Simultaneous Data Acquisition in Multiple Modalities: Videofluoroscopy, EMG and Tongue Pressure

This application note describes a protocol developed to collect simultaneous videofluoroscopic images, submental surface EMG and tongue pressure data. Time-linking these events allows investigation of the inter-relationships among oropharyngeal events visible on video, activation of the suprahyoid and floor-of-mouth muscles, and tongue function. Protocols for collection of these data are described.

Note that throughout this document, the term "individual" will be used, rather than "subject" or "patient", as this protocol can be used for either a clinical or a research application.

In the Veteran’s Administration/University of Wisconsin (VA/UW) Swallowing Research Laboratory, under the direction of JoAnne Robbins Ph.D., the Kay Elemetrics Swallowing Workstation, Model 7100, is used to collect multiple levels of physiologic swallowing data simultaneously. The time-locked physiologic data include videofluoroscopic images, EMG from surface electrodes, and tongue pressure.

DATA COLLECTION

Pressure Data

Tongue pressure data are obtained from a silica strip containing three small air-filled bulbs, which provide pressure data via a transducer. The three pressure-sensing bulbs are each 13 mm in diameter, and are spaced 8 mm apart on the strip. This strip is placed along the midline of the palate, so the anterior bulb rests close to the alveolar ridge, the medial bulb rests along the midline of the hard palate, and the posterior bulb rests near the posterior edge of the hard palate, near the junction of hard and soft palate. Precise locations are dependent on the length and shape of the individual’s hard palate.

Electromyography (EMG) Data

Surface electrodes (Kay item #7179-0025) are placed on the individual’s left upper lip (used as a control) and submentally, as well as a ground electrode placed on the forehead. The submental electrodes are placed to the left and right of the midline on the underside of the chin. The specific placement is determined by having the individual press the tongue to the hard palate, and palpating the tensed geniohyoid, mylohyoid and ABD muscles. One surface electrode is then placed along the tensed muscle on either side of midline. The submental EMG tracings are presumed to indicate activation of the suprahyoid and floor-of-mouth muscles associated with laryngeal excursion during the pharyngeal stage of the swallow.

Videofluoroscopic Data

In order to collect videofluoroscopic data, the Kay Swallowing Workstation is transported from the Swallowing Lab to GI Radiology, where it is interfaced with the GE fluoroscopy unit and an external videocounter timer. This external timer is necessary because the time code used by the Kay Swallowing Workstation does not appear on the videotape recording, and is, therefore, not available when the videotape is viewed on other equipment.

The videofluoroscopic equipment is controlled by a radiologist, and is interfaced with the Kay Elemetrics Swallowing Workstation using standard video connectors and an external videocounter. The video output usually obtained with videofluoroscopy is connected to the external videocounter, which in turn is connected to the video source plug on the Kay Swallowing Workstation. Data are collected by the research speech pathologist and the radiologist working in concert. Images are in the lateral projection, at Mag 12.

Setup/Organization of Information

Two screen setups were customized for the protocols described later. The first setup, for use when no video data are collected, is illustrated in Figure 1. The two EMG tracings are on top, and the three tongue pressure tracings are immediately beneath. All of the windows have the same time display, so that the relation between the tracings, relative to time, may be easily seen.

Figure 1 - Screen Setup for Protocol 1

The second screen setup, for use when videofluoroscopic data are collected along with EMG and tongue pressure data, is illustrated in Figure 2. The video image is in the upper 2/3 of the left side of the screen. The two EMG channels are displayed along the far right edge of the screen, and the three tongue pressure tracings are found along the bottom of the screen, from left to right. This allows all data to be viewed simultaneously, and facilitates linking the video images with the various other data.

Figure 2 – Screen Setup for Protocol 2

Procedure

1. All data collection devices are prepared and placed appropriately on the individual. After placement, but before data collection is attempted, the tongue bulbs are calibrated, using the procedures outlined in the Kay Elemetrics Swallowing Workstation manual.

2. An attempt is made to elicit maximum performance from the individual, to determine the appropriate full-scale settings for each channel of data. If peak clipping or performance near the top of the scale is observed, the full-scale range is adjusted for that channel, to avoid peak clipping during actual data collection. These tasks are used only for gain setting, and the results are not saved for further analysis.

