Cardiovascular Physiology

Front 1

What is a Newtonian Fluid?

Back 1

Def 1. Homogeneous fluid with a viscosity that does not change with flow rate.

Def 2. Shear rate and shear stress of the fluid are proportional. This is true for water but not for blood.

Front 2

What is the viscosity of water

Back 2

0.01 poise or 1 centipoise at 20 °C.

0,695 at 37°C.

1.8 at 0°

Front 3

Plasma Viscosity

Back 3

1.2 at 37°C.

Relative viscosity of 1.7

Front 4

Blood viscosity?

Back 4

Blood has a relative viscosity of 4 to 5 when measured at moderate or high shear rates, but the viscosity is much higher at low shear rates.

Front 5

Hydraulic Resistance?

Back 5

Front 6

Units of resistance

Back 6

Resistance = Pressure / Flow

=mmHg/ml/min

=Pressure drop/Cardiac Output

= Mean Aortic P - right atrial pressure

= 100/5000

=0.02mmHg/ml/min

To convert to Wood units multiply by 1000.

The absolute resistance units may be converted to Wood units by dividing by 80. For example, the normal SVR is 700–1600 dyne·s/cm5, or 9–20 Wood units.).

Front 7

Poiselle vs CVS.

Back 7

Front 8

Pressure - Flow relationships of different blood vessels

Draw the graph

Back 8

Front 9

What is shear thinning?

Back 9

The apparent viscosity of blood decreases as the shear rate is increased – an effect known as shear thinning

Front 10

List Factors that affect Anomalous Viscosity of Blood

Back 10

1. Hematocrite: direct relationship

2. Temperature: inverse relationship

3. Flow rate: inverse relationship

4: Vessel diameter : direct relationship.

Front 11

What are the units of Viscosity

Back 11

The unit of viscosity is the poise (equal to 1 dyne·s/cm2). At 20°C, the viscosity of water is 0.01 poise, or 1 centipoise.

Front 12

Types of Capillaries & location (6)

Back 12

Front 13

Alternatives for Trans endothelial transport

Back 13

Front 14

Define Wall tension incl formula (4)

Back 14

The wall tension is the force per unit length tangential to the vessel wall that opposes a distending force that tends to pull apart a theoretical split in the wall (i.e. prevents vessel rupture).

*and is related to the distending force (the product of transmural pressure and radius), by the law of Laplace: Wall tension = Pressure × Radius

Front 15

Two main functions of Capillaries

Back 15

(i) delivery and removal of nutrients and metabolites to tissues by diffusion across the capillary wall and

(ii) distribution of fluid between the intravascular and extravascular compartments by bulk flow of fluid and solutes across the semipermeable capillary wall (impermeable to large protein molecules).

Front 16

Name the four Starling Forces involved in the filtration process (4)

Use a diagram.

Back 16

capillary hydrostatic pressure, interstitial hydrostatic pressure, plasma oncotic pressure and interstitial fluid oncotic pressure

Front 17

Define & describe net filtration pressure. (4)

Write the formula & normal values (4)

Back 17

The NFP – the resultant pressure of the four Starling forces – can be calculated at the arterial and venous ends of a capillary as follows:

NFP = (Pc −Pif ) − (πp −πif )

where Pc is the capillary hydrostatic pressure, Pc at the arterial end of the capillary = 35 mmHg,

Pc at the venous end of the capillary = 15 mmHg;

Pif is the interstitial fluid hydrostatic pressure = 0 mmHg;

πp is the plasma oncotic pressure = 28 mmHg;

πif is the interstitial fluid oncotic pressure = 3 mmHg;

NFP at arterial end of the capillary = 10 mmHg and NFP at venous end of the capillary = −10 mmHg.

Bulk flow across the capillary wall = k × NFP, where k is the capillary membrane filtration constant.

Front 18

What is the net fluid loss from capillary filtration per day

Back 18

The net fluid loss from filtration in the capillaries is only 4 L/day, and this is reabsorbed by the lymphatics.

Front 19

What the factors determining Capillary Hydrostatic Pressure?

Back 19

The ratio of precapillary & post capillary resistances

CHP = Post capillary resistance / Precapillary Resistance

Front 20

Functions of the endothelium (3)

Back 20

nutrient and waste product diffusion

fluid filtration

endothelial cells produce vasoactive substances

Front 21

What vasoactive substances are produced by the Endothelium? Mention their stimulation and Effect (12)

Back 21

Front 22

List the 6 Functions of the Endothelial Glycocalyx

Back 22

Front 23

What is the endothelial Glycocalyx (4)

Back 23

1. In 2010, Levick and Michel proposed that the endothelial glycocalyx layer is the small pore system of the transvascular semipermeable membrane of the endothelium

2. Layer of Glycoprotiens & Glycosaminoglycans (mucopolysacharrides) bound to the lumina surface of the Endothelial Cells to form the interface between blood and capillary wall.

