This is the first study using HRM to evaluate effortful swallow and the Mendelsohn maneuver. We also employed novel analysis techniques which take advantage of the multi-sensor array capabilities of HRM to better capture the complexity of pressure events, area integrals, line integrals, and pressure wave velocity. Both maneuvers elicited changes in pressure patterns in the pharynx, but these patterns were specific to the maneuver. The effects of effortful swallow were observed primarily at the velopharynx and UES, and not in the region of the tongue base. Effortful swallows displayed increased pressure wave velocity and area and line integrals. Widespread effects throughout the pharynx were observed for the Mendelsohn maneuver, including the tongue base. The Mendelsohn maneuver also yielded significantly longer velopharyngeal pressure duration and increased velopharyngeal area and line integrals.
Several effects previously reported using traditional manometry were also observed in this study. The Mendelsohn maneuver decreased UES pressure (8
) and increased duration of velopharyngeal pressure, likely attributable to prolonged laryngeal elevation (3
). In contrast to previous reports (1
), a decrease in tongue base pressure occurred with effortful swallow, though this decrease was not significant. This was accompanied by an increase in total pressure generated in the velopharynx. Decreased tongue base pressure could be attributed to increased hyoid movement occurring with the increased muscle contraction during effortful swallow, but we did not directly measure this. Theoretically, this would increase the volume of the oropharynx and consequently decrease pressure measured in the area of the tongue base. As structures of the pharynx are mobile during swallowing, previous investigations using single sensors may have recorded increased velopharynx pressure as an increase in tongue base pressure.
We also found changes in pressure patterns that have not been previously reported. Both maneuvers increased minimum UES pressure, though neither increase reached statistical significance. As laryngeal elevation creates a negative pressure vacuum in the UES, one could expect that the prolonged laryngeal elevation in the Mendelsohn maneuver may actually further decrease this negative pressure in normal swallows. However, increased pressure at the velopharynx created by either maneuver could require less negative pressure necessary at the bolus head to ensure safe bolus transit into the esophagus. Maximum pre-opening and post-closure UES pressures were also affected, with pre-opening pressure decreasing and post-closure pressure increasing with both maneuvers. These changes were more pronounced with the Mendelsohn maneuver, where significantly decreased pre-opening and increased post-closure pressure (not significant) were observed. Trends were not as evident for the effortful swallow. Each of these effects on UES pressure would facilitate safe bolus transit, as decreased pre-opening pressure would provide less resistance to bolus passage into the esophagus while elevated post-closure pressure would prevent reflux. As maneuvers tend to require significant effort and modification of the swallow pattern, multiple aspects of the pharyngeal swallow can be modulated (23
The integral measurements used in this study demonstrated significant changes across tasks that were not revealed by traditional measurements of maximum pressure or duration of pressure above baseline. For example, though maximum velopharyngeal pressure was not affected by the Mendelsohn maneuver, obvious differences were observed for the area and line integrals. As integrals consider the entire shape of the pressure curve, they may be a more sensitive measurement than maximum pressure alone. Though only two-dimensional integrals were recorded in this study, considering the volume enclosed by three-dimensional pressure curves in regions of interest may provide an even more comprehensive characterization of the pharyngeal swallow.
Nadir UES pressure duration may be particularly valuable when evaluating swallowing maneuvers. As maneuvers are designed to improve bolus passage and passage can only occur through a patent UES, measuring the duration of UES patency, or duration of lowest measured UES pressure, may provide insight into why a maneuver is or is not successful. It is important to use this measurement in context, as a nadir pressure very near resting pressure, no matter how long in duration, will not contribute to bolus passage. Considering nadir UES pressure duration in the context of what that pressure is may be useful from a clinical and research standpoint.
There were three limitations to this study. First, while several significant differences could be observed between maneuvers, the sample size was relatively small. Findings that approached, but did not reach significance may do so with a larger sample size. Second, it is possible that the use of topical anesthesia affected our experimental measurements. In pilot experiments without topical anesthesia, subjects found it difficult not to gag and also displayed resting cricopharyngeal hypertonicity, both of which could confound data collection. While impairing afferent nerves in the pharynx could alter swallowing physiology, mechanoreceptors deep to the mucosa are largely responsible for modulating swallowing physiology (24
) and these fibers were likely unaffected by the anesthetic. Also, the oral mucosa was not greatly affected and afferent information from this region is important in swallowing physiology. Though we feel the benefits of increased subject comfort outweigh the cost of short-term pain and temperature afferent alteration, conducting an experiment to determine the quantitative effect of anesthetic may be beneficial. Lastly, this study was conducted in healthy subjects. Evaluating the effect of these maneuvers in dysphagic patients using HRM will be the subject of future studies. Specifically, it would be interesting to determine if the relationships among velopharyngeal, tongue base, and UES pressure during effortful swallow are upheld in patients with tongue dysmotility. Further developing the novel parameters used in this study, such as area and line integrals, will also be investigated.
Similar to our previous study on head turn and chin tuck (15
), effects were observed primarily at the velopharynx and UES. Proper muscular function in these two regions may be most critical to successful bolus passage and may also be easier to manipulate than the tongue base. Effortful swallow was introduced for patients with reduced tongue base retraction, but conflicting results on the biomechanical effects of this maneuver have been reported (25
). Rather than normalizing tongue base function in patients with tongue dysmotility, effortful swallow may promote elevated velopharyngeal pressure which can overcome low tongue base pressure. This also leads to increased hyolaryngeal excursion, which enhances UES opening. Effortful swallow, then, is a floor of mouth event rather than a base of tongue event. This hypothesis was supported not only by increases in velopharyngeal pressure, but also by decreased tongue base pressure in our measurements. Decreased pre-opening UES pressure observed in this study would also promote bolus passage, as less resistance would be encountered at the UES. While success of the maneuver has previously been attributed to improved posterior tongue base motion (2
), it may due to the elevated velopharyngeal and decreased UES pressures creating a favorable pressure gradient for bolus transit. The benefit of this gradient likely manifested in increased velocity of the traveling pressure wave that we observed.
HRM revealed several physiologic modifications that have not been previously reported. Our novel analysis techniques using area and line integrals as well as pressure wave velocity demonstrated prominent changes at the velopharynx and UES, with little effect at the tongue base. These findings increase our understanding of how effortful swallow and the Mendelsohn maneuver improve swallowing in dysphagic patients and may be used to enhance these maneuvers.