Control of Arterial Blood Pressure Lecture 1 Flashcards
what is blood pressure?
the outwards (hydrostatic) pressure exerted by the blood on the blood vessels
what is systemic systolic arterial blood pressure ?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts
what is the normal systolic blood pressure?
should not normally reach or exceed 140 mm Hg under resting conditions
what is the Systemic Diastolic Arterial Blood Pressure?
the pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes
what is the normal systolic blood pressure?
should not normally reach or exceed 90 mm Hg under resting conditions
what term describes the way blood flow in normal arteries?
laminar flow
why is no sound heard in a normal patent artery ?
laminar flow is not audible
how do we measure blood pressure then?
if external pressure (e.g. cuff pressure) exceding the systolic blood pressure is applied to an artery; the flow in that artery would be blocked and no sound heard
however, if the external pressure is kept between systolic and diastolic pressure the flow becomes turbulent whenever blood pressure exceeds cuff pressure
this turbulent flow is audible through a stethescope
when is blood flow through the vessel turbulent?
whenever blood pressure exceeds cuff pressure
what is the first korotkoff sound?
it is the sound heard at peak diastolic pressure
what are sounds 2-3 ?
intermittent sounds heard as blood pressure due to turbulent spurts of flow exceeds cuff pressure
what is the 4th sound?
the last sound is heard at minimum/diastolic pressure - it is muffled/muted sound
what is the 5th sound?
no sound is heard thereafter because of uninterrupted, smooth, laminar flow
which sound dictates the diastolic pressure
fifth sound
the right atrium pressure is close to 0 so what is the main driving force for blood flow ?
mean arterial pressure
what drives the flow of blood?
a pressure gradient is set up between the aorta and the right atrium which drives the blood around the systemic circulation
what does CVP stand for
central venous (right atrial) pressure (CVP)
what is the definition of MAP?
the average arterial blood pressure during a single cardiac cycle, which involves the contraction and relaxation of the heart
how do you calculate MAP?
([(2x diastolic pressure) + systolic pressure])/3
or
MAP = DBP + 1/3 difference between SBP and DBP
what is the pulse pressure?
the difference between SBP and DBP
what is normal arterial blood pressure below?
what is the normal range for MAP?
70-105 mmHg
what MAP is needed to perfuse the coronary arteries, the brain and kidneys?
at least 60 mmHg
what is the definition of high BP?
sustained systolicBP above 140
so MAP must be regulated within narrow ranges to ensure: ?
- pressure is high enough to perfuse the internal organs
- pressure i low enough not to damage the blood vessels or place an extra strain on the heart
Mean Arterial Pressure =
Cardiac output (CO) x Total Peripheral Resistance (TPR) =
Stroke Volume (SV) x Heart Rate (HR) x Total Peripheral Resistance (TPR)
what is the definition of total peripheral resistance?
the sum of resistance of all peripheral vasculature in the systemic circulation
which vessels are the major resistance vessels?
arterioles
what percentage of blood is carried in the veins?
about 60%
what is the effect of the parasympathetic stimulation on the MAP?
low heart rate leads to low CO leads to low MAP
what is the effect of sympathetic stimulation on the heart for MAP ?
increased HR and contractile strength of the heart (leads to increased SV)
both of these lead to increased Co so increased MAP
what is the effect of sympathetic stimulation on the arterioles for MAP ?
increased vasoconstriction leads to increased TPR leads to increased MAP
what is the effect of sympathetic stimulation on the veins for MAP ?
increased vasoconstriction leads to increased venous return leads to increased SV leads to increased CO leads to increased MAP
what is the mechanism for the short term regulation of MAP?
the baroreceptor reflex
what is the control centre for this response?
medulla
what are the effectors for this response?
heart (HR and SV) and blood vessels (TPR)
where are the two groups of baroreceptors/
- aortic arch
2. carotid sinus
what cranial nerve innervates the aortic baroreceptors?
sends signals to the medulla via the 10th CN
what cranial nerve innervates the carotid baroreceptors?
the 5th CN - glossopharyngeal
what is the effect of increasing the arterial BP on the carotid sinus afferent nerve firbes firing?
increases
what is the effect of increasing arterial BP on the cardiac vagal efferent nerve fibres activity?
increases
what is the effect of increasing arterial BP on the cardiac sympathetic efferent nerve fibres activity?
decreases
what is the effect of increasing arterial BP on the cardiac sympathetic vasoconstrictor nerve fibres activity?
decreases
during which movements are the baroreceptors important>
in moment to moment regulation - this includes during postural changes
baroreceptors reflexes in the prevention of postural hypotension
when a normal person suddenly stands up from a lying position the venous return to the heart decreases so the MAP transiently decreases.
what does the decrease in MAP do to the firing of baroreceptors?
decreases
so what happens to the vagal tone to the heart in postural hypotension?
it decreases
what happens to the sympathetic tone to the heart in postural hypotension?
it increases
what does the The vagal tone to the heart decreases and the sympathetic tone to the heart increases do to SV and HR?
they both increase
what happens to the sympathetic constrictor tone in postural hypotension?
increases. This increases the TPR
what happens to the venous sympathetic constrictor tone in postural hypotension?
increases increasing the VR to the heart and stroke volume
what is the result of all this in postural hypotension?
HR INCREASES; SV INCREASES; TPR INCREASES
what does the increase in TPR often do to the DBP when healthy people stan from a lying position?
slightly increases
what is postural hypotension?
failure of Baroreceptor responses to gravitational shifts in blood, when moving from horizontal to vertical position leading to a fal in BP
what happens to the baroreceptor firing if high BP is sustained?
the rate of firing decreases
what is baroreceptor re-set?
they will fire again only if there is an acute change in MAP above the new higher steady state level
what mechanism controls MAP in the longer term?
blood volume
