Optical fiber monitor capable of monitoring vital sign parameters of bedridden patient

Abstract

The utility model provides an optical fiber monitor capable of monitoring vital sign parameters of a bedridden patient. The optical fiber monitor comprises an air pump, an air valve switch, a four-way connector, an air bag, a light source, a first photoelectric detector, a second photoelectric detector, an optical fiber coupler, a microbend optical fiber sensing assembly, an optical power measuring module, a respiration rate and heart rate measuring module, a microcontroller MCU module and a terminal. The technical scheme is used for simultaneously monitoring the heart rate, the breathing rate and the weight of the bedridden patient. The heart rate, the respiration rate and the body weight can be measured at the same time, and the defects that the action of a patient is limited, and small-period signals are difficult to detect in large signals such as body weight fluctuation in an air cushion bed sensing system are overcome.

Description

Technical Field

[0001] The utility model relates to the technical field of optical fiber sensing, in particular to an optical fiber monitor capable of monitoring vital sign parameters of bedridden patients. Background Art

[0002] Vital sign parameters, such as body weight (BW), heart rate (HR), and respiratory rate (RR), play a crucial role in assessing human health, especially for bedridden patients and the elderly. Regular monitoring of these vital signs in clinical practice provides valuable information to healthcare professionals to assess the health status of patients and determine appropriate medical interventions. Accurate measurement of body weight, heart rate, and respiratory rate is essential for calculating drug dosages, as it directly affects the effectiveness of treatment.

[0003] In recent years, a large number of methods and devices for monitoring heart rate, respiratory rate and weight have been proposed, many of which are suitable for bedridden patients and can be non-invasively monitored without the use of cable connections or direct skin contact. Most of these sensors are capable of measuring heart rate and respiratory rate simultaneously, including devices such as Emfit sensors, air mattress sensing systems, hydraulic sensors, electrocardiogram sensors, Doppler radar sensors, acoustic sensors and electronic weighing sensors. In addition, many types of fiber optic sensors can also be used for heart rate and respiratory rate monitoring, including fiber optic sensors based on photoelectric capacitance graphs, fiber interferometer sensors, fiber speckle sensors, fiber grating sensors, heterogeneous core fiber pressure sensors, etc. Although the above-mentioned fiber optic sensors have also been used for heart rate and respiratory rate monitoring, the above-mentioned technologies lack specific designs for weight measurement.

[0004] For bedridden patients, traditional weight measurement methods are challenging due to limited mobility. Some professional scales, such as bed scales [Schneider AG, Thorpe C, Dellbridge K, Matalanis G, Bellomo R. Electronic bed weighing vs daily flfluid balance changes after cardiac surgery. J Crit Care. 2013; 28(6): 1113e1-5.] and hanging scales [Bloomfifield R, Steel E, MacLennan G, Noble DW. Accuracy of weight and height estimation in an intensive care unit: Implications for clinical practice and research. CritCare Med. 2006; 34(8): 2153-7], provide solutions that can accurately measure weight without requiring patients to move, but there are safety risks and inconvenience in operation. Load cells are commonly used sensors for weight measurement, but suffer from issues such as data drift and reduced accuracy [R. Manoj, R. Kumarasami, J. Joseph, B. George andM. Sivaprakasam, "Continuous Weight Monitoring System for ICU Beds usingAir-filled Mattresses / Pads: A Proof of Concept," 2019 IEEE InternationalSymposium on Medical Measurements and Applications (MeMeA), Istanbul, Turkey,2019, pp. 1-5,]. To address these issues, emerging technologies such as pressure sensors show potential but are still in the development stage and are not yet popular. It should be noted that traditional load cells are not designed for heart rate and respiratory rate measurements. Fiber optic sensors are well suited for weight measurement.So far, there have been some reports on fiber optic sensors for weight measurement, such as polarization sensors [G. Liu, SL Chuang, Polarimetric optical fiber weight sensor, Sensors and Actuators A: Physical, Volume 69, Issue 2, 1998, Pages 143-147,], Bragg grating sensors [D. Pal, A. Kumar, A. Gautam and J. Thangaraj, "FBG BasedOptical Weight Measurement System and Its Performance EnhancementUsingMachine Learning," in IEEE Sensors Journal, vol. 22, no. 5, pp. 4113-4121, 1 March1, 2022], and interferometric sensors [Paixão, T.; Ferreira, R.; Domingues, MF; Antunes, P. Fiber Optic Load Cells with Enhanced Sensitivity byOpticalVernier Effect. Sensors 2021, 21, 7737], bending sensors [Z.Chen, D. Lau, JT Teo, SH Ng, X. Yang, and PL Kei, “Simultaneous measurement ofbreathing rate and heart rate using a microbend multimode fiberoptic sensor,” Journal of biomedical optics, vol. 19, no. 5, p. 057001, 2014], etc. However, existing fiber optic sensors lack the ability to simultaneously measure the heart rate, respiratory rate, and weight of bedridden patients.

