Lecture 58 - Lung Volumes & Mechanics Flashcards
Compare the angels of the left and right main bronchi
Right main bronchus: more vertical
Left main bronchus: more horizontal
Where is the largest surface area in the lung located?
Most of the surface are is at the alveoli (ie where exchange is occurring)
Describe the structure of the trachea
Cartilage rings
Trachelis muscle
What keeps the lungs inflated?
Pleural sac attaching to thoracic cavity
Describe the structure of the pleura
Parietal
Visceral
What is the pressure in the lungs?
1 atm
What is the pressure in the pleural cavity?
Less than 1 atm
Keeps the lungs stuck to the pleura
What happens when the intercostal muscles contract?
The ribs pull together and increase the volume inside
What happens when there is a puncture through the ribs?
Lung collapses down because the seal has been broken
What is Boyle’s law?
P1V1 = P2V2
What happens when volume in a cavity decreases?
Pressure increases
and vice versa
What happens to make inhalation happen?
Chest wall gets bigger
Pressure decreases in the thoracic cavity
Negative pressure → air flows into the lungs
What happens to make expiration happen?
Chest wall gets smaller
Pressure increases in the thoracic cavity
Positive pressure → air expelled
When pressure is higher in the lung than the atmosphere, where does air move?
Out of the lung
Describe the volume of air moved during the respiratory cycle
**
Describe which muscles are responsible for inspiration
Diaphragm
External intercostals
Scalenes
Mastoids
Which muscles are responsible for expiration
Normally passive
Internal intercostals for forced expiration
Describe Poiseuille’s law
Resistance proportional to length an viscocity
and inversely proportional to radius of the tube
What parameters of poiseuille’s law are varibale?
Radius of the bronchi
Viscosity and length of bronchi not variable
How is the diameter of the airways altered?
Upper airways: physical obstruction
• mucous
Lower airways • ANS • CO2 • epinephrine • histamine • leukotrienes
What happens as diameter of the airways deccreases?
Resistance increases
More work required
What is lung compliance?
The ability of the lung to stretch
What happens as compliance of the lung increases?
More work required to inflate the lungs
What factors affect lung compliance?
Surface tension in alveoli
What is surface tension due to?
Attraction of hydrogen molecules
They are trying to pull in close
What is the Law of LaPlace?
Pressure in smaller bubbles is greater (if surface tension is the same)
What does small alveoli mean?
Higher resistance to stretch
Greater inward pressure causing collapse
What prevents the alveoli from collapsing?
- Surfactant
2. Alveolar interdependence
What does Surfactant stand for?
Surface Active Agents
What does surfacant do?
Reduces surface tension
(Radius is the same)
→ pressure is reduce
H+ are happy to be further apart
Where is surfactant more concentrated?
In small alveoli
According to Law of LaPlace, what is pressure proportional to?
Proportional to surface tension
Inversely proportional to radius
Describe alveolar interdependence
- An alveolus collapses
- Surrounding alveoli stretched
- Recoil of stretched surrounded alveoli
- Collapses alveolus pulled back open
What is the measurement of lung volumes?
Spirometry
Describe spirometry
Breathes in: bucket goes down
Breathes out: bucket goes down
This is recorded by a machine
We can measure the volume going in and out
What is capacity?
More than one lung volume
What is tidal volume?
Volume of one breath in
500 mL
What is the name for the total volume that we can expire if needed?
Expiratory reserve volume
1100 mL
What is the name for the total volume that we can inspire if needed?
Inspiratory capacity
3500 mL
What is the maximum volume we can expire
Vital capacity
4600 mL
What is the volume in the lung that we can’t expel?
Residual volume
1200 mL
What does the Helium dilution method tell us?
Allows estimation of:
• residual volume
• functional residual volume
When is most of the air expired?
In the first second
What is FEV1?
Volume of air expired in the first second
• 4 L
What is FVC?
Forced vital capacity
5L
What sort of diseases can occur in the lungs?
- Obstructive lung disease
• narrowed lungs
• can’t expire
2. Restrictive lung disease • decrease in lung compliance due to scar tissue • can't inhale Pulmonary fibrosis (asbestos, smoking)
What things change in obstructive lung disease?
Decrease in FEV Decrease in FVC Decrease in the ratio Decrease in vital capacity Increase in residual volume
Why do people with Obstructive lung disease swim well?
More volume in the lungs
Increased residual volume
What changes occur in restrictive lung disease?
Decrease in FEV Decrease in FVC Ratio goes up Decrease in vital capacity No change in residual volume Decrease total lung capacity
What is dead space?
- give examples of anatomical dead space
Part of the lungs that aren’t involved in gas exchange
Anatomical dead space
• trachea
• bronchi
Describe the effect of anatomical dead space
Air trapped in the trachea that is not refreshed
This is taken back in during the next inspiration
This stale air has reduced partial pressure of oxygen
What is the average tidal volume?
500mL
What is the average breathing rate
12 breaths / min
What is minute ventilation
Total ventilation over a fixed time period (usually a minute)
What is alveolar ventilation?
Volume of alveolar air exchanged per unit time
Tidal vol - dead space
What happens if we breathe TV of 150 mL at f = 40?
Minute ventilation doesn’t change
Alveolar ventilation does!
Pass out eventually, because of the dead space in the trachea
What is normal total pulmonary ventilation?
6 L/min
What is eupnea?
Normal quiet breathing
Describe the structure of the bronchioles.
Compare this with the bronchi
Bronchi: cartilage rings to keep them open
Bronchioles: no cartilage
• smooth muscle innervated by ANS
Describe what factors affect the resistance in the lungs
Resistance is proportional to:
• length of airway
• viscosity of air
Inversely proportional to:
• diameter
What is work of breathing?
What affects it?
Work of breathing is how much energy is required, ie how much resistance that needs to be overcome
Resistance affects it.
• airway diameter
• lung compliance
What is the difference between lung compliance and elastance?
Compliance: ability to stretch
Elastance: ability to spring back after stretching
What things can affect lung compliance?
Pulmonary fibrosis
• causes decrease in compliance
• scar tissue is stiff
What things can affect lung elastance?
Emphysema
• decreases elastance
• destroys elastin fibres
What is the effect of histamines and leukotrienes on the bronchioles?
Bronchoconstriction
What is the effect of epinephrine on the bronchioles?
Bronchodilation
What causes restrictive lung disease?
How about obstructive lung disease?
Restrictive: decrease in compliance
• asthma
• emphysema
Obstructive: narrowing of lower airways
• pulmonary fibrosis
What is normal Va?
4.2 L/min
What is the name for increased respiratory rate?
Hyperpnea
• due to increased metabolism
Hyperventilation
• no increase in metabolism
What is the apnea?
Cessation of breathing
What is dyspnea?
Difficulty breathing
What is tachypnea?
Rapid breathing
eg. panting
What parameters in alveoli would change if it weren’t for surfactant?
Surface tension
Diameter of alveoli doesn’t change
What would increased pressure in the alveoli result in?
- Decreased compliance
* Increased work of breathing
What is the important ratio?
• normally 80
FEV1 / FVC
