Control of Blood Pressure Flashcards
what is the mean arterial blood pressure
driving force for blood flow through organs apart from the lungs
why is maintenance of blood flow essential
for ensuring adequate blood flow to the organ systems
what is arterial blood pressure usually maintained around
120/80 mmhg
when must there be variations in blood flow to different organs
when demand arises to ensure adequate prefusion
what can arterial blood pressure provide good insight into
patient’s cardiovascular health
what is blood pressure
the measure of force to push the blood around the body
how is blood pressure determined
the systolic blood pressure over the diastolic blood pressure
when is blood pressure highest
on waking
when is blood pressure the lowest
during sleep
when does blood pressure increase
exercise, stress, sensory stimuli
why should health professionals be aware of potential variability when measuring BP
it is a variable haemodynamic phenomenon
what is the systolic blood pressure
the pressure in the arteries (aorta) during myocardial contraction
what is the diastolic blood pressure
the pressure in arteries (aorta) during myocardial relaxation ie when the ventricles are refilling
how do you determine pulse pressure
minus the diastolic blood pressure from the systolic
how do you determine the mean arterial pressure
the diastolic blood pressure plus one third of the pulse pressure
how is blood pressure measured
using a sphygmomanomater
how does a sphygmomanomater measure blood pressure
occludes the artery of an extremity like the arm with an inflatable cuff and by auscilation for detection of korotkoff sounds
what is cardiac output a product of
the stroke volume and the heart rate
what is the mean systemic arterial pressure a product of
cardiac output and total peripheral resistance
what is peripheral resistance created by
the system artery
how do you determine the mean arterial pressure
the diastolic blood pressure plus one third of the pulse pressure
should there be sounds coming from an occluded artery
no, you must release some air from the cuff to allow the blood flow to reduce occlusion. this creates turbulence as the artery is not fully open, and this creates the sounds
when in the cardiac cycle is the blood pressure highest
when the blood enters the aorta on contraction of the left ventricle
what are the two mechanisms that control and regulation of blood pressure occur by
rapid regulation and long term regulation
how does rapid regulation of blood pressure occur
through nerves and hormones
what is rapid control of blood pressure initially detected by
baroreceptors
what are baroreceptors
mechanoreceptors that detect the degree of stretch of blood vessel walls and monitor blood pressure
where are baroreceptors detected
the carotid sinus and the aortic arch
what do baroreceptors sense
difference in the stretch of the vascular wall
what is stretch in the arterial walls directly related to
blood pressure
where in the heart are baroreceptors most abundant
the carotid sinus because any increases or decreases can have a big impact when it is going to the head and neck. it is also sensitive to the rate of change, not just change in stretch
where is the aortic arch
between the ascending and descending aorta
between the carotid sinus and the aortic arch, which baroreceptors must be more sensitive to changes
the ones in the carotid arch
what innervates the carotid sinus baroreceptors
the sinus nerve of hering
which arteries supply the head and neck
the carotid arteries
how do the carotid arteries divide
into two smaller arteries each - internal and external on either side
what is the carotid sinus
the area of the artery wall which is thin and contains a large number of branching nerve endings that occurs as a bulge just before they split to become internal and external carotid arteries
what innervates the aortic arch baroreceptors
aortic nerve which combines with the vagus nerve
why are the aortic arch baroreceptors less sensitive than the carotid sinus baroreceptors
they have a higher threshold pressure
describe the series of events if baroreceptors detect a decrease in arterial pressure
- reduced action potential fires from the baroreceptors
- stimulation travels along afferent neurons
- medullary cardiovascular center is located in the medulla oblongata
- increased stimulation of the sympathetic neurons to the heart, arterioles and veins
- decreased stimulation of the parasympathetic neurons from the vagus nerve to the heart
describe the series of events that follows if the baroreceptors detect an increase in arterial pressure
- increased action potential firing from the baroreceptors
-stimulation travels along the afferent neurons - medullary cardiovascular centre is located in the medulla oblongata
- decreased stimulation of sympathetic neurons to the heart arterioles and veins
- increased stimulation of the parasympathetic neurons to the heart, arterioles and veins
what structure innervates the carotid sinus
sinus nerve of hering, a branch of the glossopharyngeal nerve
what is the valsalva manoeuvre
an attempt to expire against a close glottis and is associated with exhaling when the mouth and nose are closed or when lifting heavy weights
what is the physiological response from the valsalva manoeuvre
- increased intrathoracic pressure
- raising blood pressure, normal left ventricle contraction and an increased baroreceptor firing
- heart rate falls transiently, impeding venous return of blood to the heart
- fall in cardiac output and mean arterial pressure
- as the mean arterial pressure decreases, the heart rate rises and stabilises the blood pressure
what is the physiological response once the glottis has been reopened
- the intrathoracic pressure will fall
- the blood pressure will fall initially
- the venous return is rapidly restored
- the end diastolic volume and cardiac output increase, raising the blood pressure
- increased blood pressure is sensed by the baroreceptors and results in reflx bradycardia
what happens to baroreceptor activity when the arterial blood pressure is elevated for prolonged periods
the threshold for the activity rises to a higher value
what increases at the same level as the baroreceptor activity
heart rate
are baroreceptors effective at monitoring the absolute pressure of blood in the carotid arteries to the brain
no as the heart rate increases at the same level as their activity
are baroreceptors good regulators of blood pressure
only in short term regulation
what does the baroreceptor sensitivty reset during exercise allow for
the cardiac output to be maintained as the heart rate does not fall in response to the increase in blood pressure in accompanying exercise
how do baroreceptors have a role to play in hypertension
aids buffering of acute fluctuations in blood pressure at new higher blood pressure level
what is the major influence for long term regulation of blood pressure
blood volume
what does blood volume influence
venous pressure
venous return
end diastolic volume
stroke volume
cardiac output
what does an increase in blood volume also increase
arterial pressure
what does an increased arterial pressure cause
reduced blood plasma volume due to the increasing renal excretion of salt and water
what are arteries
small diameter muscular walled blood vessels. small changes in the arteriolar radius control blood pressure in response to locally circulating substances.
