Most of the physiological alterations observed after the administration of ganglionic blocking agents can be anticipated by a careful inspection of Figure 6-1 and by knowing which division of the auto-nomic nervous system exercises dominant control of various organs (Table 9-4). For example, blockade of sympathetic ganglia interrupts adrenergic control of arterioles and results in vasodila-tion, improved peripheral blood flow in some vascular beds, and a fall in blood pressure.
Generalized ganglionic blockade also may result in atony of the bladder and GI tract, cyclo-plegia, xerostomia, diminished perspiration, and postural hypotension (via abolition of circulatory reflex pathways); these changes are the generally undesirable effects that limit the therapeutic efficacy of ganglionic blocking agents.
Existing sympathetic tone is critical in determining the degree to which blood pressure is lowered by ganglionic blockade; thus, blood pressure may be decreased only minimally in recumbent nor-motensive subjects but may fall markedly in sitting or standing subjects. Postural hypotension limits use of ganglionic blockers in ambulatory patients.
Changes in heart rate following ganglionic blockade depend largely on existing vagal tone. Mild tachycardia usually accompanies the hypotension, a sign that indicates fairly complete
FIGURE 9-5 Ganglionic blocking agents.
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