The Effects of COPD on Swallowing

The process of swallowing requires precise coordination with the respiratory system in order to protect the airway from aspiration (Shaker, Li, Ren, Townsend, Dodds, Martin, Kern, & Rynders, 1992). The issue of coordination is particularly important to patients with COPD as they have a limited ventilatory capacity and and will therefore need to breathe more often than people without COPD (Kijima, Isono & Nishino, 1999).


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To understand how COPD affects swallowing, one needsto consider the intricate relationship of breathing and swallowing. The swallowing and respiratory systems have a common developmental origin (Moklesi, Logemann, Rademaker, Stangl, & Corbridge, 2002), and both are thought to be controlled by nuclei in the medulla;
where they are connected by interneurons (Curtis & Langmore, 1997). Both systems involve sensory and motor nerves, as well as a wide array of muscles. Moreover, the control of the two systems is both voluntary and involuntary (Mokhlesi et al., 2002). To further complicated the matter, they share a common pathway in the oro-pharynx, which is labelled in the diagram on the right.

The body manages the dual function of the oro-pharynx in normal subjects by inhibiting respiration during swallowing (swallow apnoea) (Curtis & Langmore, 1997). When swallowing occurs, the breathing apparatus can be stopped or altered, and/or the respiratory system oscillator can be reset. "Conversely, the respiratory system can govern deglutition by inhibiting the swallow or modifying its physiology.” (Gross, Atwood, Ross, Olszewski, & Eichhorn, 2009, p.559)

The picture below illustrates the two stages of the breathing cycle, which are inhalation and exhalation.


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Among healthy adults, 80% of swallowing occurs during the exhalation stage of the breathing cycle. That is,normal_swallow_flowchart.jpg swallowing interrupts the body exhaling, and once the swallow has been completed, breathing resumes with exhalation (Curtis & Langmore, 1997). This pattern is shown in the diagram to the right.

Subconscious swallows will only interrupt breathing approximately once every minute when not eating or drinking (Shaker et al., 1992), however the rate of interruption will naturally increase dramatically when food or liquids are being ingested. The coordination between breathing and swallowing can be severely disrupted in patients with COPD, due to thier reduced ventilatory capacity, which in turn poses serious health risks. A study by Gross et al. (2009) into the coordination of breathing and swallowing in COPD concluded that patients with COPD are more likely to display the following impaired patterns of breathing and swallowing when compared to the preferred exhale-swallow-exhale pattern prevalent in healthy adults:

  • When eating solid food that requires mastication, patients with COPD are more likely to swallow during the inhalation cycle of breathing.
  • When eating semi solid food, patients with COPD are more likely to inhale directly after swallowing.
  • Patients with COPD are more likely to swallow at times during the breathing cycle when they have low sub-glottic air pressure.

If the preferred pattern of exhale-swallow-exhale is altered, the risk of aspiration increases. This is because any residual food or liquid in the pharynx could be drawn into the reparatory system when inhalation immediately follows a swallow, (Mokhlesi et al., 2002). Aspiration is a likely contributing factor towards exacerbations of COPD; and as a result, exacerbations of COPD can increase the risk of further aspiration (Gross et al., 2009). Therefore, aspiration in COPD patients has the potential to cause recurring complications (McKinstry, Tranter, & Sweeney, 2009).

The occurrence of COPD patients swallowing at the end of an exhalation, and then subsequently inhaling suggests that the respiratory system’s need for air can take precedence over swallowing when required (Gross et al., 2009). Low sub-glottic air pressure occurs during early inhalation, late exhalation, or at the transition point between exhalation and inhalation. If swallowing takes place during times of sub-glottic air pressure, the physiology of swallowing can also be altered. In particular, the process of pharyngeal constriction is prolonged. This physiological change is of particular relevance to patients with tracheostomies, as it slows the transit time of the bolus, and increases the amount of pharyngeal residue, and the frequency of aspiration (Gross et al., 2009).

