David Taylor dcmtlivacuk http wwwliverpoolacuk dcmt When you have worked through this you should be able to Describe the relationships between airflow pressure gradients and resistance gas laws ID: 598958
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Slide1
Pulmonary Ventilation 1
David Taylordcmt@liv.ac.ukhttp://www.liverpool.ac.uk/~dcmtSlide2
When you have worked through this you should be able to
Describe the relationships between airflow, pressure gradients and resistance – gas lawsDescribe the mechanics of breathing – compare quiet versus forcedReflect upon the integration of heart and lungs working togetherExplain the nervous control of breathing
Pulmonary ventilation 1Slide3
These slides are available with all my other
lectures on my website http://www.liv.ac.uk/~dcmtIn the text books:Chapters 22,23 and 24 in Preston and Wilson (2013)Chapter 13 in
Naish
and Court (2014)
ResourcesSlide4
Airflow, pressure gradients and resistance – gas laws
As in so much physics and physiology:
So the pressure gradient and the resistance determine the flow per unit time.
A word about resistance (
Poiseuille’s
Law)
L is airway length,
ƞ is viscosity (dependent on density) –
Poiseuille’s
law is for laminar flow
Paradoxically the Pharynx is the site of greatest resistance
Ask yourself, why not the bronchioles….
Slide5
Changes in diameter of the airways
Autonomic controlParasympathetic: ACh binds to M3 receptors – bronchoconstrictionSympathetic: Mainly by inhibiting ACh release but also through Noradrenaline on
β
2
receptors
Endocrine:
β
2
receptors are also sensitive to adrenaline
Irritants and allergens or inflammatory agents
What affects resistance?Chapter 22 p. 273-274 in Preston and Wilson (2013)Chapter 13 p. 633 in Naish and Court (2014)Slide6
Mechanics of breathing
“Passive”
The diaphragm contracts and this pulls down on the lungs – air enters.
The diaphragm lifts the lower ribs
External intercostal muscles contract also raising ribs
Normally
breathing out is passive.
Chapter 22 p. 268 in
Preston and Wilson (2013)
Chapter 13
p. 635 in
Naish and Court (2014)Slide7
“Forced”
Inspiration can also use the accessory musclesscalenes raise first two ribs, sternomastoids raise the sternumAdditionally there is dilation of the upper airwaysExpiration also uses the abdominal muscles
Rectus abdominis,
transversus
abdominis, internal and external oblique musclesInternal
intercostals
pull ribs downward and inward
Mechanics of breathing
Chapter 22 p. 268 in
Preston and Wilson (2013)
Chapter 13
p. 635 in Naish and Court (2014)Slide8
Ventilation (alveolar ventilation)
The volume of air (L/min) entering and leaving an alveolus (4L/min)PerfusionIn this case, pulmonary blood flow (5L/min)Both change with position in the lung (V/Q range 3.3-0.8L/min)
Some words and numbersSlide9
Ventilation/perfusion ratio (V/Q)
Distance above bottom of lung
Relative blood flow
0
10
20
30
Top
Left atrium
Pulmonary venous pressure above atmospheric pressure
No blood flow
Flow is regulated by alveolar pressure
V/Q=3.3
V/Q=0.8Slide10
Take the obvious extremes
Lung is well ventilated but there is no perfusionLung is well perfused, but there is no ventilationBoth would be fatal.
The importance of matching ventilation and perfusionSlide11
If ventilation is poor
Local hypoxia (low O2)Leads to vasoconstrictionSo blood is diverted to other (better perfused regions of the lung)
The (local) ways in which perfusion is controlledSlide12
Receptors:
Central chemoreceptors (ventral surface of medulla) – increase rate and depth with ↑ CO2Peripheral chemoreceptors (carotid bodies, aortic arch) – increase rate and depth with ↓O
2
or pH
Stretch receptors (bronchi) - inhibit rate
There are several others, but these are the most important for now.
The inputs to the pathways which control breathingSlide13
The physiological control of breathing
Emotions etc.,
CO
2
O
2
and pH
Higher centres
Limbic system
Medulla oblongata and
pons
Central chemoreceptorsPeripheral
chemoreceptors
Afferent sensory
neurones
Inspiratory
(dorsal)
motor neurones
Expiratory
(ventral)
motor neurones
Scalene and
sternomastoid
External
intercostals
Diaphragm
Internal
intercostals
Abdominal
Chapter 24 p.298 and following in
Preston and Wilson (2013)
Chapter 13
p. 642-645 in
Naish
and Court (2014)