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.