CVS 2 - blood pressure Flashcards
Define arterial blood pressure
a measure of force to push blood around the body (systemic circulation)
How is arterial blood pressure displayed?
systolic BP / diastolic BP mmHg (e.g. 120/80 mmHg)
Define systolic blood pressure (SBP)
pressure in arteries (aorta) during myocardial contraction (systole)
Define diastolic blood pressure (DBP)
pressure in arteries (aorta) during myocardial relaxation (diastole - when ventricles are refilling)
Define pulse pressure
the force the heart needs to generate to eject blood into the arteries
How can the pulse pressure be calculated?
systolic blood pressure (SBP) - diastolic blood pressure (DBP)
Around what pressure is the arterial blood pressure maintained at?
around 120/80 mmHg
Why is maintenance of arterial blood pressure essential?
to ensure adequate blood flow to organ systems
Examples of variations in blood flow to different organs when demand arises
during exercise there is increased perfusion to skeletal muscles, following a meal there is increased perfusion to GIT
Why is arterial blood pressure routinely measure in clinical practice?
provides a useful insight into patient’s cardiovascular health
When is blood pressure greatest?
on waking
When is blood pressure lowest?
during sleep
When does blood pressure increase?
in response to exercise, stress, sensory stimuli
How is blood pressure measured?
using a sphygmomanometer and a stethoscope
What is a sphygmomanometer?
an inflatable cuff used to occlude the artery of an extremity (e.g. arm) attached to a pressure gauge
What sounds are heard by auscultation using a stethoscope during blood pressure measurements?
Korotkoff sounds
What are the 2 ways of calculating the mean arterial pressure (MAP)?
MAP = CO x TPR
MAP = DBP + 1/3 pulse pressure
How is cardiac output (CO) calculated?
CO = SV x HR
What is the total peripheral resistance (TPR)?
total resistance to flow of blood in systemic circulation (systemic vascular resistance)
Where is the stethoscope placed during sphygmomanometry?
over the brachial artery distal to the cuff
Outline how blood pressure is measured using sphygmomanometry
Cuff is inflated to a cuff pressure >120mmHg to stop arterial blood flow so no sound can be heard in the stethoscope. Cuff is slowly deflated (80 - 120mmHg) until Korotkoff sounds are heard (SBP) due to pulsatile blood flow. When blood flow is silent the artery is no longer compressed (DBP).
How is systolic blood pressure identified in sphygmomanometry?
the cuff pressure at which Korotkoff sounds appear
What causes the Korotkoff sounds?
pulsatile blood flow through the compressed artery
How is diastolic blood pressure identified in sphygmomanometry?
the cuff pressure at which the Korotkoff sounds disappear (silence)
What are the 2 mechanisms of controlling blood pressure?
rapid regulation (via nerves and hormones) and long term regulation (via blood volume)
How is rapid regulation of blood pressure achieved?
via action of nerves and hormones
When is blood pressure highest?
when blood enters the aorta on contraction of the left ventricle
Where are there large fluctuations in systolic and diastolic BP?
in the arterial system, then the fluctuations become non-existent in the venous system
How is blood pressure in the arterial system monitored?
by baroreceptors
What are baroreceptors?
a class of mechanoreceptors that detect the degree of stretch of blood vessel walls
Function of baroreceptors
monitor blood pressure
What is the cause of mechanical stretch (circumferential stress) in arteries?
pulsatile blood flow (increases during systole and decreases during diastole)
Where are baroreceptors most abundant?
in the aortic arch and carotid sinus
What factors are baroreceptors sensitive to?
changes in stretch (pressure) and rate of pressure/stretch change
Which two arteries supply the head and neck?
left and right carotid arteries
How do the left and right carotid arteries divide?
each divide into two smaller arteries (L+R internal and external carotid arteries)
Where is the carotid sinus?
area where the artery wall is thinner and contains a large number of branching nerve endings after dividing into ICA and ECA
Which nerve innervates the carotid sinus baroreceptors?
sinus nerve of Hering (a branch of the glossopharyngeal nerve CN IX)
Which nerve is the sinus nerve of Hering a branch of?
