M. Kagawa 1 , K . Ueki 1 , A. Kurita 2 , H. Tojima 3 , and T. Matsui 1

1Tokyo Metropolitan University

　

M. Kagawa1, K. Ueki1, A. Kurita2, H. Tojima3, and T. Matsui1

21 August 2013

Medinfo2013 Decision Support Systems and Technologies - II 　

Non-contact Screening System with Two Microwave Radars in the Diagnosis of Sleep Apnea-Hypopnea Syndrome

1 Faculty of System Design, Tokyo Metropolitan University, Japan2 Fukuinkai, A Social Welfare Corporation, Japan

3 Department of Chest Medicine, Tokyo Rosai Hospital, Japan


Outline

1. Introduction

2. Methods

3. Clinical Tests

4. Results

5. Conclusions and future work

・ Sleep Apnea-Hypopnea Syndrome and diagnosis

・ Criteria for apnea/hypopneas with radars

・ Comparison between Non-contact and Contact tests

・ Non-contact Vital Signs Measurement with Radars

・ Obstructive Sleep Apnea with paradoxical movements


1. Introduction Sleep Apnea-Hypopnea Syndrome (SAHS)

(1) Obstructive Sleep Apnea (OSA)

(2) Central Sleep Apnea (CSA)

・ Collapse of theairflowchest

・ Failure of the brain to initiate

Apnea (pauses in breathing)

No respiratory effort

airflow

SpO2

Low blood oxygen

Hypopnea (low breathing)

SpO2

abdomen

》 High prevalence: 2-4% of the adult population (still underdiagnosed)

upper airway in the presence of respiratory efforts

a breath

・ the most common type

chestabdomen

(3) Mixed Sleep Apnea (MSA)


Overnight monitoring of sleep and a variety of body functions during sleep

Polysomnography (PSG)

brain (EEG) eye movements (EOG) muscle activity (EMG) ECG

snoring

SpO2airflowchest

abdomen

The “gold standard” for diagnosis of SAHS

Apnea-Hypopnea Index (AHI)

5–15/hr = mild; 15–30/hr = moderate; and > 30/h = severe(the total number of apneic events per hour of sleep)


Motivation and Aim of the Project》 Motivation:PSG with many electrodes restrain the patient and obtrusive inspection methods could disturb the measurement itself.

》 Hypothesis: Displacements of respiratory movement measured by microwave radars have a linear relationship to tidal volumes.

》 Main goal:Developments of non-contact SAHS-diagnostic tools based on microwave radar sensors.・ Identify novel SAHS features based on the amplitude analysis of chest-abdominal radar signals.

・ Need for diagnostic alternatives

6Tokyo Metropolitan UniversityFigure 1 Monitoring system setup

(a) Measurement setup and block diagram (b) Doppler-radar system and I/Q channels

2. Methods

R1:

BPF

PC system for analysis (LabVIEW)

AGC : Automatic Gain ControlBPF : Band Pass Filter

FFT : Fast Fourier Transform SSA : Spectrum Shape Analysis

Abdomen

I - channelQ - channel

Control unitDC Amp.

A/D Conv.

25cm50cm

Respiration

LO

LPF LPF

Q-channelI-channel

Pillow

Respiration and Heartbeat

R2: Abdomen

FFT

mattressmattress

SSA

Apnea/Hypopnea SAS Diagnosis

& Heart rate

pillow

AGC

ChestR2:

Event

Chest Abdomen

R1: Chest

Body surface oscillation


(1) Characteristic of the radar

・ Output power 7mW

（ 9.5×5.8×1.7cm ）

(24.11GHz, 24.15GHz)

Microwave Doppler radars (NJR4262)

Compact microwave radar

Quadrupole plane antenna

Bed

Pillow

Radar2: abdomen

Coverage area

Incident power density:

The electric wave of this radar is weaker than that of the mobile phone and PHS.

the Japanese electromagnetic wave safety guideline

1.5×10-2 mW/cm2 < 1mW/cm2

30cm

Radar1:chest


(2) Heart Beat Measurement with Radars

Detecting the small vibration caused by pulse wave (heartbeats)

A ： Arteries (Systole)

B: Arteries(Diastole)

Radar Radar

Doppler detection

Entry from heart

Entry from heart

Expansion Contraction


(3) Samples of radar output signals

Figure 2 Radar output signals

(a) Slight vibrations due to

Am

plitu

de (V

)

(b) Apnea and hypopnea signal

Time (sec)1 5 10 15

Am

plitu

de (V

)

apneahypopnea

1 20 40 60 80

pulse

Time (sec) heartbeat are superimposed

respiration


(4) Criteria for apnea/hypopneas with radars

》 Apnea event:

》 Hypopnea event 1:

》 Hypopnea event 2:

the baseline* and rise of heart rates

※ All events last 10 seconds or more. ※ Baseline changes dynamically according

※ the American Academy of Sleep Medicine

radar amplitude < 50% of the baseline*

radar amplitude is 50% to 80% of

is accompanied.

normal breathing radar signal in latest Figure 3 Criteria for Apnea and hypopnea A

mpl

itude

(V)

Apnea event

Hypopnea event 1

1 20 40 60 80 Time (sec)

radar amplitude < 20% of the baseline*

60 seconds.

