Development of an Intermittent Pneumatic Compression System to ...

Development of an Intermittent Pneumatic Compression System to Manage Soft Tissue Mechanical Properties Chi-Wen Lung, Tse-Yu Cheng, Yi-Jhen Li, Ben-Yi Liau and Yih-Kuen Jan

Abstract The pneumatic compression system has demonstrated the potential to manage hypertrophic scar tissues using localized intermittent compressive forces. The underlying mechanism associated with these repeated, intermittent compressive forces is the remodeling capacity of collagen fibers of fibrous tissues in response to mechanical forces. Although intermittent compressive forces are clinically proven effective on managing hypertrophic scar, the optimal configurations of pressures and timing of intermittent compressive forces are largely unknown. In this study, we have developed a motor-driven ultrasound indentation system to apply programmable compressive forces and simultaneously assess soft tissue mechanical properties and responses. We further tested this system in various conditions with Institutional Review Board-approved protocols in human participants. The compressive force applied by the system was 40 mmHg on the skin of the forearm for C.-W. Lung Y.-K. Jan (&) Rehabilitation Engineering Laboratory, University of Illinois, Urbana-Champaign, Illinois, USA e-mail: [email protected] C.-W. Lung e-mail: [email protected] Y.-K. Jan Kinesiology and Community Health, University of Illinois, Urbana-Champaign, Illinois, USA Y.-K. Jan Computational Science and Engineering, University of Illinois, Urbana-Champaign, Illinois, USA C.-W. Lung T.-Y. Cheng Y.-J. Li Creative Product Design, Asia University, Taichung, Taiwan e-mail: [email protected] Y.-J. Li e-mail: [email protected] B.-Y. Liau Biomedical Engineering, Hungkuang University, Taichung, Taiwan e-mail: [email protected] © Springer International Publishing Switzerland 2017 V.G. Duffy and N. Lightner (eds.), Advances in Human Factors and Ergonomics in Healthcare, Advances in Intelligent Systems and Computing 482, DOI 10.1007/978-3-319-41652-6_30

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1 h with a frequency of 0.1 Hz. Soft tissue mechanical properties were assessed at three conditions, including (a) the forearm resting on the table with the wrist at a neutral position, (b) the forearm resting on the table with the wrist at 90° of extension or the maximal extension of the subject, and (c) forearm resting on the table with the hand holding a 1 kg weight. The effective Young’s modulus was calculated to characterize mechanical properties of forearm soft tissues. Before the 1 h intermittent compression treatment, effective Young’s modulus of conditions a, b, and c was 18.0, 11.3, and 16.8 kPa, respectively. After the treatment, the effective Young’s modulus of conditions a, b, and c was reduced by 13, 7, and 51 %, respectively. The results support our general hypothesis that intermittent compression therapy may modulate soft tissue properties (e.g. hypertrophic scar). Future work should investigate the long-term effect of intermittent compression therapy on modulating soft tissue properties in patients with hypertrophic scars.

Keywords Intermittent pneumatic compression system Massage therapy Scar Soft tissue interface

1 Introduction Hypertrophic scar is one of the most significant problems in patients after skin injury [1]. Treatment of hypertrophic scar results in an enormous financial burden to the healthcare systems in the United States and is estimated at least $4 billion per year [2]. Hypertrophic scar appears either red or pink in color, pruritic, and raised [3]. The mechanical pressures caused by the hypertrophic scar limit the supply of blood, including oxygen and nutrients to the scar tissues [4]. It has been shown that compressive forces my alter the degree of collagen synthesis and degradation [5, 6]. The intermittent compressive force therapy may improve wound healing by 45.7 % [7, 8]. However, the optimal configurations of pressures and timing of intermittent compressive forces requires further investigation [9–11]. The purpose of this study was to explore the influences of various compressive forces on soft tissue mechanical properties and responses after massage therapy by the intermittent pneumatic compression system. The details of this indentation system and pilot results were described as follows.

2 Methods In this study, we developed a motor-driven ultrasound indentation system to apply programmable compressive forces and simultaneously assess the force-deformation responses of the soft tissues at the forearm of the research participants. Three subjects were recruited into this study (N = 3; mean ± SD: age, 32.7 ± 18.5 years; height, 171.0 ± 10.6 cm; weight, 72.0 ± 21.4 kg; body mass

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index, 24.3 ± 4.5 kg/m2). We further tested this system in various conditions using an Institutional Review Board-approved protocol.

2.1

Compression System

The intermittent pneumatic compression system mainly consists of pneumatic devices (Takasima Eye-Care M-2203, Taiwan Family Enterprise CO., LTD. Taipei, Taiwan). The frequency of the intermittent compressive forces was chosen at 0.1 Hz in one indenter head with the diameter of 3 cm. The sequentially inflated and deflated pressures were regulated from 0 to 40 mmHg [12]. The compression system was in series applied to the soft tissue of the forearm 10 min for simulating the common massage protocols [13].

2.2

Soft Tissue Property Measurement

The indentation tests were conducted before and after intermittent compression therapy. Three forearm postures corresponding to different states of muscular contraction. The subject was asked to sit with the elbow rested at 180° flexion on a supporting table. Three conditions of forearm, including (a) the forearm resting on the table with the wrist at a neutral position, (b) the forearm resting on the table with the wrist at 90° of extension or the maximal extension of the subject, and (c) forearm resting on the table with the hand holding a 1 kg weight. After a preload force of less than 0.5 N was applied on the skin over the dorsal forearm perpendicularly, a load of 5.0 N or less if the indentation had reached 20 % of the total thickness from the real-time ultrasound images was applied on the same location [14, 15]. The indentation velocity was set to be about 1 mm/s and the maximum indentation was about 20 % of the initial bulk soft tissue thickness, as evaluated by ultrasound signals with a minimum loading of 0.1 N [16]. A cyclic loading of 45 s was applied on the skin of the forearm with approximately 2–5 s per loading cycle (Fig. 1). About 200–400 data points obtained from the ultrasound signals were used to extract the effective Young’s modulus of the forearm (Fig. 2).

