Lesson 21: Topic 17 - Mean Arterial Pressure Flashcards
what determines mean arterial pressure?
MAP = CO(cardiac output) x TPR(total peripheral resistance)
how do we regulate MAP?
by altering cardiac output and tpr
why is mean arterial pressure important?
- # 1 homeostatically regulated variable in your body
- provides ‘driving force’ to move blood through the circulation
- contributes to the heart’s ‘workload’
what is hypotension?
having low blood pressure
what is the diagnosis of hypotension?
systolic BP/ diastolic BP = 90/60 mm Hg
what are the symptoms of hypotension?
- dizziness
- fainting
- blurred vision
- fatigue
why do we get dizziness and faint when we have low blood pressure?
because we have an insufficient blood supply going to our brain
why do we get blurred vision when we have low blood pressure?
insufficient oxygen delivery to our eyes
why do we have fatigue when we have hypotension?
insufficient blood delivery to our brain and also to our skeletal muscles and heart
what are causes of hypotension?
- dehydration (we have less water, we have less blood volume
- pregnancy
- heart failure
- anemia
how does pregnancy lead to hypotension?
because we are taking blood flow away from our systemic circulation and into the fetus
what are risk factors of hypotension?
- age
- medications
- certain diseases (Parkinson’s and diabetes)
why is parkinsons a risk factor for hypotension?
because Parkinsons affects the autonomic nervous system so it can impair the ability to regulate blood pressure
what is hypertension?
high blood pressure
why is hypertension called the ‘silent killer’?
because many people do not have symptoms right away and its not until it gets severe that the symptoms get bad
there are three stages of hypertension, what are they and what BP is classified with it?
- stage 1: SBP/DBP = 130-139/80-89mm Hg
- stage 2: >=140/>=90
- hypertensive crisis: >180/>120
what are the severe symptoms related to hypertension?
- stroke
- heart attack
- kidney failure
- blindness
- dementia
- sexual dysfunction
what is athelerosclerosis?
plaque build up in the brain and/or heart
how is sexual dysfunction a symptom of hypertension?
it is going to be damaging the blood vessels and the endothelial layer of the organs and the endothelial layer is responsible for producing nitric oxide which helps to vasodilate
what are the potential causes of hypertension?
- atherosclerosis
- kidney disease
- sleep apnea
- thyroid issues
what are the risk factors for hypertension?
- age
- obesity
- genetics
- inactivity
- smoking
- high sodium intake
- stress
- alcohol consumption
what is another name for arteries?
conduit vessels
what is the function of an artery?
conduit arteries must take blood from the heart and distribute it to the various organs/tissues as efficiently as possible
(ie. do not want to impede the blood flow)
how is it possible for arteries to take blood from the heart and distribute it to the various organs/tissues?
- minimize resistance to flow:
- they are large
- low contractility [smooth muscle – active process]
- high distensibility (compliance) [elasticity –passive process) - artery walls must be ‘strong’ to withstand high systolic blood pressure
about how much blood is in the aorta during systole?
75mL (systole lasts 0.3 secs)
what happens during systole?
we contract the heart and empty the blood flow into the aorta and arteries
- it stretches (distends) the artery (increases the compliance passively)
what is compliance in the arteries?
the ability of an artery to respond to an increase in pressure by to distending or swell and increase the volume of blood it can hold, or with decreased pressure, a decrease in volume
what happens during diastole?
when the heart is relaxing and filling
- artery recoils passively to its original shape
what are the major benefits of compliance?
- lowers systolic blood pressure (it distends)
- aorta converts intermittent flow from the heart into continuous flow (aka Windkessel Effect)
what is the Windkessel Effect?
designed to help to dampen the fluctuation in blood pressure (pulse pressure) over a cardiac cycle and to maintain continuous blood flow when ventricular ejection ends (ie. diastole)
what allows for aortic compliance?
elastin
what is elastin?
a matrix protein that increases compliance
what is the equation for compliance?
= change in volume / change in pressure
large volume small pressure means what wrt compliance?
high compliance
what is pulse pressure?
SP - DP
- the pressure that dictates the movement of blood flow through the systemic circulation
how do we calculate mean arterial pressure from systolic and diastolic BP?
MAP = DBP + (1/3)PP(SP-DP)
which is shorter wrt time? systole or diastole?
systole
what is mean arterial pressure is a hypotensive patient who has a systolic/diastolic pressure of 90/60?
= 60 + (1/3)30
MAP = 70
what regulates pulse pressure?
- stroke volume (if heart contracts harder, we generate more pressure in the arteries(systolic))
- speed of blood ejection into the aorta (increases SBP)
- aortic compliance (decreases SBP)
how does blood pressure change as we get old?
at around 60-70 years of age we see systolic BP increasing (this could be because the aortic compliance decreases. elastin polymers break down).
does systolic BP increase very quickly during exercise?
exercise pressor reflex:
- when we contract our muscles stronger, we generate a lot of tension on our skeletal muscles and that can activate mechanoreceptors inside the muscle and that can also activate metabolite receptors
- increases SNS activity and decreases PNS in order to increase stroke volume to increase blood flow to skeletal muscle but vasoconstrict the areas that do not need blood this increases SBP and TPR
SUMMARY:
- muscle afferent feedback –> brain –> increases SNS activity
why does our PNS activity decrease when we lift weight?
because we require an increase in blood flow to the skeletal muscle during instances where we have very high loads that are being generated and we want to maintain blood flow to skeletal muscle while they contract