[0005] Electronic sensors are a widely adopted technology for measuring weight, heart rate, and respiratory rate. However, these sensors are susceptible to environmental factors such as temperature and humidity fluctuations, require frequent calibration, have limited lifespans, and are susceptible to electromagnetic interference, with risks such as reduced accuracy and delayed response time. In contrast, the emergence of fiber-optic-based sensors offers an attractive alternative for weight, heart rate, and respiratory rate. Fiber-optic sensors are immune to electromagnetic interference, easy to integrate with bed systems, and corrosion-resistant. In bed applications, both electronic and fiber-optic sensors have advantages and disadvantages for the measurement of weight, heart rate, and respiratory rate. To date, there is no consensus on which technology is more suitable for monitoring bedridden patients. Fiber-optic sensors have advantages such as small size, light weight, immunity to electromagnetic interference, and simple integration with mattress systems, as well as high accuracy and cost-effectiveness. Notably, the use of a single fiber-optic sensor to simultaneously measure heart rate, respiratory rate, and weight has not been explored in the published literature. Existing fiber-optic sensors lack the ability to simultaneously measure heart rate, respiratory rate, and weight, especially for bedridden patients.

[0006] Microbend sensors have considerable potential. However, existing microbend fiber optic sensors mainly focus on heart rate and respiratory rate measurement or weight measurement alone, and cannot monitor heart rate, respiratory rate and weight simultaneously. Utility Model Content

[0007] In view of this, the purpose of the utility model is to provide a fiber optic monitor that can monitor the vital signs parameters of bedridden patients, and is used to simultaneously monitor the heart rate, respiratory rate and weight of bedridden patients.

[0008] To achieve the above-mentioned purpose, the utility model adopts the following technical solutions: an optical fiber monitor capable of monitoring the vital signs parameters of bedridden patients, comprising an air pump, an air valve switch, a four-way connector, an air bag, a light source, a first photodetector, a second photodetector, an optical fiber coupler, a slightly bent optical fiber sensing component, an optical power measurement module, a respiratory rate and heart rate measurement module, a microcontroller MCU module and a terminal;

[0009] The air pump is connected to a four-way connector via an air valve switch, and the four-way connector is connected to the airbag and the slightly bent optical fiber sensing assembly; the slightly bent optical fiber sensing assembly is connected to the light source and the optical fiber coupler; the optical fiber coupler is connected to the first photodetector and the second photodetector; the first photodetector is connected to the optical power measurement module, and the second photodetector is connected to the respiratory rate and heart rate measurement module; the optical power measurement module and the respiratory rate and heart rate measurement module are both connected to the microcontroller MCU module; the microcontroller MCU module is connected to the terminal.

[0010] In a preferred embodiment, the airbag includes N airbag units, N>1; the air pump inflates the airbag units through an air valve switch and a four-way connector.

[0011] In a preferred embodiment, the micro-bend optical fiber sensing assembly is cylindrical and consists of an upper cover structure and a lower cover structure; a micro-bender with a tooth pitch and a pair of teeth is provided in the lower cover structure, and a multi-mode optical fiber is fixed on the teeth with glue; the upper cover structure and the lower cover structure are connected by a spiral buckle; and it also includes a movable micro-bender with four small columns, which are placed in the corresponding holes of the optical fiber upper cover structure and the lower cover structure for positioning.

