Mechanisms of swallowing and airway protection in infant mammals (Sus domesticus and Macaca fascicularis)

Protection of the airway, necessary for continued respiration, is a problem for mammals because of the relative positions of the oesophageal and laryngeal openings in the pharynx. In human infants, and all other mammals, infant and adult, the epiglottis contacts the posterior surface of the soft palate, providing a continuous passage from the nasopharynx to larynx. The function and movements of the epiglottis during swallows are debated as to whether the epiglottis bends to protect the airway or remains erect and leaves the airway open during the swallow. Using high-speed cineradiography, we examined swallows in detail for a precocious infant, Sus domesticus , the miniature pig, and the more altrical primate, Macaca fascicularis. Infant pigs swallowed in two different ways: down the midline of the oropharynx, over a bent epiglottis, and laterally, around an erect epiglottis, and presumably open airway. The epiglottis of infant macaques never bent, and milk always travelled laterally, through the pyriform recesses and around the larynx. The macaque airway was closed superiorily, however, when the soft palate sealed against the posterior pharyngeal wall. A hypothesis that could account for this pattern of swallowing involves an ontogenetic change from swallows travelling laterally through the pyriform recesses in young infants to swallows travelling over a bent epiglottis in more mature infants. This change would accompany maturation associated with weaning and the need to protect the airway from the larger and less fluid boluses of masticated solid food.     

Suppression of Abdominal Motor Activity during Swallowing in Cats and Humans

Diseases affecting pulmonary mechanics often result in changes to the coordination of swallow and breathing. We hypothesize that during times of increased intrathoracic pressure, swallow suppresses ongoing expiratory drive to ensure bolus transport through the esophagus. To this end, we sought to determine the effects of swallow on abdominal electromyographic (EMG) activity during expiratory threshold loading in anesthetized cats and in awake-healthy adult humans. Expiratory threshold loads were applied to recruit abdominal motor activity during breathing, and swallow was triggered by infusion of water into the mouth. In both anesthetized cats and humans, expiratory cycles which contained swallows had a significant reduction in abdominal EMG activity, and a greater percentage of swallows were produced during inspiration and/or respiratory phase transitions. These results suggest that: a) spinal expiratory motor pathways play an important role in the execution of swallow, and b) a more complex mechanical relationship exists between breathing and swallow than has previously been envisioned.     

Bolus transit patterns in healthy subjects: a study using simultaneous impedance monitoring, videoesophagram, and esophageal manometry

Impedance monitoring (Imp) measures bolus transit. Combining Imp with manometry (EM) allows the effect of contractile patterns on transit to be assessed. The objective of this study is to identify bolus transit patterns in normal subjects, correlate Imp findings with the gold standard barium esophagram (Ba), and compare bolus transit with concomitant EM findings. Simultaneous Ba-Imp-EM was performed for 2 min in 15 normal volunteers (women, 11; age, 43 yr). Combined impedance-pressure sites were 5, 10, 15, 20 cm above the lower esophageal sphincter (LES). Boluses (10 ml) of 45% barium mixed with 0.9% NaCl were swallowed at > or = 20-s intervals (5-6 swallows/subject). Imp and Ba showed three bolus transit patterns, and the two methods were in agreement on the pattern type in 97% (83/86) of swallows. Normal bolus transit was found in 73% (61/83), and each had normal peristalsis and contraction amplitude. Stasis in the proximal esophagus occurred in 7 of 83 swallows despite normal manometric parameters in 4 of 7 swallows. Retrograde escape of a residue of incompletely cleared bolus from just above the LES to the site 5 cm above occurred in 14 of 83 swallows. Retrograde escape was triggered by the next swallow, occurred despite normal manometric parameters, and did not occur if the swallow interval was >30 s. In 55% (47/86) of swallows, air accumulated in the distal esophagus and persisted there for a mean of 3.6 s until cleared into the stomach. We conclude that impedance monitoring is a valid transit test and describe bolus transit patterns in normal subjects for comparison with patients with esophageal motility disorders.     

