L14 Flashcards
what is inspiration
Inspiration – active process, requires the
active involvement of diaphragm and
external intercostal muscles
what is expiration
Expiration – passive process at rest, due
to elastic recoiling which pulls the thorax
inwards and relaxed diaphragm inwards
describe the events during inspiration
pressures
diaphragm and inspiratory intercostals contract causing the thorax to expand
Pip becomes more subatmospheric (more negative)
transpulmonary pressure increases causing the lungs to expand
Palv becomes subatmospheric (more -ive) because they start to expand causing air to flow into the alveoli (increase in volume = decrease in pressure)
describe the events during expiration
diaphragm and inspiratory intercostals stop contracting causing the chest wall to recoil inward
Pip starts to move towards preinspiration value
transpulmonary pressure moves back to preinspiration value
lungs recoil back to preinspiration size
air in alveoli become compressed causing alveolar pressure to become greater than atmospheric pressure causing air to flow out of the lungs
If Patm=0 mmHg and Palv = 4 mmHg, then
A) Transpulmonary pressure is -4 mmHg
B) It is the end of the normal expiration and there is no
airflow
C) Transpulmonary pressure is +4 mmHg
D) It is the end of the normal inspiration and there is
no air flow
E) Air is flowing out of the lung
E
what work has to be done in the work of breathing
overcome the elestic properties of the lungs (stiffness)
overcome airway resistance
what are the 2 things that contribute to the stiffness of the lungs
compliance and surfactant
what is lung compliance
A measure of elastic property of the lung, compliance is the
inverse of stiffness
Defined as the magnitude of the change in the lung volume (ΔVL) produced by the given change in the transpulmonary
pressure (ΔPtp)
what is the equation for compliance in the lungs
CL = ΔVL ⁄ ΔPtp
what are the 2 compliance curves
Inspiratory compliance curve
Expiratory compliance curve
the less compliance the lungs have the more work you have to do to expand the lungs
what are some diseases associated with this
emphysema = increase in lung compliance
fibrosis = decrease in lung compliance
how do we overcome surface tension at the fluid gas interface
surfactant
what creates the surface tension
The alveolar wall is lined with water molecules which always try and bond together (polar forces)
They are always trying to connect to each other therefore the water prevents the alveoli from expanding. They are always trying to collapse the alveoli
what cells produce surfactant
alveolar type II cells
what is the major constituent of surfactant
phospholipids
This is made of proteins and phospholipids but mainly phospholipids
how does surfactant lower surface tension
Reduces attractive forces between
fluid molecules lining alveoli.
Surface tension in alveoli is reduced.
Easier to increase lung size i.e. increased compliance
This prevents the smaller alveoli from collapsing. The alveoli are all different sizes therefore the smaller ones the water is closer together and they are more likely to collapse smaller alveoli
what is it called when surfactant is absent in premature babies
respiratory distress syndrome (RDS)
what happens when you are sitting down in terms of surfactant
When you are sitting down the lungs become more stiff therefore you stimulate more surfactant
what is the treatment for respiratory distress syndrome (RDS)
Therapy is – assisted ventilation and administration of natural or synthetic surfactant given through the infant’s trachea
Surfactant:
A. lowers surface tension at the fluid-gas interface of the
alveoli
B. stabilizes the smaller alveoli, thereby preventing them
from collapsing due to high pressure.
C.is a mixture of both lipids and protein, but its major
component is protein.
D. All of A, B and C are correct.
E. Only A and B are correct.
E
how can you describe air flow during quiet breathing
Air flow is mainly laminar flow during quiet breathing
what is resistance to flow determined by
Poiseuille’s Law
R is inversely proportional to r^4
what are inportant elements for airway resistance
Bronchoconstriction / bronchodilation
what does cystic fibrosis and asthma have to do with airway resistance
We don’t inhale is viscous air but in cystic fibrosis we secrete more mucus
Bronchi restriction is in asthma is when these constrict
where is the main area of airway resistance
in the larger bronchi
Most of the resistance to airflow arises in the the first 6 generations of the airway.
This is why asthma is called bronchiolar asthma
why do we have higher in larger airways
Airflow Velocity decreases substantially as the effective cross-sectional area increases.
Airway generations exist in parallel rather than in series (in vascular system arterioles are arranged in series).
what factors affect airway resistance under normal conditions
Lung volume
- increases during inspiration (due to
increase in transpulmonary pressure). this causes the airway radius to
become larger → decreasing airway resistance → lung
expands
Radial traction
- pulling of adjacent alveoli – reduces airway resistance
what diseases affect airway resistance
Asthma
Chronic obstructive pulmonary disease (COPD) such as
- Emphysema
- Chronic Bronchitis
know the work of breathing pressure volume loops
you need to look at the diagragm at the end of the lecture
what does the pressure volume loop provide us with information about
the compliance of the lung
what effect does a restrictive lung disease have on airway resistance
there is no change in airway resistance
what effect does a restrictive lung disease have on lung compliance
Lung compliance decreased mening more work needs to be done to overcome elastic resistance and non elastic resistance
how does a decrease in lung compliance affect the pressure volume curve
it shifts it to the right
what effect does a restrictive lung disease have on intrapleural pressure
A more negative Pip required to move the same amount of air (inspiratory flow rates), increases the work of breathing
what effect does a obstructive lung disease have on lung compliance
no change in lung compliance
what effect does a obstructive lung disease have on airway resistance
it increases airway resistance
when is emphysema
it is an obstructive lung disease
is when the alveoli flusses to become flaccid (they don’t recoil)
This means that you don’t need as much energy to expand the lung
However there is less elastic recoil so you have to spend more energy to push the lung back to its original position meaning that you will have to do more work breathing out (wont be a passive process)
causes you to do more work than if your system was working normally
what effect does a obstructive lung disease have on pressure volume loops
Similar work to overcome elastic resistance
More work to overcome non-elastic resistance, inspiration
More work to overcome non-elastic resistance, expiration
A more positive
expiratory pressure is required causing expiration to become an active process
what effect does a obstructive lung disease have on intrapleural pressure
A more negative intra pleural pressure (Pip) required to move the same amount of
air
Which of the following statements are correct regarding airway
resistance?
(i) . Airflow velocity decreases as the size of the airways become smaller, hence the highest resistance is seen in the respiratory bronchioles.
(ii) Air way resistance is inversely related to the fourth power of the radius (r4).
(iii). In healthy individuals, inspiration reduces the airway
resistance due to an increase in the transpulmonary
pressure (Ptp).
(iv). Asthma increases airway resistance.
A. (i), (iii) and (iv) are correct.
B. (ii), (iii), (iv) are correct.
C.(i), (ii) and (iv) are correct.
D. only (ii) and (iii) are correct.
E. all of the above are correct
B. (ii), (iii), (iv) are correct.
i should say large bronchi
Lung compliance is increased in emphysema
BECAUSE
chronic emphysema increases airway resistance.
obstructive causes no change in lung complacence
but emphysema does
therefore both statments are true but not causal