Front 24

What causes loss of the Endothelial Glycocalyx Layer (4)

Back 24

Hypervolaemia (^ANP)

Diabetes

Hyperglycaemia

Inflammatory mediators: surgery & Sepsis: Namely = CRP, TNF, Bradykinin, Mast Cell Tryptase

Front 25

What restores and protects the glycocalyx layer (4)

Back 25

Antithrombin III

Hydrocortisone

N-Acetylcysteine

Sevoflurane

Hint 25

Break down the clot

Anti-inflammation

Detoxify

Anaesthesia.

Front 26

Which tissues do NOT contain lymph Vessels

Back 26

Central Nervous System

Bone

Cartilage

Epithelium

Front 27

Rate of lymph flow

Back 27

120 mL/hr or 2–3 L/ day.

Front 28

Compare the protein conc of lymph in interstial fluid, liver & intestine (3)

Back 28

Interstial Fluid: 2g/dL

Intestine 3-4g/dL

Liver 6g/dL

Front 29

What are the determinants of the rate of venous return to the heart (6)

Back 29

The factors that determine the rate of venous blood flow back to the heart are as follows:

• The pressure gradient for venous return

• Venous valves

• The skeletal muscle pump

• The respiratory pump

• The effect of ventricular contraction and relaxation

• Venomotor tone

Hint 29

3pumps

Front 30

Draw the configurational changes in veins on a volume / pressure graph. (6)

Back 30

Front 31

What is the Mean Systemic Filling Pressure?

What does it indicate?

Back 31

mean systemic filling pressure (MSFP) – the average of all the pressures in different vessels weighted according to their relative compliances.

This is a single hydrostatic assessment of the filling of the cardiovascular system and indicates the pressure moving blood back towards the right atrium to maintain the cardiac output.

Front 32

Define the venous pressure gradient (formula)

Back 32

T he pressure gradient through the veins to the right atrium is the main factor determining the rate of venous return and is equal to the difference between the MSFP (7 mmHg) and the mean right atrial pressure (1 mmHg): T he pressure gradient for venous return = MSFP – Mean right atrial pressure = 6 mmHg

Front 33

What increases and decreases MSFP?

Back 33

The MFSP increases with venomotor tone or blood volume and falls with venodilation or blood loss. Changes in total peripheral resistance do not affect the MFSP.

Front 34

Graphically demonstrate the effect of sympathetic Outflow on the cardiac output curve. 6

Back 34

Front 35

Define venous return (equation)

Back 35

Venous return is proportional to the difference between MSFP and right atrial pressure, which is the hydrostatic pressure gradient promoting venous return. In this range of right atrial pressure (i.e. 0–7 mmHg), venous return can be defined by the following equation: Venus return = (MSFP - RAP) / Resistance to venous return

The ‘resistance to venous return’ is a term that reflects the resistance and capacitance of the venous circulation.

Front 36

Draw the normal venous return curve

Back 36

Front 37

Right heart bypass preparation;

Back 37

Front 38

Draw a graph showing the effect of MSFP on the Venous Return Curve.

Back 38

Hint 38

Note: A 15% increase in blood volume will double the MSFP, whereas a 15% decrease will reduce it to zero.

Front 39

What is the equilibrium point?

Back 39

The point of intersection of cardiac output and venous return curves is known as the equilibrium point

It intersects @ CO of 5l & RAP of zero

Hint 39

Front 40

Graph showing effects of changes in Resistance to Venous Return

Back 40

Front 41

Effect of Sympathetic Activity on the Equilibrium Point

Back 41

Front 42

How much, & at what pressure, is blood in the arteries?

Back 42

The arteries (with the arterioles) contain approximately 15% of the total blood volume (i.e. 750 mL) at a mean pressure of around 100 mmHg.

Front 43

Define Arterial pressure.

Back 43

Arterial pressure is the force exerted per unit area of the arterial wall.

Front 44

What is Mean arterial pressure?

How can MAP be measured

Back 44

The mean arterial pressure, is the average arterial pressure acting during the cardiac cycle, is the driving force for blood flow and it can be measured by averaging the pressure recorded under an arterial pressure curve over time

Front 45

What is arterial pressure?

Back 45

Arterial pressure is the force exerted per unit area of the arterial wall.

Front 46

What increases systolic blood pressure?

Back 46

Systolic blood pressure increases when there is

(i) an increase in stroke volume;

(ii) an increase in ejection velocity (without a change in stroke volume);

(iii) a decrease in aortic or arterial distensibility; and

(iv) an increase in diastolic pressure of the previous pulse

Front 47

What increases diastolic blood pressure

Back 47

a decrease in ejection velocity; (ii) an increase in aortic or arterial distensibility; and (iii) an increase in total peripheral resistance

Front 48

What is arterial pulse pressure?

Formula?

Back 48

Arterial pulse pressure is the difference between systolic and diastolic pressures: Pulse pressure = Systolic pressure − Diastolic pressure

Front 49

MAP formulas (2)

Back 49

Mean arterial pressure = Diastolic + 1/3 (Systolic − Diastolic)

Or

Mean arterial pressure = Peripheral run off × Total peripheral resistance

Front 50

Resistance formula

Back 50

Resistance = Pressure/ Flow

Front 51

How does a fall in compliance affect the pulse pressure?

