Читать книгу The Esophagus - Группа авторов - Страница 140

Deglutitive inhibition is primarily mediated centrally by the SPG. Activation of the SPG at any level is associated with inhibition of neurons and motor neurons distal to this level, with the inhibition increasing more distally (see Figure 5.2). When a swallow has reached the upper esophagus, a second swallow will inhibit progression of the first swallow after a short period of time, with a delay until the second swallow appears [208, 274, 275]. Centrally, the second swallow shuts down the firing of the motor neurons to the esophagus, with these neurons again active later for the second swallow. The inhibitory neurons in the esophagus may also be activated by separate vagal inputs from the SPG that could normally occur with the second swallow. An experiment suggesting this activation of local inhibitory neurons first produced a zone of high pressure with mild intraluminal balloon distention, likely in large part due to reflex vasovagal activation of the SPG and excitatory output to the esophagus [125]. A second swallow caused a decrease in pressure in the artificial high‐pressure zone but would also inhibit the central activation. When a sequence of many rapid repetitive swallows occurs, not only is the first swallow wave inhibited and not present, but all subsequent swallow waves are prevented until after the last swallow, which is then followed by an augmented peristaltic contraction [276]. This physiologic phenomenon is the basis for esophageal provocative testing using multiple rapid swallows (MRS) during esophageal manometry, where augmentation of contraction following the final swallow of the sequence demonstrates contraction reserve in the esophageal smooth muscle, indicating intact neuromuscular function [277, 278]. Both circular and longitudinal esophageal smooth muscle participate in deglutitive inhibition [279].

Secondary peristalsis is also inhibited by a swallow [208, 211]. However, secondary peristalsis initiated in the smooth muscle esophagus may not consistently or effectively inhibit a primary swallow when the stimulus arrives later in the SPG program.

A previous swallow or the presence of a swallow‐induced contraction in the esophagus can alter the nature of a subsequent swallow that occurs within 20–30 s. Amplitude can decrease, and velocity can decrease or increase, even to the point of the wave being non‐peristaltic [274, 276]. Therefore, routine manometry studies need to space swallows by at least 20–30 s [280].