© 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

Radar-based breathing rate monitoring

© 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

Laerdal BedAlert

© 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

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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

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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

.

Radar-based respiratory rate monitoring

Human volunteer study

© 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

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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

© GB Smith 2007

Laerdal BedAlert: summary

•accurate

•painless

•non-invasive

•safe

•radar-based method of measuring breathing rate

•potential benefits of continuous monitoring

•requires minimal human resources

•next steps