Duration of action of bupivacaine hydrochloride used for palatal sensory nerve block in infant pigs.

Bupivacaine hydrochloride is frequently used in veterinary dental procedures to reduce the amount of general anesthesia needed and to reduce post-procedural pain. The aim of this study was to develop a novel method to test local anesthetic duration in mammals. Six infant pigs were placed under deep/surgical anesthesia with 3 % isoflurane and oxygen while 0.5 ml of 0.5% bupivacaine hydrochloride was injected to block the two greater palatine and the nasopalatine nerves. They were then maintained under light anesthesia with 0.5-1.0% isoflurane. Beginning 15-minutes after the injection, 7 sites in the oral cavity were stimulated using a pointed dental waxing instrument, including 3 sites on the hard palate. The response, or lack of response, to the stimulus was recorded on video and in written record The bupivacaine hydrochloride injections lasted 1 to 3-hours before the animals responded to the sensory stimulation with a reflexive movement This study provides evidence that bupivacaine used to anesthetize the hard palate has a relatively short and variable duration of action far below what is expected based on its pharmacokinetic properties.

Swallowing kinematics and airway protection after palatal local anesthesia in infant pigs.

OBJECTIVES/HYPOTHESIS: Abnormal kinematics during swallowing can result in aspiration, which may become life threatening. We tested the role of palatal sensation in the motor control of pharyngeal swallow in infants. STUDY DESIGN: In eight infant pigs, we reduced palatal sensation using local anesthesia (PLA) and measured the impact on swallowing kinematics and airway protection. METHODS: The pigs drank milk containing barium while we simultaneously recorded videofluoroscopy and electromyography from fine wire bipolar electrodes in several hyolaryngeal muscles. We compared these results to control feedings and feedings following palatal saline injections. RESULTS: After PLA, four pigs had extreme jaw movements and abnormal tongue movement uncharacteristic of sucking. For this reason, we evaluated differences between these group B pigs and the others that could suck normally after PLA (group A). In the four group A pigs, after PLA there was less hyoid elevation (P < .001) but normal jaw and tongue movements. In group B, in addition to greater jaw movement (P < .001) there was more anterior and superior tongue movement (P < .001) and a larger range of hyoid movement (P < .001). CONCLUSIONS: The airway was protected in all of the pigs, indicating that these changes allowed successful adaptation to the reduction in palatal sensation. However, the oral and pharyngeal phases of the swallow were functionally linked, and trigeminal sensation influenced the motor control of the pharyngeal swallow. LEVEL OF EVIDENCE: N/A.

Sucking and swallowing rates after palatal anesthesia: an electromyographic study in infant pigs.

Infant mammalian feeding consists of rhythmic suck cycles and reflexive pharyngeal swallows. Although we know how oropharyngeal sensation influences the initiation and frequency of suck and swallow cycles, the role of palatal sensation is unknown. We implanted EMG electrodes into the mylohyoid muscle, a muscle active during suckling, and the thyrohyoid muscle, a muscle active during swallowing, in eight infant pigs. Pigs were then bottle-fed while lateral videofluoroscopy was simultaneously recorded from the electrodes. Two treatments were administered prior to feeding and compared with control feedings: 1) palatal anesthesia (0.5% bupivacaine hydrochloride), and 2) palatal saline. Using the timing of mylohyoid muscle and thyrohyoid muscle activity, we tested for differences between treatment and control feedings for swallowing frequency and suck cycle duration. Following palatal anesthesia, four pigs could not suck and exhibited excessive jaw movement. We categorized the four pigs that could suck after palatal anesthesia as group A, and those who could not as group B. Group A had no significant change in suck cycle duration and a higher swallowing frequency after palatal saline (P = 0.021). Group B had significantly longer suck cycles after palatal anesthesia (P < 0.001) and a slower swallowing frequency (P < 0.001). Swallowing frequency may be a way to predict group membership, since it was different in control feedings between groups (P < 0.001). The qualitative and bimodal group response to palatal anesthesia may reflect a developmental difference. This study demonstrates that palatal sensation is involved in the initiation and frequency of suck and swallow cycles in infant feeding.

The effect of unilateral superior laryngeal nerve lesion on swallowing threshold volume.

