Cardioresp mechanics Flashcards
What marks the start of rapid ejection?
Opening of semi-lunar valves
How does lung volume, flow rate and P(alv) change during inspiration and expiration?
Vol: Increases on insp, decreases on exp
Flow rate: Increases on insp, then reverses on exp
P(alv): Mirrors flow rate
What is the poiseuille’s law equation?
When using a snorkel, why does its length play a role in the ability to ventilate?
Much greater dead space in a longer snorkel, so to avoid re-breathing the same air you must be able to ventilate the entire airway, which is harder for larger volumes.
What is boyle’s law equation?
Why is there peak respiratory resistance at around generation 3-8(early) on the respiratory tree?
-Most turbulent airflow
-Cumulative cross sectional area in deeper generations is much higher
How does airway resistance relate to radius
Airway resistance is inversely proportional to the 4th power of the radius
Why does resistance decrease as lung volume increases?
Airways dilate-increasing radius-reducing resistance
How does airway conductance and resistance vary as lung volume increases?
Conductance: Increases linearly as airways dilate
Resistance: Decreases on a slope due to increasing radii
How does the proportion of systemic blood, mean pressure and total SA of vessels vary from arteries to veins?
What occurs overall to pressure over the whole circulation?
Pressure falls across the circulation due to viscous (frictional) pressure losses.
Small arteries and arterioles present most resistance to flow.
Why is this formula an approximation?
This relation is an approximation because it assumes:
-Steady flow (which does not occur due to the intermittent pumping of the heart)
-Rigid vessels
-Right atrial pressure is negligible
Physiologically, how is variation in resistance regulated?
Variation in resistance in the vessels
What 3 factors alter a vessels’ resistance?
- Fluid viscosity (η, eta)
- The length of the tube (L).
- Inner radius of the tube (r)
What was the main stipulation of poiseulles’ law?
Relatively small changes in vascular tone (vasoconstriction/vasodilation) can produce large changes in flow.
How is laminar flow different from turbulent flow?
On a BP graph, what causes the dichrotic notch?
Aortic valve closure-peak straight after caused by elastance of aorta
How do you calculate MAP?
MAP = 2/3 DP + 1/3 SP
How do you calculate pulse pressure(PP)?
PP = SP - DP
Why are our extrapulmonary airways supported with cartilage?
To prevent lung collapse as our upper airways would close on hard expiration and lead to a greater pressure in the pleural cavity compared to our trachea/bronchi
-Pressure generated in space by diaphragm can be v-high
What can severe transmural pressures cause to small-medium airways and what do large airways have to combat this?
Small-medium airway collapse, large airway cartilage helps to keep airways open
Def of compliance and elastance
Compliance: Tendency to distort under pressure
Elastance: Tendency to revert back to its original volume
How do you calculate compliance and elastance?
Why does aortic pressure fall more slowly compared to ventricular pressure after the aortic valve closes?
The elastance of the aorta buffers the change, making it decompress more slowly
What happens in the event arterial compliance decreases?
Pulse pressure widens(increases) and systolic pressure increases
What generates diastolic pressure?
The elastance of arteries which contain 40% of SV, delivered more slowly into the circulation
What causes varicose veins?
Incompetent valves in leg veins
What does prolonged elevation of venous pressure cause?
Oedema in feet
Outline the mechanism for aneurysm and diverticuli formation
Weakening in the vessel wall causes it to expand, this increased radius will require greater force to produce the same BP, leading to greater pressure on the outside vessel wall, which will continue to weaken until it bursts.
How does venous compliance compared to arterial compliance?
Venous compliance is 10 to 20 times greater than arterial compliance at low pressures.
What does vessel compliance depend on?
Vessel elasticity
Where is ventilation and perfusion greater?
Base of the lung
Does ventilation or perfusion vary more between the base and apex of the lung?
Ventilation
What law is being demonstrated with the formation of an aneurysm?
law of Laplace
