An Air Pocket Glove for Finger Rehabilitation and Quantitative Assessment of Hemiplegic Patients

1. Introduction

70% of hemiplegic stroke patients suffer from upper limb impairment, and upper limb rehabilitation is closely related to ADL function recovery.^1,2 Among other body parts, hands are densely packed with joints and nerves, making the most diverse and delicate movements.³ Finger rehabilitation of hemiplegic patients is practiced to relax stiffened fingers to increase function and ultimately to perform daily life behaviors.

Many finger rehabilitation exercises and diagnosis standards have been proposed as the necessity of finger rehabilitation was proved through various clinical studies. Patients who participated in Activity Card Sort (ACS) rehabilitation improved their leisure activity participation level in Functional Independence Measure (FIM) evaluation^4,5, and rehabilitation through the Box and Block Test (BBT) increased the finger dexterity and affected overall upper extremity function.^6,7 Furthermore, hemiplegic patients after finger rehabilitation showed higher independence and their Reintegration to Normal Living Index (RNLI) results represented positive satisfaction with life.^8,9 In addition to traditional occupational therapy, end-effector and exoskeleton devices have been developed for finger rehabilitation, and they are capable of high-dosage and high-intensity rehabilitation.¹⁰ Patients who were rehabilitated with physical therapy and rehabilitation orthosis showed higher functional restoration efficiency than rehabilitation only with physical therapy.^11-13

Fig. 1

Components of the air pocket glove, operation principle and overall manufacturing process

However, existing rehabilitation methods (occupational or physical therapies) are mostly simple repetitive exercises. In this case, it weakens the patient’s concentration. In addition, it is difficult to induce patient’s participation because it does not include patient’s intent and motivation during the exercise.¹⁴ In robotic rehabilitation, the movement of the orthosis is implemented along the direction of muscle contraction (flexion). But in actual rehabilitation field, exercises are performed toward extension motions because to relax muscles and joint spasticity.^15,16 At last, the components of the traditional devices are developed based on the rigid body, and include a linkage that acts as rotation joint of finger. Linkage has a complicated structure that makes it difficult to match the finger joints with the device joints, and it is difficult to conduct independent rehabilitation due to the material limitations.¹⁷

In this study, we propose an air pocket glove to assist the finger rehabilitation of stroke patients with limited finger movement. air pocket glove is a wearable- type that easy to don and doff, and soft finger movements are implemented using air pocket-type soft actuator with biomimetic technology. It also behaves in an extension direction similar to actual rehabilitation, allowing grip and release, and flexible operation.

This device has two modes for effective rehabilitation: Continuous Passive Motion (CPM) mode and master-slave mode. CPM exercise helps restore motor function and proprioception that are lost due to impairment.^18-20 During the master-slave mode where the motions of the normal fingers are duplicated to the affected fingers, the device induces active participation of the patient and helps neuroplasticity.

We also suggest two methods to quantitatively evaluate spasticity. First, we estimate spasticity level of patient's finger by fusion of pressure and angle data during CPM. Second, Electromyography (EMG) is used to determine the level of finger extensor muscle activation and to compare passive rehabilitation with active rehabilitation using an air pocket glove.

2. Methodology

2.3 Silicone Flexor

The silicone flexors are attached to the palm of the air pocket glove to guide finger flexion by elasticity of the silicone for those who cannot grasp. In addition, the silicone flexor acts as a dash pot that improves safety by its spring force applied to each finger joint during extension exercise. The position of the silicone flexor is determined by considering movement around the scaphoid tubercle when a person actually bends the finger.²¹

In this study, the selected silicone hardness is less than 5A (shore hardness) and the elongation was 700% or less. Table 1 is a characteristic of silicone flexor manufactured by Dragon Skin^® and Ecoflex^® silicone (Smooth-On, Inc.). As a result of application to patients, silicone less than 00-30 (shore hardness) was not suitable for application due to durability and elongation problem. Therefore, flexors are fabricated with 2A silicone.

Table 1

Characteristics of various hardness Silicone flexor

2.5 Air Pocket Glove Characteristics

We performed a test to determine safety and durability of the actuator before applying it to patient. After wearing the air pocket glove, the maximum air pressure limit was determined. Experimental conditions were as follows: After wearing the glove, air was slowly injected into actuator using a piston while finger angles and actuator pressure were monitored. The maximum pressure of the actuator measured through the above procedure is 68.6 kPa. The limit of the air regulator is determined based on the maximum pressure. When the finger reaches certain angle, the solenoid valve is closed to keep the pressure level constant. Table 2 shows the internal pressure according to angle. The angle of the finger is measured between PIP and DIP based on the anthropometric method.²² Therefore, the finger angle decreases with increasing pressure. In addition, the maximum extension is shown at index finger 10^o/ 64.4 kPa and thumb 10^o/ 68.6 kPa. The reason for the difference between the thumb and the index finger is due to the structural characteristics of the finger, RoM and internal volume (index: 55 mL, thumb: 42 mL). In the master-slave mode, patient's own intent is included and can participate in his rehabilitation. In this mode, the EMG energy level is measured during exercise.

