Physiological Regulation of Blood Pressure Flashcards

1
Q

Define blood pressure

A

The hydrostatic pressure exerted by blood on the walls of blood vessels which drives tissue perfusion with blood – there is a high bp in the arteries and low bp in the veins –must have a pressure difference in order for blood to flow

Referred to as Mean Arteriole Pressure

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2
Q

What is the calculation for mean arterial pressure?

A

Mean arterial pressure= ((2 ×diastolic)+systolic)/3

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3
Q

Explain how pressure waveforms are used

A

Pressure waveform shows the amount of blooding leaving the left ventricle into the aorta.

It is asymmetrical due to the elasticity of the arterial wall which absorb the pressure energy (reducing amplitude) but then returning the energy as recoil to maintain pressure

Systolic - the highest pressure reached during the ejection phase

Diastolic - the lowest pressure reached during the ventricular filling stage

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4
Q

Describe how blood pressure is measured

A

MAP
Dependent upon where in the body it is measured1:
This will influence size and shape of arterial pulse wave2 as:

Directly related to the stroke volume
inversely related to the compliance (elasticity) of the arterial vessels.

Can be measured by:

-Sphygmomanometer (non-invasive or indirect) in dogs, cats, pigs and horses

-Invasive methods (direct) with fluid filled catheter

-In practice, often depends on what you have
Doppler sphygmomanometer
Oscillometric
True sphygmomanometry -common in human medicine
Catheter into artery attached to pressure transducer - anesthetists

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5
Q

What impact would exercise (increased HR) have on MAP?

A

Increased HR will move MAP closer to the systolic pressure as diastole will be shortened.

Slow in the large arteries (3-5m/s) and faster in the small arteries (14-15m/s) and this also relates to elasticity.

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6
Q

What factors could affect measurement of BP?

A

Emotional state (pain/fear?), cuff size, position/posture, temperature, full bladder all impact upon the accurate assessment of BP

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7
Q

Describe what pulse pressure is and how it can be calculated

A

Difference between the systolic and diastolic pressures

	Pulse pressure = systolic - diastolic

A high pulse pressure ≠ a high MAP and therefore does not mean good tissue perfusion

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8
Q

Discuss the importance of blood pressure regulation and outline autoregulation

A

Regulation of BP is essential to maintain blood flow to organs.

However,
Some organs exhibit autoregulation

Process within many biological systems, resulting from an internal adaptive mechanism that works to adjust (or mitigate) that system’s response to stimuli.

An ability to maintain local pressure despite arterial pressure changes (up to a maximum).
Brain, heart, kidneys

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9
Q

List the factors which affect blood pressure

A

MAP is dependent on
-Cardiac output
-Total peripheral resistance
-Blood volume and composition

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10
Q

Outline how cardiac output affects blood pressure

A

Cardiac output = stroke volume x heart rate

-Increased cardiac output = increased blood pressure

-Starling effect: increased stretching of heart muscle leads to increased contraction.

-Sympathetic stimulation: increases heart rate and force of contraction.

-Activation of parasympathetic NS: mainly decreases the heart rate and slight decrease in force.

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11
Q

Outline how total peripheral resistance affects blood pressure

A

Peripheral resistance: particularly arterioles

Sympathetic tone leads to arteriolar constriction

Outflow to veins is temporarily reduced thus increases mean arterial pressure

Diameter of the arterioles in abdominal (splanchnic) region are more effective than other areas in change mean arterial pressure

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12
Q

Outline how blood volume and viscosity affects blood pressure

A

Blood volume:
A sufficient amount is required to ‘overfill’ the arterial system.
Loss of blood will lead to reduced BP

Viscosity:
Blood is 5x more viscous than water.
Increased viscosity causes an increase in resistance to blood flow and thus increased MAP
But increased work for the heart.

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13
Q

Describe the receptors that regulate blood pressure

A

In short term, BP is monitored by baroreceptors and chemoreceptors located in the carotid sinus and aortic arch and the information integrated in the medulla oblongata (have a look at the BP regulation video).

Baroreceptors are sensitive to stretch
Chemoreceptors are sensitive to p02 and pCO2 changes

The autonomic nervous system then makes appropriate changes to the cardiac function and degree of vasoconstriction.

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14
Q

Outline the altered cardiac function in repsonse to a haemorrhage

A

Preload
-Decreased

Stroke Volume
-Decreased

Mean arterial pressure
-Decreased

Viscosity
-Decreased

Tissue oxygen delivery
-Decreased

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15
Q

Describe the autonomic pathways that regulate blood pressure

A

Signals from the baroreceptors in the coracoid sinus and aortic arch are sent to the medulla oblongata. When there is reduced stretch less signals are sent.

Sympathetic nervous tone; noradrenaline released from nerve endings acts on β1 adrenoceptors (heart)

Parasympathetic vagal tone decreased

Heart rate increases (chronotropic effect)

Increased force of contraction (inotropic effect)

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16
Q

Explain the response of the adrenal system in response to a haemorrhage

A

Heart: indirect effects via adrenal

-Sympathetic stimulation of adrenal gland

-Releases adrenaline (epinephrine) in blood

-Acts on the same receptors as noradrenaline (heart)

-Adrenaline: inotropic, chronotropic effects

17
Q

In response to a haemorrhage describe the neural effect on vasculature (hypovolaemia)

A

Blood vessels: direct effects
Increased sympathetic tone to vessels
Stimulate vasoconstriction

Results in increased systemic vascular resistance and therefore moves MAP back towards normal

Also, local endothelial responses

18
Q

In response to a haemorrhage describe the indirect effects on vasculature (hypovolaemia)

A

Indirect endocrine effects include:
-Increased anti-diuretic hormone (ADH) released from the pituitary in response to reduced blood volume (vasoconstriction)

-Increased angiotensin II: increases blood vessel tone

-Increased erythropoietin (EPO): stimulates erythropoiesis, increases viscosity

-Decreased atrial natriuretic peptide (ANP): reduced release from the cardiac myocytes in response to reduced diastolic stretch.

19
Q

Describe the long term control of blood pressure

A

Regulation of the volume and composition of blood by:
-Pressure natriuresis
-Renin-angiotensin-aldosterone system
-Anti-diuretic hormone (ADH)
-Capillary-fluid shift

Importance of the kidney
-Regulates fluid volume
-Electrolyte (Na+ mainly) composition of plasma

20
Q

Explain the kidneys response to long term elevated blood pressure

A

There is increased perfusion pressure on the kidney:
Resulting in reduced Na+ and thus decreased water re-absorption in proximal tubule
Hence, increased Na+ and water excretion
Thus, ECF volume decreases and thus any elevated BP is diminished

The kidney has an almost infinite ability to excrete salt, controlling extracellular fluid (ECF) volume and hence BP

Hence Pressure Diuresis = Pressure Natriuresis

21
Q

Differentiate between dehydration and hypovolaemia

A

Hypovolaemia is fluid loss from vasculature
Hypovolaemic shock is: Loss of enough vascular fluid to cause inadequate oxygen delivery to tissues

Dehydration is loss of fluid from extracellular fluid (ECF) & intracellular fluid (ICF)

22
Q

List the clinical signs that would relate to hypotension

A

Central depression
Weakness (paresis)
Thirst
Dyspnoea if severe
Poor pulse pressure
Cold extremities
Anuria
Tachypnoea

23
Q

What is not seen in acute hypotension?

A

Skin tenting
Altered packed cell volume
These are signs of dehydration