Clinical Note

Angina pectoris is a condition in which one or more coronary arteries have become narrowed because of atherosclerosis. This causes the blood flow to the heart muscle to be inadequate (ischemia), resulting in chest pain and impaired contractility of the affected regions. Such attacks are usually brought on by physical exertion that transiently increases the oxygen requirements of the heart. Many drugs have been identified that can decrease the incidence and severity of these attacks. Virtually all of these act either to reduce the contractility of the heart (beta blockers and calcium antagonists) or to reduce the blood pressure by venous dilation (nitrates). The systolic pressure-volume area analysis predicts that either of these will reduce the oxygen demand of the heart.

contraction divided by the radius of the lumen. Therefore, increasing end-diastolic volume acutally diminishes the heart's ability to convert its fiber tension into pressure. In the physiologic range, this disadvantage is greatly overshadowed by the increase in force generation that results from the longer fiber length. Thus, the normal heart responds to an increased chamber volume with a more forceful contraction. If the radius of the lumen becomes excessive, however, as in the dilated heart, the effect of increasing fiber length can be overwhelmed (see clinical note on page 212).

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