Natalie - Pulmonary Exam Questions Flashcards
Explain intra pleural pressure
Pressure in the pleural cavity
How does intra-pleural pressure affect ventilation
(4)
Lower than atmospheric pressure
Lower than alveolar pressure (at rest) so alveoli push outwards and lungs remain inflated
Balanced by recoil pressure of lungs -> lungs recoil on exhalation to balance PIP
Pleural fluid doesn’t expand so its pressure drops on inhalation (more negative)
Explain intra-alveolar pressure
(3)
Pressure within the alveoli
themselves
Pressure is determined by:
- amount of air in the alveoli
- the volume of the alveoli themselves
How does intra-alveolar pressure affect ventilation
(3)
This pressure is higher than intra-pleural pressure (lungs exert pressure outwards so they don’t collapse)
Pressure = -1 mmHg during inhalation
Pressure = +1 mmHg during exhalation
What is a pneumothorax
The presence of air within the pleural space
How does a pneumothorax affect ventilation
Intra-pleural pressure exceeds intra-alveolar pressure and the lung collapses
Define compliance
(2)
A measure of the ease at which our lungs can stretch
The change in lung volume that results from a given change in transpulmonary pressure
Describe compliance in the normal lung
Compliance is higher as we inhale -> lung is very compliant when we inhale -> stretches out
Give the equation for lung compliance
Change in lung volume/change in transpulmonary pressure
What is the normal value for lung compliance?
200mls/cmH2O
What is compliance the inverse of?
Elastic recoil
Why is large lung compliance a good thing?
Because a smaller change in transpulmonary pressure is needed to bring a given volume of air
Therefore less work or muscle contraction is required
What can affect compliance?
(3)
The compliancy of the chest wall
Compliance of the thorax - changes in arthritis
Upper body obesity
Why are the lungs normally compliant
Elastic natures of tissues (elastin and collagen)
Surfactant
How does the normal healthy alveolus function
It resists stretching
It recoils back into shape after stretching
What does emphysema do to the lung?
(Affect on compliance)
(5)
Lung is more compliant on inhalation because the spaces fill quickly
Air cannot get out
Loss of alveoli
Loss of some large airways
Small airways are narrowed and reduced in number
There is a loss of alveoli in the lung in emphysema, what affects does this have
(3)
Alveoli near the terminal bronchioles -> airways become narrowed because alvoli around them collapse and cannot stay open (loss of radial traction)
Initially compliance increases but this leads to reduced compliance because air becomes trapped
Less diffusion occurs
Why is the initial increase in compliance not beneficial for patients in emphysema
Not beneficial as it traps air in the lung and increases the residual volume
This leads to barrel chest syndrome
Define airway resistance
Airway Resistance refers to the resistance of
the entire system of airways in the respiratory system
How does lung disease affect resisistance
ho
Why is Poseuille’s Law used?
The tubes (airways) in the lung are branching
(tortuous) so this Law is most appropriate to
determine resistance in these airways
What is the equation for Poseuille’s Law
Resistance = 8 x n x L / pi x R4
n = viscosity
L = length
R = radius
pi = pi
Define Poseuille’s Law
The resistance is directly proportional to the
viscosity of the fluid and the length of the tube and is inversely proportional to the fourth power of the radius of the tube
Describe the relationship between Poseuille’s law and resistance
small changes in radius produce large changes in
resistance. E.g. if radius is cut in half, the resistance is multiplied by 16 because resistance is inversely
proportional to the radius to the fourth power
Describe the resistance in a normal lung
(2)
resistance in the lung is
normally low, even though there are more smaller tubes than larger ones.
Resistance overall does not increase in
the lung because the resistance is evened out across the
smaller airways
Why is low resistance in the lung good?
This low resistance
means that alveolar pressure need not differ much from
atmospheric pressure to achieve normal rates of airflow
under normal conditions
What factors affect resistance in the lung?
(5)
Increased contractile activity of smooth muscle in the bronchioles. (Asthma and bronchitis)
Secretion of mucous into the airways. (Asthma and
bronchitis)
Airway collapse because of loss of alveoli. (Emphysema)
Forced expiration aggravates airway collapse.
(Coughing)
Intra-pleural pressure can be increased to greater
than airway pressure. (Pneumothorax
What causes a pneumothorax?
(4)
Pneumothorax is the presence of air within the
pleural space
Due to disruption of parietal, visceral or mediastinal
pleura
May also occur from spontaneous rupture of
subpleural bleb - tall athletic young males.
A tension pneumothorax occurs when pleura form a
one-way flap valve