Structure and postnatal transformation of the intermediate epithelium lining the mouse nasopalatine duct

In the epithelium lining the nasopalatine duct of the infant mouse, a transitional zone between the stratified squamous epithelium and the ciliated columnar one can be observed. The epithelium lining the transitional zone shows gradations ranging from the stratified squamous through the stratified cuboidal to the ciliated stratified low-columnar type, and gradually transforms into the stratified squamous epithelium with advancing ages. In the adult mouse, the nasopalatine duct is lined with the stratified squamous epithelium throughout up to the vicinity of the nasal cavity, and changes abruptly into the ciliated columnar epithelium lining the nasal cavity. It is suggested that the epithelium lining the transitional zone is identical with the 'intermediate epithelium' in the mouse nasopharynx and epiglottis.     

Effect of aging on bolus kinematics during the pharyngeal phase of swallowing

Swallowing difficulty is a common complaint in the elderly and, although there are data for the biomechanics of liquid swallows, little is known about solid bolus motion, or kinematics, in the elderly. The aims of this study were as follows: 1) to characterize and compare solid and liquid bolus kinematics in the elderly and compare the findings with those in young subjects and 2) to correlate bolus kinematics and dynamics. Concurrent manometric-fluoroscopic techniques were used to study eight young and eight elderly subjects. The subjects performed four swallows each of 0.2-cm-diameter solid barium pellets and 5 ml of liquid barium during sagittal fluoroscopy and six-channel pharyngoesophageal manometry. Images were digitized for analysis of kinematic properties such as velocity and acceleration. Dynamic pressures were recorded and coordinated with kinematic events. Image analysis showed that velocity varied as the pellet passed through the hypopharynx, pharynx, and upper esophageal sphincter. In young subjects, pellet kinematics were characterized by two zones of pellet acceleration: one over the tongue base and another as the pellet passed through the upper esophageal sphincter. Although the elderly showed a similar zone of acceleration over the base of the tongue, the second zone of pellet acceleration was not seen. Decreasing pressure gradients immediately distal to the position of the solid pellet and liquid bolus characterized dynamics for all subjects. This decreasing pressure gradient was significantly larger in elderly than in young subjects. Bolus kinematics and dynamics were significantly altered among elderly compared with young subjects. Among these differences were the absence of hypopharyngeal bolus acceleration and a significant increase in the trans-sphincteric pressure gradient in the elderly.     

Adaptation of swallowing hyo-laryngeal kinematics is distinct in oral vs. pharyngeal sensory processing

Before a bolus is pushed into the pharynx, oral sensory processing is critical for planning movements of the subsequent pharyngeal swallow, including hyoid bone and laryngeal (hyo-laryngeal) kinematics. However, oral and pharyngeal sensory processing for hyo-laryngeal kinematics is not fully understood. In 11 healthy adults, we examined changes in kinematics with sensory adaptation, sensitivity shifting, with oropharyngeal swallows vs. pharyngeal swallows (no oral processing), and with various bolus volumes and tastes. Only pharyngeal swallows showed sensory adaptation (gradual changes in kinematics with repeated exposure to the same bolus). Conversely, only oropharyngeal swallows distinguished volume differences, whereas pharyngeal swallows did not. No taste effects were observed for either swallow type. The hyo-laryngeal kinematics were very similar between oropharyngeal swallows and pharyngeal swallows with a comparable bolus. Sensitivity shifting (changing sensory threshold for a small bolus when it immediately follows several very large boluses) was not observed in pharyngeal or oropharyngeal swallowing. These findings indicate that once oral sensory processing has set a motor program for a specific kind of bolus (i.e., 5 ml water), hyo-laryngeal movements are already highly standardized and optimized, showing no shifting or adaptation regardless of repeated exposure (sensory adaptation) or previous sensory experiences (sensitivity shifting). Also, the oral cavity is highly specialized for differentiating certain properties of a bolus (volume) that might require a specific motor plan to ensure swallowing safety, whereas the pharyngeal cavity does not make the same distinctions. Pharyngeal sensory processing might not be able to adjust motor plans created by the oral cavity once the swallow has already been triggered.     

