Pathophysiology of Hypertension Flashcards
What is systolic blood pressure?
The highest level of pressure right after the ventricles contract
What is diastolic blood pressure?
The lowest level of pressure right before the next contraction of the ventricles
What is stroke volume (SV)?
The amount of blood ejected from the ventricle with each contraction
What is systemic vascular resistance (SVR)?
The resistance to blood flow offered by all of the systemic vasculature
AKA total peripheral resistance (TPR)
Vasoconstriction does what to SVR?
Vasoconstriction causes SVR to increase
Vasodilation does what to SVR?
Vasodilation causes SVR to decrease
What role does the autonomic nervous system have in regulating heart rate?
Parasympathetic System (vagus nerve, acetylcholine)
- Slows the heart
- Acetylcholine acts as muscarinic receptors
- Resting state controlled by the vagus nerve
What role does the sympathetic nervous system have on regulating heart rate?
“Fight or Flight”
Speeds up the heart
Norepinephrine acts at Beta 1 adrenergic receptors
What are the 3 determinants of stroke volume?
Preload
Afterload
Contractility
What is preload?
The amount of blood filling the heart right before it starts to contract (same as EDV)
How does volume affect preload?
A decrease in volume results in a decrease in preload
What role does the SNS have on preload?
SNS causes either venoconstriction or venodilation
Venoconstriction results in an increase in preload (bc there is more blood being squeezed toward the heart)
Venodilation results in a decrease of preload
Relaxation of the ventricle normally during diastole imfluences:
Preload
Filling time of the ventricle controls preload by:
Determining the length of diastole
Why is the venous system important to keep in mind when thinking about preload?
Increased venous return to the heart will increase preload
An increase of blood volume then also increases venous return to the heart
How does preload affect stroke volume? Describe how it does this
Increase in preload results in an increase in stroke volume
An increase in preload results in an increase stretch of cardiac sarcomeres
A stronger contraction is made which increases stroke volume
What does the Frank-Starling Mechanism describe?
A healthy heart automatically adjusts its output (SV) to match the EDV / Preload
What is afterload?
The pressure the ventricle sees after it starts to contract
“the force needed to be overcome to pump the blood out”
Afterload is determined by what two things?
Systemic vascular resistance
Valve integrity
How does systemic vascular resistance affect afterload?
Increase in SVR will increase afterload
How does valve integrity affect afterload?
A stiffened valve/one that does not fully open will increase afterload, making it more difficult for blood to pass through
How does afterload affect stroke volume? Why?
An increase in afterload causes a decrease in stroke volume
More pressure needed to be overcome will result in less blood being pumped out
What is contractility?
The intrinsic strength of cardiac contraction
How does the SNS affect contractility?
Activation of Beta 1 receptors results in an increase in contractility
How does contractility affect stroke volume?
An increase in contractility results in an increase in stroke volume
A decrease in contractility results in a decrease in stroke volume
What things determine SVR?
Vessel radius
Length and blood viscosity
Resistance is _____ proportional to the radius to the 4th power. What does this mean?
Inversely proportional
This means that as radius decreases, resistance increases
Blood flow is ____ proportional to the radius to the 4th power. What does this mean?
Directly proportional
When the radius decreases, blood flow decreases
How does the SNS prevent orthostatic hypotension?
When we go from a supine to a standing position, alpha-1 adrenergic receptors are activated
They cause vasoconstriction
How do voltage-gated calcium channels on smooth muscle affect SVR?
When activated/opened, they cause an increase in calcium inflow and cause vasconstriction
What receptors make good targets for the pharmacotherapy of hypertension?
Beta 1
Alpha 1
Calcium Channels
Why are arterioles the major blood vessel type that influences SVR?
They provide 2/3 of the resistance to flow in the systemic circulation
Their strong muscular walls allow the internal diameters to increase or decrease tremendously
Small changes in the radius of the arteriolar lumen have large effects on blood pressure
What hormones and local mediators cause constriction/increase in SR/increase in BP? How do they do this?
Angiotensin II
Aldosterone: conserve sodium and blood volume
Vasopressin/ADH: act on kidneys to preserve water and blood volume; act on vascular smooth muscle to cause vasoconstriction
Endothelin: acts locally to constrict blood vessels
Norepinephrine, epinephrine: activate alpha-1 adrenergic receptors in vascular smooth muscle
Which hormones and local mediators result in dilation/decrease in SVR/decrease in BP? How do they do this?
