Chapter 41 Hypertension and hypertensive heart disease
Pathological increases in blood pressure can affect the systemic or pulmonary circulation and may be seen in the arteries or veins. Hypertension of the systemic arteries is covered here. It is a common health problem and is a risk factor for diseases that include atheroma, heart failure, aortic dissection and renal failure. Studies have shown that the risk of these complications increases as the blood pressure rises, and that antihypertensive treatment reduces the morbidity and mortality.
The definition of high blood pressure is arbitrary in that blood pressure exhibits a Gaussian distribution so there is no clear boundary between hypertension and normal blood pressure. In general, hypertension is commonly defined as a systolic blood pressure of 140mmHg or greater or a diastolic blood pressure of 90 mmHg or greater.
If untreated, hypertension can progress to malignant hypertension, which is defined as markedly elevated blood pressure (diastolic pressure usually >120mmHg). It is associated with rapid progression of target organ disease (e.g. renal failure and retinal damage).
The principal effect of hypertension in large and medium-sized arteries is to accelerate the development of atheroma. By comparison, arterioles exhibit two different kinds of morphological change in hypertension.
Blood pressure is a function of cardiac output and peripheral resistance. Cardiac output is affected by the intravascular volume, while the peripheral resistance is controlled principally by arteriolar tone (Fig. 3.41.1).