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BIOPHYSICS > LECTURE 12 (Heart work) > Flashcards

LECTURE 12 (Heart work) Flashcards

1
Q

What are the statistics of blood in the human body?

A
  • Blood density - 1.05x10^3 kg/m^3
  • Blood volume - 4-4.5 L
  • Blood circulation - 5000 ml/sec
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2
Q

What is the difference between Hemodynamics and Blood rheology?

A

Hemodynamics = the study of blood flow or the circulation

Blood rheology = studies the properties of blood and its elements, its fluidity, viscosity and osmolarity

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3
Q

The blood circulatory system is divided into which parts?

A
  • Heart
  • Closed circulatory system (Systemic + Pulmonary)
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4
Q

Describe how real fluids motion

A

Real fluids motion in tubes with solid or elastic walls determined by the pressure difference between initial and final points

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5
Q

What is the function of the heart?

A
  • Provides a formation pressure difference required by blood fluidity in vessels in circulatory systems
  • Pump in circulatory system
  • Circulatory process is largely dependent on contraction activity of heart muscle, which is closely related to metabolism of heart
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6
Q

The work of the right ventricle of the heart A2 is _____ of the total work

A

20%

Explanation: Therefore, A2 = 0.2A1

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7
Q

What is the Pressure mean value during systole?

A

13.5 kPa

Explanation: At the initiation of systole, pressure is approximately 10 kPa while at the end it equals 17 kPa

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8
Q

What happens when physical activity is increased?

A

Blood volume pumped out in aorta + blood flow velocity in aorta is increased -> heart work value is also increased

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9
Q

Which form of energy is converted during myocardial contraction?

A

Chemical energy is converted into mechanical energy

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10
Q

Describe what happens when a heart contracts

A

1) Heart contracts which causes a decrease in volume and an increase in pressure in the chamber
2) Because of the difference in volume between the two blood cycles, blood is not equally distributed [84% in systemic cycle + 10% in pulmonary cycle]
3) Flow direction of blood is controlled by valves

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11
Q

What are the factors that influence blood pressure?

A
  • Cardiac constriction power
  • Blood volume
  • Resistance
  • Blood viscosity
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12
Q

When does Blood pressure vary?

A
  • During the day (Circadian Rhythm)
  • In response to stress, nutrition factors, drug influence and various diseases
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13
Q

What is Mean Arterial Pressure (MAP)?

A

Mean arterial pressure (MAP) = the average arterial pressure during a single cardiac cycle

MAP = (stroke volume x systemic resistance) + CVP
[determined by the interaction of the stroke volume and elasticity of major arteries]

MAP = Pdias + (Psys - Pdias)/3
[simplified since systemic resistance and stroke volume aren’t easy to measure]

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14
Q

What is Venous Pressure?

A

Blood pressure in a vein or in the arteries of the heart and is much less than arterial BP

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15
Q

What is Central Venous Pressure (CVP)?

A

The pressure of blood in the thoracic vena cava near the right atrium and reflects the amount of blood returning to the heart and the ability of the heart to pump blood into the arterial system

[Good approximation of right atrial pressure -> major determinant of right ventricular end diastolic volume]

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16
Q

What is the normal CVP?

A

Normal = 0-8 mmHg
Less than 0 = Hypovolemia
More than 0 = Hypervolemia

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17
Q

What is Cardiac output?

A

The amount of blood pumped by the heart per minute

CO = HR X SV

18
Q

What are the factors affecting HR?

A
  • Autonomic innervation
  • Hormones
  • Fitness levels
  • Age
19
Q

What are the factors affecting Stroke Volume (SV)?

A
  • Heart size
  • Fitness levels
  • Gender
  • Contractility
  • Duration of contraction
  • Preload (EDV)
  • Afterload (resistance)

[Stroke volume = EDV - ESV]

20
Q

What is Pulse pressure?

A

Pulse pressure = systolic - diastolic

21
Q

Why does pulse pressure increase with exercise?

A

Due to
- Increased stroke volume
- Reduced total peripheral resistance

22
Q

What do Low and High pulse pressure values indicate?

A

LOW (<40):
- error of measurement
- heart failure/shock

HIGH (>40):
- stiffness of major arteries
- aortic regurgitation
- extra path for blood to travel from arteries to veins
- hyperthyroidism

23
Q

Why is a High pulse pressure harmful?

