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.