# Flexible Textile-Based Pressure Sensing System Applied in the Operating Room for Pressure Injury Monitoring of Cardiac Operation Patients

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## Abstract

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## 1. Introduction

## 2. Experimental

^{2}with a spacing of 3 cm to the neighboring sensor. The total dimension of this fabricated sensing pad with a dimension of 30.8 × 56.6 cm

^{2}for 10 × 18 points was fabricated to investigate basic pressure sensing and the noise interference of capacitive sensors. The picture and schematic plot of this flexible pressure sensor array are shown in Figure 1a. The following section will present the basic operation mechanism of the pressure sensor and impedance measurement system.

_{c}is the force constant that can be determined by the material and its geometry, and Δd is the distance of deformation such as the reduced thickness of the flexible capacitance of the pressure sensor. Therefore, Δd equals F/kc, which can be applied to Equation (2) to generate Equation (4).

_{c}), which is the basic operation mechanism of the flexible pressure sensor.

_{t}is the Kalman gain with the variance predicted error divided by the difference in variance between the current and predicted error, H is the corresponding matrix of multi-parameters.$\text{}{\widehat{x}}_{t}$ is the updated impedance in estimation, z

_{t}is the current measured impedance, and P

_{t}is the error variance of the current value. The detailed block diagram of this designed Kalman filter is shown in Figure 1b. Therefore, the value can be closely forecasted and measured using a lower impact of error variance in real applications.

## 3. Results and Discussion

## 4. Discussion

## Supplementary Materials

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**(

**a**) Schematic plot and picture of the flexible pressure sensor. (

**b**) Operation of the Kalman filter. (

**c**) Block diagram. (

**d**) Image of the developed impedance readout system.

**Figure 2.**Picture of the real situation for the setup in the operation room: (

**a**) A flexible pressure mattress on an operation bed with (

**b**) a nurse lying on it.

**Figure 3.**(

**a**) Typical response between the applied weight and readout value of the single point of this pressure-sensing pad compared with impedance analyzer. (

**b**) Capacitance. (

**c**) Impedance correlation between the readout system and impedance analyzer.

**Figure 4.**Time-dependent response of the single flexible pressure sensor with (

**a**) designed noises of input by the modification of R and Q for (

**b**) 0.1/0.1, (

**c**) 0.01/0.1 and (

**d**) 0.1/0.01 in the Kalman filter.

**Figure 5.**Time-dependent response of the single flexible pressure sensor with a regular pressing force and 24% duty cycle: (

**a**) without and (

**b**) with the Kalman filter.

**Figure 6.**(

**a**) Number of patients with and without pressure injury classified by the patient body mass index (BMI). Typical interfacial pressure distribution at the 3rd hour for patients with 3 different BMIs shown in (

**b**) 2D and (

**c**) 3D images.

**Figure 7.**(

**a**) Time-dependent 2D pressure image for a typical patient with a low BMI and pressure injury and (

**b**) time-dependent pressure trending of the sacrum area for patients with and without pressure injury according to the real measurement in cardiac operations.

n | Male | Female | Height | Weight | BMI | Age | Operation Time (hr) | |
---|---|---|---|---|---|---|---|---|

PI * | 11 | 6 | 4 | 163.4 ± 12.9 | 66.2 ± 18.5 | 24.7 ± 6.1 | 54.4 ± 8.1 | 7.9 ± 2.2 |

NPI ** | 37 | 26 | 11 | 163.3 ± 10.3 | 66.8 ± 11.8 | 24.9 ± 3.5 | 58.1 ± 12.1 | 8.0 ± 2.4 |

Total | 47 | 32 | 15 | 163.3 ± 13.2 | 66.7 ± 13.2 | 24.9 ± 4.1 | 57.3 ± 11.4 | 8.0 ± 2.3 |

**Table 2.**Patient number with and without pressure injury classified by 5 different body mass index (BMI) groups.

Ratio (%) & [Total Patient Number] | |||||
---|---|---|---|---|---|

BMI | 16.5–20.5 | 20.5–24.5 | 24.5–28.5 | 28.5–32.5 | 32.5–36.5 |

PI * | 30 [3] | 20 [2] | 20 [2] | 10 [1] | 20 [2] |

NPI ** | 8.1 [3] | 35.1 [13] | 40.5 [15] | 13.5 [5] | 2.7 [1] |

Type Name/ Company | Sensor Specification | System Specification | Clinic Test | Year/ Ref. | |||
---|---|---|---|---|---|---|---|

Substrate Type | Sensor Pitch (cm) | Total Sensor no. | Digitized Level | Accuracy (%) | Patient no. | ||

CONFORMat@/ NITTA corp. | Flexible | 2.17 | 32 × 32 | N/A | ±10% | 0 | 2011/[35] |

5315/Tekscan Inc. | Flexible | 1 | 42 × 48 | 256 | ±10% | 0 | 2015/[12] |

PX100/ XSENSOR Tech. | Flexible | 1.27 | 64 × 160 | N/A | ±10% | 0 | 2015/[11] |

Mark III/ Talley Group Ltd. | N/A | 3 | 12 × 8 | N/A | N/A | 0 | 2017/[36] |

ePad-ExtraS50 /eBio Tech. | Textile | 3.2 | 14 × 18 | 1024 | ±8% [±0.2%] * | 47 | This work |

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**MDPI and ACS Style**

Shih, D.-F.; Wang, J.-L.; Chao, S.-C.; Chen, Y.-F.; Liu, K.-S.; Chiang, Y.-S.; Wang, C.; Chang, M.-Y.; Yeh, S.-L.; Chu, P.-H.;
et al. Flexible Textile-Based Pressure Sensing System Applied in the Operating Room for Pressure Injury Monitoring of Cardiac Operation Patients. *Sensors* **2020**, *20*, 4619.
https://doi.org/10.3390/s20164619

**AMA Style**

Shih D-F, Wang J-L, Chao S-C, Chen Y-F, Liu K-S, Chiang Y-S, Wang C, Chang M-Y, Yeh S-L, Chu P-H,
et al. Flexible Textile-Based Pressure Sensing System Applied in the Operating Room for Pressure Injury Monitoring of Cardiac Operation Patients. *Sensors*. 2020; 20(16):4619.
https://doi.org/10.3390/s20164619

**Chicago/Turabian Style**

Shih, De-Fen, Jyh-Liang Wang, Sou-Chih Chao, Yin-Fa Chen, Kuo-Sheng Liu, Yi-Shan Chiang, Chi Wang, Min-Yu Chang, Shu-Ling Yeh, Pao-Hsien Chu,
and et al. 2020. "Flexible Textile-Based Pressure Sensing System Applied in the Operating Room for Pressure Injury Monitoring of Cardiac Operation Patients" *Sensors* 20, no. 16: 4619.
https://doi.org/10.3390/s20164619