Respiratory Physiology Flashcards
What are the 4 stages of Respiration?
- Ventilation (gas exchange from atmosphere to alveoli)
- Gas Exchange from alveoli to blood
- Transport of O2 and CO2 in blood
- Exchange of O2 and CO2 in tissues
How is air moved into the lungs using Boyle’s law?
- normally pressure in alveoli = atmospheric pressure
=> Need to decrease this pressure to move air in - diaphragm flattens and external intercostals move ribs to increase thoracic volume
=> pressure drops and air can move in down pressure gradient
How is air moved out of the lungs following Boyle’s Law?
Passive relaxation of the diaphragm and external intercostal muscles causes thoracic cavity volume to reduce
=> intra-alveolar pressure increases to above that of the atmosphere
=> air is expelled from lungs down pressure gradient
What are the major inspiratory muscles?
Diaphragm
External intercostals
What are the accessory inspiratory muscles?
Sternocleidomastoid
scalenus
Pectoral muscles
What muscles can be used in active expiration?
Internal intercostals
abdominal muscles
What is the transmural pressure gradient and what does it cause?
intra-alveolar pressure - 760 mm Hg pushes OUT
intrapleural pressure - 756 mm Hg pushes IN
=> OUT > IN
4 mm Hg difference = transmural pressure gradient
=> stretches lungs OUT to fill the larger thoracic cavity.
Atmospheric pressure - 760 mm Hg pushes IN
Intrapleural pressure - 756 mm Hg pushes OUT
=> IN > OUT
4 mm Hg difference => pushes IN and compresses the thoracic wall
The external intercostal muscles move the ribs and sternum up and out. What is this mechanism called?
“bucket-handle” mechanism
Describe how the intra-alveolar and intra-pleural pressure change during INspiration and EXpiration?
Inspiration - both decrease
Expiration = both increase
this keeps transmural pressure gradient almost constant
What happens when the transmural pressure gradient is abolished? I.e. in a pneumothorax?
- Pressures attempt to reach equilibrium (all 760mmHg)
=> lung collapses to its unstretched size
=> chest wall springs outward
What is responsible for elastic recoil of lungs?
- Elastic connective tissue
- Alveolar surface tension
What is the alveolar surface tension and how does it help recoil?
Attraction between water molecules at liquid air interface
=> produces a force which resists the stretching of the lungs
What substance is made by the alveoli to ensure the surface tension doesnt get too high (or else they will colllapse)?
Surfactant
Smaller ALveoli have a higher tendency to collapse. TRUE/FALSE?
TRUE
- due to La Place’s law
What is the consequence of not having enough surfactant as a newborn?
Respiratory Distress of Newborn
- Baby makes strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs
What is meant by Tidal Volume and what is a normal value for this?
Volume of air entering/leaving lungs in a normal single breath
= usually 0.5L
How much air can be inspired over and above tidal volume using accessory muscles? And what is this called?
Inspiratory Reserve Volume = 3.0L
What is the maximum volume of air we can inspire in one breath? What is this called and how can it be calculated?
Inspiratory Capacity = 3.5L
Normal Tidal Volume + Inspiratory Reserve Vol.
How much extra air can be actively expired after a normal breath? What is this called?
1.0L
Expiratory Reserve Volume
How much air will remain in the lungs EVEN after a maximal expiration?
Residual Volume 1.2L
What is the Functional Residual Capacity? How can it be calculated?
Volume of air still in the lungs after normal expiration
Expiratory Reserve Volume + Residual Volume
1.0 + 1.2 => 2.2L
What is the Vital Capacity and what is a normal volume for this?
Maximal inspiration and expiration
=> TV (0.5) + IRV (3.0) + ERV (1.0) = 4.5L
What is the Total Lung Capacity and how is this different from the vital capacity?
TLC = Vital capacity AND the residual volume that cannot be moved out of the lungs
=> VC (4.5) + RV (1.2) = 5.7L
When can the residual volume in the lungs increase?
When elastic recoil of the lungs is lost
e.g. in emphysema
What is the difference between the FVC and the FEV1?
FVC = Forced Vital Capacity
=> Max. volume that can be forcibly expelled from lungs following a maximum inspiration
FEV1 = Forced Expiratory Volume in 1 second
=> Volume of air expired during the first second when measuring FVC
Measuring FVC and FEV1 is collectively known as what?
Spirometry
A normal FEV1/FVC ratio is more than what percentage?
> 70%
Describe Spirometry findings if a patient has OBSTRUCTIVE disease (i.e. asthma/COPD)
FEV1 = LOW
FVC = NORMAL
=> FEV1/FVC Ratio = LOW (<70%)
Describe the spirometry findings seen in patients with a RESTRICTIVE lung disease (i.e. Interstitial Lung Disease)
FEV1 = LOW
FVC = LOW
=> FEV1/FVC Ratio = NORMAL
Patients can have mixed Obstructive and Restrictive disease. TRUE/FALSE?