A

Accelerates the normal ageing of body organs (heart, brain + kidneys) and is an important risk factor for heart disease

24
Q

How is BP measured directly and indirectly?

A

DIRECTLY:
Placing a cannula into a blood vessel and connecting it to an electronic pressure transducer

INDIRECTLY:
Using a stethoscope and a Sphygmomanometer

25
Q

What are Korotkoff sounds?

A

Sounds of blood flow through an artery that is compressed by a blood pressure cuff

[First sound that appears when the cuff is deflated is the SYSTOLIC PRESSURE + Last sound that disappears when the cuff is deflated is the DIASTOLIC PRESSURE]

26
Q

Explain Orthostatic hypotension

A

Gravity reduces the rate of blood return from the body veins below the heart back to the heart -> reduces stroke volume + cardiac output -> a few second needed for recovery -> if too slow or inadequate, individual will suffer reduced blood flow to brain -> dizziness + potential blackout

27
Q

What does the Cardiac cycle include?

A
  • Diastole = Blood flows from the veins into the heart chambers
  • Systole = The atria briefly contract and fill the ventricles with blood then the ventricles contract and release blood
28
Q

Describe the different compartments of the conduction system of the heart

A
  • SA node = pacemaker, generate spontaneous action potentials which pass to atrial muscle cells to the AV node
  • AV node = action potentials conducted more slowly -> ensures ventricles receive signal to contract after atria have contracted
  • AV bundle = passes through hole in cardiac skeleton to reach interventricular septum
  • RIGHT AND LEFT BUNDLE BRANCHES = extend beneath endocardium to apices of right and left ventricles
  • PURKINJE FIBERS = conduct action potential to ventricular muscle cells
29
Q

What is Vascular resistance to blood flow determined by?

A
  • Physical characteristics of blood (viscosity, protein & blood cells concentration, laminar/turbulent flow)
  • Extravascular and endovascular mechanical forces
  • Vessel length, form and diameter
  • Properties of vessel wall
30
Q

What is Viscosity?

A

An intrinsic property of fluid related to the internal friction of adjacent fluid layers sliding past one another

31
Q

What is the unit of dynamic viscosity?

A

Poise (P)

32
Q

Which thermoproteins exist in the body?

A
  • Cryoglobulin = below 37 degrees C is subject to reversible and/or irreversible transformation of gel into crystal condition
  • Pyroglobulin = subject to transformation at high temp (40 degrees C)
33
Q

What happens to blood viscosity at 0 degrees C?

A

Blood viscosity increased 3-fold than normal -> decreases blood circulation in cold conditions -> can cause finger pain

34
Q

What is Hematocrit?

A

Blood cells percentage content in blood

Hematocrit = V1/V2 %
V1 - blood cells volume
V2 - blood volume

Women = 42%
Men = 38%

35
Q

Why is Blood non-Newtonian?

A

Since its velocity increases at low flow velocities

Explanation: Low flow velocities allow increased molecular interactions to occur between red blood cells and plasma proteins -> can cause cells to stick together (ROULEAU FORMATION) -> Increases blood viscosity

36
Q

What happens in severe anemia?

A

Blood viscosity is twice decreased -> causes decrease in resistance peripheral vessels towards blood flow -> intensification of venous flow + cardiac output -> increase cardiac muscle work

37
Q

What is Polycythemia?

A

When percentage content of forming cells increases per blood volume unit

CAUSES:
- increase in packed blood cells
- decrease in plasma volume
- increase in hematocrit
- oxygen saturation

38
Q

What is Thalassemia?

A

A blood disorder caused when the body doesn’t make enough of a protein called haemoglobin, an important part of red blood cells

39
Q

Blood flow through a vessel is determined by which factors?

A
  • Pressure difference of blood between the two ends of the vessel -> force that pushes the blood through the vessel
  • Vascular resistance

Explanation: Blood flow rate (Q) is directly proportional to the pressure gradient (∆P) and inversely proportional to the resistance (R) to flow

40
Q

What does Poiseuille’s equation state?

A

A pressure drop (∆P) always accompanies vicious fluid flow

BIOPHYSICS (15 decks)

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