Lung Physiology Flashcards
Water and pump handle…
Contraction of the external intercostals raises the lateral part of the ribs causing a bucket handle motion that increases the transverse diameter of the thorax. The vertebrosternal ribs also follow a pump handle motion, which raises sternum and increases the anterior-posterior dimensions of the thorax.
What is quiet breathing?
Quiet breathing, also known as eupnea, is a mode of breathing that occurs at rest and does not require the cognitive thought of the individual. During quiet breathing, the diaphragm and external intercostals must contract. … During forced breathing, inspiration and expiration both occur due to muscle contractions.
Exploration is a s passive process due to the recoil of the lungs during quiet breathing.
What nerve controls the diaphragm?
The phrenic nerve from C345 - supplies motor and sensory function.
What are the motor and sensory nerves of the respiratory pump?
Motor
C345 - phrenic
Thrace-lumbar nerve roots
Sensory
C fibres
Vagus
What is the total combined surface area for gas exchange?
50-100m2
What is dead space?
Anatomic?
Alveolar?
It is the volume of air not contributing to gas exchange consisting of a anatomic and alveolar dead space.
Anatomic = air in nasal cavity, sinuses pharynx, larynx, trachea - not involved in gas exchange
Alveolar = air not used in gas exchange due to damaged alveoli or an inadequate blood supply etc.
How much air is drawn into the lungs during inspiration?
Max fill = roughly 500ml
What allows for easily saturation of Hb with oxygen in the lungs?
There are 1000 capillaries per alveolus
Each erythrocyte may come into contact with multiple alveoli
Very short distance from RBC to air - only 2 cell thick
At rest 25% the way through the capillary Hb is fully saturated.
What do the perfusion of capillaries depend on?
Pulmonary artery pressure
Pulmonary venous pressure
Alveolar pressure
What is hypoxic pulmonary vasoconstriction?
Phenomenon where pulmonary arteries constrict during hypoxia.
Nomenclature
PaCO2 = partial pressure of CO2 in artery
PAC02 = partial pressure of CO2 in arteriole
PIO2 = pressure of inspired O2
V’A = alveolar ventilation
V’CO2 = CO2 production
R = respiratory quotient
What are the three ways CO2 is carried?
Bound to Haemoglobin - 23 %
Plasma dissolved CO2
As HCO3-
Physiological cause of a high CO2?
Reduced alveolar ventilation - reduced ventilation
Reduced alveolar ventilation - alveolar dead space increased
Increased CO2 production
PaCO2 =
K V’CO2/V’A
PAO2 =
PIO2 - PaCO2/R
Causes of hypoxia?
Alveolar hypoventiliation
Reduced PIO2
Diffusion abnormality
What is respiratory acidosis?
Lungs don’t remove enough CO2 causing the blood to become acidic.
Potential causes may be a lack of ventilation as this would increase CO2 levels of the blood.
What is the usual blood pH?
7.4
H+ conc of 40nmol/l
What is the Henderson-Hasselbalch equation?
PH= 6.1 + log(HCO3-)/(0.03*PCO2)
Ratio needs to equal 1.3 to be 7.4 pH
So as PC02 rises HCO3- must also rise (renal compensatory mechanism)
Why is control of the pH of blood important?
Optimal function of enzymes, cellular reactions etc.
How is the pH of blood controlled?
The carbonic acid/bicarbonate buffer system is important.
C02 is also removed by the lungs
HCO3- is under predominately renal control and takes longer to respond than releasing CO2 from the lungs.
Functional renal system however is needed to removed fixed acids, lungs will only remove carbonic acid.
What is a buffer system?
Minimises changes in pH on small additions of acid or alkali.
H2CO3 — HCO3- + H+
What are the 4 main acid base disorders?
Respiratory acidosis - increased PaCO2 decreased pH mild increased HCO3-
Respiratory alkalosis - decreased PaCO2, increased pH, mild decreased HCO3-
Metabolic acidosis - reduced bicarbonate and decreased pH
Metabolic alkalosis - increased bicarbonate and increased pH
An X-ray comes back with white specs over the lungs what is this likely to show?
