Respiratory Physiology II Flashcards
what is pulmonary ventilation breathing
- It is the process of air flow to the lungs during inspiration (inhalation) and out of the lungs during expiration (exhalation)
why does air flow occur
- Air flows because of pressure differences between the atmosphere and the gases inside the lungs
- muscular breathing and recoil of elastic tissues create the changes in pressure that results in ventilation
in what direction does airflow occur
air like other gases flows from a region with a high pressure to a region with lower pressure
what is the pressure at the beginning of the respiratory tract called
Patm
what is the pressure inside the lungs called
Pa
what happens if - If Patm and Pa are equal
- If Patm and Pa are equal than there is no airflow
what happens when Pa is smaller then Patm
- If Pa
what happens when Pa is larger than Patm
if Pa> Patm airflows out of the lungs
what is the law that defines the relationship between expansion and gas flow
Boyles law
Define Boyle’s Law
- If the volume of gas is made to increase the pressure exerted by the gas decreases
- As the alveoli are forced to expand the pressure inside them decreases and the gas in flows in from the conducting airways
lungs and there elastic properties
- lungs are elastic
- they return to there original shape fi a force that is distorting them is removed
- if you prevent the air escaping by blocking the lungs the recoil of the lungs will produce a recoil pressure
how do you generate inflation
- For an object to be distorted it must be subjected to a force for example pressure
- Inspiration = inflation and expiration – deflation
- Rather than blowing into the balloon: if the balloon = lungs, then they are inflated by reducing pressure outside (like a plunger in a syringe).
- Lowering the plunger (diaphragm) reduces the pressure around the balloon and generates inspiration
How do you work out inspiration
inflation and expiration - deflation
describe the elastic properties of the chest wall
- The thoracic cage is also elastic.
- Under normal conditions the chest wall has a tendency to pull outwards and the lung to pull inwards thus balancing themselves
why does the chest wall not collapse under normal circumstances
Under normal circumstances the chest wall does not collapse, this is because the lungs and chest wall are in close contract by the intrapleural fluid in the intrapleural space
This means that a pressure is created in that space
what is the sign for intrapleural pressure
Ppl
describe intrapleural space
intrapleural space has cohesive forces
- they are difficult to separate when they are adjoined to each other
- therefore as the chest wall expands during inspiration the lung follows therefore the two structures expand as a single unit
how is the intrapleural space generated
At the end of expiration when you are relaxed before you take your next breath there is a tension between the lungs whose elasticity is causing them to collapse and the chest wall whose elasticity is cause it to spring outwards this generates a pressure in the intrapleural space known as the intrapleural pressure Ppl
- Intrapleural pressure is negative with respect to atmosphere (and the air pressure in the alveoli which is connected to the atmosphere)
Describe the changes int he intrapleural pressure
- The normal pleural pressure the beginning of inspiration is negative
- During inspiration expansion of the chest cage pulls outward on the lungs and intrapleural pressure and becomes more negative
- Intrapleural pressure becomes less negative to lead to quiet expiration
describe what happens to the intrapleural pressure in a pneumothorax
- If the pleural cavity is damaged/ruptured air enters the pleural space (because the pleural pressure is less than atmosphere)
- The intrapleural pressure becomes equal to or exceeds the atmospheric pressure and the pressure surrounding the lungs will increase and may cause the lungs to collapse.
what is compliance
- Elasticity is a measure of how easily the lungs can be stretched and is conventionally expressed as compliance.
- Compliance is the ease at which the lungs expand under pressure
what is the compliance of the lungs changed by
- it is changed by most lung diseases
what is the equation of compliance
change in volume/change in pressure
how do you work out the total compliance
- Across the wall of the structure being investigated e.g. lungs (Cl) chest wall (Cw) or lungs and chest wall (Total compliance CTOT)
what happens to lung compliance at a high expanding pressure
- In normal range the lung is very complaint however at high expanding pressure the lung is stiffer and compliance is smaller
at any given pressure
- At any given pressure lung volume during inhalation is less than the lung volume during exhalation
what is airway closure
Even without any expanding pressure the lung always has some air in it. This is due to airway closure, where small airways close trapping gas in alveoli. Airway closure increases in certain conditions, such as age and lung disease
diseases that affect either the chest wall or lung structure will..
affect compliance
what causes a reduction in compliance
- Increase of fibrous tissue in the lung
- Collapse/closure of lung (atelectasis)
increase in pulmonary venous pressure
what causes an increase in compliance
- Age
- Emphysema
what is emphysema
- a lung disease which causes destruction of the normal lung architecture which includes the elastic fibres and collagen
what does emphysema cause to the structure of the lungs
- There is also impaired elastic recoil and lungs do not deflate as easily.
