Performance Comparison of Two Oscillating Positive Expiratory
Pressure Devices: Acapella Versus Flutter
Teresa A Volsko RRT FAARC, Juliann M DiFiore, and Robert L Chatburn RRT FAARC
BACKGROUND: Oscillatory positive expiratory pressure (PEP) with the Flutter device facilitates
secretion removal. In the Flutter a steel ball vibrates inside a cone, causing air flow vibration. A new
device, the Acapella, uses a counterweighted plug and magnet to create air flow oscillation. The
Acapella comes in 2 models: one for patients with expiratory flow > 15 L/min and one for < 15
L/min. We hypothesized that the Acapella and Flutter would produce similar mean PEP, oscillatory
pressure amplitude, and frequency over a clinically relevant range of flows. METHODS: We
measured oscillatory amplitude, PEP, and frequency. Values for frequency, peak, trough, and mean
pressure were recorded automatically every 3 seconds at flows of 5, 10, 15, 20, 25, and 30 L/min. The
pressure waveform for 1 second was also graphically displayed and recorded. The devices were
adjusted to give low, medium, and high mean expiratory pressure (Flutter angle at 0, 20, and 40°;
Acapella by dial setting). Data were analyzed by 2-way repeated measures analysis of variance, and
differences were considered significant when p was < 0.05. RESULTS: There were statistically
significant differences between the devices for mean pressure, pressure amplitude, and frequency,
for all experimental conditions. However, the differences were relatively small and may not be
clinically important. Both devices produced similar pressure waveforms at the medium flows. At 5
L/min the Acapella produced a more stable waveform, with a lower frequency, higher amplitude,
and a slightly wider range of PEP than the Flutter. CONCLUSIONS: Acapella and Flutter have
similar performance characteristics. Acapella’s performance is not gravity-dependent (ie, dependent on device orientation) and may be easier to use for some patients, particularly at low expiratory flows. Key words: oscillatory, oscillation, positive expiratory pressure, PEP, Acapella, Flutter,
secretion clearance. [Respir Care 2003;48(2):124 –130]
Introduction
Many disease processes interfere with normal mucociliary
clearance and require airway clearance techniques to facili-
Teresa A Volsko RRT FAARC was affiliated with University Hospitals
of Cleveland, Case Western Reserve University, Cleveland, Ohio at the
time of this study, but is now affiliated with Advanced Health Systems,
Hudson, Ohio. Juliann M DiFiore is affiliated with the Department of
Pediatrics, University Hospitals of Cleveland, Case Western Reserve
University, Cleveland, Ohio. Robert L Chatburn RRT FAARC is affiliated with the Respiratory Care Department, University Hospitals of Cleveland, and the Department of Pediatrics, Case Western Reserve University, Cleveland, Ohio.
Teresa A Volsko RRT FAARC presented a version of this report at the
OPEN FORUM of the AARC’s 46th International Respiratory Congress,
October 7–10, 2000, Cincinnati, Ohio.
Correspondence: Teresa A Volsko RRT FAARC, Advanced Health
Systems, 561 East Hines Rd, Hudson OH 44236. E-mail: tvolsko@
advancedhealthsystems.com.
124
tate secretion removal. Several types of airway clearance adjuncts are commercially available to aid in mucus mobilization and expectoration. We conducted a laboratory evaluation
of 2 airway clearance devices that combine high-frequency
air flow oscillations with positive expiratory pressure (PEP).
The Flutter (Scandipharm, Birmingham, Alabama) has
been evaluated clinically and found to aid in mucus production and have similar effects on oxygen saturation,
pulmonary function, hospital length of stay, arterial blood
gas values, and symptom scores, compared with other conventional forms of airway clearance such as chest physiotherapy, autogenic drainage, and active cycle of breathing
technique.1– 4 The Flutter has a perforated cap that contains
an inner cone and a steel ball. As exhaled gas passes
through the device, the steel ball vibrates vertically within
its casing, causing air flow vibrations or oscillations. The
angle at which the device is held by the patient affects the
amount of effort needed to cause the steel ball to vibrate,
which affects the expiratory flow and thus controls the
frequency and amplitude of the oscillations and PEP.5
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PERFORMANCE COMPARISON
OF
TWO OSCILLATING POSITIVE EXPIRATORY PRESSURE DEVICES
Fig. 1. The Flutter (top) and the Acapella (bottom). The Acapella’s
positive expiratory pressure (PEP) level is adjusted with a dial on
the distal end of the device (bottom right).
