Electromyographic activity from human laryngeal, pharyngeal, and submental muscles during swallowing

Laryngeal activity during upright vs. supine swallowing

Previous investigations of human pharyngeal muscle activation patterns during swallowing found a relatively invariant muscle activation onset sequence in the upright position. However, different gravitational forces influence a liquid bolus when supine and could modify the central timing control of laryngeal airway protection during swallowing. The purpose of this study was to determine whether laryngeal muscle onset timing during swallowing differed between the supine and upright positions. Nine subjects performed six swallowing trials with a 2-ml water bolus in each position. Simultaneous electromyographic recordings were obtained from the submental complex (SMC) and the right and left thyroarytenoid (TA) muscles. Regardless of body position, the timing, amplitude, and duration of the TA muscles did not vary relative to the SMC. Therefore, the sequence of TA muscle activation relative to the SMC during swallowing appeared unaffected by gravitational influences.

Non-invasive monitoring of functionally distinct muscle activations during swallowing

OBJECTIVES

Dysphagia is an important consequence of many diseases. As some of the muscles of deglutition tend to be deep to the surface, needle electrodes are typically used, but this limits the number of muscles that can be simultaneously recorded. Since control of swallowing involves central pattern generators (CPGs) which distribute commands to several muscles, monitoring several muscles simultaneously is desirable. Here we describe a novel method, based on computing the independent components (ICs) of the simultaneous sEMG recordings (Muscle Nerve Suppl 9 (2000) 9) to detect the underlying functional muscle activations during swallowing using only surface EMG (sEMG) electrodes.

METHODS

Seven normal subjects repeatedly swallowed liquids of varying consistency while sEMG was recorded from 15 electrodes from the face and throat. Active areas of EMG were excised from the recordings and the ICs of the sEMG were calculated.

RESULTS

The ICs demonstrated less swallow-to-swallow variability than the raw sEMG. The ICs, each consisting of a unique temporal waveform and a spatial distribution, provided a means to segregate the complex sequence of muscle activation into rigorously defined separate functional units. The temporal profiles of the ICs and their spatial distribution were consistent with prior needle EMG studies of the cricopharyngeal, superior pharyngeal constrictor, submental and possibly arytenoid muscles. Other components appeared to correspond to EKG artifact contaminating the EMG recordings, laryngeal excursion, tongue movement and activation of the buccal and/or masseter musculature At least two of the components were affected by the consistency of the liquids swallowed. Re-testing one subject a week later demonstrated good intertrial reliability.

CONCLUSIONS

We propose that the ICs of the sEMG provide a non-invasive means to assess the complex muscle sequence activation of deglutition.

The electromyographic behavior of the thyroarytenoid muscle during swallowing

The electromyographic (EMG) behavior of the laryngeal adductors (e.g., the thyroarytenoid [TA] muscle) during swallowing has been scarcely studied. However, the detailed analysis of TA muscle is important to understand the physiology of swallowing. We investigated 14 healthy adult subjects. Activation of the TA laryngeal adductor muscle was compared with the mechanically measured laryngeal up-down movement and with the onset of excitation of laryngeal elevators, such as submental (SM) muscles, during swallowing. The laryngeal adductor of TA and laryngeal elevators of SM muscles were electromyographically (integrated/rectified) recorded. The vertical laryngeal movements during swallowing were recorded using a piezoelectric sensor. The EMG behavior of the TA muscle revealed three different activities during swallowing. The basic activity was stable; it almost started with the upward movement of larynx and after the SM-EMG onset. A fore-burst was recorded just before the upward movement of the larynx and a late-burst appeared just after the downward movement. The fore-burst was proposed to be related with oral-laryngeal reflexes, and the late-burst could be a rebound activity after a short expiration of swallowing, while the basic activity is accepted to be a part of activity of central-pattern generator of swallowing program.

Modulation of laryngeal responses to superior laryngeal nerve stimulation by volitional swallowing in awake humans

Laryngeal sensori-motor closure reflexes are important for the protection of the airway and prevent the entry of foreign substances into the trachea and lungs. The purpose of this study was to determine how such reflexes might be modulated during volitional swallowing in awake humans, when persons are at risk of entry of food or liquids into the airway. The frequency and the amplitude of laryngeal adductor responses evoked by electrical stimulation of the internal branch of the superior laryngeal nerve (ISLN) were studied during different phases of volitional swallowing. Subjects swallowed water on command while electrical stimuli were presented to the ISLN at various intervals from 500 ms to 5 s following the command. Laryngeal adductor responses to unilateral ISLN stimulation were recorded bilaterally in the thyroarytenoid muscles using hooked wire electrodes. Early ipsilateral R1 responses occurred at 17 ms, and later bilateral R2 began around 65 ms. The muscle responses to stimuli occurring during expiration without swallowing were quantified as control trials. Responses to stimulation presented before swallowing, during the swallow, within 3 s after swallowing, and between 3 and 5 s after a swallow were measured. The frequency and amplitude of three responses (ipsilateral R1 and bilateral R2) relative to the control responses were compared across the different phases relative to the occurrence of swallowing. Results demonstrated that a reduction occurred in both the frequency and amplitude of the later bilateral R2 laryngeal responses to electrical stimulation for up to 3 s after swallowing (P = 0.005). The amplitude and frequency of ipsilateral R1 laryngeal responses, however, did not show a significant main effect following the swallow (P = 0.28), although there was a significant time by measure interaction (P = 0.006) related to reduced R1 response amplitude up to 3 s after swallowing (P = 0.021). Therefore, the more rapid and shorter unilateral R1 responses continued to provide some, albeit reduced, laryngeal protective functions after swallowing, whereas the later bilateral R2 responses were suppressed both in occurrence and amplitude for up to 3 s after swallowing. The results suggest that R2 laryngeal adductor responses are suppressed following swallowing when residues may remain in the laryngeal vestibule putting persons at increased risk for the entry of foreign substances into the airway.