17 Flashcards
Gas will move form ____ pressure to ____ pressure
High
Low
Right before a breath, pressure outside the body and inside the lungs is…
Equal
How do you create a pressure gradient
- as u inhale, your diaphragm drop as while your rib cage expands
- this increases the volume in your chest, which lowers the pressure
Boyes law and what needs to be kept constant for it to apply
- the pressure of gas is inversely related to its volume
- P= 1/V
- provided temperature and amount of gas molecules are kept constant
(IN A CLOSED CHAMBER the product of PXV MUST STAY THE SAME)
Creating a pressure gradient in inhalation
• Lung volume is increasing
• Pressure inside the lungs is
decreasing
• Pressure outside the lung is now
greater than inside, so air rushes in
Creating a pressure gradient in exhalation
• Lung volume is decreasing
• Pressure inside the lungs is
increasing
• Pressure outside the lung is now
lower than inside, so air rushes out
What is the direction of airflow determined by?
difference between atmospheric pressure and intrapulmonary pressure
What is intrapulmonary pressure?
Pressure inside the lungs
What are the two opposing forces that must be overcome to take a breath
- Stiffness of the lungs
• Lungs must expand to take in air
• How compliant are the lungs?
• Surface tension holds lungs in place - Resistance of the airways to the lungs
• Need to move the air from outside to the
alveoli
• How much resistance is the respiratory tract
putting on the movement of air?
What makes lungs stiff/ not stiff
- elastic tissue makes it stretchy
- low compliance means not very stretchy
What is compliance (lungs)
Defined as the magnitude of the change in the lung volume (^V) produced by the given change in pressure (^P)
Compliance equation and graph - lungs
Vital capacity =
Lung volume
Low compliance - ‘stiff lungs’ =
Need more work to expand
What is pulmonary fibrosis and was causes it and what happens to compliance?
- thickening and scaring of the alveolar membranes
- can arise from chronic inflammation or exposure to industrial chemicals
- needs a high pressure to clause a same change in volume
- shallow rapid breaths
What is surface tension
- tendency of a fluid to occupy the smallest possible surface area
Fluids surrounding the lungs exerting surface tension on alveoli
- Alveoli are lined with fluid that exert surface tension
- walls of alveoli are very thin, enhancing this effect
- makes alveoli want to collapse
- must overcome surface tension to expand the lungs
What does surfactant do?
Reduces surface tension in alveoli making them easier to expand
What is surfactant produced by?
Alveolar type 2 pneumocystis
What is a major constituent of surfacent ?
Phospholipids
Function of surfactant in alveoli
- lowers surface tension
How does surfactant lower surface tension
- reduces attractive forces between fluid molecules lining alveoli
- easier to increase lung size I.e. increased compliance
Diagram of with and without surfactant
Lack of surfactant/ failure to produce adequate surfactant —->
‘Stiff’ lungs
(Compliance is reduced)
Why do premature infants result in respiratory distress syndrome (RDS)
Premature infants do not produce surfactant
Airway resistance through the respiratory tract
- need to ,more air from outside to the alveoli
- air is conducted through the bronchi and bronchioles
- exert force (fiction) on the air (through the airways) that must be overcome
Resistance to airflow and bronchial radius
Where is the resistance to airflow primarily (yap)
- resistance to airflow primary occurs in the first 6 branchings of the respiratory tree
What is the main airway of resistance
Bronchi
Most of the resistance to airflow arises in the
Bronchi
Do the small airways contribute to airway resistance? Why?
Thesmall airways(terminal and respiratory bronchioles) contribute very little to airways resistance
(Due to high crosssectional area)
What does a spirometer measure
Volume inspired / exhaled
- how much and how fast you breathe
- the speed is indicative of resistance of airways
Spirometer is
The pulmonary function test
Diagram of a spirometer
Tidal volume
Restful breathing
- half a litre
Spirometer trace
At the end of breathing out..
Will always be some air left
- RESIDUAL VOLUME
- top one that is unlabelled in inspiration capacity
Vital capacity
Inspiratory reserve + Expiratory reserve + Tidal volume Volume of air that can be moved in and out of your lungs
Total lung capacity
Vital capacity + Residual volume
Total volume in lungs when it is filled to max
Inspiratory capacity
Inspiratory reserve + Tidal volume
Total volume of air that can be inspired from rest
Functional residual capacity
Expiratory reserve + Residual volume
Volume remaining in lungs after normal exhalation
How to to determine airway resistance
Forced exiratory volume in one second (FEV)
- ie how much of the forced vital capacity (FVC) comes out in the first second
- reduced with diseases causing resistance to airflow (e.g asthma)
FEV/FVC ratio
- normal ~ 80%
- less then 0.7 indicates airways obstruction = increased airway resistance
FEV and FVC on graph - forced expiration measurement from a spirometer
What can discern the difference between obstructive and restirctive issues?
Spirometry
features if RESTRICTIVE issues
Reduced lung capacity:
- reduced lung compliance (e.g fibrosis)
- insufficient surfactant release
Features if OBSTRUCTIVE issues
Resistance to airflow:
- asthma
- chronic bronchitis
- emphysema