baseline50% line

20% line

events

Our original criteria in accordance with the clinical guidelines of AASM*

to the mean value of the amplitudes of

11Tokyo Metropolitan UniversityFigure 4 Block diagram of SAHS diagnosis

Sampling

Four radar channel signals

Band-PassFilter

Peak Detection

AGC FFT

SSAAGC

Respiratory signal

Heartbeat signal

Apnea Hypopnea Event

SAHS Diagnosis OSACSAMSA: Mixed Sleep ApneaHypopnea

AGC : Automatic Gain Control

SSA : Spectrum Shape Analysis

(5) Flow of the signal processing

100Hz

・ Respiratory effort・ Rise of heart rate

・ Paradoxical movement

Heart rates


(6) Prototype of the system

Chest I/Q

Abdomen I/Q

hypopnea hypopneaControl unit(12×12×6.5cm ）

(b) Sample of monitoring display

LAN

Remote monitoring

(a) Monitoring system setup

Radars

Figure 5 Prototype of the monitoring system


Figure 6 The setup of the overnight test for SAHS

　 3. Clinical tests》 Subjects: eight outpatients at the sleep disorder center

》 Overnight test: between 9 PM and 6 AM the following day》 PSG as reference data

(mean age 63; range 30-90, two females and six males)

R2: AbdomenR1: Chest

Monitoring PC


4. Results: OSA with paradoxical movementsA

mpl

itude

(V)

Am

plitu

de (V

)

Time (sec)1 10 20 30 40 50 60

(a) a typical central sleep apnea (CSA)

(b) an obstructive sleep apnea (OSA) Time (sec)

paradoxical movement of

1 10 20 30 40 50 60

No respiratory effort

Figure 7 Features of CSA and OSA

the reversed phase


Results: Hypopnea accompanied by rise of heart rates

Hypopnea Hypopnea

74788286

Heart rate

Rise of HR Rise of HR

0 30 60 90 120

Time(sec)

949698

100SpO2 (PSG)

0 30 60 90 120

Time(sec)Low blood oxygen Low blood oxygen

Blo

od o

xyge

n le

vel (

%)

Nor

mal

ized

A

irflo

w R

adar

A

mpl

itude

(V

)

Rad

ar

Hea

rt ra

te

(bpm

)

Figure 8 Features of Hypopnea

Delay time 15 sec Delay time 15 sec


Results: RDIs calculated with the radar and the PSG

ＳｕｂｊｅｃｔＴｉｍｅＲａｄａｒＰＳＧＲａｄａｒＰＳＧＲａｄａｒＰＳＧＲａｄａｒＰＳＧ

22:00~ 91 88 5 4 41 49 20 17 23:00~ 96 89 2 1 48 46 11 16

0:00~ 73 79 11 9 38 46 8 9 1:00~ 58 54 24 20 26 29 2 1 2:00~ 9 6 4 6 38 40 18 19 3:00~ 17 22 32 40 15 17 63 55 4:00~ 33 31 17 16 37 31 25 26 5:00~ 57 59 27 33 35 31 34 31

mean 54.3 53.5 15.3 16.1 34.8 36.1 22.6 21.8std dev 32.4 31.4 11.5 14.1 10.1 11.0 19.2 16.3p-value

ＳｕｂｊｅｃｔＴｉｍｅＲａｄａｒＰＳＧＲａｄａｒＰＳＧＲａｄａｒＰＳＧＲａｄａｒＰＳＧ

22:00~ 19 21 24 30 17 23 5 0 23:00~ 42 36 3 0 33 30 95 92

0:00~ 75 73 7 15 9 12 91 99 1:00~ 60 58 25 20 25 23 74 81 2:00~ 21 29 9 12 30 33 82 78 3:00~ 39 38 10 11 53 50 77 73 4:00~ 48 49 28 24 6 7 73 74 5:00~ 28 21 14 12 32 29 66 64

mean 41.5 40.6 15.0 15.5 25.6 25.9 70.4 70.1std dev 19.4 18.3 9.4 9.2 15.1 13.2 28.1 30.4p-value 0.62 0.78 0.85 0.89

S1 S2 S3 S4

S5 S6 S7 S80.66 0.57 0.48 0.54

RDI: the Respiratory Disturbance Index (the total number of apnea and hypopnea events per hour of recording )

The difference of these is small.


0 20 40 60 80 1000

20

40

60

80

100

Fig. 9 Comparison between radar test and PSG

RDIs obtained from radars and PSG correlated very closely, with a Pearson correlation coefficient of 0.98 (n=64).

Results: Linear association and Bland Altman analysisR

DI

by r

adar

s

RDI by PSG [times/hour]

r = 0.98

0 20 40 60 80 100-10

-8 -6 -4 -2 0 2 4 6 8

10

Mean value of RDI between radar and PSG

Diff

eren

ce B

etw

een

RD

Is 8.65: Agreement 95% confidence line

-8.72: Agreement 95% confidence line

-0.03: mean

[times/hour]


　 5. Conclusions and future work

In a practical test at the hospital, we achieved an accurate diagnosis with RDI of SAHS (r = 0.98).

We have identified SAHS features based on the radar amplitude analysis. Developed SAHS diagnostic system can deal with body movement noises and positional changes in bed during sleep.

Our non-contact diagnostic system for SAHS shows great promise as a new screening system.

(1)

(2)

Thank you for your attention!

》 Future work: Features abstraction of mixed sleep apnea, detection of consecutive hypopnea events.

M. Kagawa 1 , K . Ueki 1 , A. Kurita 2 , H. Tojima 3 , and T. Matsui 1

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