[0012] In a preferred embodiment, a first optical fiber is connected between the light source and the slightly bent optical fiber sensing assembly, and a second optical fiber is connected between the slightly bent optical fiber sensing assembly and the optical fiber coupler.

[0013] In a preferred embodiment, an air pump inflates an airbag containing N unit airbags through an air valve switch and a four-way connector port; when the airbag is filled to a set pressure, the air valve closes; at this time, the pressure acts on the optical fiber in the micro-bend optical fiber sensing assembly through the port of the four-way connector and causes the optical fiber to bend and deform; the light emitted by the light source is incident on the micro-bend optical fiber sensing assembly through the first optical fiber and passes through the second optical fiber and then through a 1x2 optical fiber coupler (preferably a single-mode optical fiber coupler) to divide the light into two paths: one path is incident on the first photodetector, and the other path is incident on the second photodetector; after photoelectric conversion by the first photodetector and the second photodetector, the signals are respectively input into an optical power measurement module and a respiratory rate and heart rate measurement module; the microcontroller MCU module transmits the signals and results of the optical power measurement module and the respiratory rate and heart rate measurement module to the terminal by wire or wirelessly.

[0014] Compared with the prior art, the utility model has the following beneficial effects:

[0015] (1) Adjustable system sensitivity

[0016] (2) One airbag unit with inherent high sensitivity S1 is used to measure heart rate and respiratory rate, while the remaining airbags with inherent system sensitivity S1 / N are used for weight measurement.

[0017] (3) The use of anti-bedsore mattresses and optical communication components is low-cost and easy to manufacture, apply and promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of an airbag micro-bend optical fiber sensor system with adjustable system sensitivity in a preferred embodiment of the utility model;

[0019] Figure 2 The preferred embodiment of the utility model is an airbag assembly having N airbag units;

[0020] Figure 3Schematic diagram of the structure of the micro-bend optical fiber sensor assembly in the preferred embodiment of the utility model; wherein (a) is a structural diagram of the upper cover plate, (b) is a structural diagram of the lower cover plate, and (c) is a structural diagram of the movable micro-bend;

[0021] Figure 4 The relationship curve between the system light transmission coefficient and the pressure in the preferred embodiment of the utility model;

[0022] Figure 5 The relationship curve between the system light transmission coefficient and body weight in the preferred embodiment of the utility model;

[0023] Figure 6 Screen shots of a volunteer's original waveform (obtained within 12 seconds), filtered breathing waveform (obtained within 12 seconds) and BCG waveform (obtained within 6 seconds) in a preferred embodiment of the utility model: (a) N=20; (b) N=1;

[0024] Figure 7 The preferred embodiment of the utility model is an airbag assembly with 20 airbag units. DETAILED DESCRIPTION

[0025] The utility model is further described below in conjunction with the accompanying drawings and embodiments.

[0026] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0028] A fiber optic monitor that can monitor the vital signs of bedridden patients. Figure 1-7 , including an air pump 1, an air valve switch 2, a four-way connector 3, an air bag 4, a light source 5, a first photodetector 8, a second photodetector 9, a fiber coupler 7, a slightly bent fiber sensing component 6, an optical power measurement module 10, a respiratory rate and heart rate measurement module 11, a microcontroller MCU module 12 and a terminal 13;