An infection like TB
R the respiratory quotient =
about 0.8
What does: VC TLC RV FiO2 TV
VC = vital capacity = difference between RV and TLC
TLC = Total lung capacity
RV = Residual volume = volume of air in lungs after max expiration
FiO2 = fraction of inspired O2 = usually 21%
TV = Tidal volume - volume of usually air inspired or expired per breath.
We measure FEV1 and FVC and PEF what do these stand for/mean?
Note each measured value has a normal range lowest and uppermost 5% defined as abnormal.
FEV1 = forced expiratory volume over 1 second = volume of air that you can exhale in 1 second. About 80% of FVC - 4L.
FVC = forced vital capacity = the amount of air that can be forcibly exhaled from your lungs after taking the deepest breath possible (TLC — RV). About 5L.
PEF = peak expiratory flow = highest measure of flow during expiration. Produced via a peak flow meter - reading in L/min.
What is a flow volume loop and why is it useful?
… Email lecturer
What is gas dilution and how can it be used to measure lung volume?
Patient breathes in a known concentration of helium or nitrogen and after a few minutes the concentration of helium is the same in the spirometry and the lung. Use this to calculate volume of air in the lung.
Does not measure air in non-communicating bullae.
What is total body plethysmography?
A patient pants in a closed shutter to produce changes in the box pressure proportionate to the volume of air in the chest.
The volume measure represents the lung volume including gas trapped in the bullae.
Useful to note TLC =
VC + RV
What are transfer estimates and what are they used for?
A gas transfer test measures how well your lungs take up oxygen from the air you breathe. The result of the test is called the transfer factor.
CO is used in tiny quantities as it has a high affinity for binding to haemoglobin and can be measured.
A gas transfer test is used to help diagnose and monitor lung conditions including COPD and pulmonary fibrosis as it measures/ takes into account alveolar SA, capillary perfusion, Hb concentration.
What is DLCO and how is it calculated?
DLco also known as TLco refers to the transfer capacity of the lung, for the uptake of carbon monoxide (CO).
DLco = diffusing capacity for CO
Calculated from the total volume of the lung breath hold time and initial and final alveolar concentrations of CO.
What is compliance of the lungs?
What is transpulmonary pressure?
Ability of the lungs to expand under pressure.
Change in its volume per unit change in pressure.
Dynamic compliance = during retailer breath
Static “ = measured during holding breath.
Transpulmonary pressure = pressure difference between the alveoli and the pleura
Is breathing automatic?
Yes it is automatic there is no conscious effort for the basic rhythm.
There is cyclical excitation and control of many muscles.
What is your basic breathing rhythm - overview:
Respiration is controlled by the respiratory center in the brain stem in response to CO2 levels. Medulla Oblongata sets the basic rhythm of breathing (pacemaker). Pons smooths out respiratory rate and influence depth and length of respiration.
What controls the rate and pattern of your breathing?
In the pons you have the pneumotaxic center. It controls both the rate and the pattern of breathing. The pneumotaxic center is considered an antagonist to the apneustic center.
Pneumotaxic promotes inspiration, apneustic turns the signals off.
What nervous is the respiratory centre made up of?
The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal respiratory group, and the ventral respiratory group. In the pons, the pontine respiratory group includes two areas known as the pneumotaxic centre and the apneustic centre.
What is the job of the DRG and VRG?
The dorsal respiratory group controls the basic rhythm of breathing by triggering inspiratory impulses. These neurons send impulses to the motor nerves of diaphragm and external intercostal muscles.
The neutrons involved are the phrenic 345
The ventral respiratory group = responsible for both inspiration and expiration
Bot are found in the medulla oblongata
What is the physiology of inspiration:
There is an progressive increase in inspiratory muscle activation.
Lungs fill at a constant rate until tidal volume
End of inspiration there is a rapid decrease in excitation of the expiratory muscles
What is the physiology of expiration:
Largely passive due to the elastic recoil of the thoracic wall.