Upper esophageal sphincter impedance as a marker of sphincter opening diameter

The measurement of the physical extent of opening of the upper esophageal sphincter (UES) during bolus swallowing has to date relied on videofluoroscopy. Theoretically luminal impedance measured during bolus flow should be influenced by luminal diameter. In this study, we measured the UES nadir impedance (lowest value of impedance) during bolus swallowing and assessed it as a potential correlate of UES diameter that can be determined nonradiologically. In 40 patients with dysphagia, bolus swallowing of liquids, semisolids, and solids was recorded with manometry, impedance, and videofluoroscopy. During swallows, the UES opening diameter (in the lateral fluoroscopic view) was measured and compared with automated impedance manometry (AIM)-derived swallow function variables and UES nadir impedance as well as high-resolution manometry-derived UES relaxation pressure variables. Of all measured variables, UES nadir impedance was the most strongly correlated with UES opening diameter. Narrower diameter correlated with higher impedance (r = -0.478, P < 0.001). Patients with <10 mm, 10-14 mm (normal), and ≥ 15 mm UES diameter had average UES nadir impedances of 498 ± 39 Ohms, 369 ± 31 Ohms, and 293 ± 17 Ohms, respectively (ANOVA P = 0.005). A higher swallow risk index, indicative of poor pharyngeal swallow function, was associated with narrower UES diameter and higher UES nadir impedance during swallowing. In contrast, UES relaxation pressure variables were not significantly altered in relation to UES diameter. We concluded that the UES nadir impedance correlates with opening diameter of the UES during bolus flow. This variable, when combined with other pharyngeal AIM analysis variables, may allow characterization of the pathophysiology of swallowing dysfunction.     

Space-time pressure structure of pharyngo-esophageal segment during swallowing

We applied high-resolution manometry with spatiotemporal data interpolation and simultaneous videofluoroscopy to normal pharyngeal swallows to correlate specific features in the space-time intraluminal pressure structure with physiological events and normal deglutitive transsphincteric bolus flow to define normal biomechanical properties of the pharyngo-esophageal (PE) segment. Pressures were recorded by microperfused catheter, and the two-dimensional space-time data sets were plotted as isocontours. On these were superimposed bolus trajectories, anatomic segment movements, and hyo-laryngeal trajectories from concurrent videofluoroscopy. Correlation of the highly reproducible space-time-pressure structure with radiographic images confirmed that primary deglutitive PE segment functions (pressure profile, laryngeal elevation, axial sphincter motion, timing of relaxation, contraction) are accurately discernible from single isocontour pressure visualization. Pressure during bolus flow was highly dependent on axial location within PE segment and time instant. The intrabolus pressure domain, corresponding to the space-time region between bolus head and tail trajectories, demonstrated significant bolus volume dependence. High-resolution manometry accurately, comprehensively, and highly reproducibly depicts the PE segment space-time-pressure structure and specific physiological events related to upper esophageal sphincter opening and transsphincteric flow during normal swallowing. Intrabolus pressure variations are highly dependent on position within the PE segment and time.     

Effect of dry swallows and wet swallows of different volumes on esophageal peristalsis.

The effect of dry swallows and wet swallows of various volumes on esophageal function was studied in normal subjects. An intraesophageal transducer assembly was used to measure the dynamics of esophageal peristalsis. The strength of esophageal contraction (amplitude) following a 1-ml liquid bolus was similar to that following a dry swallow but was significantly less than that following a wet swallow of a larger volume. There was no difference in strength of esophageal squeeze following swallows ranging from 2 to 20 ml. In addition, a wet swallow was associated with slower wave speed, greater duration of the contraction wave, and later time of appearance of the peristaltic wave in the distal esophagus than a dry swallow. Futhermore, the incidence of peristalsis was greater with a wet swallow than a dry swallow. The results of our studies indicate that although the act of swallowing alone in man initiates peristalsis, afferent information contributes to the regulation of primary peristalsis.     

