Hypertension: Causes & Classification

 

               Hypertension is defined as an abnormal, persistent, elevation of systolic and/or diastolic blood pressure above the generally accepted normal level of up to 140/90 mmHg for adults.

Note:   Exercise, anxiety, discomfort and unfamiliar surroundings can all lead to a transient rise in blood pressure, and measurements should be repeated when the patient is resting and relaxed. For example, office or white coat hypertension refers to blood pressure that is consistently elevated in the physician’s surgery, but normal when measured at home. Patients who have high blood pressure on the first examination, but who subsequently settles with rest, may not require treatment. However, they should be kept under review because they are more likely to develop sustained hypertension. It has been estimated that approximately 15% of the general population can be regarded as hypertensive, although only a proportion of these will be diagnosed or receive treatment.

Factors influencing blood pressure

Blood pressure (BP) is influenced by three major factors: blood volume, cardiac output, and peripheral resistance.

Blood pressure=Cardiac output x peripheral resistance

Cardiac output = heart rate x stroke volume

Classification

Aetiological classification:  90 Percent of cases are primary hypertension (aka essential hypertension, idiopathic hypertension) i.e. the cause is unknown, many risk factors have been identified. These include

  • Genetic influences
  • Environmental factors,e.g. salt intake, inactivity, cigarette smoking, obesity
  • Hormonal influences
  • Neurogenic influences, e.g, anxiety.

10% of cases are secondary hypertension, Aetiology is unknown.

Clinical classification:

  • 95%of cases are benign hypertension: long course and generally compatible with a long life.
  • 5% of cases are malignant hypertension: short course and may kill a patient in months.

Common Causes

  • Stress
  • Anxiety.

Other causes

  • Endocrine Disease e.g. Cushing’s disease, Conn’s syndrome, phaeochromocytoma, hyperthyroidism.
  • Renal diseases, e.g, glomerulonephritis, chronic pyelonephritis, diabetic nephropathy, polycystic disease, renal vascular disease, obstruction, collagen diseases
  • Pregnancy, e.g. pre-eclampsia, eclampsia
  • Co-arctation of the aorta.
  • Neurogenic causes, e.g. increased intracranial pressure, hypothalamic lesions, head injury, brain stem disorders
  • Some insect and spider bites
  • Concurrent use of medication e.g. anti-inflammatories, steroids, salt tablets, etc.
  • High salt diet.
 

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