Lecture 14 - Lung mechanics and lung volumes Flashcards
What is occuring if Patm= 0 mmHg and Palv = 4 mmHg?
Air is flowing out of the lung
What work needs to be done in breathing?
Overcome elastic properties (or stiffness) of lung
Overcome airway resistance
What factors effect how hard is it to expand lungs?
• Compliance of lung
• Surfactant
What is lung compliance?
A measure of elastic property of the lung, compliance is the
inverse of stiffness
What is lung compliance defined by?
Defined as the magnitude of the change in the lung volume (ΔVL) produced by the given change in the transpulmonary pressure (ΔPtp)
CL = ΔVL ⁄ ΔPtp
What are the determinants of lung compliance?
1.Stiffness / elasticity of lung
2.Also need to overcome SURFACE TENSION at
the fluid gas interface - surfactant
What happens during emphysema?
Alveoli wall damage - big air pocket, smaller SA
“Floppy” lungs
High compliance (very stretchy)
- No effect on inspiration
Low elastic
recoil
- Requires more Energy During expiration
What happens during fibrosis?
“Stiff” lungs
Low compliance - more energy
for inspiration
High elastic recoil - No additional
energy required for expiration
Why is surfactant important?
Hydrogen/fluid attracted to each other so wants to come together. Bigger problem in smaller alveoli where things are closer.
Surfactant – reduces surface tension in alveoli
Where is surfactant produced?
alveolar type II cells
What is the major constituent of surfactant?
phospholipids
How does surfactant lower surface tension?
Reduces attractive forces between
fluid molecules lining alveoli - hydrophobic phospholipids
What occurs when there is a lack of surfactant/failure to produce adequate surfactant?
“stiff” lungs
Why do premature infants develop respiratory distress syndrome (RDS)?
Surfactant is absent in premature infants - Type II cells don’t differentiate until 34 weeks
In new-born RDS what happens to alveoli?
They become collapsed
Surfactant:
Lowers surface tension at the fluid-gas interface of the alveoli
Stabilizes the smaller alveoli, thereby preventing them from collapsing due to high pressure.
How is resistance to flow determined by?
Poiseuille’s Law
R = 8nl / πr4
What are important elements in airway resistance?
Bronchoconstriction / bronchodilation
Where is the main area of airway resistance?
BRONCHI
Most of the resistance to airflow arises in the the first 6 generations of the airway. Trachea - early bronchioles
Whys is resistance is higher in larger airways?
Resistance to air flow depends on the number of parallel pathways present - larger airways are are in parallel (bronchi)
What normal condition factors affect airway resistance?
Lung volume
Radial traction
How does lung volume effect airway resistance?
Lung volume:
- increases during inspiration (due to increase in transpulmonary pressure)
- airway radius becomes larger
- airway resistance lower
- lung expands
How does radial traction effect airway resistance?
Radial traction:
Pulling of adjacent alveoli – reduces airway resistance
What diseases affect airway resistance?
Asthma
Chronic obstructive pulmonary disease (COPD)
• Emphysema
• Chronic Bronchitis
What does the pressure-volume loop tell you?
information on compliance of lung
What happens during restrictive lung disease?
No change in airway resistance
•Lung compliance decreased, pressure-volume curve shifted to the right
• More work to overcome elastic resistance
• A more negative Pip required to move the same amount of air, increases the work of breathing
What is an example of a restrictive lung disease?
Asthma
What happens during obstructive lung disease?
No change in lung compliance
• Airway resistance has increased
Intra pleural pressure (mmHg) Intra pleural pressure (mmHg)
• More work to overcome non-elastic resistance, inspiration
• Similar work to overcome elastic resistance
• More work to overcome non-elastic resistance, expiration, a more positive expiratory pressure is required, expiration becomes active process
• A more negative intra pleural pressure (Pip) required to move the same amount of
air
What are examples of obstructive lung diseases?
Chronic obstructive pulmonary disease (COPD)
• Emphysema
• Chronic Bronchitis
Assertion question: Lung compliance is increased in emphysema BECAUSE
chronic emphysema increases airway resistance.
B. Both statements are true but are not causally related
How can we measure lung function?
Spirometry
Peak Expiratory Flow Rates (PEFR)
What is tidal volume?
~ 500 ml (VT or TV).
Volume of air moved in and out during normal quiet breath
What is inspiratory reserve volume?
~ 3 L (IRV).
Extra volume that can be inspired with maximal inhalation - external intercostal muscles.
What is expiratory reserve volume?
~ 1.2 L (ERV).
Extra volume that can be exhaled with maximal effort - internal intercostal and abdominal muscles.
What is residual volume?
~ 1.2 L (RV).
Volume remaining in lungs after maximal exhalation.
What are the different lung volumes?
Tidal
Inspiratory reserve
Expiratory reserve
Residual
What are the lung capacities?
The lung capacities are made up of lung volumes and they are:
Inspiratory
Vital
Functional residual
Total lung
What is inspiratory capacity?
maximal breath in (Vt + IRV)
What is vital capacity?
~5L.
Maximal breath into out Volume of air can shift
in/out of lungs (IC +ERV)
What is Functional residual capacity?
~2.4L.
Remaining volume at end of normal breath
out (ERV +RV)
Lung volume at the end of a normal expiration when there is no inspiratory or expiratory muscle contractions
What is total lung capacity?
~6L.
Total volume in lungs when maximally full
= (VC + RV)
Why is a large FRC important?
At all times during the breath cycle O2 and CO2 exchange can occur between alveolar gas and the pulmonary capillaries.
Prevents large fluctuations in the composition of alveolar gas
What happens to lung volumes/capacities during restrictive diseases?
VC decrease
IRV decrease
ERV decrease
RV decrease
FRC decrease
TLC decrease
What happens to lung volumes/capacities during obstructive diseases?
VC constant
IRV constant
ERV constant
RV increase
FRC increase
TLC increase
