Cardiorespiratory Mechanics Flashcards
What are the mechanics of ventilation? Use the graph below to explain the changes in pressure and how they cause changes in volume:
How does the graph change with exercise?
As the external intercostal muscles move up and out, and the diaphragm moves down, it creates a negative pressure in the alveoli as the gas moecules are stretched further apart - causes air to flow in via the open airway due to the pressure gradient from the outside air into the lungs
The diaphragm then recoils up to it’s relaxed position, which increases the pressure in the thorax (positive pressure), causing exhalation of the air as the pressure gradient is now from the lungs to the outside air. The pressure in the lungs returns to the original pressure
The graph is essentially the same, but the magnitude of the curves increase
What is the flow rate and what does the graph for it look like?
How does the graph for pleural pressure look?
Flow rate is proportional to the pressure gradient when diametre of airway is the same size
Has a weird shape
Explain this graph of the pleural pressures?
What is an example for a pulmonary function test?
How is this test carried out? (Protocol)
What is the purpose of this test?
Flow-volume loop
Patient wears noseclip and places their lips around the mouth piece. Patient takes one tidal breath (regular). Then the patient is asked to breathe in slowly and deeply as much as possible, but then to exhale as hard and fast as possible until residual volume is reached. Patient must immediately inhale again
Graph gives detailed information on how the air is flowing through different compartments of the lungs - inconsistencies and interrupted flow
What does the graph for the flow-volume loop look like?
y-axis = flow rate (L/s)
x-axis = lung volume (L)
Inspiration is the graph line going downwards (negative / below 0 flow rate), amd expiration is the graph line going upwards (positive / above 0 flow rate)
Tidal breath (A and B) = low amplitude and narrow in width
Inspiration (C) = slow and steady
Expiration (D and E) = 1st litre exhaled very fast, then steady decrease in flow rate til tidal volume is reached
2nd Inspiratino (F) = fast inhalation at first
What can you measure / see from the flow-volume graph?
PEF - peak expiratory flow
Vital capacity
IRV - inspiratory reserve volume
ERV - expiratory reserve volume
TV - tidal volume
What is the difference between obstructive and restrictive diseases?
Which of the categories does obesity fall into?
Obstructive = restrict air flow into the lungs
Restrictive = restrict ability for the chest to move out
Obstructive - excessive weight makes it more difficult for air to flow in
What would you expect the flow-volume loop to look like of a person with COPD? (a mild obstructive disease)
Narrowing of the airways = lower peak, curve of the descend when breathing out (called coving)
Graph displaced to the left - because the lungs in COPD have more air in, lungers are fuller but the amount of air being accessed is less
Vital capacity decreases
What does the flow-volume graph look like of patients with severe obstructive diseases?
Similar to mild-obstructive, but more exaggerated
What does the flow-volume graph look like of patients with restrictive diseases?
Graph displaced to the right
Narrower curve
What is the difference between extrathoracic obstruction and intrathoracic obstruction?
Why does it occur?
When is the obstruction at its maximum?
Extrathoracic = no obstruction during expiration, but obstruction during inspiration
Intrathoracic = no obstruction during inspiration, but obstruction during expiration
Occurs due to the way the blockage (e.g. a tumour) moves during the ventilation process
Obstruction is at its maximum when the airflow is fast, when the airflow is slow, the obstruction is not always necessarily evident
What are the shapes of the flow-volume graphs for variable intra and extrathoracic obstructions and a fixed airway obstruction?
Intra = blunted inspiratory curve, normal expiratory curve
Extra = normal inspiratory curve, blunted expiratory curve
Fixed = blunted inspiratory curve, blunted expiratory curve (otherwise normal)
Why can you not snorkel deeper in the water?
What is Poiseuille’s law?
What does Poiseuille’s law say about resistance if the radius of the tube is halved?
What is Boyle’s law?
Because a deeper dive call for a longer snorkel tube, which adds to the dead space. Dead space causes us to breathe harder and move a greater volume of air to maintain adequate ventilation. A dead space too large in volume would be impossible to move
Resistance = [8 x viscosity of the fluid x length of the tube] / [pi x radius of the tube4]
Halving the radius increases the resistance by x16
P Gas is inversely proportional to PVol
How does resistance to airflow change as the radius of the airway passage gets smaller?
Why is this not a linear relationship?
*look at graph*
At first, decreasing the radius of the airway with each bifurcate increases resistance (as there are more frequent collisions of the particles). However, due to the increase in the cumulative cross sectional area of the airways, resistance drops - as the greater the cross sectional area, the fewer the collisions (so less resistance)
What is conductance?
How does the airway conduct air and how does conductivity change with volume?
Willingness of the airway to conduct fluid transfer (i.e. air in this situation)
The airways are able to dilate and constrict to conduct fluid transfer - conductivity of the airway increases with volume (as resistance decreases)