The Acapella (DHD Healthcare, Wampsville, New York)
combines the principles of high-frequency oscillation and
PEP by employing a counterweighted lever and magnet.
Exhaled gas passes through a cone, which is intermittently
occluded by a plug attached to the lever, producing air
flow oscillations. A knob located at the distal end of the
device adjusts the proximity of the magnet and counterweighted plug, thereby adjusting the frequency, amplitude,
and mean pressure. The Acapella is available in 2 models:
a green device for patients who can sustain at least 3
seconds of expiratory flow ⱖ 15 L/min, and a blue device
for patients with expiratory flow ⱕ 15 L/min.
Both the Flutter and the Acapella generate PEP and
oscillations by the opposition to flow produced by an obturator acting with a metered force. The Flutter uses the
force of gravity. The Acapella uses the force of magnetic
attraction.
The objective of our laboratory evaluation was to compare the pressure waveforms generated by the Flutter and
the Acapella. We hypothesized that the Acapella and Flutter would produce similar mean expiratory pressure (PEP),
oscillatory pressure amplitude, and frequency over a range
of flow and PEP settings.
Methods
Equipment Set-up
Figure 1 shows the 2 devices. They were evaluated at
discrete, constant flows from a compressed oxygen source
connected to 2 standard medical oxygen flow meters (in
parallel, to achieve the desired flow range). One end of a
0.95-cm (inner diameter) ⫻ 2.5 cm piece of tygon tubing
RESPIRATORY CARE • FEBRUARY 2003 VOL 48 NO 2
Fig. 2. Experimental setup.
was attached to the nut and nipple adapter on each flow
meter and the other end to a 0.95-cm (inner diameter)
Y-piece. A 0.95-cm (inner diameter) ⫻ 7.6 cm piece of
tygon tubing was attached to the distal end of the Y-piece
and connected the flow sources together. Rubber flex adapters were used to connect the flow source to the data acquisition system and airway clearance device in series (Fig. 2).
Positive Expiratory Pressure and Flow Settings
The devices were adjusted to give low, medium, and
high range PEP (Table 1). The Flutter, which is available
in only one model, was tested across the full range of
flows (5–30 L/min). A flow range of 5–15 L/min was used
with the blue Acapella. A range of 20 –30 L/m was used
with the green Acapella. Flows of 5, 10, 15, 20, 25, and 30
L/min were tested with each of the PEP settings. The angle
at which the Flutter was secured (0, 20, and 40°) corresponded to PEP settings of low, medium, and high, respectively. The PEP level of the Acapella was varied by
setting the dial. A ring stand with a claw clamp was used
to set and maintain the angle at which the Flutter was held
throughout the experiment. The Flutter PEP level was varied by altering the angle of the device relative to the laboratory countertop (0° was parallel with the countertop). A
protractor was used to set the angle at which the Flutter
was secured. Both Acapella devices were studied with the
long axis parallel to the counter.
Indicator marks on the Acapella were used as reference
points for PEP settings. The middle mark designated me-
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PERFORMANCE COMPARISON
Table 1.
TWO OSCILLATING POSITIVE EXPIRATORY PRESSURE DEVICES
Experimental Conditions Used to Evaluate Oscillatory PEP
Devices
Device
Low PEP
Medium PEP
High PEP
OF
Flows (L/min)
PEP Setting
Flutter
5, 10, 15, 20, 25, 30
0°
Acapella (blue)
5, 10, 15
Fully
counterclockwise
Acapella (green)
20, 25, 30
Fully
counterclockwise
Flutter
5, 10, 15, 20, 25, 30
20°
Acapella (blue)
5, 10, 15
Middle mark
Acapella (green)
20, 25, 30
Middle mark
Flutter
5, 10, 15, 20, 25, 30
40°
Acapella (blue)
5, 10, 15
Fully clockwise
Acapella (green)
20, 25, 30
Fully clockwise
PEP ⫽ positive expiratory pressure
ure 3 are for the interaction effect from the analysis of
variance. Table 2 summarizes the data from Figure 3.
Relation Between Mean Expiratory
Pressure and Flow
Though there was a significant difference between the 2
devices in terms of mean pressure, the differences appear
to be clinically unimportant. Both devices showed a significant effect (p ⬍ 0.001) of flow on mean expiratory
pressure (ie, PEP). Mean pressure increased as flow increased, but the effect was rather small. In fact, the devices
act more like threshold resisters than flow resister positive
end-expiratory pressure valves.6 The Acapella produced
slightly higher pressures than the Flutter at the high setting.