OBJECTIVES/HYPOTHESIS: The superior laryngeal nerve (SLN) is the major sensory nerve for the upper larynx. Damage to this nerve impacts successful swallowing. The first aim of the study was to assess the effect of unilateral SLN lesion on the threshold volume sufficient to elicit swallowing in an intact pig model; this volume was defined radiographically as the maximum bolus area visible in lateral view. The second aim was to determine if a difference existed between ipsilateral and contralateral function as a result of unilateral sensory loss, measured as the radiologic density of fluid seen in the valleculae. Finally, we determined whether there was a relationship between the threshold volume and the occurrence of aspiration after a unilateral SLN lesion. STUDY DESIGN: Repeated measures animal study. METHODS: Four female infant pigs underwent unilateral SLN lesion surgery. The maximum vallecular bolus area in lateral view and the relative vallecular density on each side in the dorsoventral view were obtained from videofluoroscopic recordings in both the prelesion control and postlesion experimental states. RESULTS: In lateral view, the lesioned group had a larger maximum bolus area than the control group (P < .001). Although occasional left-right asymmetry in the dorsoventral view was observed, the vallecular densities were, on average, equal on both the left (intact) and right (lesioned) sides (P > .05). A bigger maximum bolus area did not predict aspiration in the lesioned group (P > .05). CONCLUSIONS: Unilateral SLN lesions increased the swallowing threshold volume symmetrically in right and left valleculae, but the increased threshold may not be the main mechanism for the occurrence of aspiration.

Unilateral superior laryngeal nerve lesion in an animal model of dysphagia and its effect on sucking and swallowing.

We tested two hypotheses relating to the sensory deficit that follows a unilateral superior laryngeal nerve (SLN) lesion in an infant animal model. We hypothesized that it would result in (1) a higher incidence of aspiration and (2) temporal changes in sucking and swallowing. We ligated the right-side SLN in six 2-3-week-old female pigs. Using videofluoroscopy, we recorded swallows in the same pre- and post-lesion infant pigs. We analyzed the incidence of aspiration and the duration and latency of suck and swallow cycles. After unilateral SLN lesioning, the incidence of silent aspiration during swallowing increased from 0.7 to 41.5%. The durations of the suck containing the swallow, the suck immediately following the swallow, and the swallow itself were significantly longer in the post-lesion swallows, although the suck prior to the swallow was not different. The interval between the start of the suck containing a swallow and the subsequent epiglottal movement was longer in the post-lesion swallows. The number of sucks between swallows was significantly greater in post-lesion swallows compared to pre-lesion swallows. Unilateral SLN lesion increased the incidence of aspiration and changed the temporal relationships between sucking and swallowing. The longer transit time and the temporal coordinative dysfunction between suck and swallow cycles may contribute to aspiration. These results suggest that swallow dysfunction and silent aspiration are common and potentially overlooked sequelae of unilateral SLN injury. This validated animal model of aspiration has the potential for further dysphagia studies.

Development, reliability, and validation of an infant mammalian penetration-aspiration scale.

A penetration-aspiration scale exists for assessing airway protection in adult videofluoroscopy and fiberoptic endoscopic swallowing studies; however, no such scale exists for animal models. The aim of this study was threefold: (1) develop a penetration-aspiration scale (PAS) for infant mammals, (2) test the scale's intra- and interrater reliabilities, and (3) validate the use of the scale for distinguishing between abnormal and normal animals. After discussion and reviewing many videos, the result was a 7-point infant mammal PAS. Reliability was tested by having five judges score 90 swallows recorded with videofluoroscopy across two time points. In these videos, the frame rate was either 30 or 60 frames per second and the animals were either normal, had a unilateral superior laryngeal nerve (SLN) lesion, or had hard palate local anesthesia. The scale was validated by having one judge score videos of both normal and SLN lesioned pigs and testing the difference using a t test. Raters had a high intrarater reliability [average κ = 0.82, intraclass correlation coefficient (ICC) = 0.92] and high interrater reliability (average κ = 0.68, ICC = 0.66). There was a significant difference in reliability for videos captured at 30 and 60 frames per second for scores of 3 and 7 (P < 0.001). The scale was also validated for distinguishing between normal and abnormal pigs (P < 0.001). Given the increasing number of animal studies using videofluoroscopy to study dysphagia, this scale provides a valid and reliable measure of airway protection during swallowing in infant pigs that will give these animal models increased translational significance.