Cardiorespiratory Mechanics Flashcards
Rapid ejection: What marks the start of this phase? What contracts? Where does blood flow to? Heart sounds?
What produces heart sounds?
Opening of the aortic & pulmonary valves mark the start of the rapid ejection phase
As ventricles contract pressure within them > Pressure in aorta and pulmonary arteries.
Semi lunar valves open, blood pumped out, vol of ventricles decrease
No heart sounds for rapid ejection phase
Heart sounds are produced by the flow of blood back onto a valve
Resistance and conductance:
What is the relationship between resistance and radius (of airways)?
Why doesn’t resistance continue to increase as airways get smaller?
What increases the conductivity of airways?
Resistance is inversely proportional to the fourth power of the radius
Airways aren’t rigid pipes, they dilate as lung volume increases
The conductivity of the airways increases with increasing volume
Systemic circulation:
Why do small arteries and arterioles have a lot of smooth muscle in their walls?
What are functions and properties of veins venules?
Small arteries and arterioles have:
extensive smooth muscle in their walls to regulate their diameters and the resistance to blood flow
Veins and venules:
Highly compliant
Act as a reservoir for blood volume
Pressure across the circulation:
Why is the pattern of pressure through the circulation and how do you explain this?
Which blood vessels present the most resistance to flow?
Pressure falls across the circulation due to viscous (frictional) pressure losses
Small arteries and arterioles present most resistance to flow
Haemodynamic determinants of blood pressure:
Equation to calculate change in pressure?
Equation to calculate blood pressure?
What assumptions do these relations make? Why are they inaccurate?
How is regulation of blood flow achieved?
Delta P = Q x TPR
blood pressure (MAP) = cardiac output (CO) x resistance (PVR)
Relation is an approximation bc it assumes:
1. Steady flow (which doesn’t occur due to intermittent pumping of the heart)
- Rigid vessels
- Right atrial pressure is negligible
Physiologically, regulation of flow is achieved by variation in resistance in the vessels while blood pressure remains relatively constant
Resistance to blood flow:
Poiseuilles equation?
What are the three variables that affect the resistance of a tube?
Small changes in what can produce large changes in flow? Why?
Resistance or a tube to flow depends on three variables:
- Fluid viscosity (n, eta)
- Length of the tube (L)
- Inner radius of the tube (r)
Poiseuilles equation:
R (resistance) = 8Ln / pi x r^4
Relatively small changes in vascular tone (vasoconstriction/dilation) can produce large changes in flow
Blood flow profile:
Describe laminar flow:
Velocity?
Where does blood flow fastest?
Describe turbulent flow:
What is the pattern of blood flow?
What is turbulent flow associated with?
Laminar flow:
Velocity of the fluid is constant at any one point and flows in layers
Blood flows fastest closest to the centre of the lumen
Turbulent flow:
Blood flows erratically, forming eddys, and is prone to pooling
Associated w pathophysiological changes to the endothelial lining of the blood vessels
Where is blood pressure usually measured and why here?
What causes turbulent flow?
What causes dichrotic notch?
How do you calculate pulse pressure?
How do you calculate blood pressure from pulse pressure?
Why are our large extra pulmonary airways supported w cartilage?
Blood pressure usually measured on upper arm; easily accessed and at heart level
Slow deflation of cuff causes turbulent flow which can be heard with a stethoscope
Dichrotic notch - caused by closure of aortic valve
Pulse pressure (PP) = SBP (systolic blood pressure) - DBP (diastolic blood pressure)
MAP = DBP + 1/3PP
our large extrapulmonary airways are supported w cartilage to prevent them collapsing during expiration/exercise
Structural properties of lung tissue:
What are the two structural properties of lung tissue?
Define them
How do you calculate them?
Compliance - tendency to distort under pressure
Compliance = delta V / delta P
Elastance - tendency to recoil to its original volume
Elastance = delta P / delta V
Why do ventricular and aortic pressures differ?
Once aortic valve closes, ventricular pressure falls rapidly but aortic pressure falls slowly
This is bc of elasticity of aorta and large arteries which act to buffer the change in pulse pressure
The elasticity of a vessel is related to its compliance
Arterial compliance
Describe blood blow into the aorta during ejection
What causes diastolic flow in the downstream circulation after ejection ceases?
Why do systolic blood pressure measurements increase with age, and diastolic blood pressure measurements decrease?
During ejection:
Blood enters aorta and other downstream elastic arteries faster than it leaves them (40% of SV is stored by the elastic arteries)
When aortic valve closes -> ejection ceases. But due to recoil of the elastic arteries, pressure falls slowly and there’s diastolic flow in the downstream circulation
Arterial compliance decreases w age (eg arteries become stiffer)—> blood pressure measurements increase w age. Pulse pressure increases w age
What two pumps facilitate venous return?
Skeletal muscle pump
Respiratory pump
What causes varicose veins? (In leg) what are varicose veins?
What causes oedema? (In feet)
Incompetent valves cause dilated superficial veins in the leg (varicose veins)
Dilated superficial veins = varicose veins
Prolonged elevation of venous pressure (even with intact compensatory mechanisms) causes oedema in feet
Aneurysmal disease
Over time vessel walls can weaken
Pathological example of the law of Laplace:
Vascular aneurysms increase radius of the vessel —> hence for the same internal pressure, the inward force exerted by the muscular wall must also increase
However, if the muscle fibres have weakened, the force needed cannot be produced —> aneurysm will continue to expand —> rupture
Same pathology applies for the formation of diverticuli in the gut
Arterial and venous compliance
What is compliance? What does it depend on?
Compare venous compliance to arterial compliance at low pressures
What decreases venous volume and increases venous pressure?
Where is most blood volume stored?
What do relatively small changes in venous pressure result in?
Compliance = the relationship between transmural pressure and the vessel volume. Depends on vessel elasticity
Venous compliance = 10-20x > arterial compliance : at low pressures
Increasing smooth muscle contraction decreases venous volume and increases venous pressure
Most blood vol is stored in the veins
Relatively small changes in venous pressure distend veins and increase the volume of blood stored in them
