PATHOPHYSIOLOGY - Haemorrhage and Heart Failure

Question 1

When there is significant haemorrhage, what happens to arterial pressure, systolic pressure and pulse pressure?

Answer 1

Arterial pressure, systolic pressure and pulse pressure are reduced when there is significant haemorrhage

Question 2

What is arterial pressure?

Answer 2

The measure of the pressure exerted by the blood agaisnt the walls of the arteries

Question 3

What is the average arterial pressure value?

Answer 3

120 / 80 mmHg

i.e. systolic pressure over diastolic pressure

Question 4

What is pulse pressure?

Answer 4

Pulse pressure is the difference between systolic and diastolic pressure

i.e. 120 - 80 = 40 mmHg

Question 5

What are the three main clinical signs of significant haemorrhage?

Answer 5

Rapid and feeble pulse
Pale mucous membranes
Rapid respiration

Question 6

Why is there a rapid and feeble pulse in response to haemorrhage?

Answer 6

Significant haemorrhage will cause a decrease in blood volume, resulting in a rapid and feeble pulse as the body will try and compensate for this blood loss by increasing the heart rate with the weakened pulse due to the reduced blood volume resulting in reduced central venous pressure (CVP), resulting in reduced preload and strength of contraction, resulting in reduced stroke volume and cardiac output - resulting in less pressure being exerted on the walls of the arteries

Question 7

Why is there pale mucous membranes in response to haemorrhage?

Answer 7

The blood vessels undergo vasoconstriction to redirect the blood to core organs (i.e. brain and heart), which can result in pale mucous membranes

Question 8

Why is there rapid respiration in response to haemorrhage?

Answer 8

Increased respiration brings in more oxygen to increase the oxygenation of the reduced volume of blood available to carry oxygen to the tissues

Question 9

How does the baroreceptor reflex respond to haemorrhage?

Answer 9

When blood pressure decreases, there will be reduced stimulation of the baroreceptors. This will increase sympathetic nervous system activity resulting in an increase in heart rate and vasoconstriction. The sympathetic nervous system will have also stimulated adrenaline release which will also increase heart rate and cause vasoconstriction. There will also be a decrease in parasympathetic nervous system activity.

Question 10

What are classified as the ‘primary resistance vessels’?

Answer 10

Arterioles are the ‘primary resistance vessels’

Question 11

How do arterioles increase total peripheral resistance (TPR) in response to hemorrhage?

Answer 11

Arterioles (‘primary resistance vessels’) undergo vasocontriction in response to increased sympathetic drive to redirect blood to core organs (brain and heart) and away from the periphery, increasing total peripheral resistance (TPR)

Question 12

What is total peripheral resistance (TPR)?

Answer 12

Total peripheral resistance (TPR) refers to the overall resistance to blood flow in the peripheral blood vessels within the body

Question 13

In which three organs/tissues do arterioles undergo the most significant vasoconstriction in response to haemorrhage?

Answer 13

Skeletal muscle
Skin
Splachnic circulation (blood supply to GI system)

Question 14

In which organs do arterioles only undergo vasoconstriction in response to SEVERE haemorrhage?

Answer 14

Kidneys

Question 15

How does prolonged arteriole vasoconstriction affect the kidneys and gastrointestinal tract?

Answer 15

Prolonged arteriole vasoconstriction can cause damage to the kidneys and sloughing of the intestinal mucosa

Question 16

In which two organs do arterioles NOT undergo vasocontriction in response to haemorrhage?

Answer 16

Brain
Heart

Question 17

How does the spleen respond to haemorrhage in dogs?

Answer 17

In dogs, the spleen contracts to increase blood volume and release more erythrocytes into the circulation

Question 18

How does the chemoreceptor reflex respond to haemorrhage?

Answer 18

When blood pressure drops too low, the baroreceptors become less sensitive to further changes in blood pressure. In response to this, chemoreceptors step in and detect changes in blood oxygen levels. This triggers the chemoreceptor reflex

Question 19

Describe the protective mechanism used by the brain to ensure it receives enough blood during severe haemorrhage

Answer 19

When blood pressure drops significantly and the brain isn’t receiving enough blood, the brain initiates a sympathetic discharge to trigger the sympathetic nervous system and further increase vasoconstriction to increase the blood flow to core organs

Question 20

How does the atrial volume receptor reflex respond to haemorrage?