Movement of the epiglottis in mammals

In contrast to adult humans, the epiglottis of other mammals and infant humans is situated close to the soft palate. It has been argued that this posture is maintained during swallowing, with food passing laterally around an intact airway. To test this supposition, the movement of the epiglottis in two contrasting mammalian species, pigs and ferrets, was studied by placing radiopaque markers on the epiglottis and soft palate. Swallowing was observed with videofluoroscopy while the animals were feeding on hard and soft foods, liquids, and food mixed with barium sulfate. Analysis of the images showed that bolus formation and downward movement of the epiglottis away from the soft palate were unvarying phenomena in both animals for all tested foods. The duration of the epiglottic movement was approximately 0.3 s for liquids and slightly longer for solids. Because swallowing never occurred past an upright epiglottis, the results of this study do not support the hypothesis that adult animals maintain a patent airway during swallowing. Instead, the epiglottis in nonhuman mammals downfolds similarly to that of adult humans during swallowing. © 1996 Wiley-Liss, Inc.     

Biomechanics of failed deglutitive upper esophageal sphincter relaxation in neurogenic dysphagia

Our aims were to examine the etiology and biomechanical properties of the nonrelaxing upper esophageal sphincter (UES) and the relationship between UES opening and failed relaxation. We examined the relationships among swallowed bolus volume, intrabolus pressure, sagittal UES diameter, the pharyngeal swallow response, and geniohyoid shortening in 18 patients with failed UES relaxation, 23 healthy aged controls, and 15 with Zenker's diverticulum. Etiology of failed UES relaxation was 56% medullary disease, 33% Parkinson's or extrapyramidal disease; and 11% idiopathic. Extent of UES opening ranged from absent to normal and correlated with preservation of the pharyngeal swallow response (P = 0.012) and geniohyoid shortening (P = 0.046). Intrabolus pressure was significantly greater compared with aged controls (P < 0.001) or Zenker's diverticulum (P < 0.001). The bolus volume-dependent increase in intrabolus pressure evident in controls was not observed in failed UES relaxation. The nonrelaxing UES therefore displays a constant loss of sphincter compliance throughout the full, and potentially normal, range of expansion during opening. Adequacy of UES opening is influenced by the degree of preservation of the pharyngeal swallow response and hyolaryngeal traction. In contrast, the stenotic UES displays a static loss of compliance, only apparent once the limit of sphincter expansion is reached.     

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

The durations and temporal relationships of electromyographic activity from the submental complex, superior pharyngeal constrictor, cricopharyngeus, thyroarytenoid, and interarytenoid muscles were examined during swallowing of saliva and of 5- and 10-ml water boluses. Bipolar, hooked-wire electrodes were inserted into all muscles except for the submental complex, which was studied with bipolar surface electrodes. Eight healthy, normal, subjects produced five swallows of each of three bolus volumes for a total of 120 swallows. The total duration of electromyographic activity during the pharyngeal stage of the swallow did not alter with bolus condition; however, specific muscles did show a volume-dependent change in electromyograph duration and time of firing. Submental muscle activity was longest for saliva swallows. The interarytenoid muscle showed a significant difference in duration between the saliva and 10-ml water bolus. Finally, the interval between the onset of laryngeal muscle activity (thyroarytenoid, interarytenoid) and of pharyngeal muscle firing patterns (superior pharyngeal constrictor onset, cricopharyngeus offset) decreased as bolus volume increased. The pattern of muscle activity associated with the swallow showed a high level of intrasubject agreement; the presence of somewhat different patterns among subjects indicated a degree of population variance.     

