13- Hypertension Flashcards
Primary or essential HTA?
The cause of blood pressure elevation is unknown. >90% HTA px
Secondary Hypertension
High blood pressure attributed to a definable cause
What pressure predicts more accurately cardiovascular complications?
Systolic
Stroke volume is determined by:
- Cardiac contractility
- Venous return to the heart
- The resistance the left ventricle must overcome to eject blood into the aorta (afterload)
What are the four systems responsible for blood pressure regulation?
- Heart
- Blood vessel tone
- Kidney
- Hormones
What is the normal sistolic/diastolic pressure?
<120/<80!
What are considered prehypertensive values?
120-139/80-89 mmHg
What is considered stage 1 hypertension?
140-159/90-99
What is considered stage 2 hypertension?
> 160/>100
In the presence of normally functioning kidneys, an increase in blood pressure leads to augmented urine volume and sodium excretion, which then returns blood pressure back to normal. This process is called:
Pressure natriuresis
What are the two possible reasons why pressure natriuresis is blunted in HTA patients?
- Microvascular and tubulointersticial injury within the kidneys which impairs sodium excretion
- Hormonal factors (RAA axis)
Which feedback mechanisms continuously monitor blood pressure?
Baroreceptors
Where can you find the baroreceptors?
Aortic arch and carotid sinus
How do baroreceptors monitor blood pressure?
By sensing stretch and deformation of arteries
How do baroreceptors regulate blood pressure?
They regulate bp by sending negative feedback via a Autonomic nervous system.
Signals of the carotid sinus are carried by:
Glosopharingeal nerve (IX)
Signals from the aortic arch are carried by:
Vagus nerve (X)
where do the glosopharingeal and vagus nerve converge?
Tractus solitarius
what do the baroreceptor impulses do in the tractus solitarius?
- inhibit sympathetic nervous system outflow
2. Excite parasympathetic effects
what is the net result of the baroreceptor impulses?
- decline in PVR (vasodilation)
2. reduction in CO (lower HR and reduced inotropism
what happens when baroreceptors sense a fall in systemic blood pressure?
fewer baroreceptor impulses are transmitted to the medulla leading to a reflexive increase in BP
why don’t baroreceptors prevent the development of chronic hypertension?
they regulate moment-by-moment variation of BP. After a day or two of exposure of higher than baseline pressure the baroreceptor firing rate slows back to its control value.
what is the most likely cause of EH?
a complex genetic disorder involving several loci.
what race is more frequently affected of EH?
blacks
how can the heart contribute to HTA?
through high CO-based HTA due to sympathetic over reactivity. (excessive HR acceleration in stressful conditions)
How can the blood vessels contribute to HTA?
they can by PVR based HTA by constricting in response to:
- increased sympathetic activity
- abnormal regulation of tone by NO, endothelin and natriuretic factors
- ion channel defects in contractile vascular smooth muscle
How can the kidney contribute to HTA?
it can induce volume based HTA by:
- failure to regulate renal blood flow
- ion channel defects
- inappropriate hormonal regulation
how are renin levels found in HT px?
25%: subnormal
60%: normal
10-15%: high
How should renin levels be in HT patients?
low
how does insulin play a role in the development of hypertension?
- increased sympathetic activation
2. vascular smooth muscle cell hypertrophy
How does obesity play a role in the development of hypertension?
- release of angiotensinogen from adipocytes
- augmented blood volume related to increased body mass
- increased blood viscosity caused by adipocyte release of pro fibrinogen and plasminogen activator inhibitor 1.
Where can the potential primary abnormalities in EH be found?
- blood vessels
- adrenal glands
- CNS
- Pressure and volume receptors
- Kidney
what functional and structural abnormalities of blood vessels could cause EH?
FUNCTIONAL
- less NO
- more Endothelin
- Ca++ or Na+/K+ channel defects
- Hyper-responsiveness to catecholamines
STRUCTURAL
-exaggerated medial hypertrophy
What abnormalities of Adrenal glands could be a cause of EH?
catecholamine leak or malregulation
What abnormalities of the CNS could be a cause of EH?
- Increased basal sympathetic tone
- abnormal stress response
- abnormal response to signals of baroreceptors and volume receptors
What abnormalities of the pressure/volume receptors could be a cause of EH?
Desensitization
What abnormalities of the kidney could be a cause of EH?
- RAA disfunction
2 Ion channel defects
at what age does the diastolic pressure begin to decline?
50
what is the hyperkinetic phase of EH?
high CO with normal PVR. Seen in younger px.
What abnormality is usually found in younger EH px?
elevated CO
What abnormality is usually found in older EH px?
elevated TPR
Why should we always screen for secondary HT?
1 they require different treatment
2 they can be cured often.
3 adaptative changes may cause chronic HT
What are the clues that a px may have a correctable condition (SHT)
- AGE: HT <20 or >50
- SEVERITY: often causes blood pressure to rise dramatically
- ONSET: presents abruptly in previously normotensive
- ASOCIATED SIGNS AND SYMPTOMS: eg Renal artery bruits
- FAMILY HISTORY: occurs sporadically
In the patient evaluation (history and physical) what clues should we look for to see if the pax has a secondary form of HT?
- recurrent UTI
- Excesive weight loss
- weight gain
- excesive acohol consumption
- medications
- obstructive sleep apnea
what lab tests should be performed in the initial evaluation of the HT patient?
