Ventilation and Gas Exchange Flashcards
Define minute ventilation
The volume of air expired in one minute
Define respiratory rate
The frequency of breathing per minute
Alveolar ventilation
The volume of air reaching the respiratory zone
Define respiration
The process of generating ATP either with an excess of O2 (aerobic) or a shortfall (anaerobic)
Define anatomical dead space
The capacity of the airways incapable of undertaking gas exchange
Define alveolar dead space
Capacity of the airways that should be able to undertake gas exchange bu cannot
e.g. hyperperfused alveoli
Define physiological dead space
Equivalent to the sum of alveolar and anatomical dead space
Define Hypoventilation
Deficient ventilation of the lungs; unable to meet metabolic demand
Increased pCO2- acidosis
Define Hyperventilation
Excessive ventilation of the lungs atop pf metabolic demands
Reduces pCO2- alkalosis
Define Hyperpnoea
Increased depth of breathing (to meet metabolic demand)
Define Hypopnoea
Decreased depth of breathing (inadequate to meet metabolic demand)
Define apnoea
Cessation of breathing (no air movement)
Define dyspnoea
Difficulty in breathing
Define bradypnoea
Abnormally slow breathing rate
Define tachypnoea
Abnormally fast breathing rate
Define Orthopnoea
Positional difficulty in breathing (when lying down)
What are volumes?
Discrete sections of the graph and do not overlap
What are capacities?
Sum of two or more volumes
Quantify minute ventilation
Tidal Volume (L) x Breathing frequency
Quantify alveolar ventilation
(Tidal volume - Dead space) x Breathing frequency
What are the factors affecting lung volumes and capacities?
Body size Sex Fitness Age Disease Age
What are the two component of the chest wall?
Bone + muscle + fibrous tissue
Lungs
What is FRC?
Functional residual capacity
What is functional residual capacity?
When we are at the end of tidal expiration
Where the outward recoil of the rib cage and the elastic recoil lungs are in equilibrium
What is the pleural cavity?
Space in-between parietal and visceral pleura
Fixed volume
Contains protein-rich pleural fluid
At negative pressure
What does the negative pressure of the pleural cavity allow for?
Chest wall to pull lung down as the diaphragm moves down
What are the lungs surrounded by?
Visceral pleural membrane
What is the inner surface of the chest wall covered by?
Parietal pleural membrane
What happens if you get a puncture in the chest wall or lungs?
Fixed volume pleural cavity is compromised
Air will fill cavity, elastic recoil will take over and the lung will collapse
What is tidal breathing?
The amount of inspiration and expiration the meets metabolic demands
Normal breathing
Usually nasal
What happens to tidal breathing when you exercise?
Tidal volume increases
What does the end of a tidal breath mark?
Functional residual capacity
Why can you not empty the lungs completely?
Surfactant in the alveoli
You cannot empty the lungs fully because you don’t want the alveoli to stick together
What is the remaining volume known as?
Residual volume
What are the 4 main volumes?
Tidal Volume
Inspiratory reserve volume
Expiratory reserve volume
Reserve volume
What is TLC?
Total lung capacity
All volumes combined
When you inspire all the way in and fill your lungs up as much as possible
What is VC?
Vital Capacity
How much air is within the confines of what we are able to inspire and expire
TLC-RV
What is FRC?
Functional Residual Capacity
The volume of air in the lungs when the outwards recoil of the rib cage and the inward recoil of the lungs are in equilibrium
ERV+RV
What is IC?
Inspiratory Capacity
How much extra air you can take in on top of the FRC
TV+IRV
What drives flow?
Pressure gradient
What units are used when talking about lung volumes?
cmH2O
What is transmural pressure?
Pressure across a tissue or several tissues
What is transpulmonary pressure?
Difference between alveolar and intrapleural pressure
How do we normally breathe?
Using negative pressure breathing
What is negative pressure breathing?
You inspire when there is lower pressure inside the lungs
What is positive pressure breathing?
Involves increasing the pressure outside by using a ventilator or CPR
Describe the process of ventilation
Start: no no transpulmonary pressure
The chest wall expands and creates negative pressure so more air flows in
This establishes a pressure gradient down which air flows
Eventually the pressure gradient will equalise again
How can the effect of the diaphragm be described?
A syringe
Pulling force in one direction
How can the effect of other respiratory muscles be described?
A bucket handle
An upwards and outwards swinging force
What is dead space?
The part of the airways and lung that does to participate in gas exchange
What is the conducting zone?