Intrabolus pressure gradient identifies pathological constriction in the upper esophageal sphincter during flow

Propulsion of a bolus through the upper esophageal sphincter (UES) is driven by a pressure drop in the direction of flow against frictional resisting force. Basic mechanics suggest that the axial rate of drop in intrabolus pressure (IBP), i.e., the intrabolus pressure gradient (IBPG), should be locally sensitive to abnormal constriction. We sought to quantify space-time patterns of IBP and IBPG that correlate with pathological disruption to transsphincteric bolus transport. High-resolution high-fidelity perfused manometry was applied concurrent with videofluoroscopy in 6 healthy controls and 10 patients with restricted UES opening and 4 bolus volumes. Pressures were interpolated spatially and displayed as space-time isocontours with bolus head and tail trajectories superimposed to identify the IBP domain. IBP and IBPG were averaged over an approximately steady period of transsphincteric flow. The axial location and magnitude of maximum IBPG were quantified for each swallow relative to the location of the abnormal restriction. We found that average hypopharyngeal IBP and locally maximal IBPG were significantly higher in the patient group (P < 0.001), whereas the maximum IBPG was insensitive to bolus volume, and the locations of maximum IBPG in the patient group were well correlated with axial locations of maximal UES constriction (r = 0.84, P < 0.01). Space-time structure of IBP and IBPG correlated qualitatively with swallow dysfunction. Because IBPG reflects pressure force driving the bolus against frictional force in the UES, IBPG reflects local changes in frictional resistance from pathological constriction during bolus flow. Consequently, the location and magnitude of IBPG reflect the existence and location of abnormal constriction, and IBP and IBPG structure reflect decompensation of the pharyngeal swallow.     

Deglutitive upper esophageal sphincter relaxation: a study of 75 volunteer subjects using solid-state high-resolution manometry

This study aimed to use a novel high-resolution manometry (HRM) system to establish normative values for deglutitive upper esophageal sphincter (UES) relaxation. Seventy-five asymptomatic controls were studied. A solid-state HRM assembly with 36 circumferential sensors spaced 1 cm apart was positioned to record from the hypopharynx to the stomach. Subjects performed ten 5-ml water swallows and one each of 1-, 10-, and 20-ml volume swallows. Pressure profiles across the UES were analyzed using customized computational algorithms that measured 1) the relaxation interval (RI), 2) the median intrabolus pressure (mIBP) during the RI, and 3) the deglutitive sphincter resistance (DSR) defined as mIBP/RI. The automated analysis succeeded in confirming bolus volume modulation of both the RI and the mIBP with the mean RI ranging from 0.32 to 0.50 s and mIBP ranging from 5.93 to 13.80 mmHg for 1- and 20-ml swallows, respectively. DSR was relatively independent of bolus volume. Peak pharyngeal contraction during the return to the resting state postswallow was almost 300 mmHg, again independent of bolus volume. We performed a detailed analysis of deglutitive UES relaxation with a novel HRM system and customized software. The enhanced spatial resolution of HRM allows for the accurate, automated assessment of UES relaxation and intrabolus pressure characteristics, in both cases confirming the volume-dependent effects and absolute values of these parameters previously demonstrated by detailed analysis of concurrent manometry/fluoroscopy data. Normative values were established to aid in future clinical and investigative studies.     

The coordination and interaction between respiration and deglutition in young pigs

The anatomical pathways for inspired air and ingested food cross in the pharynx of mammals, implying that breathing and swallowing must be separated either in space or in time. In this study we investigated the time relationship between swallowing and respiration in young pigs, as a model for suckling mammals. Despite the high morphological position of the larynx in young mammals, allowing liquid to pass in food channels lateral to the larynx, respiration and swallowing are not wholly independent events. Although, when suckling on a veterinary teat, the swallows occurred at various points in the respiratory cycle, there was always a period of apnea associated with the swallow. Finally, an increase in the viscosity of the milk altered this coordination, changing respiratory cycle length and also restricting the relative rate at which swallows occurred in some parts of the respiratory cycle. These results suggest that the subsequent changes in respiratory activity at weaning, associated with passage of a solid bolus over the larynx, is preceded by the ability of the animal to alter coordination between respiration and swallowing for a liquid bolus. Accepted: 29 September 1997     