1st part is active slowing with some inspiratory muscle activity
It can become active with additional abdominal wall muscle activity
Where do sensory/afferent nerves take information?
Where do motor/efferent nerves take information?
Towards the CNS
Away from the CNS — effectors
What are chemoreceptors?
Types?
Chemoreceptors are sensors that detect changes in CO2 and pH, and have been classified, based upon anatomical location, as either central or peripheral.
Central - located in the brainstem (PaCO2) - more of an influence
Peripheral - carotid sinus and aorta arch (PaCO2, PaO2, pH)
They are stimulated by H+ conc and gas partial pressures in the blood.
If you increase your respiratory rate what happens to blood CO2 and why?
Increased ventilation, will lead to more CO2 excreted from the lungs and hence a decrease in blood concentration, this will result in less H2CO3 and hence less H+ ions meaning pH will increase
What is minute ventilation and what is it proportional to?
Minute ventilation is the volume of gas inhaled or exhaled from a person’s lungs per minute.
Proportional to PaCO2
More CO2 more ventilation
Central chemoreceptors:
where are they located?
What are they sensitive to and why?
Located in the brainstem in the pontomedullary junction
Sensitive to PaCO2 of blood perfusing the brain - it diffuses into the CSF and activates the chemoreceptors.
As the blood brain barrier is relatively impermeable to H+, H+ concs not important.
Where are peripheral chemoreceptors found?
Function?
Found in carotid bodies
Afferent via the IX cranial nerve
Also found in the ascending aorta
Afferent via the Vaal nerve
The peripheral chemoreceptors are responsible to hypoxia (low PAO2)
When detected they stimulate the carotid sinus nerve.
What type of lung receptors do you have?
What is their afferent nerve?
Function?
Stretch - found on smooth muscle sense lung volume
Irritant - found in larger conducting airways
Rapidly adapt - gasp
J - pulmonary and bronchial C fibres
Afferent nerve = X
Assist with lung volumes
What other airway receptors do we have?
Nasopharynx and larynx
Have chemo and mechano receptors here
Sense and monitor flow
Pharynx
Activated by swallowing
Respiratory activity stops during swallowing protecting against food/drink down the trachea
What are muscle proprioceptors?
Proprioceptors are specialised sensory receptors that are located within joints, muscles, and tendons. As these receptors are sensitive to both tension and pressure, they play a role in relaying information concerning muscle dynamics to the conscious and subconscious parts of the central nervous system.
What happens to someone’s breathing as they ascent a mountain and why?
Ascending - PIO2 falls although FiO2 remains constant
This leads to a decreased PAO2 And a decreased PaO2
Peripheral receptors detect lower PaO2 and increase firing
This increases ventilation leading to an increased PAO2 and hence an increased PaO2
What are the circulation system found int the lungs?
Pulmonary circulation - 100% of blood flow from right ventricle
Bronchial circulation - 2% of blood flow from left ventricle
What is the bronchial circulation?
Circulation system that received blood from the aorta to supply the lungs with O2 and nutrient and take away waste products
How do the pulmonary and systemic arteries compare?
Pulmonary - thin, little muscle
Systemic - Thick, thick muscle
Due to blood being pumped with a higher pressure
PA = 25/8 Aorta = 120/80
What is pouiseuille’s Law?
Resistance of a system = (8 x L x viscosity)/ (Pi x r4)
R to the power of 4
Radius has an exponential effect on resistance
A small change in radius will cause a large decrease in resistance
Pressure across pulmonary circuit =
Cardiac output x resistance
MPAP - PAWP = CO x PVR
Mean pulmonary arterial pressure - left atrial pressure = …
on exercise mPAP remains stable but CO increases how is this possible?
PVR must decrease - it’s does this recruitment (more capillaries) and distention (allow more blood through) therefore there is decreased PVR
WHAT IS HYPOXAEMIA?
How does it differ to hypoxia?
What cause hypoxaemia?
