Causes Of Hypertension

Causes Of Hypertension
Prof. Dr. Magdy Abdel Hamid , MD , FSCAI
Professor of Cardiology
Cairo University
Hypertension (HPT) can be divided into primary type called essential HPT when constitute the majority of the cases of HPT. And secondary HPT due to many other causes like renal renovascular, endocrinal HPT and others.
Essential hypertension
Blood pressure (BP) is the product of cardiac output and peripheral vascular resistance.
A variety of factors influence cardiac output and vascular resistance and therefore, ccntribute to Bl.p regulation.
Although the exact mechanisms of essential HPT have not yet been elucidated, several variables have been suggested to contribute to sustained Bl.p elevations in humans .
The renin-angiotensin system (RAS) plays a pivotel role in the regulation of Bl.p and is a key mediator target organ damage, cardiovascular events , and progression of renal disease. RAS regulates both peripheral vascular resistance directly through the effects of angiotensin ıı (All) and intervascular volume indirectly through the actions of both all and aldosterone.
Many humoral mediators both autocrine and Paracrine influence peripheral vascular resistance and contribute to the modulation of (BP). Other plays in the humora'l milion of blood pressure,regulation in clude endothelin a potent vasconstrictor, vasopress in antidiuretic hormone (ADH) and the natriuretic peptides .
A widely accepted hypothesi s
suggests that the sympathetic. system is a critical initiating factor in the development of essential HPT in humans but has little if any effect on maintaining chronically elevated (BP).
This hypothesis suggests that HPT begin as a syndrome of high cardiac output caused by overactivity of cardiac sympathetic nerves.
This hyperdynamic phase eventually leads to sustained heightened systemic vascular resistance , which is the hall mark of essential HPT.
During this period. of chronically elevated arterial pressure, structural changes such as vascular hypertrophy are believed to contribute to the maintenance of increased vascular resistance.
Renal Parenchymal Hypertension
Hypertension associated with renal Parenchymal disease is the most common form of secondary
renal disease.
Hypertension is prevalent in renal disease of patients with pre-end stage renal disease (ESRD) ■80% are hypertensive, and hypertension is present in 90% by the time ESRD ensures.
In addition to increasing cardiovascular morbidity and mortalty , hypertension in patient with renal disease accelerates the loss of renal function .
Glomerular filtration rate (GFR) declines more rapidly in hypertensive patients with renal disease compared with their normotensive counterparts.
The kidney Plays a central role in blood pressure (BP) regulation because of its ability to regulate salt excretion .
A positive salt balance is crucial to the initiation and maintenance of renal parenchymal hypertension activation of the internal renin angiotensin aldosterone system (RAAS) and increased central
sympathetic outflow have been linked to the development of hypertension in the pre ESRD and ESRD.
Ranovasoular Hypertension
Renovascular hypertension results from activation of the renin angiotensin aldosterone axis mediated by ischema. Decreased perfusion to the affected kidney results in the release of renin, which accelerates the conversion of giotensinogen to angiotensin ı.
Angiotensin ı.
Converting enzyme (ACE) converts angiotensin ı to angiotensin ıı, a peptide with potent vsoconstrection.
Angiotensin ıı .
Also stimulates the adrenal gland to release aldosterone, leading to renal sodium retension.
The most common causes of renovascular HPT are atherosclerosis and fibromuscular dysplasia.
Other rare causes include neuro fibtomulosis , extrinsic compression, congenial anomalies, radiation arterial thromboembolism and vasculitis.
Hyperaldosteronism
Hyperaldosteronism is a syndrome characterized by excessive reduction of aldoster one leading to sodium retention weight gain and hypertension , usually accompanied by hyperkalemia and metabolic alkalosis.
The most common cause of primary hyperaldesteronism is an aldosteron producting adenorma , accounting for about 70 % to 80 % of all cases.
Another 20% to 30% of cases are caused by idiopathic hyperaldesteronism resulting form either bilateral (common) or unilateral (rare) hperplasia of the zona glomerulosa of the adrenal cortex.
Other rare disorders include adrenocortical carcinoma which may overproduce aldosteronism, and the syndrome of glucocorticoid remodrable aldosteroism (GRA) sometimes called dexamethasone suppressible hyperaldosteronism.
