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The present study was designed to provide additional insights into the neural mechanisms underlying respiratory-swallowing coupling by studying potential alterations in movement coordination when upper airway protection is no longer necessary. Twelve laryngectomized participants, all at least 3 years postsurgery, were compared to age- and sex-matched controls. Respiration and swallowing were monitored before, during, and after mastication. No significant differences were found between the laryngectomized and normal control participants in the distribution of the respiratory phase in which swallowing occurs, our primary measure of respiratory-swallowing stability. Data suggest that the coupling between the swallowing and respiratory pattern generators is highly stable. Pronounced masticatory-related apnea was observed in 3 of the laryngectomized participants but in none of the controls, suggesting that masticatory/respiratory interactions may become abnormal in these patients.
KEY WORDS: respiration, swallowing, mastication, laryngectomy, motor control
Respiration and deglutition are two fundamental motor patterns that must be tightly coordinated because they share a common passageway and aspiration has to be prevented. Common muscles must be differentially activated as the goal changes from modulating airflow during breathing to transporting the food bolus and protecting the airway during swallowing (as reviewed in Jean, 2001; Jean, Car, & Kessler, 1997; Sawczuk & Mosier, 2001). Lack of coordination can have severe clinical consequences including choking and aspiration-related pneumonia (Logemann, 1988; Selley, Flack, Ellis, & Brooks, 1989). Despite this, we know relatively little about how these behaviors are normally coordinated or the factors that influence their coupling, particularly in humans.
Respiration is inhibited to accommodate swallowing in all species including man (e.g., Kawasaki, Ogura, & Takenouchi, 1964; Klahn & Perlman, 1999; McFarland & Lund, 1993; Perlman, Ettema, & Barkmeier, 2000; Shaker et al., 1992), and this interruption increases the duration of the coincident and following respiratory cycles (Hiss, Treole, & Stuart, 2001; McFarland & Lund, 1995; Miyazaki, Yamashita, & Komiyama, 1994; Nishino, Yonezawa, & Honda, 1985; J. Smith, Wolkove, Colacone, & Kreisman, 1989). The cessation of breathing is one of the earliest swallowing events, and together with laryngeal elevation and vocal fold closure, it protects the airway prior to and during the passage of food and liquid through the oropharynx (Ren et al., 1993; Shaker, Dodds, Dantas, Hogan, & Arndorfer, 1990). Swallowing occurs most frequently in the late expiratory...