HSC Section 6 Nov2016 Green Book

Annals of Otology, Rhinology & Laryngology 123(4)

is to be determined with any degree of accuracy. In fact, intensity would be expected to contribute to changes in the RMS value of the LEMG signal. A near linear relationship between muscle force and EMG activity has been found in classic EMG studies. 22-24 Although EMG does not measure muscle force directly, vocal intensity can be viewed as a global indicator of performance effort and muscle loading on the vocal apparatus. It was not surprising, then, that con- trolling for intensity revealed changes in our calculated RMS values. It has been previously demonstrated that both intensity and vocal frequency contribute to variability in quantita- tive LEMG output with frequency being the greater factor in TA recruitment variability, suggesting the need for con- trol of both parameters for improved clinical assess- ment. 25,26 In this study, participants were generally able to maintain and regulate the intensity of their vocalization constant at 65 dB across all trials. Although participants were trained to reach the 75 dB target, many could not produce this intensity level consistently for 1 second with the LEMG needle in place. In the 75 dB condition, inten- sity levels actually ranged from 66.70 dB to 75.22 dB with a mean value of 70.42 dB. Thus, it can be inferred that not only does intensity play a role in LEMG signal stability but relatively small changes in intensity level (approxi- mately 5 dB) can strongly affect RMS values, further arguing for the need and importance of regulating vocal intensity during LEMG diagnostics. Limitations The small sample size of 7 participants in this repeated mea- sures study limits the ability to generalize our results to a larger clinical population. Changes in vocal intensity were limited to a 10 dB interval. Larger intensity intervals and addi- tional participant data may better demonstrate differences in mean RMS values across testing conditions. The standard deviations of the RMS values in this study were large. This is an inherent problem with attempting to quantify LEMG because it is difficult to determine which variable(s), such as ambient noise, movement artifact, interpersonal differences in phonation, and so on, may be causing deviations in the sig- nal. 11,27 Needle electrodes, as used in this study, have been shown to demonstrate greater artifact at greater intensities. 28 Movement/vibration artifact cannot be alleviated but is a con- cern because of the unsteadiness of the needle electrode and the vibration of the vocal fold mucosa. Asolution to this prob- lem may be to consider the use of hooked wire electrodes in clinical LEMG studies to ameliorate these concerns. Clinical Relevance and Future Directions The results of this study demonstrate that even during con- trolled laboratory conditions, the LEMG signal appears

Figure 1.  Interval plot with the mean of each data set presented with 95% confidence bars. The x-axis is scaled with regard to intensity and testing session. The y-axis for root mean square (RMS) is scaled in microvolts.

RelaƟonship between Session 1 & 2

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R² = 0.047

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Figure 2.  Scatter plot for voice task at the 65 dB target between sessions 1 and 2. These sessions represent the most consistent data from this study. Data points are mean root mean square (RMS) values in µV for each participant. The R 2 value does not indicate a strong association between the data for the 2 sessions. Approximately 5% of the data from Session 1 can be explained by Session 2. been suggested that additional evidence-based research concerning LEMG methodology and validity be con- ducted. 8 Data from this study suggest that variables such as data collection time (multiple sessions) and possibly vocal intensity may play a role in the outcomes of LEMG assess- ment, suggesting methodological limitations of LEMG in terms of its clinical accuracy. Our results indicated that to be 95% confident that a true detectable change could be observed between testing ses- sions, a change of 51 µV RMS was necessary with intensity level held constant. It is likely, then, that uncontrolled vocal intensity during LEMG procedures may operate as a con- founding variable. Careful regulation of vocal intensity dur- ing LEMG may be necessary if the clinical utility of LEMG

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