3. Protocols

Protocol 1: The first protocol is used to evaluate maximum tongue pressure and EMG activity exerted in a relatively static task, and during saliva swallows.

1. The individual is asked to exert maximum pressure on one designated bulb at a time. The pressure is maintained for several seconds, and then released.
2. Following a pause of 6-8 seconds, the individual is asked to repeat the task.
3. Pressure is exerted on each bulb three times, before proceeding to the next bulb.
4. Once the individual has performed this task on all three tongue bulbs in isolation, s/he is asked to exert maximum pressure on all three bulbs simultaneously. This task is also repeated three times, with a 6-8 second pause between successive efforts.
5. When this portion is complete, the individual is asked to swallow saliva. This is also done three times, with at least 8 seconds between swallows.

One difficulty noted on this protocol is that a number of individuals performing these tasks had noticeable difficulty isolating the most posteriorly-placed tongue bulb. When this was observed, the individual was given specific instruction and training to assist in performing this task.

 

Protocol 2: The second protocol is used to evaluate the tongue pressures and EMG tracings associated with swallows of various bolus sizes and consistencies of material. In addition, there are two trials of a "hard swallow", where the individual is instructed to swallow as hard as s/he can. No specific instructions are given to the individual on how to achieve this. Videofluoroscopic recording of the swallows are acquired at the same time, also using the Kay Elemetrics Swallowing Workstation.

These data are used to evaluate the tongue pressures and muscle activation that are associated with swallowing in different conditions, and to examine more specifically the pressure and EMG data that are associated with particular videofluoroscopic events during the oropharyngeal swallow. This protocol is described in detail below:

1. The individual is seated in a narrow, armless chair, as is typically used for videofluoroscopic swallowing evaluation. The Kay Swallowing Workstation is placed to the right of the individual, where both the radiologist and the speech pathologist administering the boluses can see the display.
2. The video image is centered on the screen, and a specially designed brass shield is taped onto the fluoro unit, positioned to dampen the effects of the very white airspace inferior to the mandible and anterior to the neck, thereby improving contrast. The image is checked to verify that no anatomic structures are blocked.
3. Before the protocol is run with the tongue pressure bulbs in place, the individual is asked to press with his/her tongue on each bulb. This is done to verify that none of the bulbs have become de-pressurized.
4. The tasks for this protocol consist of three swallows each of 3 cc of liquid, 10 cc of liquid, and 3 cc of semisolid. In addition, the individual is asked to swallow two 3 cc boluses of liquid, while using maximal effort (i.e., a "hard swallow"). The order of these four tasks is randomized, though each group or condition of 2 or 3 swallows is kept together.
5. For each swallow, with the exception of "hard swallows", the individual is instructed to hold the bolus in his/her mouth until given the verbal instruction to swallow, and then to swallow in a normal fashion.
6. Prior to administration of the boluses for the hard swallows, the individual is given verbal reminders to exert maximum pressure, and verbal encouragement is provided during the swallow. The individual’s self-report is accepted as to whether maximum effort was used.
7. There is pause of approximately 8-10 seconds between each swallow in a group, and 20-25 seconds between groups.
8. If the videofluoroscopic image is incomplete, the swallow is repeated. The image can be incomplete if the individual begins to swallow the bolus before the fluoroscope is turned on. Aspiration, gagging, coughing, or other similar events do not warrant repetition of the swallow.
9. This sequence of tasks is performed twice by each individual; once with the tongue bulbs in place, and once without the tongue bulbs. The sequence of these two conditions is also randomized.

4. At the end of each protocol, the individual is asked to hold his/her mouth open, to determine the zero-point for each of the tongue bulbs. Since this point is generally not 0.00, this assists in maintenance of accurate measures of the pressures exerted on each bulb.

DATA ANALYSIS

Our initial work with the Kay Elemetrics Swallowing Workstation, Model 7100, was an effort to determine the impact of the bulb strip on oropharyngeal swallowing. To this end, videofluoroscopic and EMG swallowing data were obtained from 12 individuals (6 young and 6 old, with each group gender-balanced). The protocol for these 12 individuals included 3 trials each of a variety of bolus sizes and consistencies, in each of two conditions: 1) with the bulb strip in place, and 2) without the bulb strip in place. The pilot work allowed us to determine that the presence of the bulb strip did not have any significant effect on oral and pharyngeal swallowing as measured by temporal and amplitude aspects of the EMG signal. There may, however, be an increase in the frequency and amount of residual material in the oral cavity as a result of the presence of these bulbs1.

