w3: Regulation of arterial blood pressure Flashcards
What is haemodynamics?
The study of how blood flows through your blood vessels.
What is diastolic pressure?
The lowest arterial pressure measured during the cardiac cycle.
Is the pressure during ventricular relaxation, when no blood is being ejected from the left ventricle.
What is systolic blood pressure?
The highest arterial blood pressure measured during a cardiac cycle.
Is the pressure measured just after blood has been ejected from the ventricles.
What is the dicrotic notch?
A brief dip in systolic blood pressure, is caused when the aortic valve closes, causing brief backwards flow of blood towards the valve, this briefly decreases aortic pressure.
What is the pulse pressure?
The difference between the systolic and diastolic pressure, if all other factors are equal the value will be equal to the stroke volume.
What is the mean arterial pulse?
How is it calculated?
What is the normal range?
The average pressure over a complete cardiac cycle.
= Diastolic pressure + 1/3Pulse pressure.
or
= cardiac output * total peripheral resistance
The normal range is 70-100mmHg.
How does blood pressure change with age?
Blood pressure increases with age.
What two factors determine blood flow through a vessel?
How is this reflected in an equation?
The pressure difference between the two ends of the vessel
The resistance of the vessel to blood flow
Flow (Q) = change in pressure (triangle) / resistance (R)
What is the total peripheral resistance?
The sum of the resistance to blood in all the bodies blood vessels.
This is also called systemic vascular resistance of the entire systemic vasculature.
The driving force for blood flow is ……
Mean arterial pressure.
Why does every main vessel supplying an organ have the same mean pressure?
Due to the parallel arrangement of arteries in circulation.
*arterioles then regulate blood flow to the organs independently.
What are baroreceptors?
What affects how they detect stimuli?
Barorecoptors are mechanoreceptors that detect changes in pressure, when blood pressure increases the baroreceptors becomes more stretched changing their membrane potential to generate an action potential.
The strongest stimuli comes from a rapid change in pressure.
They are sensitive to the degree and the speed at which the pressure changes.
How do baroreceptors in the heart relay information to the brain?
Carotid sinus (neck) baroreceptors are carried to the brain by the carotid sinus nerve which joins the glassopharyngeal nerve at CNIX
The aortic arch baro receptors are carried to the brainstem on the vagus nerve. CNX
Explain the mechanisms for which blood pressure can be decreased by the brain stem and cardiovascular centres after baroreceptor action potential is generated.
Carotid sinus bararecptors signal is carried to the brain stem by CNIX
Aortic Arch baroreceptors signal is carried to the brain stem by CNX
Increased peak impulses from the barorecptors
The Nucleus Tractus Solitarus receives the signal.
Inhibits the sympathetic nervous system, and activates the parasympathetic nervous system.
Fewer signals are initiated by the SAN, vasodilation occurs and decreases contractility.
This decreases venous return hence cardiac output through Frank Starling mechanisms.
This happens through the inhibitor vasomotor centre and the cardioinhibitory centre
What is the mechanism of increasing blood pressure involving barorecptors and cardiac centres in the brain?
Decreased blood pressure means barorectors in the carotid sinus and aortic arch are inhibited so less impulses are carried along CNIX and CNX.
These decreased impulses activated the cardioacceletory centre and stimular the vasomotor centre.
This leads to activation of the sympathetic nervous system leading to more impulses to the SAN, so increases HR. Also increased vasoconstriction to increase pressure and increases contractility, this increases the venous return to increases the cardiac output and blood pressure.
What are the different physiological responses to a hemorrhage to change blood flow?
Blood pressure drops, baroreceptors activate the sympathetic nervous system to increase heart rate and total peripheral resistance
Capillaries - decreases hydrostatic pressure so more fluid absorption by starling law, replaces volume of blood lost
Renin-Angiotensin II-Aldosterone response.
What is the Renin-Angiotensin II-Aldosterone response to hemorrhage?
Increased angiotensin 11
Leads to increased total peripheral resistance
Also leads to increased aldosterone, which causes increased Na+ reabsorption in the kidney, this causes an increase in blood volume.
Eventually increases the mean arterial blood pressure.
What is the unstressed volume of the blood?
The minimum volume of blood required to exert pressure on the veins walls.
Any volume above this is know as the stressed volume.
Explain how the nervous response to hemorrhage can damage vital organs.
Hemorrhage, sympathetic nervous systems causes vasconstriction in order to increase the blood pressure and increase total peripheral resistance.
Due to the parallel arrangement of blood vessels this is not uniform meaning that the constriction can be controlled separately, with more constriction in certain areas such as the skeletal muscle.
The muscle is quite resistant to low oxygen conditions, however prolonged vasconstriction to other areas can cause ischaemic damage and eventually organ failure.
How does a carotid sinus massage work?
What does it aim to do?
Aims to decreases heart rate, treat tachycardia.
Massaging the carotid sinus stretches the baroreceptors, this leads to an increased frequency of impulses being sent along the vagus nerve.
This slows the frequency of impulses released from the SAN, leading to a decrease in heart rate as fewer action potentials are passed through the ventricles, so the time span between QRS complexes increases.
Why is a carotid sinus massage not recommended for the elderly?
More likely to have build-up of atherosclerotic plaque, this could be dislodged during the massage, the plaque can then travel in the blood stream to the brain, where is forms a blood clot, this causes ischemic damage to brain tissue and may causes a stroke.
What is the diving reflex?
What does it aim to do?
The diving reflex aims to decrease the heart rate.
This is caused by the stimulation of the trigeminal nerve, the nasopharyn and the oropharynx being stimulated by cold water.
Unable to breath and the oxygen supply to the heart decreases.
This activates the vagus nerve to decrease the heart rate.
The high level of sympathetic vasoconstriction in the periphery maintains the blood pressure and conserves oxygen for the most vital organs, such as the brain and the heart.
How do you perform the valsalva manoeuvre?
- Breathe in deeply and how the breath
- Push downwards and tighten the stomach and abdomen as if constipated.
- Hold the breath for 10 seconds
- Forcibly release the breath rapidly
- Return to normal breathing.
What are the different phases of the Valsalva manoeuvre?
- Increased intrathoracic pressure increased pulmonary return into the left atrium. And compresses the aorta this originally leads to increased blood pressure
- Eventually the build up of intrathoracic pressure, impedes venous return leading to a decrease in store volume so a decrease in blood pressure, this leads to temporary baroreceptor increase in heart rate.
- When the pressure is released the compression stops and the blood pressure increases, this triggers baroreceptors to decrease the heart rate inorder to return the blood pressure back to normal.
