Physiological Regulation of Blood Pressure Flashcards
Define blood pressure
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
What is the calculation for mean arterial pressure?
Mean arterial pressure= ((2 ×diastolic)+systolic)/3
Explain how pressure waveforms are used
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
Describe how blood pressure is measured
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
What impact would exercise (increased HR) have on MAP?
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.
What factors could affect measurement of BP?
Emotional state (pain/fear?), cuff size, position/posture, temperature, full bladder all impact upon the accurate assessment of BP
Describe what pulse pressure is and how it can be calculated
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
Discuss the importance of blood pressure regulation and outline autoregulation
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
List the factors which affect blood pressure
MAP is dependent on
-Cardiac output
-Total peripheral resistance
-Blood volume and composition
Outline how cardiac output affects blood pressure
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.
Outline how total peripheral resistance affects blood pressure
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
Outline how blood volume and viscosity affects blood pressure
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.
Describe the receptors that regulate blood pressure
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.
Outline the altered cardiac function in repsonse to a haemorrhage
Preload
-Decreased
Stroke Volume
-Decreased
Mean arterial pressure
-Decreased
Viscosity
-Decreased
Tissue oxygen delivery
-Decreased
Describe the autonomic pathways that regulate blood pressure
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)
