Mechanics of breathing Flashcards
Breathing definition
The bodily function that leads to ventilation of the lungs. Also known as (external) respiration
Ventilation definition
The process of moving gases in (inspiration) & out (expiration) of the lungs
Mechanics of breathing definition
Describes the structural & physiological bases of ventilation
What are examples of obstructive conditions
Asthma, chronic obstructive pulmonary disease (COPD), lung cancer
What are examples of restrictive conditions- intrinsic and extrinsic
- Intrinsic, e.g., pulmonary fibrosis- idiopathic disease (don’t know what causes it)
- Extrinsic – pneumothorax, disorders of the thoracic skeleton
When inspiring is the pressure constant (atm) large or smaller than the pressure variable (alveoli)?
Pressure constant is larger than the pressure variable.
When expiring is the pressure constant (atm) large or smaller than the pressure variable (alveoli)?
Pressure variable is larger than the pressure constant.
What inspiratory muscles are used for quiet breathing?
Diaphragm, external intercostals stabilise rib cage
What inspiratory muscles are used for increasing effort?
Diaphragm, external intercostals lift & expand rib cage, accessory muscles, neck muscles, shoulder girdle muscles
What expiratory muscles are used for quiet breathing?
Elastic recoil of tissues
What expiratory muscles are used for increasing effort?
Internal intercostals and abdominal wall muscles
How are respiratory muscles innervated?
Diaphragm- phrenic nerves (C3, C4, C5)- nerves supply the muscle
Intercostals- segmental thoracic nerves
Why are the pleura important?
The pleura are important in transmitting thoracic cage expansion into lung volume expansion.
What does thoracic cage expansion do?
Thoracic cage expansion exerts an increasing negative pressure on the intrapleural space.
Is pressure in the pleura less than the pressure change in the alveolus?
Yes
Why is change in pressure outside always 0?
End inspiration and end of expiration no movement in gas so equilibrium between the pressure in alveoli and atm P.
When individual breathes in- what happens to the intrapleural P? Does the chest expand? What happens to alveolar P?
First reduction of intrapleural P as chest expands and alveolar P becomes negative
When individual breathes out- what happens to the intrapleural P? Does the chest expand? What happens to alveolar P?
When individual breathes out, relax muscles that enable to breathe in, V in chest goes down, intrapleural rise and becomes less negative, increases alveolar pressure, reverses P gradient so gas moves out until the alveolar goes up and then comes down. Equilibrates with atm P.
How does the respiratory cycle work in terms of pleural P?
R cycle initiated by changes in pleural P, pleura P goes down and then returns back to 0. When you breathe out you raise intrapleural P, alveolar P goes and as breathing slows down eq back to 0.
How can volume of air be measured?
The volume of air moving in and out of the lungs during ventilation can be measured using a spirometer.
Tidal volume
The volume of air moved in or out of the lungs during normal breathing
Inspiratory reserve volume
After a normal expiration, take as deep a breath in as possible
Expiratory reserve volume
After a normal inspiration, breath out as deeply as possible
Residual Volume
Even after a maximal expiration, air remains in the lungs.
Why does air remain in the lungs?
This is because of the rigid nature of the thorax and the pleural attachments of the lungs to the chest wall that prevent complete emptying of the lungs.
How do you work out total lung capacity?
Total lung capacity = TV + IRV + ERV + RV
How do you work out vital capacity?
Vital capacity = TV + IRV + ERV
How do you work out functional residual capacity?
ERV + RV
Vital capacity defintion
After a maximal inspiration make a maximal expiration
Functional residual capacity definition
FRC- amount of air that is left in the lungs at the end of a normal expiration
What is a restrictive lung disease?
Can breathe normal at rest but at exercise they can’t increase their ventilation
What does a restrictive lung disease reduce?
Reduced RV, FRC, VC, TLC
What is a obstructive lung disease?
Increased RV- as obstruction of air passages, bronchioles air becomes trapped
What does a obstructive lung disease affect?