Glossopharyngeal nerve (CN IX)
Which nerve innervates the aortic arch baroreceptors?
the aortic nerve (combines with vagus nerve CN X)
Which baroreceptors have a higher threshold pressure?
aortic arch baroreceptors so they are less sensitive to stretch than carotid sinus baroreceptors (which have a greater firing rate)
Describe the sequence of events to return BP to normal after a decrease
- Baroreceptors detect decrease in arterial pressure
- reduced AP firing from baroreceptors
- travels along afferent neurons
- to medullary cardiovascular centre
- increased stimulation of sympathetic neurons to heart/arterioles/veins
- decreased stimulation of parasympathetic neurons (vagus nerve) to heart
Describe the sequence of events to return BP to normal after an increase
- baroreceptors detect increase in arterial pressure
- increased AP firing from baroreceptors
- along afferent neurons
- to medullary cardiovascular centre
- decreased stimulation of sympathetic neurons to heart/arterioles/veins
- increased stimulation of parasympathetic neurons (vagus) to heart/arterioles/veins
What is the valsalva manoeuvre?
attempt to expire against a closed glottis (exhaling when mouth and nose are closed e.g. lifting heavy weights)
What is the physiological response to the valsalva manoeuvre?
1) increased intrathoracic pressure
2) this raises blood pressure
3) along with a normal LV contraction this increases baroreceptor firing
4) heart rate falls
5) impedes venous return of blood to heart
6) fall in CO and MAP
7) As MAP decreases, HR rises and alongside the TPR this stabilises BP
Describe the physiological response when the glottis (pharynx) is reopened to allow expiration following the valsalva manoeuvre
1) intrathoracic pressure falls
2) BP falls initially
3) venous return rapidly restored
4) EDV and CO increase which raises BP
5) detected by baroreceptors which results in reflex bradycardia (slowing HR)
How is baroreceptor resetting triggered?
by prolonged periods of elevated arterial BP (e.g. >15 min)
Describe what happens during baroreceptor resetting
when mean arterial BP is elevated for prolonged periods, the threshold for baroreceptor activity rises to a higher value so baroreceptor activity is decreased
As MAP increases, how does baroreceptor activity change?
As MAP increases, baroreceptor activity will also increase. If the MAP increase is prolonged, baroreceptor resetting occurs so baroreceptor activity is lower for a given MAP compared to before resetting.
How does baroreceptor resetting affect heart rate?
following baroreceptor resetting, HR is higher for a given MAP because baroreceptor activity is decreased for the given MAP
How does heart rate change as MAP increases?
as MAP increases, HR decreases to regulate BP
Examples of certain physiological conditions where resetting of baroreceptor sensitivity is beneficial
during exercise and in hypertension
Why is baroreceptor resetting beneficial during exercise?
despite increase in BP due to exercise, HR does not fall so CO is maintained
How is baroreceptor resetting beneficial in hypertension?
aids buffering of acute fluctuations in BP at new higher BP level
How is BP regulated in the long term?
via blood volume (negative feedback loop)
What factors are influenced by blood volume?
venous pressure, venous return, end diastolic volume, stroke volume, cardiac output
How does an increase in blood volume affect arterial pressure?
increased blood volume, increases arterial pressure
How does an increased arterial pressure affect blood volume?
increased arterial pressure leads to increased renal excretion of salt and water which reduces blood plasma volume
How is blood pressure controlled locally?
by local changes in systemic vascular resistance (total peripheral resistance, TPR)
How are arterioles involved in local control of BP?
locally circulating substances cause small changes in arteriolar radius which modulates blood pressure and blood flow
Examples of circulating substances that can cause local changes in systemic vascular resistance (TPR)
metabolites, blood gases, endothelium derived factors
What stimulates a decrease in arteriolar radius (constriction)?
stimulation of sympathetic nerves
How do sympathetic nerves cause arterioles to constrict?
sympathetic nerves release noradrenaline which binds to a1 adrenoceptors causing constriction
How can arteriolar radius be increased?
by sympathetic cholinergic nerves, plasma (circulating factors), or local controls
How do sympathetic cholinergic nerves cause dilation of arteriolar radius?
