ELEC 371 - Respiration

1

Respiratory System : Review

• Transport– Motion of air in / out of lungs

• Distribution– Route air through network of passages

• Exchange– Air & blood

– Oxygen & Waste

Transport

Lung

Visceral Pleura(attached to lung)

Parietal Pleura(attached to thoracic cage - ribs)

Pleural Fluid

Inspiration

Expiration

ELEC 371 - Respiration

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SRC: PNP, p.555

Chest wall: Stiffens during quiet breathingAssists (expands) during heavy breathing

Transport

Natural state of lung

Alveoli

Pharynx(throat)

Larynx(voice box / Adam’s Apple)

Trachea

Bronchi

Nose &Mouth

UpperRespiratory

Tract

LowerRespiratory

Tract

SRC: PNP

Bronchioles Lung:

DistributionExchange

Distribution

ELEC 371 - Respiration

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SRC: PNP, p.554

CO2

O2

Cardio-VascularExchange

Exchange

Measurements

• Volume / Capacity (CC – cubic centimetres)– Spirometry– Nitrogen washout– Plethysmography

• Flow (l/min – litres per minute)– Tidal flow– Peak expiry

• Composition (% CO2)– End-tidal CO2

• Rate (bpm – breaths per minute)– ET CO2

– EKG

ELEC 371 - Respiration

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Lung Volume / Capacity

SRC: MI, p.391

• Absolute– TLC = total lung capacity

– FRC = functional reserve capacity

– RV = reserve volume

• Relative– IC = inspiratory capacity

– ERV = expiratory reserve volume

– VC = vital capacity

– Vt = tidal volume

Spirometer

Mechanical integrator

ELEC 371 - Respiration

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Nitrogen Washout Apparatus

SRC: MI, p.396

Air ≈ 78% N2, 22% O2

Human

2

lung volume ( )

78%

lung temperature ( )

spirometer reading ( )

molar fraction of in spirometer (%)

spirometer temperature ( )

L

L

L

S

S

S

S S SL L LL S

L S S L

V TLC cc

M

T Kelvin

V cc

M N

T Kelvin

V M MV M TV V

T T T M

Nitrogen Washout Test

At start of test At end of test

ELEC 371 - Respiration

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Limb Plethysmography Whole Body Plethysmography

Boyle’s Law: pV = K (constant)

1

2

Assume human is incompressible

Volume of chamber (known)

Volume of human (computed)

Volume change of chamber (known)

Chamber pressure before volume change (1 ATM)

Chamber pressure after volu

c

h

V

V

V

p

p

21 2

2 1

me change (measured)

( ) ( )c h c h h c

VpV V p V V V p V V

p p

Plethysmography

c hV V V

c hV V 1p

2p

Boyle’s Law: pV = K

ELEC 371 - Respiration

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SRC: www.anaesthesiauk.com

Pflow

R

Flow : Tidal Flow

Constant P required to supportconstant bobbin weight

SRC: www.anaesthesiauk.com

ELEC 371 - Respiration

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SRC: www.anaesthesiauk.com

Doppler effect

Flow : Peak Flow

ELEC 371 - Respiration

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2 21 1 2 2

1 22 2

V P V Pgh gh

Bernoulli’s Equation

V = velocityP = pressureρ = fluid densityg = gravity (9.81)h = height

1 2

2 21 1 2 2

2 2

h h

V P V P

Bernoulli’s Equation (orifice)

V2V1

P1

2P 1 2h h

ELEC 371 - Respiration

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2 21 1 2 2

2 21 2

2 2

2 2

V P V P

V VP

Orifice = Virtual Chamber

V2

V1

P1

P2=0

Recall: P = F / unit area1Pa = 1N / m2

Reference pressure

Peak Flow Meter

2 21 2

2 2 21 1 1 1

1 1 2 2 2 1 22 2

22

1 2 21 2

2 3

2 1 2 2 21 1 1 1

2 2

2 2

2

( )

2

( )

V VP

A V V APV A V A V V

A A

PAV

A A

F Kl Kw lA wl P V

A A A A w l

Bernoulli’s Eqn.

Assume Incompressible

Rearrange

Variable Orifice Size(note: A1 = constant)

ELEC 371 - Respiration

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Composition : Beer’s Law

0

0ln

( )

alct

t

P P e

PP

ca l

0

ower / unit area (transmitted)

for air (c=0)

concentration of absorbing gas

( ) absorption coeff of gas (func of )

length (transmission path)

t

t

P P

P P

c

a

l

0or if no gas presenttP

P

ET CO2 Meter

ELEC 371 - Respiration

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End-Tidal CO2

AbsorptionPeak

Noise Compensation

• Noise– Lamp intensity– Condensation– Temperature

• Beam splitter– Reference filter– IR CO2 filter

ELEC 371 - Respiration

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Rate

• Count Breaths– Stethoscope

– ET CO2

– EKG

• Divide by Time– Stop-watch

– Patient monitor