2.3

Motor-Driven Ultrasound Indentation System

The motor-driven ultrasound indentation system mainly consists of four parts: ultrasound system, load cell, stepper motor, and standoff holder. Details of the indentation system have been described in our previous publications [17]. In brief, a 7.5 MHz ultrasound transducer (32-Channel BSUS20-32C, Broadsound Corporation, Hsinchu, Taiwan) with a 49-N load cell (Model UKA-E-005, Li-Chen Measure CO., Ltd., Kaohsiung, Taiwan) in series was applied to indent the soft

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Fig. 1 The intermittent pneumatic compression system. a Pneumatic device; b an example of applying intermittent compression therapy in a subject

Fig. 2 Three conditions of forearm, including a the forearm resting on the table with the wrist at a neutral position, b the forearm resting on the table with the wrist at 90° of extension or the maximal extension of the subject, and c forearm resting on the table with the hand holding a 1 kg weight

tissue and the ultrasonic signal was collected to extract the initial thickness and force-deformation responses of the tissue. The sampling rate of the images frame and force data were recorded at 22.5 and 100 Hz DAQ data acquisition device (USB-6218, National Instrument, Austin, TX, USA). In this indentation system, a stepper motor (Model TL-SL1010-X, Tanlian Electro Optics CO., Ltd., Taoyuan, Taiwan) with a total travel of 50 mm and a step travel of 0.000625 mm which is driven by a 1600 microstepper per revolution (Model TL-1T, Tanlian Electro Optics CO., Ltd., Taoyuan, Taiwan) was adopted to accomplish an automatic cyclic


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indentation instead of a manual operation. A standoff pad was mounted on the ultrasound transducer head with accommodative standoff holder that can be used for reduced transducers probe surface into 4.5 mm radius for soft tissue indenter size [18]. The standoff holder comprised of a standoff pad (coupling medium, cylinder with 4.5 mm radius and 20 mm thickness, Aquaflex ultrasound gel pad, Parker Laboratory, Orange, NJ) also can provide an optimal acoustic characteristics. The indenter was motor-driven or pneumatically [16] onto the skin surface to apply programmable compressive forces and assess soft tissue mechanical properties and responses. The test itself very much resembles that of palpation of the plantar soft tissues [19, 20]. The first ultrasound echo is associated with the standoff pad and skin interface while the second one represents the tissue-bone interface. The thickness of the soft tissue is presented by the distance between the first and second echoes [21] (Fig. 3).

2.4

Data Analysis

To quantify elastic properties of soft tissues, we used the effective Young’s modulus (E). It is a traditional material constant [22, 23]. To extract effective Young’s modulus E, the equation is defined as below. E¼

ð1 v2 Þ P 2a kðv; a=hÞ w

ð1Þ

v, Poisson’s ratio; a, the indenter radius; k, a scaling factor dependent on the Poisson’s ratio (0.45) [23], indenter radius (4.5 mm), and tissue thickness [22]; h, the soft tissue thickness; P, the force of pressure loading (indentation); w, the depth of indentation. Paired samples t tests were used to compare the effective Young’s modulus between before and after intermittent pneumatic compression under each forearm postures (wrist neutral position, wrist extension, and hand holding). The statistical tests were performed using SPSS 22 (IBM, Somers, NY) at the significance level of 0.05.

3 Results and Discussion The effective Young’s modulus was calculated to characterize of mechanical property of forearm soft tissues. Before the 1 h intermittent compression treatment, effective Young’s modulus of conditions a, b, and c was 18.0, 11.3, and 16.8 kPa, respectively. After the treatment, the effective Young’s modulus of wrist neutral position, wrist extension, and hand holding was reduced by 34, 11, and 38 %, respectively. However, there were no significant pairwise differences in before and after intermittent pneumatic compression.

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Fig. 3 Motor-driven ultrasound indentation system. a The motor-driven ultrasound indentation system. b It shows the ultrasound echo trains. After the standoff pad, the first echo is associated with the ultrasound standoff-skin interface while the second one represents the tissue-bone interface. The thickness of the soft tissue is present by the distance between the first and second echoes

Compare to the mechanical properties of the forearm in the wrist extension position, the forearm with the wrist in the neutral position and with the hand holding a weight increased the effective Young’s modulus [24].


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Fig. 4 Comparison of effective Young’s modulus under the three forearm postures (wrist neutral position, wrist extension, and hand holding) responded to before and after intermittent compression treatment

After the intermittent compression therapy, effective Young’s modulus of the soft tissue decreased by 11–38 %. This finding indicates that the intermittent compression therapy (e.g. compression massage therapy) may soften the soft tissues. This study had limitations. First, the intermittent compression therapy was applied only on the skin of the forearm. Future work should study other locations of hypertrophic scar. Second, only 3 subjects were recruited into this study. Future work should test the efficacy of intermittent compression therapy in a larger sample size. Third, the future work should investigate the long-term effect of intermittent compression therapy on modulating soft tissue property in patients with hypertrophic scars (Fig. 4).

4 Conclusion The results support our general hypothesis that intermittent compression therapy, massage therapy, may modulate soft tissue property. Acknowledgments This study was supported by Ministry of Science and Technology, Taiwan (MOST 104-2221-E-468-020).

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