The data collected during the first protocol described above are used to evaluate maximum tongue pressures that individuals are able to generate, and examines this as a function of age. Further, the pressure that the individual generates during a typical swallow can be compared to the maximum pressures generated, to determine to what extent swallowing utilizes maximum pressures available.

The data are analyzed along a variety of parameters, including EMG tracing, tongue pressure tracings from each of the three tongue bulbs, and videofluoroscopic recording of the swallowing tasks. The tracings from the EMG leads and the tongue bulbs are analyzed using various software on other computer systems. For this to be possible, the data must be extracted and decoded into a form that can be imported by graphics or spreadsheet computer software programs for interpretation.

The Kay Elemetrics Swallowing Workstation enables us to time-link and compare the muscle activity reflected in the submental EMG tracings, which is presumed to indicate activation of the suprahyoid and floor-of-mouth muscles, with pressure exerted by the tongue on the roof of the mouth during the course of bolus manipulation and retropulsion, and muscle activation associated with laryngeal excursion during the pharyngeal swallow. In addition, these data can be compared and time-linked with events identified on the videofluoroscopic recording of the swallow.

A portion of the EMG tracing from the submental electrodes is selected, based on analysis of the videotape. The specific portion that is used is from 1.5 seconds before the beginning of hyoid movement associated with a swallow, to 1.5 seconds after this point, yielding a tracing that is 3 seconds in duration. A number of these tracings are compared, and a time series analysis is used, as one means of evaluating the effects of bolus size and type on swallowing function1. This analysis is not done using the Kay Elemetrics Swallowing Workstation. Rather, the waveform data are extracted using software written at this facility, and analyzed using commercially available statistical software packages. (Note: The most recent software version released by Kay contains a built-in utility for easily exporting raw waveform data and images.)

Tongue pressures are also analyzed, in several ways. One analysis, using the Kay Elemetrics Swallowing Workstation, involves examination of the correlation between pressure peaks on the different bulbs and certain events during the swallow (e.g., beginning of posterior bolus movement). The videotape is used in conjunction with this analysis to select appropriate segments to examine. Segments are selected on the basis of the videotape information to include bolus manipulation and posterior movement of the bolus into the pharynx. In addition, the videotape image is examined at pressure peaks for each bulb, to correlate movements of the bolus and/or the oral and pharyngeal structures involved in swallowing with these pressure peaks. The feature allowing the cursor placement to be linked to a specific video frame is essential to this analysis.

One way that events are compared involves the use of tags. Once the timing of a particular event is determined, based on pre-established criteria and descriptions, a tag is placed at the point corresponding to that reading on the videotape’s external timer. The time-code on the videotape allows this tag to appear on all other channels of recorded data (EMG and tongue pressure) tracings, so that the precise EMG and pressure values that co-occur with the videofluoroscopic event can be determined.

Further analysis of tongue pressure tracings involves examination of the entire pressure tracing associated with a swallow for each bulb. The total area is closely approximated: to compare the total pressure generated during the swallow with the peak pressure generated, and evaluate changes that occur across age groups. This calculation is done using commercially available software on a PC after the waveform had been extracted from the stored data set.

The Kay Elemetrics Swallowing Workstation, Model 7100, allows the time-linked comparison of swallowing data from a variety of modalities, yielding a more complete and integrated picture of the complex process of swallowing.

_________________________________

Goodman, B.M., Robbins, J., Wood, J., Dengel, G., and Luschei, E. Influence of Intra-Oral Pressure Sensors on Normal Swallowing Patterns as Measured by Submentally Located Surface Electromyography. Presented at the Fifth Annual Scientific Meeting, Dysphagia Research Society, Aspen, Colorado. October 31-November 2, 1996.

Work is supported by the Geriatric Research, Education and Clinical Center, Madison, WI, and NIH grant NS24427. This is manuscript number 97-17 of the Madison GRECC.

Appreciation to Dr. Erich Luschei for his consultation during this work and to lab members Deb Brauer, Gail Dengel, and Jackie Hind for their assistance in conducting this work and writing this document.