Definitive diagnosis is made when one renal vein has 10 times the aldosterone concentration of the contralateral vein.
Pheochromocytoma
Pheochromocytoma is a catecholamine producing tumour arising from the chromaffin cells of the sympathetic nervous system that are distinguished by the embryonic denervation from the primitive neural crest cells and their uptake of chromium sails.
Most most pheochromocytomas arise from the adenal gland .
About 10% arise from extraadrenal sites, such as the carotid body and abdominal sympathetic ganglia including the organ of znckerkundl, which consists of ganglia at the bifurcation of the aorta.
Norepinephrine is the catecholamine secreted predominantly by most pheochromacytoma.
Pheochromocytoma is responsible for Cushing’s syndrome
Cushing’s syndrome is a symptom complex that reflects excessive tissue exposure to cortisol.
Cushing’s syndrome is characterized by progressive physical changes, often best appreciated in serial photographs central ( truncal ) obesity, moon facies , and a buffalo trump are classic physical finding.
Additional physical finding include purple str-iae plethora echymoses hypertrichosis and muscle atroPhy.
Other feature of cushing‘s syndrome include emotional and cognitive changes, menstrual irregularity, glucose intolerance and hypertension.
Although 80 % of patients with cushing's syndrome are hypertensive, cushing's sydrome is a relatively rare cause of hypertension in children and adults.
Hypertension in patients with hypercortisolism is multifactorial in origin.
Excessive cortisol exposure increase peripheral resistance by:
● Enhancing the effects of catcholamines and angiotensin II.
● Suppressing synthesis of endogenous vasodilatory agents including nitric oxide and prostaglandins.
Cortisol directly stimulates sodium reabsorption in the distal nephron while indirectly increasing sodium reabsorption in the proximal nephron by enhancing the activity of various transporters.
Synthesis of certain mineralocorticoids is increased in adrenocorticotropic hormone (ACTH) dependent types of cushing’s syndrome .
The most common causes of cushing’s syndrome are either .
a)ACTH dependent
Pituitary adenoma
Ectopic ACH production .
Ectopic corticotropin releasing hormone secretion or.
b)AC’IH independent.
Endogenous glucocorticond administration Adrenal adenoma.
Adrenal adenocarcinoma.
Primary Pigmented nodular adrenal hyperplasia .
Other forms 0F SECONDARY hypertension
Coarctation of the aorta:
Coarctation of the aorta is a congenitaly narrowing of the aorta usually occuring somewhere between the aortic arch and the abdominal aorta
Although coarctation of the aorta is the fourth leading cause
of congenital heart disease, it is relatively uncommon cause of hypertension in childhood .
The diagnosis always should be considered , however, because repair of coarctation can correct hypertension and exert a favorable effect on patient survival .
Thyroid disorders
1- Hyperthyroidism often is associated with an increased cardiac output and systolic hypertension .
ß blockers are effective in the setting but definitive managment consists of treating the underlying cause ol excessive thyroid hormone production
2- Thyroid patients exhibit Phreefold incease in the incidence of hypertension . The pathophysiology is poorly understood .
Hyperparathyroidism
Hypertension most often is attributed to the vasoconstrictive effects of the associated hypercalcemia .
Hypertension is not observed routinely , however, in patients with other disorders associated with hypercalcemia (e.g. sarcoidosis , multiple myeloma , carcinomatosis).
Only 10% to 60% of patienm with primary hyperparathyroiclism exhibit hypertension , and remission of hypertension variable after successful parathyroidectomy.
Obstructive steep apnea
1- Obstructive steep apnea occurs more commonly in hypertensive than non hypertensive individuals.
2- Apneic spells can be associated with transient and marked increase in BP . that eventually may become sustained during walking hours.
Drug induced Hypertension
The mechanism of action involved in hypertension caused by drugs are either:
1- Salt and water retention (e. g. corticostroids , sex hormones , mineralocorticoids , nonstroidal anti-inflammatory drugs) .
2- Sympathomimetic effects (e. g. decongestants , antidepressants, coaine).