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Article Excerpt
Given the previously reported potential link between aberrant patterns of breathing-swallowing coordination (BSC) and aspiration in patients with neurological impairment, if a particular body position is associated with aberrant BSC this may have important clinical implications. This pilot study compared BSC and swallowing apnea duration (SAD) between horizontal (supine, side-lying, and prone) and vertical (sitting upright) body positions. Twenty healthy adults in two age groups were included: 10 young (20-35 years) and 10 elder adults (65-80 years), gender equally represented. Concurrent measurements of submental muscle activity (surface electromyography), nasal airflow (nasal cannula), and thyroid acoustics (laryngeal microphone) were used to determine BSC and SAD, while a custom-made mercury switch position monitor recorded body position. Breathing-swallowing coordination was defined by the number of swallows in each of the following categories: midinspiratory (II), midexpiratory (EE), inspiratory-expiratory (IE), and expiratory-inspiratory (EI). We found that BSC differed marginally between horizontal and vertical body positions. This suggests that BSC is subject to the position-related physiological changes that influence respiration and swallowing rather than being a purely predetermined and invariant brainstem-generated pattern. Body position also altered SAD, with SAD being longer in the supine than the prone position. This may be attributed to the position-related impact on hyolaryngeal excursion.
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There is evidence that an unusual pattern of breathing-swallowing coordination (BSC), specifically a high incidence of post-swallow inspiration, is associated with neurological disorders in which aspiration is common, such as cerebral palsy (Rempel & Moussavi, 2005), stroke (Selley, Flack, Ellis, & Brooks, 1989b), motor neurone disease, spinal cord, and peripheral nervous system disease or damage (Hadjikoutis, Pickersgill, Dawson, & Wiles, 2000). Patients with respiratory disorders such as chronic obstructive airway disease also have a higher incidence of postswallow inspiration (Shaker et al., 1992). Although a direct link between aberrant BSC patterns and adverse outcomes has yet to be established, the literature indicates a high likelihood that aberrant BSC is associated with (McPherson et al., 1992) but may not be the cause of (Hadjikoutis et al., 2000) aspiration. Thus, clinically, it is important to determine whether phenomena such as body position, influence BSC.
Research comparing the effects of vertical and horizontal body positions on BSC has produced conflicting evidence. McFarland, Lund, and Gagner (1994) compared BSC in the upright position to resting on the hands and knees (quadruped position) and found that swallowing apnea shifted from early to late expiration in the upright position. Conversely, using a slightly different definition of BSC, Shaker et al. (1992) found no change in BSC between vertical and horizontal positions.
Evidence to support a likely impact of position on BSC comes from the respiratory and swallowing literature. On the whole, the effect of body position on respiration, such as lung capacity, compliance, and maximal expiratory pressure, is most apparent between vertical and horizontal positions, with a detrimental effect observed in the latter (Badr, Elkins, & Ellis, 2002; Behrakis, Baydur, Jaeger, & Milic-Emili, 1983; Manning, Dean, Ross, & Abboud, 1999). In terms of swallowing, a change in body position from vertical to horizontal may alter upper esophageal sphincter (Castell, Dalton, & Castell, 1990; Johnsson, Shaw, Gabb, Dent, & Cook, 1995) and distal esophageal functioning (Chang, Lee, Yeh, & Lee, 1996), as well as pharyngeal transit times (Ingervall & Lantz, 1973). Given the latter effect on swallowing duration measures, it is therefore possible that a similar vertical-horizontal dichotomous effect is observed for the duration of swallowing apnea (SAD).
Thus, the present pilot study investigated whether BSC differs between four body positions: three in the horizontal plane (supine, side-lying, and prone) and one in the vertical plane (sitting upright) in healthy adults. The presence of a position effect would imply that BSC is subject to the position-related physiological changes that influence respiration and swallowing and is not a robust, predetermined, and invariant pattern. Only "dry" swallows were included to specifically address the effect of body position on BSC without introducing possible confounding effects of sensory stimulation provided by an ingested bolus. Since there is no prior research on the influence of these four body positions on SAD, the present pilot study also aimed to determine whether this feature of BSC is subject to a position effect.
METHODS
Participants
Five healthy young males (mean age of 28.2 [+ or -] 6.1 years), five healthy young females (mean age...
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