[0029] The air pump 1 is manual, and the air valve switch 2 is an electromagnetic valve switch. The 20 airbag units can be combined and connected to each other or not, and the airbag units are cylindrical. Each airbag unit has a diameter of 7.5 cm and a length of 80 cm. The light source 5 is a light emitting diode with a wavelength of 1320 nm. The 1x2 fiber coupler 7 is a single-mode fiber coupler. The microcontroller MCU module 12 is used to perform a series of processing such as amplification, filtering, analog-to-digital conversion and calculation on the optical power measurement module 10 and the respiratory rate and heart rate measurement module 11, and transmits it to the terminal 13 via Bluetooth to report information such as heart rate, respiratory rate, and weight. Terminal 13 is a computer terminal. The photodetector matches the working band of the light source. Figure 7 The airbag assembly 4 has 20 airbag units, wherein the airbag unit 45 is connected to the four-way joint 33 through 451, preferably between the neck and the waist. All other airbags are connected together and connected to the four-way joint 32 through 411. In addition to the airbag No. 45, the airbag No. 41 is connected to the airbag No. 42, the airbag No. 43, the airbag No. 44 and the airbag No. 46, and is connected to the airbag No. 420. Figure 7 As shown, each airbag has an air inlet and an air outlet. However, 45 and 420 have only one port. When deflated, the connection with the airbag can be disconnected through 411 and 451. Figure 1 The configuration shown uses a 1x2 fiber coupler to split the signal, allowing the simultaneous recording of output signals with weight, heart rate, and respiration rate information.

[0030] The air pump 1 is connected to the four-way connector 3 through the air valve switch 2, and the four-way connector 3 is connected to the airbag 4 and the slightly bent optical fiber sensing assembly 6; the slightly bent optical fiber sensing assembly 6 is connected to the light source 5 and the optical fiber coupler 7; the optical fiber coupler 7 is connected to the first photodetector 8 and the second photodetector 9; the first photodetector 8 is connected to the optical power measurement module 10, and the second photodetector 9 is connected to the respiratory rate and heart rate measurement module 11; the optical power measurement module 10 and the respiratory rate and heart rate measurement module 11 are both connected to the microcontroller MCU module 12; the microcontroller MCU module 12 is connected to the terminal 13.

[0031] The airbag 4 includes N airbag units, where N>1; the air pump 1 inflates the airbag units through the air valve switch 2 and the four-way connector 3.

[0032] The micro-bend optical fiber sensing assembly 6 is cylindrical and consists of an upper cover structure and a lower cover structure; a micro-bender with a tooth pitch and a pair of teeth is provided in the lower cover structure, and a multi-mode optical fiber is fixed on the teeth with glue; the upper cover structure and the lower cover structure are connected by a spiral buckle; and it also includes a movable micro-bender with four small columns, which are placed in the corresponding holes of the optical fiber upper cover structure and the lower cover structure for positioning.

[0033] A first optical fiber 56 is connected between the light source 5 and the slightly bent optical fiber sensing assembly 6, and a second optical fiber 67 is connected between the slightly bent optical fiber sensing assembly 6 and the optical fiber coupler 7. The first optical fiber 56 and the second optical fiber 67 can be multimode optical fibers or single-mode optical fibers.

[0034] The air pump 1 inflates the airbag 4 including N unit airbags through the ports of the air valve switch 2 and the four-way connector 3; when the airbag 4 is filled to have pressure, the air valve is closed; at this time, the pressure acts on the optical fiber in the micro-bend optical fiber sensor component 6 through the port of the four-way connector 3 and causes the optical fiber to bend and deform; the light emitted by the light source is incident on the micro-bend optical fiber sensor component 6 through the first optical fiber 56 and passes through the second optical fiber 67 and then passes through the 1x2 optical fiber coupler 7, and the light is divided into two paths: one path is incident on the photoelectric detector 8 through 78, and the other path is incident on the photoelectric detector 9 through 79; after the photoelectric conversion by the first photoelectric detector and the second photoelectric detector, the signal is input to the optical power measurement module 10 and the respiratory rate and heart rate measurement module 11 through 810 and 911 respectively; the microcontroller MCU module 12 transmits the signals and results of the optical power measurement module 10 and the respiratory rate and heart rate measurement module 11 to the terminal 13 by wire or wireless.

[0035] The preferred optical fibers 56, 67, 78 and 79 are single-mode optical fibers. The microbend optical fiber sensor assembly 6 is cylindrical and consists of an upper cover structure (such as Figure 3 (a)) and a lower cover structure, in which a micro-bender with a 3 mm pitch and 11 pairs of teeth is arranged (as shown in FIG. Figure 3 (b) shows a 100-micron multimode optical fiber with a length of 4.3 cm fixed to the teeth with glue. These cover structures are connected by a screw buckle. A movable microbender ( Figure 3 (c)), having four small pillars, which are placed in the corresponding holes of the upper and lower cover structures of the optical fiber for positioning.

