RS Lecture 3 and 4 - Ventilation & Gas Transport and Exchange Flashcards
What are normothermic ex vivo ventilated perfused lungs?
No restriction to movement as no chest wall and expand freely in all directions
What is minute ventilation?
Volume of air expired in one minute or per minute
What is Resp rate?
Frequency of breathing per minute
What is Alveolar ventilation?
Volume of air reaching the resp zone
What is respiration?
Process of generating ATP either with an excess of O2 (aerobic) or a shortfall (anaerobic)
What is anatomical dead space?
Capacity of airways incapable of undertaking gas exchange
What is alveolar dead space?
Capacity of airways that should be able to undertake gas exchange but cannot
What is physiological dead space?
Equivalent to the sum of alveolar and anatomical dead space
What is hypoventilation?
Deficient ventilation of the lungs - unable to meet metabolic demand > Acidosis (^CO2)
What is hyperventilation?
Excessive ventilation of lungs atop of metabolic demands > Alkalosis (decreased CO2)
What is hyperpnoea?
^ depth of breathing to meet metabolic demand
What is hypopnea?
Decreased depth of breathing - inadequate to meet metabolic demand
What is apnoea?
Cessation of breathing
What is dyspnoea?
Difficulty in breathing
What is bradypnoea?
Abnormally slow breathing rate
What is tachypnoea?
Abnormally fast breathing rate
What is orthopnea?
Positional difficulty in breathing (mainly when lying down)
What are the 2 components of the chest wall?
Bone, muscle, fibrous tissue AND lungs
What way does the rib cage recoil?
Outwards
What way do the lungs recoil?
Inwards
What is the functional residual capacity?
At the end of tidal expiration: Elastic recoil of lungs inwards = ER of ribs outwards
What is needed to remove the FRC equilibrium?
Muscular effort to push equilibrium to one way/another
What is the volume of the pleural cavity?
Fixed and contains protein-rich pleural fluid
What is the pressure of the pleural cavity?
Negative
What happens when we do a full inspiration (in terms of walls/pressure)?
Chest wall expands and pulls diaphragm down and lungs need to be pulled with it - negative pressure in pleural cavity pulls lungs with chest wall
What can happen to disturb the connection between lungs and chest wall?
Lungs will deflate - caused by puncture in chest wall/lung so pleura will fill with air or blood, so elastic recoil of lung takes over and causes collapse
Whats the difference between time taken in development of haemo and pneumothorax?
Haemo overtaking f elastic lung recoil occurs much slower
What is tidal breathing?
The amount of inspiration and expiration that meets metabolic demand - usually nasal
How is the Functional Residual Capacity measured?
Trough of a tidal breath to 0
Why can you not fully empty the lungs?
Surfactant in alveoli prevents them from sticking together and not reopening
What is the residual volume?
The volume that remains in the lungs after full expiration
What are the four main volumes of air?
Tidal, Inspiratory reserve, Expiratory reserve and Reserve (can be combined to capacities)
What is TLC?
Full volume of lungs - TV+IRV+ERV+RV
What is vital capacity?
How much air is in the range we’re able to inspire/expire - TLC-RV
What is functional residual capacity?
Vol of air in the lungs when recoil in ribs and lungs are in equilibrium - ERV+RV
What is inspiratory capacity?
How much air can be taken in on top of FRC - TV+IRV
What factors affect lung volumes and capacities?
Body size (HEIGHT, shape), sex, fitness, disease (pulm or neuro), age
What drives flow?
Pressure - from high to low
What unit is used when talking about lung volumes?
cmH2O
When does positive pressure breathing occur?
Atmospheric pressure is increased above Alveolar pressure such as in Ventilation, CPR
When does negative pressure breathing occur?
Alveolar pressure is reduced below atmosphere pressure such as in healthy breathing
How do you work out transmural pressures?
P-inside - P-outside
What leads to inspiration (pressures)?
A negative transrespiratory pressure
What leads to expiration (pressures)?
Positive transmural pressure - recoil of lungs expires, but air is pushed in
What is transmural pressure?
Pressure across a tissue/several tissues
What is a transpulmonary pressure?
Difference between alveolar and intrapleural pressure
What is the transrespiratory pressure?
IMPORTANT - tells if airflow in/out of lung
What is intrapleural pressure?