- The lung is more easily distended, and the compliance of the lung is increased (more compliant
what’s the differences between emphysema and fibrosis
Emphysema – same amount of pressure, easier to inflate
Fibrosis – same amount of pressure harder to inflate
what is the effect of kyphoscoliosis on the compliance of the chest wall
- Structural change in the thorax
- Kyphoscoliosis – a disorder characterised by progressive deformity of the spine will affect compliance
- However more usual that lung complacence is affected
what 2 main components generate the elastic properties of the lungs
1) elastic fibres and collagen
2) surface tension forces caused by the alveolar-liquid interface.
name the structure of the elastic fibres in the lungs
- Elastic fibres form the bulk of connective tissue present in the walls of the alveoli
- Elastin fibres act like stocking when stretched
filling a lung with …
fluid makes it easier to inflate
what happens in inflation to an air filled lung
- Inflation of the lung follows a different pressure/volume curve from deflation.
- This is known as hysteresis which literally means “to lag behind”.
- A greater pressure is required to reach a specific lung volume when you are inflating it rather than deflating it.
what happens to inflation in an saline filled lung
- Hysteresis is abolished.- no lagging behind
- Much easier (less pressure) to expand fluid filled lungs.
- In fluid filled lungs only the elastic forces are working - there must be another component that also contributes.
- In the fluid filled lungs the air-fluid interface has been abolished.
What is hysteresis
this is when the inflation of the lung follows a different pressure/volume curve from deflation
where is surface tension presence
in the alveoli
describe what surface tension does
- The cohesive forces between liquid molecules at the surface are responsible for the phenomenon known as surface tension.
- The molecules at the surface of the liquid do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface.
- This forms a surface “film” which makes it more difficult to move an object through the surface than to move it when it is completely submersed.
- the water molecules on the boundary have an especially strong attraction for one another and therefore as a result the water surface is always trying to contract
what is the surface tension elastic force
- On the inner surface of the alveoli the water surface is always trying to contract
- This results in the alveoli trying to collapse (forming air out through bronchi)
- The net effect is to generate an elastic contractile force throughout the entire lungs, this is known as the surface tension elastic force
what does Lapacales law relate to
relates pressure to surface tension and radius
what is the equation of Lapacales law
P = 2T/r
- P = pressure within the bubble
- T = surface tension
- R = radius
explain how Lapacles law works
- the smaller bubble the greater the internal pressure that is required to keep it inflated, the smaller the radius
How do the lungs compensate with problem of pressure differences arising from having alveoli of different sizes
- Surfactant this stabilises the alveoli
what do surfactants do on the alveoli
- Surfactants greatly reduce the surface tension and therefore reduce the surface tension elastic forces
what is the surfactant made up of
- Pulmonary surfactant is a complex mixture of lipids and proteins.
- A major component (approx. 50%) of surfactant is the phospholipid Dipalmitoylphosphatidylcholine (DPPtdCho)
describe the properties of the surfactant
- Amphipathic character (hydrophilic/water loving head groups and hydrophobic tails towards air) and resultant packing reduces surface tension.
what is surfactant secreted by
type II alveolar epithelial cells
describe how surfactant is formed
- Assembly of surfactant occurs in the lamellar bodies and is secreted into the alveolar fluid where it undergoes structural changes to form a meshwork known as tubular myelin before eventually forming a surfactant layer at air water interface
describe what happens in infant respiratory distress syndrome
- Caused by developmental insufficiency of surfactant production and structural immaturity in the lungs
• A baby normally begins producing surfactant between weeks 24 and 28 of pregnancy.
