Pressure and flow waveform characteristics of seven highfrequency ventilators
Harcourt ER1,2 , John J3, Dargaville PA4, Zannin E5, Davis PG3,6, Tingay DG1,3,6
1Royal
Children’s Hospital, Parkville, Australia 2Swinburne University of Technology, Hawthorn 3Royal Women’s Hospital, Parkville 4Royal Hobart Hospital, Hobart
5Politecnico di Milano University, Milano, Italy 6Murdoch Children’s Research Institute, Parkville, Australia
BACKGROUND
OBJECTIVE
• The pressure and flow waveform characteristics of older highfrequency ventilators (HFV) varies between machines.
• Gas exchange in HFV is complex and waveform characteristics
may contribute to effectiveness of ventilation.
• The waveform characteristics of the newer HFV is unknown.
To describe the pressure and flow waveform characteristics
in seven commercially available HFV in a bench top study
Table 1. Summary of waveform characteristics, maximum
and minimum Pao and V’ao and FTN ratio in seven HFV
METHODS
HFV
Experimental Setup:
• Infant test lung (560li, MI Instruments, Grand Rapids, MI) with 1.0
mL/cm H2O Compliance and 3.5mm diameter ETT.
• Airway pressure measured (1000Hz) at the ETT hub (Pao; SciReq,
Montreal, Canada).
• Flow (V’ao; Florian) measured (200Hz) at the airway opening.
• Table 1 describes the HFV units tested and the Amplitude (DP).
• In all units, a Paw of 10 cm H2O and Frequency 10 Hz was used.
Data Analysis:
• Recordings were made for 600 consecutive oscillatory cycles and
the Pao and V’ao waveform graphed (Figure 1).
• Power spectral density analysis of the Pao waveform was
performed.
• The ratio of fundamental signal (10 Hz) power to non fundamental
signal (total harmonics) power frequencies (FTN) was calculated to
determine the waveform harmonic properties (Table 1).
• Lower FTN indicates a waveform with more frequency components.
Sensormedics
(SM3100B)
Square
Drager VN500 Sinusoidal
Drager
Babylog
(BL8000)
Fabian
Leoni+
Sophie
Set ΔP
Paomax
(cm H2O)
Paomin
(cm H2O)
V’aomax
(L/min)
V’aomin
(L/min)
FTN
Ratio
1:2
1:1
30
cmH2O
21.2
1.9
18.1
-12.1
0.65*
1:2
30
cmH2O
13.4
0.3
17.3
-11.4
1.46
1:2
30% of
Max
13.0
4.8
8.2
-6.7
1.74
1:2
30
cmH2O
15.9
0.3
12.8
-10.4
1.39
1:2
30
cmH2O
14.7
0.8
12.8
-11.0
1.80
1:2
40% of
Max
13.1
2.0
11.0
-6.9
1.33
1:1
30
cmH2O
15.4
-7.8
15.2
-15.8
1.12
Waveform
I:E
shape
Sinusoidal
Sinusoidal
Sinusoidal
Sinusoidal
SLE5000
Square
ΔP set at 30 cm H2O or the % of maximum that resulted in 30 cm H2O at the proximal end of the
ventilator circuit. * 1:2 ratio
Figure 1. Representative Pao and V’ao waveforms during two oscillatory cycles for each HFV tested. Unique incisurae
patterns were noted within the waveforms of the SM3100B and SLE5000.
Flow (L/min)
Pressure (cm H2O)
Sensormedics 3100B
Leoni+
Fabian
SLE 5000
Dräger VN500
Sophie
Dräger BabyLog 8000
20
20
20
20
20
20
20
10
10
10
10
10
10
10
0
0
0
0
0
0
0
-10
-10
-10
-10
-10
-10
-10 0
0
0
0
0
0
Time
Time
Time
Time
Time
Time
Time
Sensormedics 3100B
SLE 5000
Fabian
Leoni+
Sophie
Dräger VN500
Dräger BabyLog 8000
20
20
20
20
20
20
20
10
10
10
10
10
10
10
0
0
0
0
0
0
0
-10
-10
-10
-10
-10
-10
-10
-20
0
-20
0
Time
-20
0
Time
-20
0
Time
-20
0
Time
-20
0
Time
-20
0
Time
0
Time
CONCLUSION
The HFV studied use different waveforms to generate pressure change within the lung. The clinical implications of the varying
pressure and flow waveforms warrants investigation.