Blood Pressure - Pharmacology, HR, SV, CO, Contractility Flashcards
What is Systolic Blood Pressure?
Pressure exerted when the blood is ejected into the systemic circulation
What is Diastolic Blood Pressure?
pressure blood exerts within arteries between heartbeats
What is the normal systolic blood pressure?
100-120 mmHg
What is the main factor influencing diastolic blood pressure?
TPR (total peripheral resistance) - the amount of resistance encountered by the blood will be inversely proportional
What is the main factor influencing diastolic blood pressure?
TPR (total peripheral resistance) - the amount of resistance encountered by the blood will be inversely proportional to the gradient of the drop in blood pressure. When the resistance is high the decrease in blood pressure will be less than if the resistance was low.
What is pulse pressure?
Pulse pressure is the difference between the systolic blood pressure and diastolic blood pressure
PP= SBP - DBP
What value is the pulse pressure proportional to?
SV - stroke volume
What is the mean arterial pressure?
The mean arterial pressure is the diastolic blood pressure added to a third of the pulse pressure.
MAP = DBP + 1/3 PP
MAP = DBP + 1/3 (SBP-DBP)
Why do we use only 1/3 of the SBP -DBP?
The heart spends more time is diastole than systole (roughly 3 times more time)
What are the four determinants of cardiac output?
- Preload
- Afterload
- Contractility
- Heart Rate
What is the preload?
The preload is the amount of blood in the left ventricle prior to ventricular contraction.
An increase in preload results in an increase or decrease to the cardiac output
The cardiac output will increase - the heart muscle must do more work so the preload increases.
The starling mechanism describes what?
The starling mechanism states that the more the left ventricle is loaded - fibres will stretch or increase in length more so the left ventricle will contract more forcefully.
Which 3 main mechanisms can cause an increase in preload?
An increase in blood volume (blood transfusion, IV fluids)
Decrease in heart rate (increased ventricular filling time)
Constriction of veins - veins are large storage containers for fluid within the body (fluid can be pushed into the left ventricle) upon venous constriction.
Which 3 main mechanisms can cause an increase in preload?
An increase in blood volume (blood transfusion, IV fluids)
Decrease in heart rate (increased ventricular filling time)
Constriction of veins - veins are large storage containers for fluid within the body (fluid can be pushed into the left ventricle) upon venous constriction.
Which autonomic nervous system division is responsible for venous constriction (and which receptor type is able to trigger this)?
The sympathetic NS and alpha-1 receptors.
Which interventions trigger venous pooling (aids in decreasing pre load)
Nitrates
What is LVEDV?
It stands for left ventricle end diastolic volume - it refers to the volume of blood in the left ventricle when the heart is completely filled (end of diastole)
What is LVEDP?
It stands for left ventricle end diastolic pressure - it refers to the pressure in the left ventricle when it is completely filled with blood
What is after load?
After load is the amount of resistance that the left ventricle must overcome to pump blood into the systemic circulation.
What are some factors that increase after load?
Blood pressure (MAP) - makes it more difficult for the blood to pop open the aortic valve so blood can enter the systemic circulation. Aortic valve is stiff (aortic stenosis)- not able to stretch to accomodate for blood being pushed inside of it. An obstruction
What are some factors that decrease after load?
Decrease blood pressure
Treat/remove the obstruction or stenosis.
What is the main regulator of heart rate?
The sympathetic nervous system
What are the main drivers of the sympathetic nervous system’s effects on the heart?
Sympathetic innervation
Circulatory catecholamines (NA, adrenaline)
Increase in calcium released from sarcoplasmic reticulum
Stress, exercise
What are the main non-pharmacological SNS drivers of increased contractility of the heart?
Sympathetic innervation
Circulatory catecholamines (NA, adrenaline)
Increase in calcium released from sarcoplasmic reticulum
Stress, exercise
What are the main pharmacological drivers of increased contractility of the heart?
Sympathomimetic drugs - dopamine, dobutamine, NA, adrenaline
Digoxin
What is the action of digoxin in reducing contractility?
Digoxin inhibits the Na/K ATPase pump - leading to an increase in intracellular calcium in cardiac myocytes.
What are the main non-pharmacological drivers of decreased contractility of the heart?