TRUE
- this often presents as FEV1, FVC and ratio ALL LOW on spirometry
What determines how resistant an airway is?
diameter of airway
=> Parasympathetic stimulation = bronchoconstriction
Sympathetic stimulation = bronchodilatation
What is dynamic airway compression and when is it used?
- Used during active expiration to put pressure on alveoli and airways
- Pressure on alveolus helps push air out of lungs
When is dynamic airway compression not desirable?
- In patients with obstructive disease
- it makes active expiration more difficult for them by compressing the airway
What is Peak Flow used to assess?
- Airway function in obstructive lung disease (e.g. asthma and COPD)
How is a Peak Flow measurement taken?
- patient gives short sharp blow into the peak flow meter
- best of three attempts taken
- compared to normal for their height and weight
What is meant by pulmonary compliance?
- Effort to inflate the lungs
- If less compliant, it takes more work to inflate
What can cause a decrease in pulmonary compliance?
- pulmonary fibrosis
- pulmonary oedema
- lung collapse
- pneumonia
- absence of surfactant
What symptom does a decreased pulmonary compliance usually cause?
- causes lungs to become stiff
=> patients become short of breath on exertion
=> may cause restrictive spirometry pattern also
What happens in INCREASED pulmonary compliance?
- lungs can inflate, but struggle to recoil
=> often they are hyperinflated and patients have to work harder to get the air out
(e.g. emphysema)
Pulmonary compliance increases with age. TRUE/FALSE?
TRUE
What can increase the work of breathing?
- decreased pulmonary compliance
- increased airway resistance
- decreased elastic recoil
- Need for increased ventilation
What is the difference between Pulmonary Ventilation and Alveolar Ventilation?
- some air remains in airways and cant take part in gas exchange (dead space)
=> This cannot get to alveoli to take part in alveolar ventilation
Is it more advantageous to increase the rate or depth of breathing when exercising?
Depth
- Increasing rate of breathing has no effect on the dead space
=> need to increase depth of breathing to increase alveolar ventilation
Transfer of gas from lung -> blood depends upon what?
Ventilation - rate that gas is passing through lungs
Perfusion - rate that blood is passing through the lungs
In what area of the lung are ventilation and perfusion at their lowest? What effect does this have on the V/Q ratio
- apex (top) of lung = poorest perfusion and ventilation
=> this causes V/Q ratio to rise
What is meant specifically by the ALVEOLAR dead space?
- air in the alveolar airways
- BUT no blood in perfusing that area in order to perform gas exchange
There is usually a small mismatch in ventilation/perfusion between the PO2 in arterial blood and in the alveoli. TRUE/FALSE?
TRUE
- Large gradient would indicate problems with gas exchange
- OR right to left shunt in the heart
Describe each step of the respiratory tree.
CONDUCTING ZONE
- Trachea
- Bronchi
- Bronchioles
- Terminal Bronchioles
TRANSITIONAL and RESP ZONES
- Respiratory bronchioles
- alveolar ducts
- alveolar sacs
What are the four factors which influence gas exchange in alveoli?
- partial pressures of O2 and CO2
- diffusion coefficient (how soluble gas is in membrane)
- surface area
- Thickness of alveolar membrane (e.g. interstitial fluid)
HOw is O2 transported around the body?
- bound to Hb
- Hb has 4 haem groups, each carries one O2
=> maximally saturated
What is the primary factor that determines how saturated Hb are with O2 in body?
PO2
- this is highest in lungs and most Hb are maximally saturated in lungs
- oxygen begins to dissociate in tissues with lower pO2
What are the 3 main ways that O2 dedlivery to tissues can be impaired?
Respiratory disease
Heart failure
Anaemia
Describe why the oxy-haemoglobin dissociation curve is sigmoid shaped?
Binding of one O2 to Hb increases the affinity of Hb for O2
What happens when the Bohr Effect shifts the Oxy-haemoglobin dissociation curve to the right?
- increased release of O2 in tissues
What causes the Bohr Effect to shift the Oxy-haemoglobin dissociation curve to the right?
INCREASE IN:
- 2,3-Biphosphoglycerate
- Temperature
- [H+]
- PCO2
Compare the Oxy-haemoglobin dissociation curve for foetal and adult Hb and explain why they are different
Foetal haemoglobin = 2 alpha and 2 gamma subunits
=> HbF interact less with 2,3- Biphosphoglycerate
=> higher affinity for O2 than HbA
=> curve shifted to the left
=> This allows O2 transfer from mother to foetus even if the PO2 is low
Where is myoglobin found and what is its function?
- present in skeletal and cardiac muscles
- releases O2 at very low PO2
=> short-term storage of O2 for anaerobic conditions
How many O2 molecules can be carried by myoglobin at any one time?
One
- only one haem group per myoglobin molecule
Describe the shape of the oxy-myoglobin dissociation curve in comparison to the oxy-Hb dissociation curve
Hyperbolic (not sigmoidal)
What does myoglobin in the blood indicate has occurred?
Muscle damage