Ectoparasites cause increased bilateral asymmetry of naturally selected traits in a colonial bird

Abstract Parasitism has been shown to correlate with levels of bilateral symmetry in some organisms, with more asymmetric individuals often having more parasites. However, few studies have shown experimentally that parasitism directly causes increased asymmetry. By fumigating some cliff swallow (Petrochelidon pyrrhonota) colonies and leaving others untreated, we investigated experimentally whether ectoparasitism by the cimicid swallow bug led to higher levels of asymmetry in length of wings, outer tail feathers, and tarsus among juvenile and adult birds. Juveniles from fumigated colonies measured soon after fledging had significantly less asymmetry in wing and outer tail length than juveniles from nonfumigated colonies; asymmetry in tarsus length was unaffected by parasitism. Adults that had undergone one or more post‐juvenal molts on the wintering grounds showed no differences in asymmetry between those reared in fumigated vs. nonfumigated colonies. These results show that ectoparasitism directly leads to increased feather asymmetry in cliff swallows, probably through parasite‐induced nutritional stress. Because wing and tail asymmetry impair flight performance and reduce foraging efficiency, the increased asymmetry caused by parasites represents a fitness cost to cliff swallows. This is among the few experimental studies to show an effect of parasites on asymmetry of naturally selected characters.     

Physiology of the esophageal pressure transition zone: separate contraction waves above and below

Manometrically measured peristaltic pressure amplitude displays a well-defined trough in the upper esophagus. Whereas this manometric "transition zone" (TZ) has been associated with striated-to-smooth muscle fiber transition, the underlying physiology of the TZ and its role in bolus transport are unclear. A computer model study of bolus retention in the TZ showed discoordinated distinct contraction waves above and below. Our aim was to test the hypothesis that distinct upper/lower contraction waves above/below the manometric TZ are normal physiology and to quantify space-time coordination between tone and bolus transport through the TZ. Eighteen normal barium swallows were analyzed in 6 subjects with concurrent 21-channel high-resolution manometry and digital fluoroscopy. From manometry, the TZ center (nadir pressure amplitude) and the upper/lower margins of the pressure trough were objectively quantified. Using fluoroscopy, we quantified space-time trajectories of the bolus tail and bolus tail pressures and maximum intraluminal pressures proximal to the tail with their space-time trajectories. In every swallow, the bolus tail followed distinct trajectories above/below the TZ, separated by a well-defined spatial "jump" that terminated an upper contraction wave and initiated a lower contraction wave (3.32 +/- 1.63 cm, P = 0.0004). An "indentation wave" always formed within the TZ distal to the upper wave, increasing in amplitude until the lower wave was initiated. As the upper contraction wave tail entered the TZ, it slowed and the tail pressure reduced rapidly, while indentation wave pressure increased to normal tail pressure values at the initiation of the lower wave. The TZ was a special zone of segmental contraction. The TZ is, physiologically, the transition from an upper contraction wave originating in the proximal striated esophagus to a lower contraction wave that moves into the distal smooth muscle esophagus. Complete bolus transport requires coordination of upper/lower waves and sufficient segmental squeeze to fully clear the bolus from the TZ during the transition period.     

The impact of continuous positive airway pressure on the lower esophageal sphincter

