Theme 3: Lecture 2 - Blood pressure Flashcards
Units of BP
mmHg (or kPa)
What is a portal system
2 capillary beds in series (When a capillary bed reassembles to a blood vessel that splits again into another capillary bed)
What does a capillary system allow
transport of chemicals from one tissue to another without being diluted by mixing with blood at the heart.
Give an example of a portal system
Hepatic portal system
An increase in what things will cause an increase in BP
- Peripheral resistance
- Cardiac output
- Blood volume
Why is there not one measurement of BP
The arterial pressure changes due to systole and diastole
Equation for mean arterial pressure
P mean = P diastole + (P systole - P diastole)/3
Stroke volume
Volume of blood pumped out of a ventricle during one beat of the heart
Heart rate
measured in beats per minute. Its reciprocal is the RR interval, which is 60 ÷ HR.
RR interval
Time elapsed between 2 heart beats (reciprocal of heart rate)
Cardiac output
Volume of blood pumped out of a ventricle per minute
Cardiac output equation
CO = HR x SV
Normal stroke volume
70mL
Normal heart rate
70 bpm
Normal RR interval
0.86 s
Normal cardiac output
4.9 L/min
End diastolic volume
Volume of blood in a ventricle at the end of filling (diastole). EDV is associated with “pre-load”, how stretched the muscle is.
End systolic volume
Volume of blood remaining in a ventricle at the end of contraction (systole). So: SV = EDV – ESV
Ejection fraction
Percentage of filled ventricular volume pumped out during a heart beat: SV / EDV
How much does atrial systole add to total fill of ventricles
20-25%
Normal end diastolic volume
120mL
Normal end systolic volume
50mL
Normal ejection fraction
58% (50-70%)
Vasomotor
actions on a blood vessel that alter its diameter
What does vasoconstriction lead to
a smaller radius which leads to a higher resistance which leads to a lower flow rate
What causes dilation on constriction of individual blood vessels
- Central regulation (CNS, autonomic, endocrine)
- Local regulation of pressure
- Immune
- Haemostasis
What happens to blood vessels during exercise
- Peripheral vasodilation (skin/muscle)
- Vasoconstriction of splanchnic circulation
What happens to blood pressure and heart rate in exercise
- Increased systolic BP
- Decreased diastolic BP
- Increased heart rate
What happens initially when you stand
-Initially a drop in BP then compensatory recovery (ie increase back to normal)
What happens to the blood vessels and heart rate during standing
- peripheral vasoconstriction (arterial + venous)
- increased HR
What happens to blood pressure and heart rate after standing up
- no change in systolic BP
- increased in diastolic BP
- increased heart rate
How is blood pressure controlled systemically
- Local (Endothelial, Nitric Oxide (NO))
- Neurological – the autonomic system
- Humoral – renal / pituitary / adrenal
What does nitric oxide do
causes smooth muscle relaxation leading to vasodilatation
What is nitric oxide released by
endothelial cells
What are the local blood flow conditions that would cause vasodilatation
- increased hydrostatic pressure
- increased shear force
What is shear force protective for
it’s atherogenic (protective against atherosclerosis)
What is shear force increased by
laminar flow (smooth, opposite to turbulent flow)
What does increased sympathetic stimulation cause in relation to BP and cardiac output
- Constricts blood vessels
- increase in peripheral resistance
- increase in pressure
- increase in heart rate
- increase in cardiac output
What do baroreceptors do
- Detect pressure and feed back to the brain
- Activity leads to a decrease in BP
Where are baroreceptors located
- transverse aortic arch
- carotid sinuses of the left and right internal carotid arteries
What do chemoreceptors do
Detect when CO2 levels are low and feed back to the brain
Where are chemoreceptors located
- carotid bodies
- aortic bodies
How does the heart pump the right amount of blood as the volume of blood entering the heart must equal the volume of blood leaving the heart
Due to the Frank Starling mechanism
Frank Starling law
the stroke volume of the heart increases in response to an increase in the stretching of blood filling the heart (the end diastolic pressure)
Venous return
the rate of blood flowing back to the heart through the veins
Preload
the initial stretching of the cardiac myocytes during diastole (prior to contraction). Depends on venous return
Volume overload
Results when preload becomes too large
5 factors that cause an increase in preload
- decrease in heart rate
- increase in aortic pressure
- increase in atrial contractility
- increase in ventricular compliance
- increase in central venous pressure
2 factors that cause an increase in central venous pressure
- decrease in venous compliance
- increase in thoracic venous blood volume
Afterload
the resistance that the chambers of the heart must overcome in order to eject blood out of the heart (resistance during systole)
What is afterload increased by
- back pressure from aorta or pulmonary arteries
- if the exit valve fails to open completely
Pressure overload
- results from elevated afterload
- a pathological state
What is the thoracic pump for venous return
- “pulls” the blood (from below) towards the right atrium.
- during inspiration intrathoracic pressure is negative and abdominal pressure is positive (compression of abdominal organs by diaphragm).
- Creates a pressure gradient
What is the muscle pump in venous return
- Rhythmical contraction of limb muscles as occurs during normal locomotor activity
- Squeezes blood out of nearby veins
- Venous valves assure one-way flow toward heart
Describe the pulmonary circulation
- High Capillary Density
- Low Vascular Resistance
- Acts as Blood Reservoir
- Acts as Filter
What controls the BP of the pulmonary circulation
endocrine control via ACE
What happens to arterioles if O2 is low in a region of the lung
they constrict
What happens to arterioles if CO2 or H+ are high in an area of the lung
they constrict
What does poor ventilation in the lung lead to
- reduced perfusion
- this minimises the amount of blood that is poorly oxygenated
Describe the coronary circulation
- Cardiac Muscle has High Demand
- Most Flow occurs during Diastole (unusual)
- Obtains blood almost before aorta
What is hypertension
high blood pressure (esp high diastolic pressure)
What may chronic hypertension result in (7 things listed)
- Coronary artery disease
- MI
- Aneurysm
- Stroke
- Kidney failure
- Heart failure
- Cardiac hypertrophy
Symptoms of hypertension
often asymptomatic
What is hypertension caused by
- mismatch in blood volume and circulatory capacity
- most cases are idiopathic
- often secondary to kidney disease
What is orthostatic hypotension
low BP on standing up due to decreased venous return
Symptoms of orthostatic hypotension
- dizziness
- syncope
hypovolaemia
too little blood volume
Causes of orthostatic hypotension
- drugs
- hypovolaemia
- age
What is cardiogenic shock
shock due to heart not pumping enough blood to meet body’s demands
Signs and symptoms of cardiogenic shock (7 things listed)
- tachycardia
- tachypnoea
- low urine output
- hypotension
- confusion
- syncope
- acidosis
Compensatory mechanisms of cardiogenic shock
- tachycardia
- tachypnoea
Things seen when the body fails to compensate cardiogenic shock
- low urine output
- hypotension
- confusion
- syncope