Heart failure - leads to death and disease of cardiac myocytes which decreases contractility.
What are the main pharmacological drivers of decreased contractility of the heart?
SNS blockers - beta blockers
Calcium channel blockers - verapamil, diltiazem
What is the main autonomic NS regulator of heart rate?
Sympathetic nervous system
Fill in the blank. Without _______ also increasing, an increase in HR will lead to a decrease in stroke volume because of insufficient ventricular filling time.
Contractility.
This is because there is inadequate ventricular filling time to increase cardiac output without a coupled release in contractility - so our bodies use the same guy to control both these mechanisms (the SNS). But, this relationship has a narrow range of efficiency - as if the HR is too high the increase in contractility cannot compensate for lack of filling time.
Heart rate and contractility are BOTH controlled by what?
The sympathetic nervous system.
Fill in the blank. Under pathological conditions such as arrhythmias the _______ may be too high so the ventricle cannot be adequately filled and _____ decreases.
HR; SV
The after load is often estimated using which value?
MAP - mean arterial pressure
Preload is often estimated using which value?
LVEDP - left ventricle end diastolic pressure
Contractility is often estimated using which value?
EF - ejection fraction
Why is maintaining blood pressure important?
Allows for adequate perfusion of tissues
What system in the body is mainly responsible for blood pressure regulation?
The nervous system.
What is the name of the type of receptors which detect changes in blood pressure. Hint - they are located in the kidneys, aortic arch and carotid sinus.
Baroreceptors.
How are baroreceptors able to assist in detecting changes in blood pressure?
The baroreceptors stretch in response to increases in blood pressure and increase firing of signals send to the brain.
Which system is the brain able to use to respond to changes in blood pressure?
The autonomic nervous system which includes the sympathetic and parasympathetic nervous system.
What are 4 key ways the autonomic nervous system can affect blood pressure?
Affect HR/heart contractility
Arterial tone (vasoconstriction, vasodilation)
Venous tone - veins are like reservoirs for blood)
Renin release (RAAS)
Baroreceptors found in the aortic arch are most receptive to ________ (elevated blood pressure/ low blood pressure) and least receptive to ______ (elevated blood pressure/ low blood pressure).
elevated blood pressure ; low blood pressure.
Baroreceptors in the ________ (kidneys/aortic arch/carotid sinus) are considered to be the most important baroreceptors overall.
carotid sinus
The carotid sinuses are able to sense which type of blood pressure.
The carotid sinuses are able to sense both high and low blood pressure - as the carotid sinuses are able to modify the signals over a broad range of blood pressures.
Through which cranial nerve does the baroreceptors of the carotid sinus send its afferent nerve impulses?
CN IX - the glossopharyngeal nerve
Through which cranial nerve does the baroreceptors of the aortic arch send its afferent nerve impulses?
CN X - the vagus nerve
What is the name of the part of the brain which receives signals from the baroreceptors of the carotid sinus and aortic arch?
The nucleus solitarius
Where is the nucleus solitaires found?
In the medulla
Outline the main steps the body would take to decrease blood pressure in the event it was too high.
Kidneys - water and salt retention is reduced - decreases blood volume
Carotid sinus and aortic arch - venous and arterial tone vasodilated. Arteries - increases diameter of vessels to reduce pressure. Veins- keeps blood away from the heart to reduce preload
Increased heart rate and contractility
Outline the main steps the body would take to increase blood pressure in the event it was too low.
Kidneys - water and salt retention is increased - increases blood volume
Carotid sinus - venous and arterial tone vasoconstrictor. Arteries - decreases diameter of vessels to increase pressure. Veins- pushes blood towards the heart to increase preload.
Decreased heart rate and contractility
Aortic arch baroreceptors are not present as they are least receptive to low BP.
Massaging the carotid sinus tricks the baroreceptors into signalling that the blood pressure has been_______(raised, lowered) due to its stretch mechanism.
raised - can lead to the blood pressure falling.
What might be the effect of damage to CN IX related to the CVS?
The glossopharyngeal nerve (CN IX) innervates the carotid sinus. Weak or no signals from CN IX signals to the brain that blood pressure is low - this results in the brain stimulating an autonomic response to increase blood pressure.