16 generations
No gas exchange
Typically 150ml in adults at FRC
Equivalent to anatomical space
What is the respiratory zone?
7 generations
Gas exchange
Typically 150ml in adults
Air reaching here is equivalent to alveolar respiration
What are non-perfused parenchyma?
Alveoli without blood supply
No gas exchange
Alveolar dead space
Generally 0ml in adults
Why do lungs have a sigmoidal volume-pressure relationship?
To get an elastic lung to expand
The bigger the volume the more pressure is needed
What is FVC?
Forced Vital Capacity
What is FEV1?
The amount of air forced out of the lung in 1 second
What is the % FEV1 in a healthy person?
75%
What is FET?
Forced Expiratory Time
The time taken to expel all the air from the lungs
What would be seen in an obstructive lung disease?
FEV1 would be much lower (can’t expel air fast)
FET is much higher (takes longer to expel all air)
FVC is much lower
Give an example of an obstructive lung disease
COPD
What would be seen in a restrictive lung disease?
Imagine you are trying to breathe and then someone gives you a big bear hug from behind - it limits the expansion of the thorax
FVC is lower
FEV1 is relatively high - because their conducting airways are quite clear they can expel air relatively easily
Give examples of values for FEV1/FVC ratios
o NORMAL = 73
o Restrictive = 87
o Obstructive = 53
How is the rate of flow show on a flow-volume loop?
Y axis is the flow rate - the further it deviates from the x-axis, the greater the rate of flow
How would a F-V loop differ for a mild obstructive disease?
Displaced to the left
Indented exhalation curve
Residual volume expanded
How would a F-V loop differ for a severe obstructive disease?
Shorter curve
Displaced to the left
Indented exhalation curve
Deeper indentation = more severe
How would a F-V loop differ for a restrictive disease?
Displaced to the right
Narrower curve
Unable to get to high TLC , restriction to the expansion of the lungs
How would a F-V loop differ for a variable extra thoracic obstruction?
Blunted inspiratory curve
Otherwise normal
How would a F-V loop differ for a variable intra thoracic obstruction?
Blunted expiratory curve
Otherwise normal
How would a F-V loop differ for a fixed airway obstruction obstruction?
Blunted inspiratory curve
Blunted expiratory curve
Otherwise normal
What does P stand for?
Partial pressure
What does S stand for?
Hb Saturation
What does A stand for?
Alveolar
What does a stand for?
Arterial
What is Dalton’s law?
Partial pressure of a gas mixture is equal to the SUM of the partial pressures of gases in the mixture
What is Fick’s law?
Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the CONCENTRATION GRADIENT, the exchange SURFACE AREA and the DIFFUSION CAPACITY of the gas, and inversely proportional to the THICKNESS of the exchange surface
What is Henry’s law?
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the PARTIAL PRESSURE of that gas in equilibrium with that liquid
What is Boyle’s law?
at a constant temperature, VOLUME IS INVERSELY PROPORTIONAL TO PRESSURE
What is Charles’ law?
at a constant pressure, VOLUME IS DIRECTLY PROPORTIONAL TO TEMPERATURE
What happens to air as altitude increases?
As you get higher the pressure of the atmosphere decreases but the PROPORTIONS OF THE GASES REMAINS THE SAME
What is total O2 delivery rest?
16 mL∙min-1
What is the shape of the oxygen dissociation curve for Hb?
Sigmoidal
What is P50?
The partial pressure of O2 when when Hb is 50% saturated
What happens to the ODC during exercise?
Shifts to the right
Reflect higher engird consumption
What happens to cause the shift to the right?
Increase in temperature
Acidosis
Hypercapnia (elevated CO2 because there is more cellular metabolism0
Increase in 2,3-DPG
What can happen to cause a shift to the left?
Decrease in temperature Alkalosis Hypocapnia Decrease in 2,3-DPG pH is lower in the tissues that in the lungs which helps it unload
What can cause a downwards shift?
Anaemia
Impaired oxygen carrying capacity
What can cause an upwards shift?
Polycythaemia
What is polycythaemia?
An increase in the packed cell volume (haematocrit) in the blood - it could be due to an increase in the number of red blood cells
What is the overall effect of carbon monoxide on Hb?
Reduces amount of Hb that can bind to O2
Decreases capacity
How to CO affect the ODC?
Downward and leftward shift
Why does foetal Hb have a high affinity?
Needs to steal O2 from mothers blood
What should deoxygenated blood be called?
Mixed venous blood
Blood driving has aground 75% oxygen bound
How saturated will the blood be when it reaches the tissues?
97%
