The Respiratory System at a Glance doc

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The Respiratory System at a Glance
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The Respiratory
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Jeremy P.T. Ward
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Contents 5
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List of abbreviations 9

r
1 Structure of the respiratory system: lungs,
airways and dead space
(a) Lung lobes
Right lateral
aspect
Anterior aspect
Left lateral
aspect
RU
RM
RL
LU
LL
= Right upper
= Right middle
= Right lower
= Left upper
= Left lower
Posterior aspect
(c) Bohr equation for measuring
dead space
Anatomical dead space,
Volume = V
D
Respiratory zone:
Alveolar CO
2
fraction = F
A

CO
2
End of inspiration End of expiration
End-tidal =
alveolar gas
Anatomical dead space,
Volume = V
D
In an expired breath
none of the CO
2
expired
came from the dead space region
∴ Quantity of CO
2
in mixed expired air = quantity of CO
2
from alveolar region
V
T
x = (V
T
–V
D
) x
∴ V
D
= V
T
( – )/

Mixed expired gas: Volume = V
T
;
Mixed expired CO
2
fraction =
CO
2
-free gas CO
2
-containing gas
RU
RM
RL
LU
LL
RU
RM
RL
LU
LL
LU
LL RL
RU
T1
T12
T2
T3
T4
T5

T6
T7
T8
T9
T10
T11
C7
C6
(b) The airways
Sternal angle
(angle of Louis)
Sternum
Xiphoid
process
Diaphragm
Nasal cavity
Pharynx
Epiglottis
Larynx
Cricoid
Trachea
(generation 0)
Carina
R and L main bronchi
(generation 1)
Bronchi
(generations 2–11)
Bronchioles (generations 12–16)
Respiratory bronchioles
(generations 17–19)

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(generations 20–23)
Body
Manubrium
F
E
CO
2
F
E
CO
2
F
E
CO
2
F
A
CO
2
F
A
CO
2
F
A
CO
2
10
The Respiratory System at a Glance

, 3e. By J.P.T. Ward, J. Ward, R.M. Leach. Published 2010 Blackwell Publishing Ltd.
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r
2 The thoracic cage and respiratory muscles
c
1
2
3
4
5
6
7
8
9
10
(a) The sternum and ribs and their relationship to the lungs and pleural cavities
Pleural
Horizontal
fissure
Oblique

fissure
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recess
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fissure
Xiphoid
process
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facets of
the head
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facet of
the tubercle
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Costal
groove
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cartilage
joins here
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Artery
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intercostal muscle
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pleural effusion) should pass close to the top of the rib
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Costal
part
Right
phrenic
nerve
Inferior
vena
cava
12th rib
Right crus
Left crus
Psoas major
Quadratus lumborum
Lateral arcuate
ligament
Medial arcuate
ligament
Median arcuate
ligament

Aorta
Oesophagus
Vagi
Left
phrenic nerve
Central tendon
of diaphragm
External
intercostal muscle
Internal
intercostal muscle
Costal
part
L1
L2
L3
L4
T1
Lung lobes
12
The Respiratory System at a Glance
, 3e. By J.P.T. Ward, J. Ward, R.M. Leach. Published 2010 Blackwell Publishing Ltd.
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The thoracic cage and respiratory muscles Structure and function 13
r
3 Pressures and volumes during normal breathing
Total lung capacity (TLC)
Functional residual capacity (FRC)
Residual volume (RV)
7300 mL
mL
mL3500
1 800
mL
Open thorax:
Pressure gradient distending
the lung (transmural =
alveolar – intrapleural)
Pressure gradient driving air
along airways (mouth – alveolar)
Intrapleural
Alveolar pressure
Mouth
–0.5
0.5

–0.1
0
0
0.1
–0.75
–0.5
0
0.5
Volume
above FRC
(L)
Intrapleural
pressure
relative to
atmospheric
(kPa)
Alveolar
pressure
(kPa)
Airflow
(L/sec)
Inspiration Expiration Inspiration Expiration
(b)
(a) Functional residual
capacity
(c)
(d)
(e)
Air
Air

Outward recoil
of chest wall
Inward recoil
of lungs
‘Negative’
intrapleural
pressure
Chest wall
expands
‘Zero’
pressure
Lungs collapse
Intrapleural
pressure,
–0.5 kPa
Alveolar
pressure, 0 kPa
Heart
Oesophageal
pressure, –0.5 kPa
Table 1
Tidal volume (V
T
) (at rest)
Vital capacity (VC)
Inspiratory reserve volume (IRV)
Expiratory reserve volume (ERV)
500 mL
5500 mL
3300 mL