A further consideration when looking at the disrupted swallow-respiration pattern of COPD patients is ‘lung-thoracic unit recoil’ (Gross et al., 2009, p.563). This refers to the fact that, during the exhalation cycle of breathing, the body does not actively push air out of the lungs. Instead it is a passive action where the muscles of respiration, the lungs and the ribs naturally recoil to their resting postion, and in doing so, expell air from the thorax. As respiratory muscles are inhibited, and the cocal cords are adducted during duglitition, it is likely that this recoil potential is a factor in increasing sub-glottic air pressure. Any condition that either affects lung expansion, or an external restrictive disorder will affect the potential of this recoil.

COPD can also affect the phsyiology of deglutioion by differences in laryngeal elevation. In the study by Mokhlesi et al. (2002), the COPD group's laryngeal elevation was significantly lower during swallowing than the control group. In normal swallowing, the elevation of the larynx is a key step in airway protection, as it enables the epiglottis to fold down and protect the enrance to the larynx from food and liquid. This Physiological change in patients with COPD is another risk factor for aspiration.

Interestingly, Mokhlesi et al (2002) found that some patients with stable COPD perform voluntary protective maneuvers during swallowing, such as early and prolonged closure of the airway. They predict that the protective maneuvers explain the absence of aspiration in their study group, and suggests that these maneuvers may not be useful during and exacerbation of their condition. Similar occurrences of increased swallow apnoeas were also recorded in the study by Gross et al. (2009).

The figures for prevalence of dysphagia in patients with COPD vary greatly, ranging from 20 to 90% (McKinstry, Tranter, & Sweeney, 2009) In another study of oropharyngeal deglutition in stable COPD, Mokhlesi et al. (2002) state that dysphasia is underdiagnosed in patients with COPD, as people do not often recognise that they have any swallowing problems. Out of the 20 participants with stable COPD in the study, none of them displayed the following signs of dysphagia: reduced lip closure, tongue thrust, apraxia of swallow, absent pharyngeal swallow. Reduced VP closure, incomplete closure of the laryngeal vestibule, reduced glottal closure, unilateral or bilateral pharyngeal weakness, reduced CP opening, aspiration. The absence of these swallowing disorders indicates that dysphagia in COPD presents very differently from dysphagia owing to a neurological aetiology (Gross et al., 2009), and that SLTs should be aware of this when assessing clients .

Suggested causes for oropharyngeal dysphagia are muscle fatigue of the upper aerodigestive tract, abnormal physiology that occurs in protective maneuvers, and the anxiety of the COPD patient (Gross et al., 2009)





References:

Curtis, J., & Langmore, S. (1997). Respiratory function and complications related to deglutition. In A. Perlman, & K. Schulze-Derieu (Eds.), Deglutition and its disorders: Anatomy, physiology, clinical diagnosis, and management (pp. 99-122). San Diego, CA: Singular Publishing Group.

Gross, R., Atwood, C., Ross, S., Olszewski, J., & Eichhorn, K. (2009). The coordination of breathing and swallowing in chronic obstructive pulmonary disease. American Journal of Respiratory and Critical Care Medicine, 179(7), 559-565.

Kijima, M., Isono, S., & Nishino, T. (1999). Coordination of swallowing and phases of respiration during added respiratory loads in awake subjects. American Journal of Respiratory and Critical Care Medicine, 159(6), 1898-1902.

Mckinstry, A., Tranter, M., & Sweeney, J. (2010). Outcomes of dysphagia intervention in a pulmonary rehabilitation program. Dysphagia, 25(2), 104-111.

Mokhlesi, B., Logemann, J., Rademaker, A., Stangl, C., & Corbridge, C. (2002). Oropharyngeal deglutition in stable COPD. CHEST, 121(2), 361-369.

Shaker, R., Li, Q., Ren, J., Townsend, W., Dodds, W., Martin, B., Kern, M., & Rynders, A. (1992). Coordination of deglutition and phases of respiration: Effect of aging, tachypnea, bolus volume, and chronic obstructive pulmonary disease. American Journal of Physiology, 263(5), 750-755.