Pleura stretches outwards, alveoli inwards so pressure is negative
Ventilation cycle:
Start: No transpulmonary pressure
What is the conducting zone?
16 generations with no gas exchange and is equivalent to anatomical dead space (150mL)
What is the respiratory zone?
7 generations -> gas exchange (350mL) and is equivalent to alveolar ventilation
What is non-perfused parenchyma?
Alveoli without blood supply -> no gas exchange (0mL), equivalent to alveolar dead space
What 2 reversible procedures can increase and decrease a persons dead space?
Increase: Ventilation tube Decrease: Tracheostomy (avoiding first part)
What is Poiseuille’s law?
Resistance = 8*viscosity of gas*length of tube / pi*radius^4
What are the ventilation mechanics?
Diaphragm does a pulling force in one direction (syringe). Intercostal respiratory muscles are an upwards and outwards swinging force (bucket handle)
What is the chest-wall relationship?
Intact lung has a sigmoid shaped lung (greater pressures to achieve same change in volume when the lungs are at higher/lower volumes)
What is a volume-time curve?
FVC is amount of air pushed out at force; FEV1 is how rapid someone can remove air in lungs, index of airways resistance
How can you tell if patient has obstructive pulmonary disease from a volume-time curve?
FEV1 is much lower related to FVC; FVC is lower
How can you tell if patient has restrictive pulmonary disease from a volume-time curve?
FVC is lower; FEV1 much higher and FEV1:FVC is high, nearing 1
What are the 3 ventilation tests that are done to test lung function?
Volume-time curve, peak expiratory flow, flow volume loop
What is peak expiratory flow test?
Patient exhales as fast as possible from TLC, with value measured against ‘normal’ values
What is the flow-volume loop?
Maximum inspiratory and expiratory curves are main important and you can read VC, TV, ERV, IRV from the graph
How does the flow-volume loop reflect mild and severe obstructive and restrictive diseases?
MOD: Operate at higher volumes, [caving] as when emptying of smaller airways is difficult, so greater muscular effort (same with SOD just worse) RD: lower volumes
How does flow-volume loop reflect variable extra/intrathoracic obstruction and fixed airway obstructions?
VEO: Only blunted on inspiratory portion -> sucking the mass
VIO: Only blunted on expiratory portion -> pushing mass into airway when breathing out
FAO: Unable to deviate so only be able to breathe in small amounts
Which of the following combinations would be greatest in a healthy adult? A: TV + ERV + RV + IC B: TLC + TV + RV + IC C: IRV + VC + TV + TLC D: ERV + VC + IC + RV
C
Which word describes short of breath? A: Apnoeic B: Orthopnoeic C: Hypopnoeic D: Dyspnoeic E: Bradypnoeic
D
- Which is the least likely feature of a COPD patients flow volume curve? A: Blunted inspiratory curve B: Caving C: Low peak flow rate D: Reduced vital capacity
A
Distinguish between pulmonary and alveolar ventilation
Pulmonary is air ventilating the entire airway; alveolar is air ventilating respiratory surfaces
What are the 5 Gas laws? (Dalton Flicks Henry’s Boil Cheerfully)
Dalton mixes gases, Fick’s gases diffuse proportionally, Henry’s gases dissolve proportionally, Boyle’s volume is inversely proportional to pressure, Charles’ volume is proportional to temperature
What are the relative proportion of gases in room air, O2 therapy, house fire and high altitude?
How do the inspiratory gases change from the air to the respiratory airways?
Air is warmed, humidified, slowed and mixed
What is haemoglobin and what are they made up of?
Consists of Fe2+ at centre of 4 polypeptides, with adults usually having 2 alpha and 2 beta chains (some 2 alpha and 2 delta chains - HbA2) and foetal Hb containing 2 alpha and 2 gamma chains
How does O2 bind to HbA?
At rest, Hb has a low affinity for O2 and when the first molecule binds it undergoes a conformational change, so there is a higher affinity for the second and higher for the 3rd molecule of O2 -> greater competition for each spot -> affinity for the 4th is 300x greater than for the first -> COOPERATIVITY phenomenon
How does HbA change when O2 attaches to it?
There is a change in the protein structure forming a binding site for 2,3-DPG, which promotes O2 unloading by shifting Hb into the tense state
What type of protein is Hb?
Allosteric protein
What is metHb?
When Fe2+ is further oxidised to Fe3+, where it cannot bind to O2, with metHbaemia causing functional anaemia
What causes metHb?
