© GB Smith 2007
Radar-based breathing rate monitoring:
manikin + human volunteer study
Dave Parry 1
Gary Smith 2
Sheena Farrell 2
David Prytherch 2
Nicholas Hirsch 3
Sarah Harrison 2
Lynsey Woodward 2
University of Portsmouth 1
Portsmouth Hospitals NHS Trust 2
National Hospital for Neurology & Neurosurgery 3
© GB Smith 2007
Breathing rate
should be routine component of clinical monitoring
is difficult to measure
affected by many clinical states
important predictor of cardiopulmonary arrest, death and readmission to a critical care unit
importance and usefulness often underestimated by clinicians
poor level of breathing rate recording in general hospital wards
© GB Smith 2007
Potential benefits of continuous monitoring of breathing rate
30
20
10
Breathing rate
continuous
monitoring
Nurse
Time
Nurse
© GB Smith 2007
Laerdal BedAlert
device development funded by Laerdal Medical
resources provided by Laerdal Medical
research undertaken jointly by Portsmouth Hospitals NHS Trust and University of Portsmouth
© GB Smith 2007
Radar head unit
PC Controller
1.7 metres
Network cable
Laerdal BedAlert: arrangement of study components
© GB Smith 2007
Laerdal BedAlert: manikin study
simulation study
breathing rate recorded by the BedAlert vs that of an
intubated, human manikin lying supine on a standard bed,
ventilated using a positive pressure ventilator
measurements were taken at ventilator tidal volumes 150-950
mls
manikin breathing rates varied from 5 to 45 breaths/minute in
steps of 5 breaths/minute
each manikin breathing rate kept constant for 5 minutes
average value of the BedAlert breathing rate recorded
© GB Smith 2007
0
5
10
15
20
25
30
35
40
45
0 5 10 15 20 25 30 35 40 45
Laerdal BedAlert: manikin study
BedAlertbreathingrate (bpm)
Manikin breathing rate (bpm)
n = 52
© GB Smith 2007
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
2 7 12 17 22 27 32 37 42
Difference
Mean Difference
Mean Diff. ± 2SD
Bland Altman plot of results for all tidal volumes combined
Ventilator-driven manikin breathing rate
Laerdal BedAlert: manikin study
Mean difference (bias) = 0.899 bpmSD of the difference (precision) = 0.873Limits of agreement = +2.61 to -0.812 bpm
© GB Smith 2007
Tidal Volume Range
Bias Precision Limits of Agreement
Low(100-150ml)
1.39 1.43 -1.47 to +4.26
Medium(300-550 ml)
1.09 1.01 -0.93 to +3.12
High(600-950 ml)
0.44 0.44 -0.43 to +1.31
Laerdal BedAlert: manikin study
© GB Smith 2007
Laerdal BedAlert: manikin study
the BedAlert radar system gives a clinically
acceptable agreement in breathing rate with that
of a ventilator-driven human manikin.
no obvious influence of tidal volume on
measured breathing rate
in 2002 Lim et al showed inter and intra-observer
limits of agreement of +4.4 to -4.2 breaths per
minute (experienced clinical staff vs experienced
clinical staff).
© GB Smith 2007
Laerdal BedAlert: human volunteer study
•6 human volunteers
•computer metronome played repetitive tone at set rate
•tone rate 5 – 35 breaths/minute
•tone maintained for 2 minutes at each stage
•breathing rate simultaneously recorded by BedAlert.
•studied in 4 different positions
© GB Smith 2007
Radar head unit
PC Controller
1.7 metres
Network cable
Laerdal BedAlert: arrangement of study components
© GB Smith 2007
Laerdal BedAlert: human volunteer study
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40
Tonerate (bpm)
BedAlert breathing rate (bpm)
n = 2105
© GB Smith 2007
-6
-5
-4
-3
-2
-1
0
1
2
3
4
0 5 10 15 20 25 30 35 40
Difference
Mean Difference
Mean Diff. ± 2SD
Bland Altman plot of results for all positions
Ton
e r
ate
– B
ed
Ale
rt b
reath
ing
ra
te
Mean difference (bias) = 0.010 bpmSD off the difference (precision) = 0.348Limits of agreement = +0.692 to -0.672 bpm
Laerdal BedAlert: human volunteer study
© GB Smith 2007
Laerdal BedAlert: human volunteer study
Bias, precision and limits of agreement for the positions studied
Position Bias Precision Limits of Agreement
Prone 0.32 0.31 -0.58 to +0.64
Sitting 0.03 0.3 -0.57 to +0.63
Right lateral decubitus
0.02 0.51 -1.01 to +1.05
Supine -0.02 0.26 -0.53 to +0.50