The lower esophageal sphincter (LES) is the primary barrier to gastroesophageal reflux. Reflux is associated with periods of LES relaxation, as occurs during swallowing. Continuous positive airway pressure (CPAP) has been shown to reduce reflux in individuals with and without sleep apnea, by an unknown mechanism. The aim of this study was to determine the effect of CPAP on swallow-induced LES relaxation. Measurements were made in 10 healthy, awake, supine individuals. Esophageal (Pes), LES (Ples), gastric (Pg), and barrier pressure to reflux (Pb = Ples - Pg) were recorded using a sleeve catheter during five swallows of 5 ml of water. This was repeated at four levels of CPAP (0, 5, 10, and 15 cmH(2)O). Pressures were measured during quiet breathing and during the LES relaxation associated with a swallow. Duration of LES relaxation was also recorded. During quiet breathing, CPAP significantly increased end-expiratory Pes, Ples, Pg, and Pb (P < 0.05). The increase in Pb was due to a disproportionate increase in Ples compared with Pg (P < 0.05). During a swallow, CPAP increased nadir Ples, Pg, and Pb and decreased the duration of LES relaxation (4.1 s with 0-cmH(2)O CPAP to 1.6 s on 15-cmH(2)O CPAP, P < 0.001). Pb increased with CPAP by virtue of a disproportionate increase in Ples compared with Pg. This may be due to either reflex activation of LES smooth muscle, or nonspecific transmission of pressure to the LES. The findings suggest CPAP may make the LES less susceptible to reflux by increasing Pb and decreasing the duration of LES relaxation.     

Model-based optimal PEEP in mechanically ventilated ARDS patients in the Intensive Care Unit

Background

Swallowing accelerometry has been suggested as a potential non-invasive tool for bedside dysphagia screening. Various vibratory signal features and complementary measurement modalities have been put forth in the literature for the potential discrimination between safe and unsafe swallowing. To date, automatic classification of swallowing accelerometry has exclusively involved a single-axis of vibration although a second axis is known to contain additional information about the nature of the swallow. Furthermore, the only published attempt at automatic classification in adult patients has been based on a small sample of swallowing vibrations.

Methods

In this paper, a large corpus of dual-axis accelerometric signals were collected from 30 older adults (aged 65.47 ± 13.4 years, 15 male) referred to videofluoroscopic examination on the suspicion of dysphagia. We invoked a reputation-based classifier combination to automatically categorize the dual-axis accelerometric signals into safe and unsafe swallows, as labeled via videofluoroscopic review. From these participants, a total of 224 swallowing samples were obtained, 164 of which were labeled as unsafe swallows (swallows where the bolus entered the airway) and 60 as safe swallows. Three separate support vector machine (SVM) classifiers and eight different features were selected for classification.

Results

With selected time, frequency and information theoretic features, the reputation-based algorithm distinguished between safe and unsafe swallowing with promising accuracy (80.48 ± 5.0%), high sensitivity (97.1 ± 2%) and modest specificity (64 ± 8.8%). Interpretation of the most discriminatory features revealed that in general, unsafe swallows had lower mean vibration amplitude and faster autocorrelation decay, suggestive of decreased hyoid excursion and compromised coordination, respectively. Further, owing to its performance-based weighting of component classifiers, the static reputation-based algorithm outperformed the democratic majority voting algorithm on this clinical data set.

Conclusion

Given its computational efficiency and high sensitivity, reputation-based classification of dual-axis accelerometry ought to be considered in future developments of a point-of-care swallow assessment where clinical informatics are desired.     

The incidence of American swallow bugs (Oeciacus vicarius) in barn swallow (Hirundo rustica) colonies in northeast Texas

The American swallow bug (Oeciacus vicarius) is an important ectoparasite of cliff swallows (Petrochelidon pyrrhonota) and is known to harbor several types of arbovirus. A recent study in northeast Texas suggested that O. vicarius might occur in barn swallows (Hirundo rustica) at rates much higher than previously thought. The purpose of this study was to determine the extent to which barn swallows in northeast Texas are parasitized by O. vicarius and how well this parasite is adapting to this novel host. A sample of 498 nests at 54 colonies was inspected for O. vicarius. Forty colonies (74.1%) were infected, while 310 nests (62.2%) were infected. Large colonies were more likely to be infected than small colonies. Colonies that also contained cliff swallows were more likely to be infected than colonies without cliff swallows. Infection levels in barn swallow nests were comparable to those reported for cliff swallows, though age and sex class ratios differed. Demographic changes among swallow species, including range expansions, increased colony sizes, and more frequent interspecific nesting associations have likely facilitated the movement of O. vicarius from the cliff swallow into a novel host, the barn swallow.