1700 mL
Inspiratory capacity (IC) 3800
V
T
VC
IRV IC
ERV
TLC
FRC
0
RV
(i)
(ii)
(i)
(ii)
14
The Respiratory System at a Glance
, 3e. By J.P.T. Ward, J. Ward, R.M. Leach. Published 2010 Blackwell Publishing Ltd.
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r
4 Gas laws
(a) Altitude, barometric pressure, O
2
fraction and PO
2

Mt Everest summit 8850 m (29 035 ft)
Sea level 0m (0ft)
5486 m (18 000 ft)
P
B
= 250 mmHg (33.3 kPa)
1
⁄
3
sea level value
FO
2
dry air = 0.209 (20.9% O
2
)
∴ PO
2
dry air = 0.209 x 250 = 52 mmHg (7 kPa)
P
B
= 380 mmHg (50.6 kPa)
1
⁄
2
sea level value
FO
2
dry air = 0.209 (20.9% O
2
)

PO
2
dry air = 0.209 x 380 = 79 mmHg (10.6 kPa)
P
B
= 760 mmHg (101.3 kPa)
FO
2
dry air = 0.209 (20.9% O
2
)
PO
2
dry air = 0.209 x 760 = 159 mmHg (21 kPa)
Barometric pressure with increasing altitude
800
700
600
500
400
300
200
100
0
0 10000
10 000 12 000 13000 14 000 16 000
18000
20000 30000 40000 50 000 60000
20000 4000 6000 8000
Altitude (metres)

Altitude (feet)
Barometric pressure (P
B
, mmHG)
Sea level (0m, 0ft)
Mexico City
(2240 m, 7349 ft)
Lhasa, Tibet
(3600 m, 11810 ft)
La Rinconda, Peru*
(5100 m, 16
732 ft)
Mt Everest summit
(8850 m, 29 035 ft)
Cruising altitude
typical passenger jet
(11
278 m, 37 000 ft)
*Highest permanently inhabited town P
B
= barometric pressure; FO
2
= O
2
fraction
(b) Correction factors for gas volumes
Volume
(BTPS)
= volume
(ATPS)

Volume
(STPD)
= volume
(ATPS)
273 + 37
273 + t
O
C
P
B
– PH
2
O
P
B
– 6.3*
*47 if P
B
and P
H
2
O
are in mmHg
*760 if P
B
and P
H
2
O
are in mmHg

(c) Pa rtial pressure of a gas in a liquid
Gas
phase (Pg)
Liquid
phase
liquid X
(P

Xg)
Gas
phase (Pg)
Liquid
phase
liquid Y
(P

Yg)
P
1
Liquid X containing dissolved gas, g, is exposed to a gas phase
containing g at three different partial pressures, P
1
, P
2
, P
3
. Only
when the Pg = P
2
does the number of gas molecules leaving the

liquid per minute ( ) equal the number entering the liquid ( )
– i.e. the liquid and gas phases are in equilibrium.
∴ Partial pressure of gas, g, in liquid X (P

Xg) = P
2
Liquid Y also contains gas, g, and is also in equilibrium with the
gas phase when Pg = P
2
∴ Partial pressure of gas, g, in liquid Y (P

Yg) = P
2
However, the solubility of gas, g, in liquid Y is less than in liquid X,
so at the same partial pressure, liquid Y contains a lower
concentration of g.
273
273 + t
O
C
P
B
– PH
2
O
101*
2
P
3
P

1
2
P
3
Note: In the bottom left flask, gas moves against its
concentration gradient.
P
P
P
B
= 760 mmHg
101.3 kPa
P
B
= 380 mmHg
50.6 kPa
P
B
= 250 mmHg
33.3 kPa
16
The Respiratory System at a Glance
, 3e. By J.P.T. Ward, J. Ward, R.M. Leach. Published 2010 Blackwell Publishing Ltd.
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r
5 Diffusion
(a) The alveolar–capillary membrane
(c) Diffusion through a sheet of tissue
(d) The diffusion path through the alveolar–capillary membrane
Alveolar
epithelium
O
2
Alveolus
Red blood cells
Capillary
(e) The oxygen cascade: oxygen tension from ambient air to mitochondria
mmHg
P
O
2
200
150
100
50
0
25
20
15
10
5

0
kPa
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l
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2
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2
added)
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l (R to L

shunt, e.
g. bronchial circulatio
n)
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ery variable)
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ery variable)
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us varies with tissue)
(b) Transfer of gases across alveolar–capillary membrane
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Capillary partial
pressure
00

