Flashcards in Blood Pressure Deck (49)
What is the Mean Arterial Blood Pressure (MABP)?
The driving force for blood flow through the organs/systemic circulation (everything except the lungs)
Why is Mean Arterial Blood Pressure important?
Ensures adequate blood flow to organ systems
What value is arterial blood pressure maintain at?
What is systolic blood pressure (SBP)?
Pressure in arteries (aorta) during myocardial contraction (systole)
What is diastolic blood pressure (DBP)?
Pressure in arteries (aorta) during myocardial relaxation (diastole) i.e. when ventricles are refilling
How do you calculate pulse pressure?
SBP - DBP
How do you calculate Mean Arterial Blood Pressure?
DBP + 1/3 pulse pressure
CO x TPR
What does TPR stand for?
Total peripheral resistance
Refers to systemic vascular resistance
When is blood pressure the highest?
When is blood pressure the lowest?
What can you use to measure blood pressure?
Occlude the artery of an extremity (e.g. arm) with an inflatable cuff and by auscultation of for detection of Korotkoff sounds
What are the 2 main mechanisms of blood pressure regulation?
1. Rapid regulation e.g. nerves, hormones
2. Long-term regulation e.g. blood volume
What are baroreceptors?
Mechanoreceptors that detect changes in blood pressure by detecting the degree of stretch in the blood vessel walls
Which 2 locations are baroreceptors most abundant?
1. Aortic arch
2. Carotid sinus
Describe the carotid sinus
- Two carotid arteries supply the head and neck (right and left)
- Each carotid artery divides into 2 smaller arteries
- Where the artery wall is thinner and contains a large number of branching nerve endings - this are is the carotid sinus
Which nerve innervates the carotid sinus baroreceptors?
Nerve of Hering (a branch of the glossopharyngeal nerve; CN IX)
Which nerve innervates he aortic arch baroreceptors?
Aortic nerve (combines with vagus nerve)
Which baroreceptors (carotid sinus or aortic arch) are most sensitive to pressure change/changes in stretch?
Aortic arch baroreceptors
Have a higher threshold pressure
What is 'normal' BP?
Describe the frequency of baroreceptor firing when blood pressure is increased or decreased
- Frequency of baroreceptor firing is constant within normal blood pressure ranges
- Elevation in BP: frequency of AP firing by baroreceptors is quickened
- Decrease in BP: decrease in AP firing by baroreceptors
What effect does an increase in baroreceptor AP firing have on sympathetic discharge?
Increased baroreceptor AP firing leads to decreased sympathetic discharge. Trying to reduce cardiac output and reduce blood pressure
What effect does a decrease in baroreceptor AP firing have on sympathetic discharge?
Decreased baroreceptor AP firing leads to increased sympathetic discharge. Trying to increase heart rate and blood pressure
Where is the medullary cardiovascular centre located?
In the medulla oblongata
What is the Vasalva Manoeuvre?
Attempting to expire against a closed glottis
Associated with exhaling when mouth and nose are closed e.g. lifting heavy weights
What does the vasalva manoeuvre lead to ?
1) Increased intra-thoracic pressure
2) Raising BP. Increased baroreceptor firing
3) Heart rate falls transiently - impeding venous return of blood to the heart
4) Fall in CO and MAP
5) As MAP decreases, HR increases and stabilises blood pressure
What happens after the vasalva manoeuvre i.e. when the glottis is re-opened to allow expiration?
1) Intra-thoracic pressure falls.
2) BP falls initially
3) Venous return is rapidly restored
4) EDV and CO increase, increasing BP
5) Increased BP is sensed by baroreceptors and this results in bradycardia - slowing of the heart
Why are baroreceptors ineffective monitors of absolute pressure of blood in carotid arteries to the brain?
Because baroreceptor activity adapts over time and heart rate will increase at the same level
Baroreceptors are short term regulators of blood pressure only
What effect does baroreceptor resetting have during exercise?
Maintains cardiac output as heart rate does not fall in response to increased blood pressure accompanying exercise
What is the major influence for long-term regulation of blood pressure?