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Pharmacology

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Autonomic Nervous Systems

Question
54 out of 75
 

The therapeutic actions of - adrenergic receptor blockers in chronic stable angina pectoris are primarily the result of which of the following?



A Coronary vasodilation

B Decreased myocardial oxygen demand

C Reduced total peripheral resistance

D Antiplatelet / antithrombotic effects

Ans. C Reduced total peripheral resistance

a. Beta- adrenergic receptor blockers slow resting heart rate and reduce contractility, both of which reduce myocardial oxygen demand.

b. They also blunt the cardiac stimulatory effects, which increase oxygen demand, whenever the sympathetic nervous system is activated (e.g., in response to exercise or drugs that tend to cause reflex sympathetic activation). Recall, too, that coronary blood flow occurs during diastole. By slowing heart rate they prolong diastole, thereby indirectly allowing more time for the myocardium to be perfused.

c. These drugs have no antiplatelet / antithrombotic effects; they do not cause coronary vasodilation and they may increase total peripheral resistance by blocking dilation in some vascular beds (the effect is usually slight and insignificant).

d. The blockers do slow A-V nodal conduction velocity, but that effect per se contributes little to the reduced oxygen demand that is mainly derived from the drugs’ effects on overall rate and contractility.

e. Beta-blockers are devoid of antiplatelet, vasodilatory properties. These are used in hypertension because, of their negative inotropic activity.

f. This then, causes decreased in cardiac output (CO). As a result of reduced CO, vasodilation occurs. Beta-blockers are the drugs of choice for prophylaxis of chronic stable angia.

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