Fig. 2

Finger joint angle based on anthropometric method

Fig. 3

Block diagram of overall finger rehabilitation system

Table 2

Air pocket-type actuator characteristics

3. Finger Rehabilitation System

4. Result and Discussion

The subject is a left side hemiplegic patient and a brunnstrom stage 3rd - 4th (estimated by physical therapist). This patient is capable of voluntary exercise using orthosis, resistance is stronger at the end of the finger movement during physical therapy. The patient had a MAS score of 1 and a BBT score of 39. The experiment was performed at the Pohang rehabilitation hospital.

4.1 CPM Mode Analysis

In CPM mode, three cases were compared: 1) normal hand, 2) hand before rehabilitation, and 3) after rehabilitation.

The angle-time graph of the normal hand shows that it reaches 0 to 20^o in 3.7 seconds immediately after the pneumatic pressure is applied. In addition, the pressure in the pressure-time graph starts to rise from 2 seconds and rises slowly (4.4 sec) in all three cases. Before rehabilitation, the patient's graph is shown to take 7.8 seconds to reach 0 to 20^o. In addition, it can be confirmed that the finger is extended only up to 20^o. There is angle difference between the normal hand and the before rehabilitation about 13 deg. Above results indicate that the device has a potential to diagnose spasticity according to the RoM of a patient's finger.

Fig. 4

A graph comparing the EMG energy

In the case of pressure data, it takes 3.6 seconds to reach 40 kPa and tends to rise the fastest. The highest pressure is 61 kPa. After rehabilitation case took 5 seconds to reach 0 to 20^o, and the max angle is 7^o In the CPM mode, the inside pressure of the actuator and the patient's finger angle information are determined to confirm the correlation with the patient’s spasticity level. Table 3 shows the lowest pressure value (55 kPa) for the normal hand and the highest pressure value (61 kPa) for the affected hand before rehabilitation. This is because the patient's fingers act as springs trying to return to their neutral positions due to spasticity thus increasing the air pressure inside the actuator. Thus, the pressure data can be used to determine the resistance level of the patient to exercises, and a spasticity level can be estimated based on the resistance level.

Table 3

Graph analysis applying various measurements

Finally, the angle-pressure graph is modelled with linear fitting. A modeled spasticity Eq. (1) is expressed as follows:

$\[ \begin{array}{c}P: pressure, \theta : MCP to PIP angle\\ Patient \left(before\right): P= -0.4961 \times \theta +73.93\\ Patient \left(after\right): P= -0.4836 \times \theta +64.22\\ Normal hand: P= -0.5095 \times \theta +60.22\end{array} \]$

(1)

In the angle-pressure graph in Fig. 5(3), the y-intercept (Eq. (1)) difference between the normal hand and the before rehabilitation hand was 21.1% (before rehabilitation > normal hand). Y-intercept difference between normal and after rehabilitation is measured as 6.6%. At last, the y-intercept value before and after rehabilitation shows a difference of 15.1%. The higher the spasticity level of the subjects, the greater the y-intercept difference. This result shows that the stroke patient’s spasticity level can be diagnosed according to the correlation between the measured angle and pressure using the air pocket glove.

Fig. 5

Graphs measured from CPM mode

5. Conclusion

The Air Pocket Glove is a system that allows both rehabilitation and evaluation. It can numerically assess the patient’s condition, motivate and engage high involvement by actively participating in rehabilitation. In addition, since voluntary rehabilitation is possible without the help of a therapist, the independence of the patient can be improved, and time-unlimited rehabilitation and evaluation are possible. This study was conducted based on rehabilitation and MT mechanism of the references. MT exercise increases gripping ability and improves strength of the fingers, and the ROI of the joints is increased in experiments on subacute stroke patients.^32,33 Based on the above theoretical backgrounds, the experiment were designed and it is expected to be used appropriately for the rehabilitation and assessment of stroke patients because it shows a similarity with the previous experimental results. However, existing rehabilitation studies are based on delicate experiments based on patients with acute, subacute, and chronic conditions, so future studies will focus on the patient's age, damaged area, and duration to increase reliability.

Acknowledgments

This paper was presented at ISGMA 2017

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MOE) (No. 2017R1D1A3B03035973).

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