Cardiorespiratory mechanics Flashcards
Resistance is ( x ) to the fourth power of the radius?
inversely proportional
if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times.
Why doesn’t resistance continue to increase as airways get smaller
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Airways are not rigid pipes?
They dilate as lung volume increases
The conductivity of the airways ( a ) with increasing volume?
Increases
Why do small arteries and arterioles have extensive smooth muscle?
regulate their diameters and the resistance to blood flow
What proportion of the blood is in the veins at any given time?
70%, due to high compliance and act as a reservoir
What pressure changes are seen across the circulation?
Pressure falls across the circulation due to viscous (frictional) pressure losses.
Small arteries and arterioles present most resistance to flow.
What is the calculation for blood presure?
(CO) Cardiac output x Resistance (PVR)
What is the calculation for change in pressure?
Q x TPR
Q = flow rate
TPR = Total peripheral resistance
What approximations have to be made to calculate blood pressure?
it assumes:
steady flow (which does not occur due to the 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.
What three variables does resistance of a tube depend on?
Fluid viscosity (n, eta)
The length of the tube (L)
Inner radius of the tube (r)
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How does distribution of blood to organs change during exercise
Decreases to digestive organs,
Increases most:
skeletal muscle 0.75-16L
Heart 0.25-1.25L
Bones 0.15-0.25L
brain same 0.75
kidney same 0.75
skin same 0.25
What is 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.
What is Turbulent flow?
Blood flows erratically, forming eddys, and is prone to pooling
Associated with pathophysiological changes to the endothelial lining of the blood vessels..
During blood pressure measurement, what does slow deflation of the cuff cause to the flow of blood?
Causes turbulent flow which can be heard by a stethescope
Calculation for pulse pressure?
SBP - DBP
the difference between systolic and diastolic blood pressure.
measured in (mmHg).
It represents the force that the heart generates each time it contracts. Resting blood pressure is normally approximately 120/80 mmHg, which yields a pulse pressure of approximately 40 mmHg.
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What stage is Patent, +5 airway transmural pressure?
- 0 pressure in tubes, -5 in lungs
Preinspiration
What characteristics of mid-inspiration?
Airway Transmural Pressure -2 - -8 = +6 PATENT
- -2 = airways
- 8 = lungs
What characteristics of end-inspiration?
Airway Transmural Pressure 0 - -8 = +8 PATENT
What stage is collapsed +22 , -2 airway transmural pressure?
Hard expiration
How can lung tissue be categorised?
Complaint = V/P
The tendency to distort under pressure
or
Elastance = P/V
The tendency to recoil to its original volume
Why do ventricular and aortic pressures differ?
Once aortic valve closes - ventricular pressure falls rapidly but aortic pressure falls slowly
This can be explained by the elasticity of the aorta and large arteries which act to “buffer” the change in pulse pressure.
The elasticity of a vessel is related to its compliance.