– TLC may be reduced (COPD) or increased (emphysema)
– FRC increased in emphysema
What is compliance?
The change in lung volume per unit change in intrathoracic pressure
Equation for compliance
C = ΔV/ΔP
How to measure compliance
Spirometry for volume and oesophageal balloon for pressure
- Take atm P as 0
- Measurement end of inspiration or end of expiration
- At end alveolar P has equilibrated with atm P
- Interpleural P- P transducer used with built in balloon- subject swallows the tube
What is the recoil pressure of the lung?
Difference between alveolar P and pleural P.
What is the chest recall P?
Chest wall recall P difference between intrapleural and barometric P.
What is the lung compliance curve?
Recoil pressure against V of the lung.
At maximal expiration/residual V what happens to the alveolar pressure?
What happens to intrapleural P?
First maximal expiration then wait for equilibrium. Alveolar P equilibrates with the with atm P. Glottis is open.
Intrapleural P is as positive as it gets.
What is recall P of the lung (equation)?
Recall P of the lung = alveoli P – intrapleural P
Alveolar P is what all the time?
0
What is the intrapleural pressure at end expiration?
Intrapleural P less negative at full expiration.
What is the intrapleural pressure at peak inspiration?
Deep breath, generate very negative P in the intrapleural space in the chest e.g. -30 cm of water.
What is chest wall compliance? (equation)
Chest wall P= Pleural P- atm P
Chest wall curve- how does maximal expiration work and what does it cause the intrapleural pressure to do?
At residual V, maximal R. To measure recall P of lungs, muscles have to be relaxed to expand and contract. Thus have to do maximal expiration, close glottis, relax muscles. Without letting any air out. Generate a negative intrapleural pressure (-30). Therefore at RV- chest wants to spring out due to negative P.
What is the intrapleural P at FVC? What happens to the muscles and glottis?
Neutral position at FVC. Same as end expiration and tidal V. If perform that manoeuvre breathe all the way out close the glottis relax the muscles, open the glottis and let the system to come back to its natural position.
What is the relaxation point of the respiratory system?
FRC is the relaxation point of the respiratory system when chest wall & lung recoil pressures are equal but opposite.
Diseases associated with reduced compliance- circumferential burn
Burn that goes round the chest- get tissue damage and scar formation which pulls on the skin around it. As scar from a burn is healing and contracts all away around the chest. So severe can’t breathe. Escharotomy- cutting down to the sternum so patient can breathe.
Diseases associated with reduced compliance- Pulmonary fibrosis -caused by what?
Caused by smoking, particulate matter, unknown autoinflammatory condition
Diseases associated with reduced compliance- Kyphoscoliosis
Abnormal curvatures of the spine- back to front curvature, scoliosis- natural deviation of the spine- ribs don’t expand as they normally would so compliance is reduced
Diseases associated with increased compliance- emphysema
Emphysema- obstructive condition destroys the elastic tissue of the lung itself so there is less of it. More easily expanded. Increase of compliance of the lung tissue.
Compliance is not equal throughout the lung why?
This is due to the role of gravity- alveoli are always open- at the bottom are open but not completely shut. Alveoli have different compliances according to position in the lung. Compliance curve at the bottom is steep and flattens at the top. Changes in P end up and down in the lung- bigger change in basal alveoli compared to the upper alveoli. Alveoli at base of lungs better ventilated at the bottom due to gravity pulling blood down towards the base.
What happens if closing capacity exceeds FRC?
If the closing capacity exceeds FRC, alveoli in dependent lung regions will be poorly ventilated.
What is closing capacity?
V of the lung within the chest when you get the closing of the basal alveoli is called the closing capacity.
What is the law of Laplace?
Determined in a sphere the P is proportional to the surface tension and inversely proportional to radius.
What is surface tension?
Surface tension is a force on a membrane on an air fluid interface that is always tried to compress down.
Why is a sphere formed by gas/liquids?
Energy is required to maintain a gas-liquid interface.