what causes a decrease in arteriolar radius
sympathetic nerves - noradrenaline leading to constriction
what causes an increase in arteriolar radius
sympathetic cholinergic nerves - acetylcholine which binds to muscarinic receptors, plasma like adrenaline and local controls like an increase in potassium adenosine
overall leads to dilation
what does local control of blood pressure modulate
blood pressure and blood flow
what is blood pressure modified by
local changes in systemic vascular resistance - total peripheral resistance
what does change in blood pressure occur in response to
factors like metabolites, blood gases endothelium derived factors
what causes capillary fluid shift
venous dilators which are caused by reduced proximal capillary hydrostatic pressure
what vessels do most vasodilators have effects on
arteries and veins
how do mechanisms that locally regulate long term blood pressure originate
- the RAAS system
(renin angiotensin aldosterone system) - blood vessels
- maintenance of constant blood flow
- blood volume and fluid regulation
how does blood pressure change with age
it increases
does hypertension have symptoms
not unless very severe
how is risk of hypertension increased
age
cigarette smoking
high salt intake
lack of exercise
being overweight
regularly drinking large amounts of alcohol
stress
genetic predisposition
family history
which system of the body is most vulnerable to chronic hypertension
the renal system
how often is it the case that hypertension is a result of an underlying health condition
one in twenty cases
what are the health conditions that raise the risk of hypertension
kidney conditions such as
- chronic kidney disease
- renal hypertension (narrowing of the arteries that supply blood to the kidneys)
- long term kidney infections
- glomerulonephritis (damage to glomeruli filters in the kidney)
also diabetes, obstructive sleep apnoea and hormone problems like an over active thyroid
what are therapeutics that can increase hypertension risk
contraceptive pill
non steroidal antiinflammatory drugs
recreational drugs like cocaine
what are some clinical consequences of damage caused by prolonged hypertension
aneurysms in cerebral arteries
left ventriclar hypertrophy
thickening of arteries
atherosceloris
these can then lead to
renal disease
heart failure due to myocardial adaptation
malignant hypertension
myocardial infection or angina (cardiac ischaemia)
stroke
why is it important to consider hypertension in dentistry
many hypertensive drugs have drug -drug interactions with local anaesthetics and analgesics which may lead to local anaesthetic intoxity
how does dentistry and blood pressure correlate
dental treatment is stressful for many patients and any increase in blood pressure may lead to acute complications like myocardial infarction or stroke
why do patients with cardiovascular disease have a higher risk of complications
due to release of endogenous catecholamines due to pain or stress
what is postural hypotension
abnormal drop in blood pressure when individuals stand up after sitting or lying down
what are symptoms of hypotension
dizziness, fainting, headedness when standing up after being stationary
can hypotension lack symptoms
yes
when is hypotension more common
older people and those with certain underlying conditions that affect the SNS or PNS like parkinsons or diabetes
what can cause hypotension
dehydration or certain medicines like anti hypertensives
how is blood pressure calculated
cardiac output multiplied by the total peripheral resistance
how to calculate cardiac output
equal to heart rate multiplied by stroke volume
what can affect heart rate
parasymapthetic nervous system
sympathetic nervous system
hormones
ions
what is the main thing to think about regarding preload
anytime there is an increase in blood volume, this increases end diastolic volume. this increases the preload, or the stretch, of the heart and increases the stroke volume
what three components can stroke volume be broken down into
preload, contractility, afterload
what is an afterload
the amount of pressure you have to overcome to push blood from the ventricles to the arteries
what does an increase in contractility mean for stroke volume
it will increase
what is the end diastolic volume
the volume in the heart before ejection
what is contractility dependent on
the sympathetic nervous system, which increases contractility using adrenaline and noradrenaline. could also be affected by glucagon and thyroxine
how is heart rate measured
in beats per minute
how is stroke volume measured
in ml per beat
what is flow defined as
the volume of blood
what can hypertension increase
the afterload
what can peripheral resistance increase
the afterload
how is cardiac output measured
in ml per minute
how does diameter (cross sectional area) affect the velocity of blood flow
a decrease in cross sectional area increases the velocity of the blood flow
what is velocity equal to
flow over the area of blood vessels
how does increasing flow affect velocity
increases i
what could an increase in cardiac output also be described as
an increase in blood flow
how is the cross sectional area of the aorta
small
describe the branching of blood vessels
aorta gives off arteries which give off arterial branches which give off capillary branches which then drain to become venules which become veins which join at the vena cava
why is it important for flow of blood to be slow at the capillaries
to allow good exchange of the nutrients and substances from the capillaries to the tissues
what can increase the afterload
hypertension and peripheral resistance
