Figure 3.

Laryngeal and pharyngeal drive during swallow increases after cervical spinal cord injury. A: while both of the lower pharyngeal muscles (thyropharyngeus and cricopharyngeus) are involved in pharyngeal constriction and maintaining tone in the upper esophageal sphincter, we record from the thyropharyngeus to assess inferior pharyngeal constriction and from the cricopharyngeus to assess upper esophageal sphincter activity. B: representative traces of electromyogram (EMG) activity recorded from muscles during swallow prior to (blue) and ∼20 min (gray) and 90 min (purple) after C2 lateral hemisection (C2-lHx) in cats show changes after injury. The laryngeal adductor is the thyroarytenoid muscle, and traces are waveform averages of the rectified and smoothed (50 ms) EMGs. Swallows were induced with infusion of 3 mL of water into the oropharynx. The control waveform (blue) demonstrates the actuation of the diaphragm during swallow (termed “Schluckatmung”) during expiration. Oral infusion of water reliably elicits swallow, and peak EMG amplitude during swallow for laryngeal closure and pharyngeal constriction significantly increased after injury; swallow-related activity of the crural diaphragm significantly decreased on both sides. C: postmortem and illustrated images of the diaphragm show locations of the EMG placements. The plot shows decreases in waveform average amplitudes for swallow-related diaphragm activity at ∼20 (gray) and 90 (purple) min postinjury as a percent of the control amplitude. Contralateral crural diaphragm amplitude was decreased compared with control at ∼20-min [t(3) = 3.082, P = 0.03] and 90-min postinjury [t(3) = 4.7, P = 0.02]; ipsilateral crural diaphragm amplitude was also decreased at ∼20-min [t(3) = 18.5, P < 0.001] and 90-min postinjury [t(3) = 17.6, P < 0.001] (paired t tests). D: laryngeal adductor (thyroarytenoid) EMG activity during swallow was significantly increased at ∼20-min [t(3) = −6.9, P = 0.003] and 90-min postinjury [t(3) = −2.1, P = 0.04] compared with control. Inferior pharyngeal constrictor (thyropharyngeus) activity during swallow was significantly increased at 90-min postinjury [t(3) = −3.3, P = 0.045]. E: representative EMG example of breathing are shown with breathing phases defined using laryngeal drive. The percentages of swallow in each phase were plotted across a 180° circle plot (white indicates swallows in E1; gray indicates swallows in E2; inner circle with blue outline indicates early time point; outer circle with pink outline indicates 90-min time point). A Wilcoxon signed-rank test detected a significant change in swallow breathing coordination, with significantly greater number of swallows occurring during E1 after injury (Z = −1.9, P = 0.05).