Relation Between Pressure Amplitude and Flow
dium PEP. The marks furthest clockwise and counterclockwise designated high and low PEP, respectively.
Acapella produced higher amplitudes at the medium
and high settings but not at the low setting. The differences
were several centimeters of water pressure at some flow
levels, which may be clinically important.
Data Acquisition
Relation Between Oscillatory Frequency and Flow
Oscillation amplitude, mean pressure (PEP), and frequency were measured with data acquisition software designed for blood pressure measurement (Biosystems XA,
Buxco Electronics, Sharon, Connecticut). The sample rate
was 200 Hz. Digital values for frequency, peak, trough,
and mean pressure were recorded automatically every 3
seconds, yielding a table of 13 data points for each variable. The first 3 data points for each experimental condition were used for the statistical analysis. The pressure
waveform for 1 second was also graphically displayed and
recorded.
Statistical Analysis
Data were analyzed using commercially available software (Excel, Microsoft, Redmond, Washington, and SigmaStat, SPSS, Chicago, Illinois). Mean values for frequency,
mean pressure, and amplitude were calculated from 3 data
points for each experimental condition of flow and PEP
setting. Two-way analysis of variance for repeated measures was used to compare the outputs of the 2 devices
across the range of flows. Differences were considered
statistically significant when p ⬍ 0.05.
Results
Figure 3 shows the mean values for frequency, amplitude, and mean pressure across the range of flows and PEP
settings. The standard deviations for all measurements were
negligible and thus are not included. The p values in Fig-
126
Though there was a significant difference in frequency,
the effect was small for most experimental conditions.
However, the Flutter produced frequencies from 1–5 Hz
higher than the Acapella at the medium setting. Five Hz
represents 17% of the maximum frequency of these devices (see Table 2), which may be large enough to produce
a clinical effect when coupled with the Flutter’s tendency
to produce lower amplitudes. The effect of flow level on
frequency was only significant at the high setting, but,
again, there would seem to be little clinical importance.
The graphical representation of each airway clearance
device’s amplitude and frequency during the 1-second sampling period for each flow and PEP setting was randomly
selected and printed. We selected representative waveforms for Figures 4 and 5. From visual inspection, the
Acapella and the Flutter produce similar waveforms at the
medium flows (see Fig. 4). The Acapella, however, produced a more regular waveform (ie, more like a simple
sine wave) at the high flows (see Fig. 5).
Discussion
Oscillating PEP (OPEP) is designed to be used with a
steady expiratory maneuver. In the clinical setting patients
are instructed to take a slightly larger than normal tidal
volume breath but not to completely fill the lungs, then to
maintain a steady exhalation for at least 4 seconds but not
to exhale all the way down to functional residual capacity.
Thus, the OPEP maneuver is different from the forced
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PERFORMANCE COMPARISON
OF
TWO OSCILLATING POSITIVE EXPIRATORY PRESSURE DEVICES
Fig. 3. Mean values for frequency, pressure, and amplitude displayed across the range of flows and positive expiratory pressure (PEP)
settings tested. The standard deviations were negligible. The p values are for the interaction effects from analysis of variance.
expiratory maneuver performed during pulmonary function testing. However, a consideration of pulmonary function results from sick patients guided our selection of flows
for the bench study. We reasoned that exhaled volume
would be somewhere between a large tidal volume (eg, 10
Table 2.
Data Summary
Variable
Mean expiratory pressure (cm H2O)
Pressure amplitude (cm H2O)
Oscillatory frequency (Hz)
Device
Acapella
Acapella
Flutter
Acapella
Acapella
Flutter
Acapella
Acapella
Flutter
(blue)
(green)
(blue)
(green)
(blue)
(green)
Range
3–24
6–21
5–19
3–11
1–12
2–10
8–25
13–30
15–29
RESPIRATORY CARE • FEBRUARY 2003 VOL 48 NO 2
mL/kg) and a forced vital capacity available in patient
charts. We have observed very sick cystic fibrosis patients
who have forced vital capacity of ⬍ 1.0 L but are still able
to perform OPEP. On the other extreme, we have seen
cystic fibrosis patients who use OPEP and have forced
vital capacity around 2.0 L. Thus, a low value for expiratory flow would be approximately 10 mL/kg ⫻ 40 kg ⫽
400 mL over 4 seconds or about 6 L/min. A high value
would be 2.0 L exhaled in 4 seconds ⫽ 30 L/min. We
selected a flow range of 5–30 L/min for the study. We
validated this selection by measuring the mean expiratory
flow during simulated OPEP maneuvers with 3 pediatric
patients with cystic fibrosis ranging from mild to severe.