sympathetic cholinergic nerves release acetylcholine which binds to muscarinic receptors causing vasodilation
What circulating factors in the plasma can cause vasodilation of arterioles?
adrenaline
How can adrenaline increase arteriolar radius?
adrenaline (circulating in plasma) binds to B2 adrenoceptors causing vasodilation
What local controls can increase arteriolar radius?
increased K+, adenosine, decreased PO2 cause vasodilation
Name a mechanism of local BP control in capillaries
capillary fluid shift
Describe the action of the capillary fluid shift mechanism when arterial BP is increased
increased arterial BP leads to increased capillary HP, so there is increased filtration of fluid from the plasma into tissues, leading to decreased plasma volume which decreases venous return therefore arterial BP is decreased
Describe the action of capillary fluid shift mechanism when arterial BP is decreased
decreased ABP decreases capillary HP, so less fluid filtered into tissues, increased reabsorption in venule end (?), increased plasma volume, increased venous return which increases arterial BP
What can trigger the capillary fluid shift?
venous dilators (reduce proximal capillary HP)
Example of a system that regulates long term blood pressure
renin angiotensin aldosterone system (RAAS)
What clinical blood pressure is considered hypertensive?
140/90 or higher
How does blood pressure vary with age?
blood pressure increases with age (as arterial walls thicken)
Why is hypertension referred to as a silent disease?
usually lacks noticeable symptoms until it’s very severe
What interventions can lower blood pressure?
lifestyle changes and/or pharmacological interventions
Risk factors for hypertension
age, smoking, high salt intake, lack of exercise, overweight, high alcohol consumption, stress, family history, genetic predisposition
What is secondary hypertension?
hypertension caused by an underlying health condition or taking certain medication
What proportion of hypertensive cases are due to secondary hypertension?
1 in 20 cases
Examples of health conditions that can raise hypertension risk
kidney conditions, diabetes, obstructive sleep apnoea, hormone problems
Which kidney conditions can increase risk of hypertension?
chronic kidney disease (CKD), renal hypertension (narrowing of arteries that supply blood to kidneys), long term kidney infections, glomerulonephritis (damage to glomeruli filters in kidney)
Which therapeutics can increase hypertension risk?
contraceptive pill, non-steroidal anti-inflammatory drugs (NSAIDs), recreational drugs
Where can information about medicines for prescribers be found?
British National Formulary (BNF)
What are possible clinical consequences of hypertension?
aneurysms in cerebral arteries, left ventricular hypertrophy (LVH), thickening of arteries, atherosclerosis deterioration
What can the effects of clinical consequences of hypertension lead to?
renal disease, heart failure (due to myocardial adaptation to compensate for LVH), malignant hypertension (severely high BP), angina, myocardial infarction, stroke
Cause of myocardial infarction
cardiac ischaemia due to blockage of coronary arteries
Cause of stroke
disruption of atherosclerotic plaque in arteries supplying brain (causes cerebral ischaemia)
What factors can increase cardiovascular risk when associated with hypertension?
diabetes mellitus, CKD, HMOD (hypertension mediated organ damage)
What considerations must be made with respect to hypertension in dentistry?
anti-hypertensive drugs may interact with local anaesthetics and analgesics, increase in BP due to stress of treatment can lead to acute complications (e.g. myocardial infarction, stroke), patients with CVD have higher risk of complications due to release of endogenous catecholamines as a result of pain/stress
What blood pressure is considered hypotensive?
90/60 mmHg or less
What is postural hypotension?
an abnormal drop in blood pressure when individual stands up after sitting/lying down
What is postural hypotension also known as?
orthostatic hypotension
Cause of postural hypotension / orthostatic hypotension
delay in baroreceptor reflex
Symptoms of hypotension
dizziness, light-headedness, fainting, possible fall, or can be asymptomatic
What group of the population is hypotension more common in?
elderly and those with underlying conditions affecting the autonomic nervous system (parasympathetic or sympathetic NS)
Examples of underlying conditions that can be associated with hypotension
Parkinson’s disease or diabetes
Possible causes of hypotension
dehydration or certain medicines (e.g. anti-hypertensives)
