Page 458 - Clinical Application of Mechanical Ventilation

424 Chapter 13

TABLE 13-1 Two Autonomic Nervous System (ANS) Pathways for Bronchodilation

Sympathetic Pathway Parasympathetic Pathway

Stimulation of adrenergic response Interference of cholinergic response

T T

c c Sympathomimetic activity c Parasympatholytic activity
(Stimulation of sympathetic activity) (Inhibition of parasympathetic activity)

T T

Bronchodilation Relative increase of sympathetic activity

T
Bronchodilation
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In the lungs, b-2 receptors are found in the smaller airways, alveolar walls, and
submucosal glands. The primary goal of beta-2 adrenergic drugs is to combine with
these receptors to initiate bronchodilation.
Adrenergic bronchodilators are classified as catecholamines or catecholamine
derivatives.
Catecholamines. Catecholamines such as norepinephrine, epinephrine, and iso-
proterenol share the following characteristics: (1) rapid onset, (2) rapid degradation
by catechol-O-methyltransferase (COMT) in the liver, kidney, and throughout the
body, and the intraneuronal enzyme monoamine oxidase (MAO), (3) ineffective
when taken enterally, and (4) nonspecific receptor binding.
Catecholamine derivatives. Catecholamine derivatives such as metaproterenol,
terbutaline, albuterol, and pirbuterol have a more complex chemical structure than

TABLE 13-2 Major Effects of Alpha and Beta Receptors

Receptor Major Effects

Alpha-1 (α-1) Vasoconstriction
Constriction of pupils

Alpha-2 (α-2) Decreased gastrointestinal activity
Beta-1 (β-1) Positive inotropic effect (c muscular contractility)
inotropic: Affecting the contraction.
Positive chronotropic effect (c heart rate)
chronotropic: Affecting the rate. Beta-2 (β-2) Bronchodilation
Peripheral vasodilation
Decreased gastrointestinal activity
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