- URINALISIS
- K+ serum levels
- blood glucose
- cholesterol
- EKG
HT px with recurrent UTI, you think of..?
chronic pielonefritis
HT px with excessive weight loss. you think of..?
pheochromocytoma
HT px with excessive weight gain, you think of..?
Cushing syndrome
What are the main causes of HT?
- essential
- Chronic renal disease
- primary aldosteronism
- Renovascular
- Pheochromocytoma
- Coartation of Aorta
- Cushing syndrome
what percentage of px are ESSENTIAL HT and what are the clues?
~90%
- age onset: 20-50 years
- family history of HT
- Normal serum K+, urinalisis
What % of HT patients are caused by CHRONIC RENAL DISEASE and what are the clinical clues?
2-4%
- rise in creatinine
- abnormal urinalisis
What % of HT px are caused by PRIMARY ALDOSTERONISM and what are the clinical clues?
<2-15%
-LOW SERUM K+
What % of HT px are caused by RENOVASCULAR DISEASE and what are the clinical clues?
1%
- abdominal bruit
- sudden onset (especially if <20 or >50)
- low serum K+
What % of HT px are caused by PHEOCROMOCYTOMA and what are the clinical clues?
- 2%
- paroxysms of palpitations, diaphoresis and headache
- weight loss
- episodic HT in 1/3 of px
What % of HT px are caused by COARCTATION OF THE AORTA and what are the clinical clues?
- 1%
- BP in arms> legs or right arm>left arm
- Midsystolic murmur between scapulae
- Chest X-ray: aortic indentation, rib-notching due to arterial collateral’s
What % of HT px are caused by CUSHING SYNDROME and what are the clinical clues?
- 1%
- “cushingoid” appearance (e.g. central obesity, hirsutism.)
What are the EXOGENOUS causes of HT?
- oral contraceptives
- glucocorticoids
- cyclosporine
- eryhtropoietin
- sympaticomimetic drugs
- NSAIDS
- Ethanol
- Cocaine
renal disease contributes to two important endogenous causes of secondary HT which are:
- renal parenchymal disease (2-4%)
2. renal arterial stenosis (1%)
How can renal parenchymal disease induce HT?
- increased Intravascular Volume
2. excessive elaboration of renin
What are the causes of renovascular HT?
- atheroesclerotic lesions
- fibromuscular lesions
- emboli
- vasculitis
- external compression of the renal arteries
RH ateroesclerotic lesions are most common in:
elder men
RH fibromuscular lesions are most common in:
young women
by what mechanism does RH evolve?
there is reduced renal blood flow therefore the kidney releases renin which raises blood pressure
what clinical findings suggests RH?
abdominal bruit or unexplained hipokalemia hypokalemia
what % of RH patients present abdominal bruit?
40-60%
where can we find ANG II receptors?
- arterial smooth muscle
- adrenal gland
- sympathetic nervous system
- kidney
- brain
- heart
what the function of ANG II receptors on arterial smooth muscle?
vasoconstriction
whats the function of ANG II receptors on the adrenal glands?
secretion of aldosterone (Na+ reabsorption in distal nephron, K excretion)
whats the function of ANG II receptors in the sympathetic nervous system?
facilitates release of norepinephrine (vasoconstrictor, raises TPR)
whats the function of ANG II receptors in the kidney?
raise renal tubular absorption of Na+
whats the function of ANG II receptors in the brain?
stimulates thirst and vasopresin secretion
whats the function of ANG II receptors in the heart?
ENHANCES CONTRACTILITY AND VENTRICULAR HYPERTROPHY
how can RH be corrected?
- percutaneus catheter intervention
- surgical reconstruction of a stenosed vessel
- Ace inhibitors (unilateral stenosis ONLY)
mechanical cause of HT?
Coarctation of the aorta
what could cause lower pressure in the left arm compared to the right arm?
coartation of the aorta that involves the origin of the left subclavian artery
by what mechanisms does coarctation of the aorta rise blood pressure?
- reduced blood flow to kidneys stimulates the renin angiotensin system
- high pressures proximal to the coarctation stiffen the aortic arch through medial hyperplasia and accelerated ateroesclerosis blunting the normal baroreceptor response to elevated intravascular pressure.
what are the clinical clues to the presence of coarctation?
- inadequate blood flow to legs or left arm
- claudication or fatigue
- weakened or absent femoral pulses
- midsystolic murmur
5 RX: indentation of the aorta - notched appearance of the ribs
treatment of coarctation of the aorta
angioplasty of surgery
*HT may not abate completely due to desensitisation of the baroreceptors
how can we evaluate endocrine causes of hypertension?
- HISTORY of characteristic signs and symptoms
- measurement of hormone levels
- Assessment of hormone secretion in response to stimulation inhibition
- imaging studies to identify tumours secreting the excessive hormone.
what are the endocrine causes of hypertension?
- pheocromocytoma
- Adrenocortical Hormone Excess
- Thyroid hormone abnormalities
what are pheocromocytomas?
Catecholamine secreting tumours of neuroendocrine cells (usually in the adrenal medulla)
what % of hypertension is caused by pheochromocytomas?
0.2%
what is the characteristic presentation of a pheochromocytoma?
paroxysmal rises in blood pressure with “autonomic attacks”
What are “autonomic attacks”?
- severe throbbing headaches
- profuse sweating
- palpitations
- tachycardia
caused by the increased catecholamine levels in pheochromocytomas
what % of pheochromocytomas are malignant?
10%