Ventilation Flashcards
Minute ventilation?
volume of air expired in one minute (VE) or per minute
Respiratory rate?
Rf
frequency of breathing per minute
Alveolar ventilation
Valv
volume of air reaching the respiratory zone per minute
Respiration?
process of generating ATP either with excess oxygen (aerobic) or shortfall (anaerobic)
Alveolar dead space?
capacity of airways that should be able to undertake gas exchange but cannot (e.g. hypoperfused alveoli)
Physiological dead space?
equivalent to the sum of alveolar and anatomical dead space
Anatomical dead space?
capacity of the airways incapable of undertaking gas exchange
Hypoventilation?
deficient ventilation of lungs
unable to meet metabolic demand
increase PO2 - acidosis
Hyperventilation?
excessive ventilation of the lungs
atop of metabolic demand
leads to reduced PCO2 - alkalosis
Hyperpnoea
increased depth of breathing to meet metabolic demand
Hypopnoea
decreased depth of breathing (inadequate to meet metabolic demand)
Apneoa
cessation of breathing
Dyspnoea
difficulty in breathing
Bradypnoea
slow BR
Tachypnoea
fast BR
Orthopnoea
positional difficulty in breathing (when lying down)
Ventilation
amount of air going in and out of the body in relation to what the body needs
Why does exercise not cause hyperventilation?
causes hyperpnoea and tachypnoea
breathing is at increased rate and depth but to match requirement
Tidal volume
amount of air breathing in and out per breath
0.5L normal
increases with exercise
Inspiratory reserve volume
amount of extra volume you can breathe in
Expiratory reserve volume
amount of extra air you can breathe out
Residual volume
volume of air left in lungs after maximum expiration
beneficial to prevent lungs entirely collapsing on themselves
Functional residual capacity
amount of air left in lungs after normal expiration
Total lung capacity
total amount of air that can fill the lungs
Vital capacity
how much air in the lungs that you can influence
Inspiratory capacity
how much air can be taken in from neutral position
What 5 factors affect lung volumes and capacities?
Body size (height and shape) Sex Disease (pulmonary or neurological) - affect control, tone of muscles, emphysema Age (chronological, physiological) Fitness (innate, training)
How does height affect lungs?
taller people have bigger lungs
fatter people dont necessarily have bigger lungs as obesity is on outside of thorax
How does sex affect height?
males have larger lungs
How does inheritance affect lungs?
inherited fitness
larger barrel shaped chest with large lungs to promote faster gas exchange
What is the conducting zone?
16 generations (bifurcations) no gas exchange typically 150ml in adults at FRC = anatomical dead space (not meant for gas exchange)
What is the non perfused parenchyma?
generation 23 alveoli without a blood supply no gas exchange typically 0ml in adults = alveolar dead space
What is the respiratory zone?
7 generations
gas exchange
typically 350ml in adults
= air reaching here is equivalent to alveolar ventilation
What reversible procedures can decrease dead space?
tracheostomy
cricothyrocotomy
What reversible procedures can increase dead space?
anaesthetic circuit
snorkelling
What irreversible process increases dead space?
smoking
Why is it hard to breathe deep under water?
hydrostatic pressure increases with depth
harder to breathe deeper down
What two laws govern the increase in TV deeper underwater?
Poiseuille’s Law – radius makes a big difference
Decreased resistance - more effort needed to breathe
Boyle’s Law – pressure and volume are inversely proportional
Increasing the ambient pressure causes volume to decrease
What does tidal breathing involve?
pressure changes
Describe stages of tidal breathing?
- FRC air in lungs
- Inspiratory muscles activated to expand lung tissue creating a negative pressure
- Alveolar pressure inside the lung decreases
- Pressure gradient
- Air flows in
- Airs flows in with inspiratory effort applied till both pressures balance out
- Airs stops flowing
- Remove inspiratory effort
- Pressure becomes more positive
- lungs compress air and pushes air out
- till net change in volume reversed
Ambient pressure?
0cm of water IDEAL
or 160kPa
or 760mmHg
or 1atm
Where does TV start and end?
at FRC
Tendency of chest wall and lung?
chest wall tends to spring forward
lung had tendency to recoil inwards
both units work together
BUT chest recoil = lung recoil
the forces are in equilibrium at end tidal expiration (FRC)
What allows us to change things in the lungs?
muscle effort
INSPIRATION inspiratory muscle effort + chest recoil > lung recoil
EXPIRATION
chest recoil < lung recoil + expiratory muscle effort
What is the neutral position of the intact chest?
