressure to return to CPAP after its initial rise at the initiation of exhalation (Time 1), time of pressure relief below CPAP (Time 2), and maximal pressure drop below CPAP. Summary data are provided for 3 breaths.

Results: There was a significant decrease in Time 1 with C-Flex (0.68 ± 0.15 s for setting 0, 0.22 ± 0.04 s for setting 1, 0.21 ± 0.04 s for setting 2, and 0.21 ± 0.06 s for setting 3; P<0.001). There was a significant increase in Time 2 as the C-Flex level was increased (1.0 ± 0.17 s for setting 1, 1.1 ± 0.09 s for setting 2, 1.3 ± 0.2 s for setting 3; P = 0.003). The pressure drop below CPAP was 1.1 ± 0.1 cm H2O for C-Flex setting 1, 1.6 ± 0.4 cm H2O for C-Flex setting 2, and 2.1 ± 0.8 cm H2O for C-Flex setting 3 (P < 0.001). These results are illustrated in the figure.


Conclusions: C-Flex produces a significant pressure relief at the beginning of exhalation. The clinical importance of this in improvement of patient comfort and compliance should be tested further.

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