What is increased blood pressure? When there is resistance in the blood vessel to the flow of blood then the blood vessel has to increase its pressure to allow the blood to pass through.
There are many factors that influence the development of hypertension (increased blood pressure). It could be genetics or environmental. Factors include increased Nacl (salt) intake, alcohol consumption, psychosocial stress, obesity and low levels of physical activity.
There are two forms of hypertension:
Essential hypertension – influenced by the above risk factors and is not caused by any organ damage and does not have any definite cause. Hence it is said to be idiopathic hypertension.
Secondary Hypertension- influenced by disease of a particular organ. For example Renal disease is 80% cause of secondary hypertension, Endocrine causes including Conn’s syndrome, Adrenal Hyperplasia, Phaeochromocytoma, cushing’s syndrome, Acromegaly, Cardiovascular causes, drugs and pregnancy.
When is one said to have hypertension? (Increased blood pressure)
Two or more reading must have increased blood pressure in two or more outpatient visits. The blood pressure reading of threat can differ from patient to patient.
Hence it can be defined as the blood pressure measurement of an individual where treatment is necessary to control the adverse effects of increased blood pressure.
| Blood Pressure Classification | Systolic, mmHg | Diastolic, mmHg |
| Normal | <120 | and <80> |
| Prehypertension | 120–139 | or 80–89 |
| Stage 1 hypertension | 140–159 | or 90–99 |
| Stage 2 hypertension | 160 | or 100 |
| Isolated systolic hypertension | 140 | and <90> |
Source: Fauci As, Kasper DL, Braunwald E, HauserSL, Longo DL, Jameson JL, Loscalzo : Diabetes Mellitus in Harrison’s principles of Internal medicine, 17th edition
How to measure blood pressure?
Sphygmomanometer is the device used to measure blood pressure. We have different methods for measurement of blood pressure.
An individual is said to have white coat hypertension when the increase in pressure is due to anxiety to the patient caused by the examination of the patient by medical staffs.
In that case patient could opt for an ambulatory blood pressure monitoring (day and night) i.e. blood pressure can be measured throughout the day and night at home.
Blood pressure is usually increased in the morning and decreased at night. This is the reason of increased prevalence of myocardial infarction (heart attack) and stroke occurring during the early hours of morning.
Most common causes of hypertension:
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Source: Fauci As, Kasper DL, Braunwald E, HauserSL, Longo DL, Jameson JL, Loscalzo : Diabetes Mellitus in Harrison’s principles of Internal medicine, 17th edition
Factors influencing blood pressure
Blood pressure is determined by
Cardiac output * Peripheral resistance (resistance of blood vessel)
1. Cardiac output - It is the amount of blood pumped by the heart (ventricle) in one minute.
Cardiac output = Heart Rate * Stroke volume
Heart Rate - Number of heart beats per unit time
Stroke volume- Volume of blood pumped from ventricle with each beat
2. Peripheral resistance - It is the resistance of the blood vessel to the flow of blood which must be overcome to allow normal flow.
It is manipulated by the structure of the blood vessel and function of the vessel.
Mechanism involved in hypertension:
Increased intravascular volume
Extracellular fluid - Interstitial space and Blood plasma.
Fluid is always attracted towards the hypertonic space i.e. space which is rich in electrolytes will attract the fluid towards it. As sodium is the major component of extracellular fluid, when for some reason the sodium in blood is increased the fluid from intracellular space is moved into the extra cellular space. This increases the volume in the extracellular space.
There will be an increased in the cardiac output due to the expanding intravascular volume. To allow normal volume of blood, organs including kidney and brain starts to auto regulate the amount of blood by increasing the peripheral resistance of the blood vessel. As the peripheral resistance increases, cardiac output returns to normal. This increased sodium may be due to increased reabsorption of sodium in renal tubules.
Autonomic Nervous system
This maintains the blood pressure by sensing the pressure, volume and chemoreceptor signals. Adrenergic system controls the blood pressure by stimulating the secretion of Epinephrine, Norepinephrine and dopamine.
In Aorta and Carotid sinus, we have baro receptors which sense the change in the pressure in the artery and act accordingly. When there is increased arterial pressure, then the sympathetic flow is decreased which lessens the arterial pressure.
Renin-Angiotensin-Aldosterone
Renin is a protease secreted from juxtaglomerular cells(afferent arteriole of kidney). It facilitates the reasborption of sodium in the renal tubules by the production of aldosterone. It is stimulated by three mechanisms
Vascular Mechanisms:
The radius and the changeability of the vessels determine the arterial pressure. These two play a role in increasing arterial pressure.
Changes that occur in organs due to high blood pressure:
Heart:
Just hypertension can lead to death of a patient with hypertensive heart disease. It leads to left ventricular hypertrophy, chronic heart failure, diastolic dysfunction, abnormal flow of blood in an atherosclerotic artery and cardiac arrhythmia.
Brain:
Hypertension is an important risk factor for brain infarction and haemorrhage (bleeding). Cerebral flow is always unchanged by a process called auto regulation. When this auto regulation fails, this can lead to hypertensive encephalopathy.
Kidney:
Kidney diseases are the most common reason for hypertension but hypertension of some other origin can effect kidney and lead to end stage renal failure. Macroalbuminuria and microalbuminuria are the first indicator of kidney dysfunction
Peripheral artery:
Hypertension results in intermittent claudication (pain during walking) which is relieved by rest.
How to assess a patient with hypertension?
Reaching the necessary evidence is based on doctors’ talent to search out for the medical history. We must consider all possible symptoms like sweating, headaches, palpitations, breathlessness, chest pain, visual disturbances, and transient loss of consciousness. The above mentioned symptoms give significant clues and play a main role in diagnosis. Usually high blood pressure is diagnosed when an individual go for a random check up. So it is necessary for the patient and the doctor to discuss each and every symptom.
The following must be considered before continuing further:
-Duration of hypertension.
-Treatment undergone and any side effects from drugs.
-Take notice of any symptoms including insomnia, weakness of extremity muscles, snoring, symptoms of hypo and hyperthyroidism.
-Occurrence of any other systemic disease such as renal disease, diabetes mellitus & cardio vascular disease.
-Risk factors such as smoking, obesity, physical activity, and diabetes mellitus must be considered.
-After a thorough history taking and physical examination is performed the following lab analysis must be undertaken.
| System | Test |
| Renal | Microscopic urinalysis, albumin excretion, serum BUN and/or creatinine |
| Endocrine | Serum sodium, potassium, calcium, ?TSH |
| Metabolic | Fasting blood glucose, total cholesterol, HDL and LDL (often computed) cholesterol, triglycerides |
| Other | Hematocrit, electrocardiogram |
Source: Fauci As, Kasper DL, Braunwald E, HauserSL, Longo DL, Jameson JL, Loscalzo : Diabetes Mellitus in Harrison’s principles of Internal medicine, 17th edition
Next blog will follow up with treatment principles of hypertension and about malignant hypertension.
