breathing mechanics II Flashcards
What are four ways in which lung function can be investigated?
1) LUNG VOLUMES: what total volume of air can an individual breathe in/out?
2) VENTILATION: what volume of fresh air reaches respiratory surfaces over a given time?
3) LUNG COMPLIANCE: how much force is required to overcome the recoil of the lungs?
4) AIR FLOW: at what rate can air be moved between the lungs and the atmosphere?
Describe the pathway air needs to take in order to reach the alveoli
• Trachea • Primary bronchi • Smaller bronchi • Bronchioles Alveoli
What 2 things does the rate of airflow depend on?
Pressure gradient
Level of airway resistance
Describe Ohms law
Airflow (V) = Change in pressure (P)/Resistance ( R )
* This means that a bigger change in pressure will result in more airflow * This means greater resistance will result in less airflow
Hagen-Poiseuille equation
Resistance = 1/radius^4
R= 8ηl/πr^4
As an airways radius decreases, the resistance increases (and the airflow decreases) DRAMATICALLY
What type of airflow increased airway resistance?
Turbulent airflow (producing a wheezing noise)
Describe the structure of a healthy airway
Elastin in surrounding alveoli provides radial traction to splint bronchioles against positive alveolar pressure
Describe the structure of an airway of someone with COPD
No radial traction = bronchioles collapse
How do you calculate the % of total lung capacity an individual can exhale in the first second
100 x FEV1/FVC
FVC: forced vital capacity
FEV1: forced expiratory volume in 1 second
Give an example of an obstructive airway and explain how it is different to a normal airway
FEV1/FVC < 70%
Example: asthma
Increased resistance in airway
Give an example of a restrictive airway and explain how it is different to a normal airway
FVC < 80%
FEV1/FVC > 70%
Example: fibrosis
Less compliance in airway
If a patients FEV1= 2.4L and FVC=4.3L then what sort of respiratory disease is indicated by the spirometry reading?
Answer this given that the normal readings should be:
FEV1: 3.9L
FVC: 4.7L
Asthma because FEV1/FVC < 70% (it is 55.8%)
What is and how is the transpulmonary pressure calculated?
Alveolar pressure - intrapleural pressure
• Transpulmonary pressure is roughly equal to the level of force acting to expand the lung
Transpulmonary pressure reflects the difference between P(alveoli) and P(intrapleural pressure) and is equivalent to the level of force being exerted to change lung volume
What is meant by lung compliance?
The relationship between transpulmonary pressure and the lung volume
Compliance = change in volume/ change in pressure
What is lowered compliance caused by?
- Scoliosis
- Muscular dystrophy
- Obesity
- NRDS
- Fibrosis (scarring and deposition of collagen; lung is VERY stiff)
What is higher compliance caused by?
COPD Emphysema (elastin degradation; lung is equivalent to plastic bag = WEAK)
Describe the graphical changes when lung compliance is affected by disease
Higher compliance:
Shifts normal curve up and left
Lower compliance:
Shifts normal curve down and right
How does the alveoli resist inflation?
Alveoli are lined with fluid to enable gas exchange (allowing gas molecules to dissolve into water before diffusing)
Within the bubble formed by the water-air interface, surface tension arises due to H-bonds between the water molecules, exerting a collapsing force toward the centre of the bubble
What law can be used to describe the pressure generated by the surface tension within a bubble?
The collapsing forces generates pressure. The amount within a specific bubble is described by the law of Laplace
P= 2T/r
P: pressure
T: surface tension
R: radius
Therefore is T remains constant, then P = 1/r
Meaning the smaller the alveoli, the larger the pressure generated
What would happen if 2 bubbles of different radius were connected to each other (eg-different size alveoli connected via airways)?
Pressure gradients would be created between different sized alveoli, resulting in smaller alveoli emptying into larger ones. This would make inflation of the lungs very difficult. The alveolar surface tension is reduced by the presence of pulmonary surfactant, secreted by type II pneumocytes.
What is pulmonary surfactant secreted by and what is its function?
Pulmonary surfactant is secreted by type II pneumocytes.
Function: reduces alveolar surface tension
It acts by equalising the pressure and volume across varying alveoli
• As the alveoli expand, the concentration of surfactant molecules decreases, increasing the surface tension
Pulmonary surfactant helps to prevent alveolar oedema, explain how
Surface tension produced at the air-liquid interface also reduces hydrostatic pressure. Fluid is then pulled out of surrounding capillaries and into the alveoli.
By reducing surface tension, pulmonary surfactant helps to prevent alveolar oedema. This is observed in patients with insufficient surfactant.
What happens in patients with low pulmonary surfactant?
Decreases hydrostatic pressure in tissues surrounding capillary
Fluid pulled from capillary into alveolus
This produces a collapsing force produced by surface tension
Describe how neonatal respiratory distress syndrome is caused and its outcomes
CAUSED BY INSUFFICIENT PRODUCTION OF PULMONARY SURFACTANT
• Premature birth, maternal diabetes, congenital developmental issues
• Insufficient surfactant production
• Stiff (low compliance) lungs, alveolar collapse, oedema
• Respiratory failure
• Hypoxia
Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary + cerebral haemorrhage
State 2 ways insufficient surfactant production can be treated
- Maternal glucocorticoid supplementation
2. Artificial surfactant supplementation of infant
State the possible outcomes of neonatal respiratory distress syndrome
- Pulmonary vasoconstriction
- Endothelial damage
- Acidosis
- Pulmonary and cerebral haemorrhage
Describe how neonatal respiratory distress syndrome arises
- Premature birth
- Maternal diabetes
- Congenital developmental issues