Hypoxemia is defined as a decrease in the partial pressure of oxygen in the blood whereas hypoxia is defined by reduced level of tissue oxygenation.
Causes = hypoventilation, diffusion impairment, shunting and V/Q mismatch
What is hypoventilation?
What does it cause?
What may it be due to?
Hypoventilation is breathing that is too shallow or too slow to meet the needs of the body.
Leads to type 2 respiratory failure
May be due to muscular weakness - MND
Obesity
Loss of respiratory drive - opiates
What is a diffusion impairment? How can it lead to hypoxemia?
When oxygen can not diffuse into the blood and CO2 can not diffuse out.
This may be due to pulmonary oedema (alveoli filled with fluid)
Anaemia (lack of Hb)
Interstitial fibrosis = thicker membrane
What is a pulmonary shunt?
A pulmonary shunt is a pathological condition which results when the alveoli of the lungs are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region. In other words, the ventilation/perfusion ratio (the ratio of air reaching the alveoli to blood perfusing them) is zero.
What is a V/Q mismatch?
Ventilation perfusion mismatch or “V/Q defects” are defects in total lung ventilation perfusion ratio. It is a condition in which one or more areas of the lung receive oxygen but no blood flow, or they receive blood flow but no oxygen due to some diseases and disorders
What does V and Q stand for?
The ventilation rate (V) refers to the volume of gas inhaled and exhaled from the lungs in a given time period, usually a minute. It can be calculated by multiplying the tidal volume (volume of air inhaled and exhaled in a single breath) by the respiratory rate. In an average man, the ventilation rate is roughly 6L/min.
The perfusion (Q) of the lungs refers to the total volume of blood reaching the pulmonary capillaries in a given time period.
What is the V/Q ratio?
What is the ideal number?
The ideal V/Q ratio would be 1 for maximally efficient pulmonary function. However, the ratio varies depending on the part of the lung concerned. For example, when standing up straight, the ratio is roughly 3.3 in the apex of the lung, and only 0.63 in the base. This is to say that ventilation exceeds perfusion towards the apex, and that perfusion exceeds ventilation towards the base.
The different ratios for different areas are due to where each area lies in relation to the heart, with areas of lung below the heart having increased perfusion relative to ventilation due to gravity, reducing the V/Q ratio. As such the overall value in the average human lung is closer to 0.8.
Gravity triggers these changes in ventilation and perfusion
How can shunts effect V/Q ratios?
Shunt blocks off alveoli - blood travels through a non ventilated part of the lung would = 0/X = 0
Partials shunt of alveoli = decreased V = decreased ratio
Blockage of the capillary X/0 tends to 0 so answer tends to infinity
Reduced perfusion increased ratio as deciding by a smaller number
What may cause a V/Q mismatch?
Asthma, pneumonia, pulmonary oedema
What is polycythaemia?
An increased number of RBCs in the body
Look at shunts in more detail using the resources…
….
Why is hypoxic pulmonary constriction beneficial when alveoli bronchi become blocked?
The blood vessels around the blocked alveoli become constricted and hence there is an increased perfusion to the functional alveoli bronchi etc meaning this air can continue to be oxygenated.
Limits V/Q mismatching
What is pulmonary embolism?
Consequences
A pulmonary embolism is when a blood vessel in your lungs is blocked by a blood clot.
Due to a DVT clot moving to the lungs
Central pulmonary embolism = main trunk or right to left pulmonary artery becomes blocked
Peripheral = a further branch
Blocks blood exiting the right ventricle - lead to a build up of venous return — oedema or if blood trapped it lungs it can lead to pulmonary oedema
What is pleuritic pain?
A condition in which the pleura — two large, thin layers of tissue that separate your lungs from your chest wall — becomes inflamed. Worsens during inspiration.
What is Virchows triad?
It a triad of - circulatory stasis, endothelium injury’s and hypercoagulable state - all of which lead to an increased chance of a blood clot.
What can an increased PVR cause?
Lead to pulmonary hypertension
