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Respiratory > Cardiorespiratory mechanics > Flashcards

Cardiorespiratory mechanics Flashcards

1
Q

Resistance is ( x ) to the fourth power of the radius?

A

inversely proportional

if an artery or arteriole constricts to one-half of its original radius, the resistance to flow will increase 16 times.

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2
Q

Why doesn’t resistance continue to increase as airways get smaller

A

?

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3
Q

Airways are not rigid pipes?

A

They dilate as lung volume increases

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4
Q

The conductivity of the airways ( a ) with increasing volume?

A

Increases

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5
Q

Why do small arteries and arterioles have extensive smooth muscle?

A

regulate their diameters and the resistance to blood flow

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6
Q

What proportion of the blood is in the veins at any given time?

A

70%, due to high compliance and act as a reservoir

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7
Q

What pressure changes are seen across the circulation?

A

Pressure falls across the circulation due to viscous (frictional) pressure losses.

Small arteries and arterioles present most resistance to flow.

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8
Q

What is the calculation for blood presure?

A

(CO) Cardiac output x Resistance (PVR)

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9
Q

What is the calculation for change in pressure?

A

Q x TPR

Q = flow rate

TPR = Total peripheral resistance

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10
Q

What approximations have to be made to calculate blood pressure?

A

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.
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11
Q

What three variables does resistance of a tube depend on?

A

Fluid viscosity (n, eta)

The length of the tube (L)

Inner radius of the tube (r)

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12
Q

…

A

…

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13
Q

How does distribution of blood to organs change during exercise

A

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

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14
Q

What is Laminar flow?

A

Velocity of the fluid is constant at any one point and flows in layers

Blood flows fastest closest to the centre of the lumen.

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15
Q

What is Turbulent flow?

A

Blood flows erratically, forming eddys, and is prone to pooling

Associated with pathophysiological changes to the endothelial lining of the blood vessels..

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16
Q

During blood pressure measurement, what does slow deflation of the cuff cause to the flow of blood?

A

Causes turbulent flow which can be heard by a stethescope

17
Q

Calculation for pulse pressure?

A

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.

18
Q

…

A

…

19
Q

What stage is Patent, +5 airway transmural pressure?

  • 0 pressure in tubes, -5 in lungs
A

Preinspiration

20
Q

What characteristics of mid-inspiration?

A 
Airway
Transmural 
Pressure
-2 - -8 = +6
PATENT
  • -2 = airways
  • 8 = lungs
21
Q

What characteristics of end-inspiration?

A 
Airway
Transmural 
Pressure
0 - -8 = +8
PATENT
22
Q

What stage is collapsed +22 , -2 airway transmural pressure?

A

Hard expiration

23
Q

How can lung tissue be categorised?

A

Complaint = V/P
The tendency to distort under pressure

or

Elastance = P/V
The tendency to recoil to its original volume

24
Q

Why do ventricular and aortic pressures differ?

A

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.

25
Q

During ejection, blood enters the aorta and other downstream elastic arteries ( a ) than it leaves them

A

a -faster

26
Q

After blood ejection through the aorta - Why does pressure fall slowly and there is diastolic flow in downstream circulation

A

When the aortic valve closes, ejection ceases - due to recoil of the elastic arteries,

27
Q

How would you expect blood pressure to change if arterial compliance decreased - become stiffer

A

systolic - goes up

dystolic - goes down

28
Q

What is facilitated venous return?

A

Skeletal muscle pump

Respiratory pump - diaphragm changes pressure so blood comes up into veins

29
Q

What causes vericose veins?

A

Incompetent valves cause
dilated superficial veins in
the leg (varicose veins

30
Q

What causes Oedema in feet?

A

Prolonged elevation of venous pressure (even with intact compensatory mechanisms) causes oedema in feet

31
Q

Characteristics of aneurysmal disease?

A

Vessel wall weakening can cause distension

Pathological example of the Law of Laplace. Vascular aneurysms increase radius of the vessel. This means that 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 and so the aneurysm will continue to expand …
often until it ruptures.

underlying physical forces involved also holds for the formation of diverticuli in the gut.

32
Q

are arteries or veins more compliant?

A

Veins because it depends on vessel elasticity ( 10-20x greater at low pressures )

Compliance : refers to the ability of a vessel to respond to an increase in pressure by to distending or swell and increase the volume of blood it can hold, or with decreased pressure, a decrease in volume

33
Q

Where is perfusion and ventilation greatest in the lung

A

Near the bottom than the top : gravity controlled

Similar with blood flow.

Higher intravascular pressure 
(gravity effect)
More recruitment
Less resistance
Higher flow rate
34
Q

What makes alveoli larger and less compliant leading to less ventilation?

A

PPL is more negative (-8 cmH2O)

Greater transmural pressure gradient (0 vs. -8)

35
Q

What makes alveoli smaller and more compliant leading to more ventilation?

A

PPL is less negative (-2 cmH2O)

Smaller transmural pressure gradient (0 vs. -2)

36
Q

How would compliance of lungs and resistance of airways be affected by chronic obstructive pulmonary disease?

A

↑ compliance and ↑ resistance

Emphysemic breakdown of structural lung tissue increases compliance and bronchitic swelling of the airway and mucous hypersecretion increase resistance to airflow

Respiratory (5 decks)

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