Nitric Oxide: act locally to dilate/relax blood vessels
ANP, BNP: get rid of salt and decrease blood volume; acts on vascular smooth muscle to cause vasodilation
Epinephrine on B2 receptors in certain vascular beds
Presynaptic alpha-2 adrenergic receptors: prevent further release of norepinephrine
What do baroreceptors do?
They are mechanoreceptors that respond to changes in stretch/tension of arterial walls
Primarily found in the arch of the aorta and carotid artery
Monitor MAP variations on a moment-by-moment basis
What is a baroreceptor reflex?
Changes initiated by baroreceptors
Describe the process in which baroreceptors cause a rise in BP
Decrease in MAP
Decrease in blood vessel wall stretch
Baroreceptors sense this decrease in stretch
Describe the process in which baroreceptors cause a rise in BP
Decrease in MAP
Decrease in blood vessel wall stretch
Baroreceptors sense this decrease in stretch
——
Decrease in APs
Increased SNS activity
Activation of alpha-1 in smooth muscle (increase in SVR)
Beta-1 receptors in the heart (increase HR and CO)
Decreased vagal activity (increase HR and CO)
OVERALL: rise in BP
How does the baroreceptor reflex apply to patients in bed?
Important mechanism when changing positions
The reflex can become downregulated even after a short hospital stay
Keep in mind when getting patients out of bed for the fist time
How does chronic hypertension affect baroreceptors?
The baroreceptors adapt and become less sensitive
They are best suited to respond to sudden, acute changes in BP
What is elevated BP?
120/80 - 139/89
What is essential hypertension?
Hypertension common and correlated with prevalence of obesity and a diet high in fats and sodium/low in fruits and vegetables
We cannot pinpoint a cause of their HTN
What is white coat hypertension?
HTN in the healthcare setting that is higher than the person’s actual normal, day-today BP
Dysfunction in what organs/systems contribute to HTN?
Kidneys (effect on blood volume, Na + H2O movement)
CNS (SNS signaling)
Vasculature (Contraction, relaxation)
What are some potentially treatable causes of hypertension?
CKD
Renovascular (renal artery stenosis)
Endocrine (aldosterone excess, pheochromocytoma tumor on adrenal gland producing epinephrine, cortisol excess)
Preeclampsia
How must we assess hypotension? What should we look at?
In general, it is <90/60
Is the person symptomatic? (dizzy, falls)
Is it due to a drop in BP, or is this their baseline BP?
Potential infectious process occurring? (sepsis)
Is the BP falling? (like how we see in shock)
Why is kidney disease a major risk factor for hypertension?
The kidneys control blood volume, H2O and Na excretion
What are the clinical manifestations of HTN?
May be asymptomatic for many years (“the silent killer”)
Nonspecific headaches
End organ damage with untreated HTM
What are the major organ systems affected by uncontrolled HTN?
Heart and arteries
Kidneys
Brain
Eyes
Reproductive system
What effect does HTN have on blood vessels?
It enhances atherosclerosis
What is the difference between arteriosclerosis and atherosclerosis?
Arteriosclerosis:
- Umbrella term
- Often age-related
- General increased collagen disposition –> increased stiffness and decreased elastic recoil of vessels
Atherosclerosis:
- Specific type of arteriosclerosis
- Due to cholesterol
- Seen in younger ages
Hypertrophy occurs in HTN because:
Cardiac stress overworks the heart
More work is needed to pump blood out
Makes the cells grow bigger
How does uncontrolled HTN do to afterload as the heart pumps blood into the aorta?
Increases afterload
If the left ventricle hypertrophies and the walls of the ventricle get bigger and bigger, what will it do to the size of the ventricular chamber (the space inside the ventricle)?
It will become smaller
Less room for blood
Will a hypertrophied muscle be able to relax as well as a normal ventricle?
No
What will happen to stroke volume in a hypertrophied ventricle? Why?
Decrease in SV
There is less possible volume in the chamber
There is a decreased ability to refill
What overall effect does HTN have on the renal arterioles?
Hypertrophy and constriciton
What overall effect does HTN have on the brain?
Hemorrhage, stroke
What overall effect does HTN have on the eyes?
Retinopathy
Retinal detachment
