Suppression of Abdominal Motor Activity during Swallowing in Cats and Humans
May
Suppression of Abdominal Motor Activity during Swallowing in Cats and Humans
Teresa Pitts 0 1 2 3
Albright G. Gayagoy 0 1 2 3
Melanie J. Rose 0 1 2 3
Ivan Poliacek 0 1 2 3
Jillian A. Condrey 0 1 2 3
M. Nicholas Musslewhite 0 1 2 3
Tabitha Y. Shen 0 1 2 3
Paul W. Davenport 0 1 2 3
Donald C Bolser 0 1 2 3
0 Funding: Funding for this study included National Institutes of Health HL103415, HL109025, and HL111215. There are no other financial disclosures to report. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
1 Data Availability Statement: All relevant data are within the paper
2 Academic Editor: Carlos E. Ambrosio, Faculty of Animal Sciences and Food Engineering, University of Sao Paulo , Pirassununga, SP, Brazil, BRAZIL
3 1 Department of Neurological Surgery, Kentucky Spinal Cord Injury Research Center, University of Louisville, Louisville, KY, United States of America, 2 Department of Physiological Sciences, University of Florida , Gainesville, FL , United States of America
Diseases affecting pulmonary mechanics often result in changes to the coordination of swallow and breathing. We hypothesize that during times of increased intrathoracic pressure, swallow suppresses ongoing expiratory drive to ensure bolus transport through the esophagus. To this end, we sought to determine the effects of swallow on abdominal electromyographic (EMG) activity during expiratory threshold loading in anesthetized cats and in awake-healthy adult humans. Expiratory threshold loads were applied to recruit abdominal motor activity during breathing, and swallow was triggered by infusion of water into the mouth. In both anesthetized cats and humans, expiratory cycles which contained swallows had a significant reduction in abdominal EMG activity, and a greater percentage of swallows were produced during inspiration and/or respiratory phase transitions. These results suggest that: a) spinal expiratory motor pathways play an important role in the execution of swallow, and b) a more complex mechanical relationship exists between breathing and swallow than has previously been envisioned.
-
Competing Interests: The authors have declared
that no competing interests exist.
The precise coordination of breathing and swallowing plays an important role to prevent
entrance of food and other materials into the lower respiratory tract. Diseases which effect
pulmonary mechanics such as chronic obstructive pulmonary disease (COPD), and or lung
tumors result in changes to the coordination of swallow and breathing [13]. COPD is one of
the thirteen statistically significant influencing factors that were implicated in the development
of aspiration pneumonia [37]. Additionally, patients with COPD swallow more often during
inspiration and consequently are at increased risk for post-swallow aspiration events [8, 9].
This disrupted breathing/swallow pattern could increase the risk of aspiration in patients with
advanced COPD and may contribute to exacerbations [10, 11].
Expiratory threshold loading is an experimental technique which reliably elicits abdominal
recruitment in human [1220] and animal models [2125]. A 15 cm H20 expiratory threshold
load increases rectus abdominis, internal oblique, transverses abdominis and gastric pressure
to approximately 530% of maximum activity produced during cough [26]. Previous work
[27] has increased our understanding of the interaction of swallow with other airway protective
behaviors, and pressure threshold loading allows for the testing of its interaction with
active expiration.
Pitts et al [28] proposed a dual valve system composed of highly coordinated control of
both the laryngeal adductor and upper esophageal sphincter in regulating pressures between
upper airway and the thoracic cavity, which controls the passage of air/bolus into or out of the
lungs and esophagus. During swallowing, the pressure differential produced by upper
esophageal relaxation and the maximal activity of tongue and pharyngeal muscles propels the bolus
into the esophagus. During the expiratory phase of breathing, requirements for the production
of swallowing are low because trans-laryngeal flows (i.e air movement through the larynx) and
intra thoracic pressures are minimal. However, in patients with alterations in respiratory
mechanics leading to increases in intra-thoracic pressure, such as with abdominal muscle
recruitment, dysphagia may be promoted by hindrance of bolus movement across the upper
esophageal sphincter.
The aims of this study were to determine if swallowing and breathing are coordinated
during active expiration and if swallows affects pressure regulation by altering laryngeal and
respiratory muscle activity. We hypothesized that swallows increase the duration and decrease the
maximal activity of expiratory muscles during expiratory loading.
Approval for this study was granted from the University of Florida Institutional Animal Care
and (...truncated)