Usual Predominance of Sympathetic or Parasympathetic Tone at Various Effector Sites and Consequences of Autonomic Ganglionic Blockade

Site

Predominant Tone

Effect of Ganglionic Blockade

Arterioles Veins

Heart Iris

Ciliary muscle Gastrointestinal tract

Urinary bladder Salivary glands Sweat glands Genital tract

Sympathetic (adrenergic) Sympathetic (adrenergic)

Parasympathetic (cholinergic) Parasympathetic (cholinergic) Parasympathetic (cholinergic) Parasympathetic (cholinergic)

Parasympathetic (cholinergic) Parasympathetic (cholinergic) Sympathetic (cholinergic) Sympathetic and parasympathetic

Vasodilation; increased peripheral blood flow; hypotension Dilation: peripheral pooling of blood; decreased venous return; decreased cardiac output Tachycardia Mydriasis

Loss of visual accommodation Reduced tone and motility; constipation; decreased gastric and pancreatic secretions Urinary retention Xerostomia Anhidrosis

Decreased stimulation ganglionic blockade. However, a decrease may occur if the heart rate is high initially. In patients with normal cardiac function, these drugs may reduce cardiac output as a consequence of diminished venous return resulting from venous dilation and peripheral pooling of blood. In patients with cardiac failure, ganglionic blockade frequently results in increased cardiac output owing to a reduction in peripheral resistance. In hypertensive subjects, cardiac output, stroke volume, and left ventricular work are diminished.

Although ganglionic blockade decreases total systemic vascular resistance, changes in blood flow and vascular resistance of individual vascular beds vary: reduction of cerebral blood flow is small unless mean systemic blood pressure falls below 50-60 mm Hg; skeletal muscle blood flow is unaltered; splanchnic and renal blood flow decrease.

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