define systolic blood pressure
maximum blood pressure in the arteries
at the brachial artery, what is the systolic blood pressure?
120 mmHg
at what pressure is the systolic marginal hypertension?
140 mmHg
at what pressure is the definite intervention threshold?
160 mmHg
define diastolic blood pressure
minimum blood pressure in the arteries
define pulse pressure
difference between the systolic and diastolic blood pressures
how is the mean arterial pressure calculated?
diastolic pressure + 1/3 pulse pressure
what causes compliance in arteries?
the elastic fibres in the artery wall
why is compliance good?
reduces the work of the heart because some blood is stored in the arteries
explain the effect of smoking on arteries, systolic volume and cardiac output
hardens arteries
increases systolic volume because aorta cannot stretch to accommodate SV
decreases CO bc ventricular contraction is longer
what does the windkessel effect do?
helps reduce fluctuations in pulse pressure over the cardiac cycle
maintains organ perfusion during diastole
what are the windkessel vessels?
aorta
large arteries
explain the windkessel effect
arteries distend when BP rises in systole and recoil in diastole
in systole there is a net storage of blood bc of difference in rate of the blood entering and leaving the artery
net storage of blood is then released through recoil in diastole
define hypertension
abnormally high blood pressure over 140/90
what is prehypertension?
BP higher than normal but not enough to need medication
what are the range of pressures for prehypertension?
systolic: 120-139
diastolic: 80-89
how is local flow calculated?
pressure/local resistance
what does Poiseuille’s law state?
at a constant pressure, the flow is proportional to the radius of the tube to the power of 4
small changes in arterial diameter produce large changes in flow
how is cardiac output calculated?
heart rate x stroke volume
define cardiac output
total blood flow out of the heart
how can heart rate be measured?
from an ecg
how can stroke volume be measured>
from echocardiography
what is the usual heart rate?
70bpm
what is the usual stroke volume?
70ml
what is the typical cardiac output of a healthy adult male?
4.9L/min
what method can be used to measure cardiac output?
doppler ultrasound
explain how doppler ultrasound can be used to measure cardiac output?
blood velocity through the first part of the aorta causes a doppler shift in the frequency of the returning ultrasound waves
ultrasound can measure cross sectional area of the aorta and uses this to calculate CO
what are the advantages of doppler ultrasound?
non-invasive accurate inexpensive reliable reproducible
explain how trans oesophageal doppler works
ultrasound probe inserted into the oesophagus at mid-thoracic level
measures blood velocity in adjacent descending thoracic aorta
what factors affect heart rate?
autonomic innervation
hormones
fitness levels
age
what factors affect stroke volume?
heart size fitness levels gender contractility duration of contraction preload afterload
what are the oxygen requirements of vital organs?
brain - 700ml/min
heart - 200ml/min
kidneys - 1250ml/min
how is blood flow through the skin varied?
increased via AV shunts
decreased via vasoconstriction
how much can cardiac output be increased by?
3.75 times to 19L/min
how is stroke volume increased during exercise?
contraction of atria - transfers blood to atria
increased ventricular contractility - smaller residual volume
how does oxygen uptake increase during exercise?
faster breathing
dilation of bronchi and trachea means less resistance
what does the work of the heart depend on?
blood viscosity
arteriole diameter
what does the viscosity of the blood depend on and which factor has the biggest impact?
haematocrit - strongest impact
RBC deformability
RBC aggregation
plasma viscosity
what is haematocrit?
proportion of red blood cells in the total volume of blood
what is polycythemia?
a disease where there’s increased haematocrit
what are the types of polycythemia
absolute - excessive production of RBCs
relative - decrease in plasma volume
explain how nitric oxide is released by blood vessels
edges of RBCs interact with polypeptide chains connected to proteins in the endothelium
calcium moves into the endothelium
nitric oxide forms and relaxes and dilates the walls
what effect does nitric oxide have on the capillary wall?
local anticoagulant
what does laplace’s law state?
the pressure an elastic vessel can withstand depends on the tension produced in the walls by their elasticity divided by the radius of the vessel
in a cyclinder, what is the pressure withstood proportional to?
T/R
tension/radius
in a sphere, what is the pressure withstood proportional to?
T/2R
describe the relationship between the radius of a vessel and the pressure it can withstand
the smaller the radius, the greater the pressure the wall can withstand
what is an atheroma?
a fatty deposit on the inside of an artery
what happens if an artery wall weakens?
radius increases
balancing pressure that the tissue generates is less
walls balloon out so its less effective at withstanding pressure
aneurysm
what is an aneurysm?
localised and abnormal weak spot on a blood vessel that can cause outward bulging
what vessels are common sites for aneurysms?
aorta
cerebral arteries
at what point in a blood vessel do aneurysms tend to occur?
just before points where the blood vessel branches
what are risk factors for aneurysm formation?
hypertension
artery disease
why do aneurysms commonly occur in cerebral arteries?
more convoluted and twisted than other arteries
more stress on the walls
how can aneurysms present?
discovered incidentally during MRIs or angiography
rupture causing subarachnoid brain haemorrhage
symptoms of mass effect on neural structures
how can cerebral aneurysms be treated?
clipping or coiling
explain the process of coiling
fine wire is pushed into the swollen artery to form a coil
blood clots around the coil and takes pressure off the wall