Back 51

A fall in arterial compliance increases the pulse pressure for two reasons:

(i) the ventricular ejection of blood into the stiff arteries produces a greater increase in systolic pressure and

(ii) the hydraulic filter (Windkessel), which normally maintains diastolic pressure, is impaired by the reduced arterial elasticity

Front 52

How does arteriolar constriction and dilation affect arterial pressure and capillary pressures?

Back 52

Arteriolar dilation tends to reduce the hydrostatic pressure drop across these vessels: arterial pressure decreases, and capillary pressure increases. Arteriolar constriction tends to increase the hydrostatic pressure drop: arterial pressure increases, and capillary pressure decreases.

Front 53

What are the arteriolar functions? (3)

Back 53

Alter total peripheral resistance.

• Alter the vascular resistances of individual organs.

• Alter capillary hydrostatic pressure.

Front 54

In Which organ is myogenic conrol more important?

Back 54

myogenic activity is dominant in the brain and the kidneys and is the mechanism of the autoregulation of blood flow seen in those organs over a wide range of mean arterial blood pressures.

Front 55

Diagrammatic representation of the mechanisms by which the cardiovascular system is controlled.

Back 55

Front 56

The sympathetic and parasympathetic nerves in the brain and spinal cord involved in cardiovascular control.

Back 56

Front 57

Draw the Haemorrhage: effects on venous return and cardiac output curves.

Back 57

Front 58

Endocrine response to Haemorrhage Flow Chart

Back 58

Front 59

What is the use of a valsalva maneuver?

Back 59

The Valsalva manoeuvre may be used clinically to assess autonomic function and also to slow supraventricular tachycardia. The autonomic function can be assessed by determining the Valsalva ratio.

Front 60

What is the Valsalva Ratio? And what is the normal value?

Back 60

The Valsalva ratio is equal to the minimum heart rate (longest R–R interval) in phase IV divided by the maximum heart rate (shortest R–R interval) in phase IV. The Valsalva ratio is normally greater than 1.5, but in patients with impaired autonomic function, it is less than 1.5

Front 61

Valsalva Maneuver in autonomic dysfunction?

Back 61

Front 62

The Valsalva manoeuvre in Congestive Heart Failure

Back 62

Front 63

What are the 3 factors determining exercise tolerance?

Back 63

Cardiovascular performance incl peripheral vasculature Pulmonary gas exchange Skeletal muscle metabolism

Pulmonary gas exchange

Skeletal muscle metabolism

Front 64

What determines the capacity for Peak Exercise Performance

Back 64

The capacity for peak exercise performance therefore depends on the maximum ability of the cardiovascular system to deliver O2 to the skeletal muscles and of the exercising muscles to extract O2 from blood

Front 65

What is the formula for oxygen uptake?

Back 65

Ficks equation

Oxygen uptake = (Cardiac output) X (content of arterial oxygen - content of mixed venous oxygen)

= (SV x HR) X (CaO2 - CvO2)

Front 66

How does the cardiovascular system respond to exercise (4)

Back 66

1. Increased Cardiac output up to six times: this facilitates oxygen uptake.

2. Redistribution of cardiac output from non-active (splanchnic & Renal) tissues to skeletal muscles : enhances oxygen delivery

3. Greater O2 extraction >> widened ateriovenous oxygen difference.

4. Increased pulmonary blood flow (by increase in CO & vasodilation)

Front 67

What is maximal oxygen capacity?

Back 67

At maximal exercise, the maximal ability of a person to take in, transport and use oxygen (functional aerobic capacity) is called maximal oxygen capacity ( VO2max)

Front 68

Equation for VO2max?

Back 68

Front 69

Diagrammatic representation of the negative feedback arterial baroreceptor reflex.

Back 69

Front 70

Diagram: Cardiovascular Changes During Hemorrhage

Back 70

Front 71

What is the mechanism for training induced improvements in VO2max?

Back 71

*The primary mechanism for training-induced improvements in VO2 max is an increase in cardiac output secondary to an increased stroke volume in response to exercise.

*Peaked heart rate is generally not affected by training.

Front 72

What is the Bain Bridge Reflex.

Back 72

When there is stimulation of the Vagal VenoAtrial Stretch Receptors it results in;

1. Increase in HR - Selective sympathetic activity to the SA node.

2. Increase in Urine Volume

3. Increase in Salt excretion

2&3 are due to:

A. Renal sympathetic activity

B. Inhibition of ADH secretion

C. Increase in ANP production

Front 73

What is the function of the Vagal Myelinated VenoAtrial Stretch Receptors?

Back 73

It functions to regulate cardiac size when venous pressure is high and to adjust blood volume.

Front 74

Where are the Unmyelinated Vagal and sympathetic cardiac mechanoreceptors?

Back 74

Form a fine network in Atria and mainly left ventricle

Front 75

Where are the Myelinated Vagal mechanoreceptors found?

Back 75

Around the coronary arteries

Front 76

Difference between Ventricular vs Atrial Unmyelinated Vagal & Sympathetic Mechanoreceptors.

Back 76

Atrial: fire during height of atrial filling during Inspiration.

Ventricular : Fire during contraction