PATHOPHYSIOLOGY - Haemorrhage and Heart Failure Flashcards
When there is significant haemorrhage, what happens to arterial pressure, systolic pressure and pulse pressure?
Arterial pressure, systolic pressure and pulse pressure are reduced when there is significant haemorrhage
What is arterial pressure?
The measure of the pressure exerted by the blood agaisnt the walls of the arteries
What is the average arterial pressure value?
120 / 80 mmHg
i.e. systolic pressure over diastolic pressure
What is pulse pressure?
Pulse pressure is the difference between systolic and diastolic pressure
i.e. 120 - 80 = 40 mmHg
What are the three main clinical signs of significant haemorrhage?
Rapid and feeble pulse
Pale mucous membranes
Rapid respiration
Why is there a rapid and feeble pulse in response to haemorrhage?
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
Why is there pale mucous membranes in response to haemorrhage?
The blood vessels undergo vasoconstriction to redirect the blood to core organs (i.e. brain and heart), which can result in pale mucous membranes
Why is there rapid respiration in response to haemorrhage?
Increased respiration brings in more oxygen to increase the oxygenation of the reduced volume of blood available to carry oxygen to the tissues
How does the baroreceptor reflex respond to haemorrhage?
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.
What are classified as the ‘primary resistance vessels’?
Arterioles are the ‘primary resistance vessels’
How do arterioles increase total peripheral resistance (TPR) in response to hemorrhage?
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)
What is total peripheral resistance (TPR)?
Total peripheral resistance (TPR) refers to the overall resistance to blood flow in the peripheral blood vessels within the body
In which three organs/tissues do arterioles undergo the most significant vasoconstriction in response to haemorrhage?
Skeletal muscle
Skin
Splachnic circulation (blood supply to GI system)
In which organs do arterioles only undergo vasoconstriction in response to SEVERE haemorrhage?
Kidneys
How does prolonged arteriole vasoconstriction affect the kidneys and gastrointestinal tract?
Prolonged arteriole vasoconstriction can cause damage to the kidneys and sloughing of the intestinal mucosa
In which two organs do arterioles NOT undergo vasocontriction in response to haemorrhage?
Brain
Heart
How does the spleen respond to haemorrhage in dogs?
In dogs, the spleen contracts to increase blood volume and release more erythrocytes into the circulation
How does the chemoreceptor reflex respond to haemorrhage?
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
Describe the protective mechanism used by the brain to ensure it receives enough blood during severe haemorrhage
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
How does the atrial volume receptor reflex respond to haemorrage?
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
Which three physiological mechanisms can be used to restore blood volume in response to haemorrhage?
Reabsorption of tissue fluids
Renin-angiotensin-aldosterone mechanism
Increased antidiuretic hormone (ADH) secretion
How long does it take for the body to replace the blood volume lost during haemorrhage?
1 -2 days
How long does it take for the body to replace the plasma proteins lost during haemorrhage?
Several days
How long does it take for the body to replace the erythrocytes lost during haemorrhage?
Several weeks
What is the most effective treatment option for severe haemorrhage?
Blood transfusion
What are the five decompensatory mechanisms as a result of haemorrhage?
Heart failure
Acidosis
Central nervous system (CNS) depression
Clotting changes
Immune system inhibition
Describe the first decompensatory mechanism as a result of haemorrhage - Heart failure
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
Describe the second decompensatory mechanism as a result of haemorrhage - Acidosis
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
Describe the third decompensatory mechanism as a result of haemorrhage - Central nervous system (CNS) depression
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
Describe the fourth decompensatory mechanism as a result of haemorrhage - Clotting changes
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
Describe the fifth decompensatory mechanism as a result of haemorrhage - Immune system inhibition
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
What are the two main physiological responses to heart failure?
Frank-Starling mechanism
Baroreceptor reflex
What are the four main complications of heart failure?
Oedema
Exercise intolerance
Inadequate renal perfusion
Decompensatory mechanisms
What are the two decompensatory mechanisms as a result of heart failure?
Inadequate renal perfusion
Increase in left ventricular volume
Describe the first decompensatory mechanism as a result of heart failure - Inadequate renal perfusion
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
Describe the second decompensatory mechanism as a result of heart failure - Increase in left ventricular volume
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