FRC
What are the lungs surrounded by?
visceral pleural membrane
What is inner chest surface covered by?
parietal pleural membrane
What is the pleural cavity?
gap between pleural membranes
fixed volume
contains protein rich pleural fluid
double folded layer that allows lots of dynamic movement in this space
How does haemothorax affect lung?
vessel bleed in pleural cavity
compress lung
give lung less space to expand and fill with air
How does pneumothorax affect lung?
perforated chest wall also caused by punctured lung
allows air in space
breaks vacuum
interrupts ability of lung to work as single unit
What is negative pressure breathing?
lower Palv to below Patm to create a pressure gradient
What is positive pressure breathing?
Patm is increased above Palv - create negative pressure
rescue breaths (mouth to mouth)
ventilators
fighter pilots
Three compartment model?
visualise pressure in the lung
Palv = 0cmH2O
Patm = 0cmH2O
Ppl = -5cmH20
Why is intrapleural pressure negative?
not equal along length of lung
under negative pressure - lungs recoil in, chest recoil out
What is the transmural pressure?
Pinside - Poutside
transpulmonary pressure (Ptp) pressure inside alveoli - pressure in intrapleural space
transthoracic pressure (Ptt) pressure in intrapleural space - pressure in atmosphere
transrespiratory system pressure (Pts)
What dictates air flow?
Pts transrespiratory system pressure
if positive air flows in
if negative air flows out
What force is the diaphragm?
unidirectional force
pulling force
contraction - pulls down
used mostly for quiet breathing
What force do the ribs exert?
inhalation - upwards and outwards
Why is change in volume for same change in pressure reduced at extremes of volume?
at middle of lung volumes
less effort to change things
at higher/lower lung volumes, significantly higher pressures must be applied to change things
What happens at high extremes?
plateau
regardless of extra pressure added, cannot deflate or inflate the lungs further
here changes in pressure no longer generate change in air flow
What does the independent chest wall and lung lines show?
distance between the two is the same
intact lung line is a product of the other 2
What does spirometry produce?
volume time curve
Why do you wear a noseclip?
measure air flow through mouth
How is spirometry performed?
- noseclip
- patient inhales to TLC
- patient exhales as hard and fast as possible till RV reached / 6s gone
What does volume time curve test for?
FVC
airway resistance
What does the FEV1/FVC ratio show?
compares how much air coming out in 1 sec
normal 73%
restrictive 97%
obstructive 53%
What happens in person with restrictive lung disease?
reduced ability of lung to fill
FEV1/FVC ratio increases
empty almost all air in 1 second
What happens in person with obstructive lung diseases?
reduced ability to inspire and expire
FEV1/FVC ratio decreases
What do you look for in spirometry curve?
Slow starts
Early stops
Intramanouever variability
How is a peak flow test performed?
- noseclip
- patient inhales to TLC and exhales hard and fast
- do not need to reach RV
- repeat 2x and take highest measurement
What is peak flow used for typically?
asthma
How is peak flow assessed?
compare to reference values
How to calculate peak expiratory flow rate?
USE SMALLEST DENOMINATION OF TIME
e.g. 0.2s (2L) x 5 x 60
Why might spirometry trace decrease straight away?
reflex to fill lungs as soon as emptied
How is a flow-volume loop performed?
- noseclip
- one tidal breath (A, B)
- inhale steadily to TLC
- exhale as hard and fast as possible
- continue exhalation until RV
- inhale again to TLC
What is inspected on flow volume loop?
Visually inspect performance and volume time curve and repeat if necessary. Look out for:
Inconsistencies with clinical picture
Interrupted flow data
What does peak flow test?
tests airway resistance (how fast can air be expired?)
What do flow volume loops test?
tests airway resistance, flow rates, TV, IRV, ERV and FVC
What is the pleural cavity physiologically?
partial vacuum
What predominantly induces tidal breathing?
diaphragm
What does maximum ventilation involve?
full inspiratory muscle recruitment
How might recovery from burns affect lung volumes capacities?
most reduced
scar tissue formed
less elastic
restrict chest expansion at most volumes
How does intrapleural pressure change at start of tidal inspiration?
small decrease
diaphragm contracts and pulls down (external intercostals may contract to pull ribs up and out)
pulls parietal pleural membrane away from lung
stretches intrapleural space as lungs fill
lung tries to recoil in so visceral pleura pulled in and this increases the partial vacuum from -5 to -8cmH2O
