Hypertension: Definition & Forms

by Joseph Alpert, MD

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    00:00 The definition of hypertension is: a chronic increase in blood pressure generally agreed upon as greater than 140/90 mm Hg. 140 is the systolic blood pressure. 90 is the diastolic pressure.

    00:18 In very elderly patients these days, we’re allowing blood pressures as much as 150 systolic because of stiffening of the arteries with age.

    00:28 Another definition of hypertension of course is if the patient has had high blood pressure diagnosed in the past and is currently receiving antihypertensive medications.

    00:36 Hypertension results from increased vascular resistance. Let’s think about that for a moment.

    00:46 Remember the formula for blood pressure is the same as the formula for measuring resistance or voltage in an electrical current. The voltage in an electrical current = resistance × flow.

    00:59 In other words, the amps × resistance.

    01:04 In the cardiovascular system it’s the same. Blood pressure = flow × peripheral vascular resistance. When the peripheral vascular resistance goes up and the flow is maintained constant, blood pressure goes up.

    01:19 Approximately one third of Americans have hypertension and often there are serious complications.

    01:28 The reason for this is that patients very often do not realise that they have high blood pressure because it’s often without symptoms until the patient gets to the point that there’s a complication.

    01:41 I’ve just repeated for you the so-called Ohm’s law. Ohm’s Law is the electrical law of the circulation that is pressure = current × resistance. Or in electricity, E is voltage, I is amperage or flow and R is the resistance. And in the circulation, remember, it’s the same formula: blood pressure = cardiac output (which is the flow in the system) × vascular resistance. And patients with hypertension have elevated vascular resistance.

    02:14 There are two forms of hypertension that are recognized by physicians: the so-called essential hypertension – that’s the vast majority of patients – where there’s no obvious cause for the hypertension. It’s thought to be genetics as well as environment. Things like high salt diet and obesity play into this. We know families where everybody in the family has a tendency to hypertension and other families where there’s no tendency to hypertension. So there’s clearly genetic factors involved here.

    02:49 Secondary hypertension is the result of another factor, not genetic. It can be the use of abusive drugs such as cocaine or amphetamine; it can be due to kidney disease, usually renal vascular – we’ve already talked about that in the last lecture and we’re going to talk some more about that in this one; pheochromocytoma which is a tumour that releases adrenaline and noradrenaline; and coarctation of the aorta – we’ve talked about that a little bit in the past.

    03:18 Many of these secondary causes are effectively treated either by medicine or by surgery.

    03:23 Let’s talk a little bit about coarctation of the aorta as a typical example of a secondary form of hypertension.

    03:33 Remember what coarctation is? It’s a narrowing of the aorta, just like the diagram shows you, just distal to the left subclavian artery. This results in hypertension of the blood vessels on the upper part of the body and low blood pressure in the lower part of the body because blood doesn’t get down there because of the stenosis in the aorta just after the left subclavian artery.

    03:58 There’s often a pressure difference of 20 mm Hg or more between arm and leg. And remember that was one of the test we used also for diagnosing peripheral vascular disease.

    04:12 Coarctation is usually picked up in young people before atherosclerosis has developed.

    04:15 And, again, it requires either surgical repair or a balloon angioplasty often with a stent to reopen the narrowed area in the aorta and restore normal blood flow.

    04:28 Even after successful therapy, patients who have had a coarctation are at risk to maintain high blood pressure and need medical therapy.

    About the Lecture

    The lecture Hypertension: Definition & Forms by Joseph Alpert, MD is from the course Arterial Diseases.

    Included Quiz Questions

    1. Peripheral resistance.
    2. Stroke volume.
    3. Capillary diffusion capacity.
    4. Interstitial edema volume.
    1. Essential and secondary.
    2. Initial and subsequent.
    3. Complicated and essential.
    4. Primary and rebound.

    Author of lecture Hypertension: Definition & Forms

     Joseph Alpert, MD

    Joseph Alpert, MD

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