The average flow ranged from 13 to 24 L/min. On a normal adult volunteer we observed a mean expiratory flow
of 18 –37 L/min. Actual expiratory maneuvers would result in an exponential decay flow waveform within these
flow limits, with much of the expiratory time at lower than
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PERFORMANCE COMPARISON
OF
TWO OSCILLATING POSITIVE EXPIRATORY PRESSURE DEVICES
Fig. 4. Representative pressure waveforms for Flutter and Acapella at the medium flows (10 and 25 L/min). The waveforms are comparable
for amplitude and frequency.
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PERFORMANCE COMPARISON
OF
TWO OSCILLATING POSITIVE EXPIRATORY PRESSURE DEVICES
Fig. 5. Representative pressure waveforms for Flutter and Acapella at the low and high flows (5 and 30 L/min). The Acapella produced a
more stable waveform, with a higher amplitude and lower frequency.
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PERFORMANCE COMPARISON
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TWO OSCILLATING POSITIVE EXPIRATORY PRESSURE DEVICES
average flow. Observing the devices’ behavior at constant
flows describes the performance envelope for exponential
flows.
Both Flutter and Acapella can be thought of as simply
“black boxes” that take a flow input and deliver a pressure
waveform output. Hence, the relation between flow and
pressure waveform characteristics (mean, amplitude, and
frequency) was the basis of our comparison. We can only
speculate about the relative clinical effects of these devices. However, such speculation can be founded on both
clinical and bench data.7 Specifically, the patient supplies
the flow, which is periodically occluded (partially or completely) so that the flow approaches zero in the device.
Consequently, the flow energy is transformed to stagnation pressure, causing pressure to increase and expiratory
flow to decrease. We speculate that enhanced mucus clearance has a lot to do with the increased acceleration and
short bursts of high flows that result when the pressure that
builds up behind the occlusion is released; the higher the
pressure build-up, the higher the subsequent flow burst.
This pressure builds up because of the tension in the elastic components of the lungs, relaxation of inspiratory muscles, and contraction of expiratory muscles. During the
short bursts of expiratory flow caused by the OPEP devices, high flow spikes of turbulence may exist farther
down in the lungs, as well as in the upper airways, causing
increased drag on the mucus on the airway walls. The
OPEP devices produce this increased drag only during
expiration, so there would tend to be a net mucus movement out of the lungs. We may think of the phenomenon
as akin to a rapid series of short coughs.
Figures 4 and 5 show that the Acapella and the Flutter
produce similar pressure waveforms at medium flows
(10 –25 L/min). At extremes of the flow ranges tested (5
and 30 L/min), our evaluation produced interesting results.
The Acapella created more stable air flow oscillations (less
variation in amplitude and frequency). Furthermore, compared to the Flutter, the Acapella consistently generated
higher-amplitude oscillations with the lowest flow tested
(5 L/min). That higher pressure build-up during occlusion
results in a higher subsequent flow burst and presumably
a greater mucus transport effect.
Our clinical experience indicates that the ability of the
Acapella to produce effective oscillations at low flows (5
L/min) allows the use of OPEP with a broader spectrum of
130
patients. Patients with low expiratory flow due to severe
air flow obstruction, age, and/or size may now be included
among those who are able to perform and perhaps benefit
from OPEP. Because the Acapella is not gravity-dependent, it may be used while positioning the patient for postural drainage.
One subject that remains to be explored is how to determine at the bedside whether a patient can perform OPEP
therapy and, if so, which device to select. The Acapella is
labeled as a single-patient-use item and retails for about
$45 (comparable to the Flutter). It is wasteful of time and
money to open a package (or 2) only to find the patient
cannot perform the maneuver.
Conclusions
The Acapella has pressure-flow characteristics similar
to the Flutter. This confirms the Food and Drug Administration’s consent to manufacture the Acapella, under section 510(k) of the Food, Drug, and Cosmetics Act, with
Flutter as the predicate device. We expect the Acapella to
be an appropriate choice of devices when applying OPEP.
The Acapella may offer advantages to some patients by
virtue of its ability to generate OPEP at any angle (eg, with
the patient supine) and at very low expiratory flows (eg, in
children with severe obstructive lung disease).
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