Answer 20

Specialised receptors detect decreased blood volume within the atria and trigger the sympathetic nervous system to increase vasoconstriction to core organs and to increase contraction

Question 21

Which three physiological mechanisms can be used to restore blood volume in response to haemorrhage?

Answer 21

Reabsorption of tissue fluids
Renin-angiotensin-aldosterone mechanism
Increased antidiuretic hormone (ADH) secretion

Question 22

How long does it take for the body to replace the blood volume lost during haemorrhage?

Answer 22

1 -2 days

Question 23

How long does it take for the body to replace the plasma proteins lost during haemorrhage?

Answer 23

Several days

Question 24

How long does it take for the body to replace the erythrocytes lost during haemorrhage?

Answer 24

Several weeks

Question 25

What is the most effective treatment option for severe haemorrhage?

Answer 25

Blood transfusion

Question 26

What are the five decompensatory mechanisms as a result of haemorrhage?

Answer 26

Heart failure
Acidosis
Central nervous system (CNS) depression
Clotting changes
Immune system inhibition

Question 27

Describe the first decompensatory mechanism as a result of haemorrhage - Heart failure

Answer 27

Haemorrhage can result in heart failure which will cause decreased coronary blood flow to the heart tissue. This causes decreased ventricular function and cardiac output causing a further drop in blood pressure and blood flow, causing further decompensation

Question 28

Describe the second decompensatory mechanism as a result of haemorrhage - Acidosis

Answer 28

Haemorrhage reduces the blood flow and thus oxygenation of the tissues, resulting in anoxia and the activation of anaerobic metabolism. This results in increased lactic acid production and reduced H+ excretion by the kidneys. This buildup of lactic acid and H+ in the blood causes acidosis. Acidosis reduces the cardiovascular response to catecholamines, causing decompensation

Question 29

Describe the third decompensatory mechanism as a result of haemorrhage - Central nervous system (CNS) depression

Answer 29

To start with, the reduced blood flow due to haemorrhage will increase sympathetic tone, however, if the blood volume and pressure drop too low, this will reduce the blood flow to the cardiac and vasomotor centres in the brain which regulate heart rate and blood vessel tone. This will cause a decrease in sympathetic activity and CNS depression, causing a further decrease in cardiac output and a further decrease in cerebral blood supply, causing decompensation

Question 30

Describe the fourth decompensatory mechanism as a result of haemorrhage - Clotting changes

Answer 30

Initially, clotting will increase to try and control the haemorrhage, however, as haemorrhage continues and blood loss increases, so does the loss of clotting factors resulting in prolonged clotting and worsened haemorrhage

Question 31

Describe the fifth decompensatory mechanism as a result of haemorrhage - Immune system inhibition

Answer 31

In response to haemorrhage there will be vasoconstriction to redirect blood to the core organs. This results in a decreased blood supply and thus decreased immune response within the gastrointestinal tract. Without an adequate immune system, the bacteria within the gastrointestinal tract can invade the GI mucosa and enter systemic circulation, causing endotoxic shock which causes vasodilation and results in a further decrease in blood pressure

Question 32

What are the two main physiological responses to heart failure?

Answer 32

Frank-Starling mechanism
Baroreceptor reflex

Question 33

What are the four main complications of heart failure?

Answer 33

Oedema
Exercise intolerance
Inadequate renal perfusion
Decompensatory mechanisms

Question 34

What are the two decompensatory mechanisms as a result of heart failure?

Answer 34

Inadequate renal perfusion
Increase in left ventricular volume

Question 35

Describe the first decompensatory mechanism as a result of heart failure - Inadequate renal perfusion

Answer 35

In response to heart failure and decreased cardiac output there will be vasoconstriction to re-direct blood to core organs. This will result in inadequate blood flow and renal perfusion, preventing the kidneys from filtering the blood normally. This results in waste product accumulation in the blood causing uraemia. Uraemia causes a decrease in cardiac contractility and cardiac output, resulting in further vasoconstriction, exacerbating the problem

Question 36

Describe the second decompensatory mechanism as a result of heart failure - Increase in left ventricular volume

Answer 36

Increased left ventricular volume originally acts as a compensatory mechanism to increase preload and cardiac output, however this will result in pulmonary oedema due to fluid overload. Pulmonary oedema reduces oxygenation of blood which results in hypoxia. Hypoxia causes decreased cardiac output