Pressure and Flow in Arteries Flashcards
What is the main method used for measurement of arterial pressure?
Auscultation of Korotkoff sounds using sphygmomanometer and stethoscope
What is the function of elastic arteries?
Act as a pressure reservoir to dampen down pressure variations (prevents pressure getting too high in systole and too low in diastole)
What is the pressure wave affected by?
Stroke volume
Velocity of ejection
Elasticity of arteries
Total peripheral resistance
What is the ‘normal’ arterial pressure?
120/80 mmHg
What happens to arterial pressure with age?
It increases as blood vessels lose elasticity
What happens to pressure in blood vessels moving from the arteries all the way through to the veins?
Decreases
Between which two types of vessels is the decrease in pressure the greatest?
Arteries and arterioles
Moving into these resistance vessels the area increases dramatically as the diameter of the vessels decreases, this increase in area means that pressure decreases dramatically too
What is the systemic filling pressure?
The pressure of blood exiting the circulatory system - created by the arterioles and pushes blood into the veins
What is the pressure drop through the arteries?
95 to 90 mmHg
What is the pressure drop through the arterioles?
90 to 40mmHg
What is the pressure drop through the veins?
20 to 5 mmHg
What is the pressure in the pulmonary circulation in comparison the to the pressure in the systemic circulation?
1/5th of systemic
What is the main determinant of blood velocity?
Total cross-sectional area - higher it is the lower the velocity is
Fastest in aorta and slowest in capillaries
Why do external influences affect flow in veins?
They are distensible and collapsible
Is the pressure in the veins high or low?
Low
Does gravity affect the driving pressure from arteries to veins?
No
What does gravity cause in the veins of the legs and why?
Venous distension - Gravity causes increase in pressure in lower limbs and as the veins cannot cape with increased pressure, the expand and absorb the velocity of the blood
How does the distension in the veins on the legs affect the mean arterial pressure?
Decrease in venous return -> EDV -> decrease preload-> decrease SV -> decrease CO -> decrease MAP
What is orthostatic (postural) hypotension?
Decrease in BP when standing due to gravity
What can jugular (venous) collapse in the neck be used to estimate?
Central venous pressure
What sound is heart when cuff pressure is just less than systolic pressue?
Tapping - blood flow through for short time
What sound is heard when cuff pressure is between diastolic and systolic pressure?
Thumping - blood flows through for longer time
What sound is heard when cuff pressure is the same as diastolic pressure?
Muffled
What sounds id heard when cuff pressure is above systolic or below diastolic pressure?
Nothing - flow is laminar
What occurs during the ejection phase?
Ventricle muscle contracts and pushes blood through the aortic valve, making the elastic walls of the aorta swell and absorb energy
What occurs during the relaxation phase?
Ventricles are filling with blood, the aortic valves are shut and the elastic energy is released from the walls of the aorta, changing the pressure
How does SV affect the pressure wave?
Affects rising phase - pushing more blood into the aorta would increase the pressure
How does the velocity of ejection affect the pressure wave?
If blood is pushed out fast, the elastic walls don’t have time to absorb so much energy, increasing pressure
Faster rising phase and higher peak systole
How does the elasticity of the arteries affect the pressure wave?
If arteries are not elastic then the pressure will rise higher during systole and have less energy to release during the diastolic phase so the pressure will further fall
Effects rising and falling phase
How does total peripheral resistance affect the pressure wave?
Affects the falling phase - if the arteries are constricted, resistance is increased, and blood flows much slower which means that pressure fall much slower during diastole
What drives blood back to the heart?
The pressure difference between veins and atrium - the veins must have a higher pressure
Describe the skeletal pump
Some veins travel through muscle and are squeezed during muscle contraction - valves prevent back flow so blood is pushed to heart
Static contraction of muscle does not act as a pump
Describe the respiratory pump
Pressure in thorax decreases during inspiration, which also affects the vessel, and the decrease draws blood to the heart
What is the venomotor tone?
The state of contraction of the smooth muscle surround the venues and veins
How does the venomotor tone affect pressure?
Constriction increases pressure
What 5 factors affect venous pressure and hence venous return?
Gravity Skeletal muscle pump Respiratory pump Venomotor tone Systemic filling pressure