0
.25 0.5 0.75
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CO
O
2
N
2
O
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blood
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1
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2
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fluid
Endothelium
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2
O
2
O
2
O
2
Red blood cells
Pore of Kohn

(gap between
alveoli)
Endothelium
Alveolar
epithelium
Collagen and
elastin fibres
Alveolus
Alveolus
Alveolus
Plasma
pressure
of N
2
0,
0
2
or CO
18
The Respiratory System at a Glance
, 3e. By J.P.T. Ward, J. Ward, R.M. Leach. Published 2010 Blackwell Publishing Ltd.
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r
6 Lung mechanics: elastic forces
(a) Static pressure–volume loop
Volume % TLC
100
50
0
FRC
RV
ΔP
ΔV
C
L
= slope ΔV/ΔP
012
10 20 cm H
2
O
kPa
Transmural pressure (= – intrapleural pressure
since measurements taken at zero airflow)
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TLC
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= Total lung capacity
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C
L
= Functional residual capacity
= Lung compliance
(c) Surface tension
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T= Surface tension
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above ambient = P
1
P
2
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1
> P
2
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bubble empties into the large
(d) Effect of surface area
R
1
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Surfactant molecule
R
2
R
2
< R
1
but T

2
< T
1
because surface concentration of surfactant
is higher when the alveolus is small
The fall in R is more than offset by the fall in T,
∴ since P = 2T , P does not rise, but falls as the alveolus shrinks
P= 2T
R
(b) Dynamic pressure–volume loop
If intrapleural pressure and volume are recorded continuously
(lower panel), a pressure–volume loop (upper panel) can be
constructed from pairs of simultaneous measurements of volume,
e.g. (b) with pressure (b'). Alternatively the pressure and volume
signals can be fed into an X-Y plotter.
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FRC (litre)
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pressure relative
to atmospheric
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0
–0.5
–1.0
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The Respiratory System at a Glance
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Lung mechanics: elastic forces Structure and function 21
r
7 Lung mechanics: airway resistance
(a) Laminar and turbulent flow
Laminar flow
Turbulent flow
(b) Main factors influencing bronchomotor tone
(d) Dynamic compression of airways
= Flow–volume curve for maximum effort from partly filled lungs
A = Peak expiratory flow rate with lungs filled to total lung capacity
B = Peak expiratory flow rate for partly filled lungs filled (RV + 3 L)
TLC = Total lung capacity, RV = Residual volume
Normal curve
Obstructive airway disease of smaller airways. Note:
• concave appearance of forced expiratory curve
• forced inspiratory flow affected less than forced expiratory flow
Upper airway obstruction (e.g. tracheal stenosis). Note:
• flat topped flow–volume curve
• forced inspiratory flow affected as much as expiratory flow
Restrictive lung disease. Low peak flow rates are related to low
volume. (Note: this figure is drawn to show the relationship
between these traces by using absolute lung volume which cannot
actually be obtained from a flow–volume loop alone).
(c) The effect of effort on inspiratory and expiratory airflow
Effort dependent
600

300
0
300
600
Airflow (L/min)
ExpirationInspiration
TLC RV
Volume (L)
Effort
independent
A
B
(e) Maximum flow–volume loops
6420
Lung volume (L)
6
5
4
3
2
1
1
2
3
4
5
6
600
300
0

300
600
Airflow (L/min)
ExpirationInspiration
Beginning of
inspiration
Alveolus
Intrathoracic airway
Intrapleural space –0.5
0
8.7 8 6 4 0
+8.0
Numbers are pressures in kPa (1 kPa = 7.5 mmHg)
0
0
During forced
expiration
Airway
smooth
muscle
Synapse
Vagal
efferents
Pulmonary
stretch
r
eceptors
(inhibit)
Vagal
afferents

Brainstem
(Chapter 12)
Airway
irritant
receptors
(activate)
NANC
nerves
(excitatory)
Mast cells, eosinophil
(Chapter 23)
Histamine,
Prostagladins
Leukotrienes etc
β
2
-Receptor
β-Adrenergic agonists
(e.g. adrenaline and
saltbutamol)
NANC
nerv
es
(inhibitory)
NO and VIP
CO
2
ACh via
M
3

receptors
BronchodilationBronchoconstriction
SP and
neurokinins
= Receptor
= Nerve ending
Nitric oxide
Vasoactive intestinal peptide
Substance P
NO =
VIP =
SP =
ACh =
M3 =
Acetylcholine
Muscarinic
type 3 receptor
22
The Respiratory System at a Glance
, 3e. By J.P.T. Ward, J. Ward, R.M. Leach. Published 2010 Blackwell Publishing Ltd.
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Lung mechanics: airway resistance Structure and function 23