Potential energy is minimised through reducing surface area to volume ratio by formation of a sphere.
Natural tendency is for liquids/ gases to form a sphere to minimise surface tension.
What is a type 2 alveoli cell?
Type 2 alveoli cell which has defence functions- as fights infections- key function is to secrete surfactant- detergent that lines the inner membrane of the alveoli- reduces surface tension of the alveolus.
What produces surfactant? What is is made of?
- Produced by type II alveolar cells
* 90% phospholipid, 10% protein
What does surfactant do?
• Acts as a detergent to reduce alveolar surface tension – Increases pulmonary compliance – Prevents atelectasis – Aids alveolar recruitment – Minimises alveolar fluid
Why is a type 2 alveoli disease?
Deficient in infant respiratory distress syndrome- problem with premature babies- type 2 cells don’t produce surfactant- surface tension- collapsing of small airways
Why does surfactant becomes more dispersed as alveolar volume increases?
Equalises pressure between alveoli of different size. Done because present in the same quantity. In small alveolus molecules tightly packed together big effect on surface tension. Larger alveolus molecules less tightly packed so reduces surface tension. This equalises the surface tension and P.
Hysteris
Any process where the energy required to move in one direction is different energy in the opposite direction is called hysteresis.
What are the causes of hysteria?
- Reduced compliance
2. Airway calibre
What is laminar flow?
Laminar flow is where all the air molecules are in an organised path, they flow smoothly.
Where do you get more turbulent flow?
In upper airways, they are wider and the flow is quicker you get more turbulent flow- pressure differential requires to have the same effect on flow is affected the square of the pressure differential, compared to a directional relationship in laminar flow.
What is turbulent flow?
Turbulent flow, type of fluid (gas or liquid) flow in which the fluid undergoes irregular fluctuations, or mixing.
Where do you get laminar flow?
Get laminar flow in the more distal (the lower branches of the alveolar tree).
Where do you get turbulent flow?
In upper airways, they are wider and the flow is quicker you get more turbulent flow.
What does pressure differential require?
Requires to have the same effect on flow is affected the square of the pressure differential, compared to a directional relationship in laminar flow.
What does a vitolgraph spirometer used to measure?
- the forced vital capacity (FVC).
- the forced expiratory volume in 1 second (FEV1)
What does peak flow measure?
The peak expiratory flow rate (PEFR)
What is Peak Expiratory Flow Rate (PEFR)? How does it work?
- Patients can use a peak flow meter to monitor their asthma or COPD at home
- Wide diurnal variations occur in PEFR, with the highest readings in the evening and the lowest in the early hours of the morning
- PEFR is less dependent on effort than the FEV1 but only measures expiratory flow rate
Blow in a tube- arrow moves to a number
What is a flow volume loop?
The flow-volume loop is a plot of inspiratory and expiratory flow (on the Y-axis) against volume (on the X-axis) during the performance of maximally forced inspiratory and expiratory manoeuvres.
How does a flow volume loop work?
Start from residual volume breathing all the way out and then breathe in- total lung capacity.
Expiration, then return to residual volume.
Dynamic air collapse- what are the four different manoeuvres
- Pre inspiration- end expiration- alveolar P is 0. Want to see the transpulmonary P = P in alveolus - pleura
- During inspiration- When start to breathe in, inside becomes more negative
- End inspiration- finish breathing all the way out- transpulmonary P is keeping airway open
- Forced expiration- increase P in intrapleural space- pressure differential between alveolus and intrapleural will be the same. P in the conducting tube is +19 but the P within the chest round it is +30. Thus transpulmonary P is 11cm downwards compressing the airway. When forcefully breathe out- reduces diameter of airway, increases resistance, limits the flow.
How is energy used in inspiration?
The energy used in inspiration to overcome elastic forces is stored as potential energy which is dissipated in expiration.
How is work expended?
Work is expended in the form of heat during inspiration & expiration to overcome resistance forces
What is the equation for work?
Work = volume x pressure