• Most babies produce enough surfactant to breathe normally by week 34.
• In babies born prematurely not enough surfactant produced and may lungs collapse
what is airway resistance
- Airway resistance Raw is defined as the resistance to the flow of gas within the airways of the lung
what happens in asthma
- Reduction of airway diameter due to contraction of smooth muscle or swelling due to inflammation and mucus production
- Contraction of bronchial smooth muscle narrows the airways and increases airway resistance
- Tone of the smooth muscle in the airways is under control of autonomic nervous system
what does the pattern of flow through tubes vary with
- varies with the velocity and physical properties of the fluid
what are the two types of flow
laminar and tuberlent
what is the difference between laminar and tuberlent flow
- In laminar flow the movement is orderly and streamlined whereas in turbulent flow movement is chaotic.
- In most circumstances flow can be considered laminar as a first approximation.
what is poiseullies law
relationship between driving pressure and flow
- smal changes in the dieter of airways leads to relatively big changes in flow
what type of flow is described by poiseuilles law
Laminar flow
do the example of working out the percentage increase
Airway radius of 4 units dilates to a radius of 5units.
• What is the percentage increase in the radius of the airway?
5-4/4)100=25%
• What is the percentage increase in the airflow?
• r=4, r4=256 and r=5, r4=625
• (625-256/256)100=144%
Relatively small changes in the diameter of airways ….
leads to big changes in flow
what are the sites of airway resistance
- upper respiratory tract
- lower respiratory tract
- small bronchi and bronchioles
describe airway resistance in the upper respiratory tract
- Almost half of resistance to airflow resides in the upper respiratory tract
- Significant resistance is nose such as inflammation and cold
- Reduced resistance when breathing through mouth e.g. shift during exercise
Describe airway resistance in the lower respiratory tract
- Half of resistance to airflow comes from the lower respiratory tract
- Assuming laminar flow poiseuille’s law would predicts that major resistance to airflow would occur in airways with smaller radius but this does not happen because the total cross sectional area increases as you go down the tracheobronchial tress although the diameter of each airway is small there is a larger number of them
describe airway resistance in the small bronchi and bronchioles
- The most important part of the bronchial tress in terms of physiological control of airway resistance are small bronchi and bronchioles
- Found at the level in bronchial tree where the increase in number of airways has not yet exerted its effects and the cross sectional area is small
- Virtually no cartilage but innervated smooth muscle
- Resistance of small bronchi and bronchioles is variable and under the influence of neuronal and hormonal factors.
- For example asthma is a spasm of the bronchial smooth muscle, which may be hyper responsive.
- Bronchodilators act to relax the muscle.
how does the parasympathetic system act on the bronchial smooth muscle
: postganglionic fibres release Ach which stimulate muscarinic receptors on smooth muscle causing them to contract.
how does the sympathetic system act on the bronchial smooth muscle
occurs mainly via circulating catecholamines. Adrenalin activates β2 receptors causing smooth muscle to relax.
what are the other factors that contribute to bornchomotor tone
- Non-adrenergic non cholinergic systems, NANC: includes bronchodilators (and possibly constrictors).
- Mediator release (e.g histamine etc): mast cell degranulation, neutrophils and eosinophils important in various stages of asthma
- Rapidly adapting pulmonary receptors: also known as irritant or cough receptors
- Slowly adapting/stretch pulmonary receptors: activity reduces bronchomotor tone
- Carbon dioxide: causes bronchodilation in underventilated areas where the gas builds up
what cause the work of breathing
- Resistance to airflow
2. Elastic recoil of the lungs
what is the equation for the work of breathing
- Energy measured in joules
- W = P . ∆V
what happens to work when disease happens in the lungs
- Normally respiration is very efficient and represents a small fraction of the total cost of metabolism; however this changes in disease.
- Changes in compliance and airway resistance may lead to increased work load.
what happens in COPD with energy requirements
severe COPD, energy requirements increase in order to breath. A situation may be reached in which the increased oxygen supplied from increasing ventilation is all consumed by respiratory muscles.