Nitrites oxidise Hb into ferric MetHb or can be genetic
What is P50?
Partial pressure at which Hb is 50% saturated
What happens to P50 when the O2 dissociation curve shifts to the right and what causes this?
For any given pressure there is less O2 bound, so releasing O2 more easily: DECREASES AFFINITY -> ^ temperature, acidosis, hypercapnia, ^2,3-DPG -> occur when exercising
What happens to P50 when the O2 dissociation curve shifts to the left and what causes this?
INCREASES AFFINITY caused by decreased temperature, alkalosis, hypocapnia, decreased 2,3-DPG
What happens to P50 when the O2 dissociation curve shifts down and what causes this?
Anaemia -> causes impaired O2-carrying capacity - P50 stays the same
What happens to P50 when the O2 dissociation curve shifts up and what causes this?
Polycythaemia -> increased O2-carrying capacity - P50 stays the same
What happens to P50 when the O2 dissociation curve shifts down and to the left and what causes this?
Hb has greater affinity for CO than O2, so occupies binding sites and changes the cooperativity -> so increases affinity, so P50 is very low
What is the O2-dissociation curve of HbF?
Has greater affinity for O2, to extract the oxygen from the mother’s HbA in the placenta
What is the O2 dissociation curve of myoglobin?
Much much greater affinity that HbA to extract O2 from circulating blood and store it for when necessary - hyperbolic curve
How does O2 transport occur from the alveoli to the capillary?
HbA (RBC) with 75% saturation arrive at alveoli and O2 diffuses from alveoli to capillary down the conc grad as the PAO2 is larger than PaO2, and since SVO2 is 75%, the last O2 adds on with ease, with the SaO2 becoming 100% and PO2=PAO2=13.5kPa
How is O2 transported in the blood?
O2 moves down the concentration gradient into the cells, diffusing across -> used for respiration and then the rest of the Hb continues round the body and to the heart then repeats the cycle again
Why is the saturation of the blood in the pulmonary vein that reaches the heart not 100% saturated?
Blood from the bronchiole arteries drain into the pulmonary vein just before entering the heart, so the blood goes down to 97% saturation
How much O2 is transported in the blood?
2% O2 is carried in the plasma, and 98% in the Hb -> amount of dissolved O2 is inadequate for life, but is used for O2 unloading
What is the oxygen flux in the capillary in respiring tissues?
Amount of O2 lost -> 250mL O2min^-1
How is CO2 transported in the blood?
CO2 crosses membranes faster and binds to water forming H2CO3, forming a buffer to maintain the pH -> venous blood is slightly more acidic than arteriolar blood
What is the CO2 flux in the capillary of respiring tissues?
200mL CO2min^-1, leaving the cells
What happens to CO2 in the RBC?
CO2 enters the RBC, where it binds with water to form H2CO3 (carbonic anhydrase), which then dissociates and HCO3- is exchanged with Cl- via AE1 transporter [Chloride shift to maintain membrane potential], H2O enters the RBC as well -> CO2 bind to Hb, to the amine end to form carbaminoHb -> excess H+ in RBC are bound by Hb (has some H+ acceptor chains) to maintain the pH, until they are needed to be released
What are the 3 roles of Hb?
O2 transport, CO2 transport and buffering inside of the RBC
How is CO2 transported in the arterial vs venous blood?
Not much difference in quantity of CO2 but how it is transported varies
What is the pulmonary transit time?
0.75s (RBC in touch with pulm. membrane), gases are very soluble, so move across very rapidly, and when exercising you are still able to get efficient gas exchange -> takes 0.25s for O2 to diffuse and less for CO2 because it is more soluble
What is ventilation perfusion mismatching?
Due to gravity, blood follows path of least resistance, so there is more perfusion in the lower lobes of the lung -> at rest apical ones are basically closed. Ventilation is also higher at basal than apical due to gravity as the lung has a net weight, which makes the intrapleural pressure higher at the bottom, making it easier to ventilate at the bottom than the top
NB: Perfusion is impacted much more than ventilation
What is the equation for CO?
CO=SV*HR mL/min
What is the alveolar ventilation equation?
AV= (TV-dead space)*respiratory frequency mL/min
How do you calculate ventilation perfusion ratio?
V/Q ratio=Alveolar ventilation/CO with no units
