The use of surface electromyography in dysphagia evaluation

Abstract

Dysphagic patients usually have a variety of clinical problems such as malnutrition, significant weight loss, and aspiration pneumonia. Dysphagia is a complication commonly caused by strokes, and surface electromyography (sEMG) provides a simple, non-radioactive, and non-invasive method to measure the patterns of muscle activity during swallowing, allowing clinicians to describe the physiology of swallowing behavior. Most previous studies have described swallowing behavior in terms of amplitude and duration. However, there is no objective and precise approach available for the evaluation of swallowing coordination. In order to evaluate swallowing coordination more precisely, a wireless and wearable monitoring device for dysphagia evaluation was designed for the present study in order to measure four muscle groups simultaneously during swallowing. In this context, the variations of the cross-correlation coefficients were defined as the discoordination index, a metric which can effectively reflect the differences between the surface EMG patterns of the bilateral muscle groups. The experimental results of this study show that the discoordination indices for dysphagic patients are significantly larger than those for healthy subjects and that these discoordination indices can be used as an effective means of evaluating the coordination between bilateral swallowing muscles.

Keywords

Surface electromyography dysphasia evaluation medical device swallowing

1. Introduction

Dysphagia denotes a swallowing malfunction that is commonly caused by muscular disorders, structural lesions, strokes, and other central neurological impairments [1]. Every year, in the North of America, especially in United States, about 16 million patients are affected by this disease [2]. Clinically, stroke is the most common cause of dysphagia. The incidence of dysphagia after stroke is about 23% to 50%, and about 30% of patients with unilateral stroke also suffer from it [3]. In these patients, malnutrition, dehydration, and aspiration pneumonia can occur and lead to serious medical consequences [4, 5].

Dysphagia also causes dramatic impairments to quality of life because it prevents patients from interacting with others during mealtimes. Therefore, it is critical to identify and ameliorate the effects of dysphagia as much as possible. A video fluoroscopic swallowing study (VFSS) is the evaluation tool most commonly used to locate structural lesions and swallowing disorders in the pharyngeal, oral, and esophageal phases in order to make a diagnosis of dysphagia [6, 7, 8].

However, VFSS has disadvantages in terms of cost and radiation issues. These years, swallowing studies has been extensively developed by the utility of surface electromyography (sEMG). sEMG is a easy way, with non-radioactive, and non-invasive screening tool to measure the activity patterns of various muscles during swallowing, that making it suitable for identifying the occurrence of swallowing and for describing the physiology of swallowing. Swallowing is a complex process involving the coordination of various muscle groups [9, 10]. It can be observed and quantified by using sEMG with the patterns of specific muscle activities during swallowing.

In this article the design of a wireless and wearable monitoring device for the evaluation of dysphagia is described that allows to analyse the swallowing coordination of dysphagic patients with unilateral stroke more precisely. In order to measure four muscle groups simultaneously during swallowing behaviour, cross-correlation coefficients [11, 12, 13] were used to determine the correlations between the sEMG patterns of bilateral muscle groups (i.e., the masseter, orbicularis oris, submental muscle groups, and laryngeal strap muscles) during swallowing. This study showed the discoordination indices of dysphagic patients in comparison with and healthy subjects.

2. Presentation of process and device

In Fig. 2 a photograph of the proposed wireless and wearable monitoring device for dysphagia evaluation is shown. The device mainly consists of a wireless multi-channel bio-signal acquisition module, a mechanical design, sEMG electrodes, and a back-end host system.

Figure 1.

Photograph of proposed wireless and wearable monitoring device for dysphagia evaluation.

Figure 2.

Illustration of Block diagram for the proposed wireless multi-channel bio-signal acquisition module.

Figure 2 exhibits a function block diagram of the proposed wireless multi-channel bio-signal acquisition module. The module includes several parts: a microprocessor unit, front-end bio-amplifiers, and a wireless transmission circuit. A 12-bit analog-to-digital converter built in the microprocessor unit digitizes the signal with a sampling rate of 2000 Hz, and the microprocessor pre-processes the signal to remove low frequency interference. Next, the front-end bio-amplifiers were designed to amplify and filter the sEMG signals. It mainly contains a pre-amplifier and a band-pass filter. The total gain of each front-end bio-amplifier was set to 5000 times with a frequency band of 100 Hz–1000 Hz. Each sEMG signal acquired from the sEMG electrodes is amplified by the front-end bio-amplifiers. Next, the sEMG signal is sent to the wireless transmission module, from which it is transmitted wirelessly to the back-end host system. The wireless transmission module is fully compliant with the Bluetooth v2.0 $+$ EDR specification.

Figure 3.

Surface EMG signals and cross-correlation coefficient of (a) OO, (b) MS, (c) SUB, and (d) LSM obtained from one of healthy subjects.

3. Results and discussions

In this section, the relationship between the discoordination index and the swallowing activity for different cases were investigated. Figure 3 shows the results of the bilateral integrated sEMG signals of the OO, MS, SUB, and LSM and their discoordination indices for one of the healthy participants. The subject was a 62-year-old male who had no medical history of neuromuscular disorder and had not undergone head and neck surgery. The subject was instructed to swallow 10 mL of water. The right-side sEMG amplitudes (OO $=$ 11.84 $\mu$ V, MS $=$ 11.08 $\mu$ V, SUB $=$ 14.86 $\mu$ V, and LSM $=$ 16.15 $\mu$ V) were similar to those of the left-side sEMG (OO $=$ 10.63 $\mu$ V, MS $=$ 11.37 $\mu$ V, SUB $=$ 16.93 $\mu$ V, and LSM $=$ 16.66 $\mu$ V). Here, the amplitude of sEMG was defined as the averaged RMS value of sEMG from onset point to offset point. And the latencies of the bilateral sEMG for OO, MS, SUB, and LSM were close to each other. The discoordination indexes for OO, MS, SUB, and LSM were 4.77, 29.39, 2.74, and 8.75 respectively. However, the amplitude of the unaffected-side sEMG of the MS (15.35 $\mu$ V) was obviously larger than that of the affected-side sEMG (9.87 $\mu$ V). Moreover, the difference between the offset points of the bilateral OO sEMG (1.15 seconds) was significant. In addition, the waveforms of the bilateral OO sEMG were obviously different from each other. Here, the discoordination indexes for the OO, MS, SUB, and LSM were 1115.20, 30.03, 4.89, and 2.36, respectively.

4. Conclusion

In this study, the proposed monitoring device was designed and implemented to continuously monitor four muscle patterns under swallowing. In addition, a novel approach consisting of the use of cross-correlation coefficients was proposed to compare the coordination of the bilateral muscle groups for dysphagic patients with unilateral stroke with the coordination of the same muscle groups in healthy adults.

The experimental results showed that, under different swallowing conditions, the discoordination indices of the OO, MS, and SUB muscle groups for dysphagic patients were significantly larger than those for healthy subjects. In contrast with other previous studies that used the terms of amplitude and latency to describe swallowing coordination, the proposed approach can provide more detailed information regarding swallowing coordination.

Conflict of interest

None to report.

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