[0036] In order to seal the microbend fiber optic sensing assembly 6, the larger opening of the upper cover is covered with elastic rubber (1 mm thickness, Shore hardness 80), while the smaller opening is connected to the four-way connector through tube 34 to form a closed space. The pressure change in this space causes the elastic rubber to deform, thereby moving the movable microbender, thereby changing the distance between the two microbenders. A multimode optical fiber with a length of 4.3 cm is clamped between these microbenders. The initial bending degree of the sensing optical fiber can be changed by adjusting the spacing of the spiral structure between the upper and lower cover structures. The pressure change in the closed space causes the change in the bending of the optical fiber, resulting in a change in the transmission coefficient of the light propagating through this section of optical fiber. By measuring the change in the light transmission coefficient at the receiving end and performing algorithm analysis, parameters such as heart rate, breathing rate and body weight can be extracted.

[0037] The equivalent total force F and total area A in the sealed inflatable structure are introduced:

[0038] F=PA=PNA0 (1)

[0039] Here, P represents the pressure on the airbag system. The proposed system includes an airbag assembly consisting of N small airbag units. Each airbag unit has the same equivalent area, denoted as A0. The total area A of the airbag assembly is determined by multiplying the number of airbag units N by the equivalent area A0 of each airbag unit, resulting in A=NA0. In order to simplify and clearly analyze the physical phenomena involved, all small tube connections and the space inside the slightly bent optical fiber pressure sensor are ignored. When inflated, regardless of the presence or absence of body weight load, the equivalent forces generated are denoted as F1 and F2, respectively, which can be expressed as:

[0040] F1=P1NA1 (2)

[0041] F2=P2NA2 (3)

[0042] Here, A1 and A2 represent the equivalent area of ​​the system without and with body weight load, respectively. As body weight load is applied to the mattress, the initial pressure P1 will change to P2. The pressure change can be expressed as:

[0043] (4)

[0044] Assume that A2≈A1, which is true in our experiment. BW represents body weight. From equation (4), it is obvious that the sensitivity of the system is inversely proportional to 1 / NA1. Therefore, the larger the value of A1, the lower the system sensitivity, or in other words, the larger the number of airbag units N, the lower the system sensitivity, provided that A1 remains unchanged.

[0045] For example, the sensitivity of a small air-cell inflated pillow is about 1 kPa / kg. In contrast, for a typical air-filled mattress, the system sensitivity is significantly lower (about 0.04 kPa / kg). This difference highlights the importance of understanding the relationship between the system sensitivity and its structural parameters, such as the area and number of air-cell units.

[0046] Body vibrations include motions from heartbeat and respiration. However, in bedridden patients, parts of the body remain stationary for long periods of time, making any potential motion negligible within this simplified analysis. Therefore, body weight BW can be expressed as:

[0047] BW(t)=F s (t)+F rr (t)+F hr (t) (5)

[0048] Here, t represents time, F s is the force due to static body weight, Frr is the dynamic force generated by the breathing movement, F hr is the dynamic force generated by the ballistocardiogram. According to our research and other sources, typical values ​​of Fhr range from 0.1 to 0.3 kg, while F rr It is about 5 to several dozen times of Fhr. hr The pressure change caused is very small, about the same as F s The induced pressure change is two to three orders of magnitude smaller.

[0049] In the proposed system, microbend fiber is used to sense and measure pressure. A section of multimode fiber is clamped between two microbenders. According to the microbend fiber theory, the sinusoidal amplitude of the clamped multimode fiber will change and fluctuate with the displacement between the two microbenders, and thus will change with the weight and body vibration. s (t) + F rr (t) + F hr (t) modulates the pressure applied to the microbend fiber. Therefore, the transmission coefficient T of light propagating in the microbend fiber is modulated by the pressure. Some light is lost from the fiber core through coupling between the guided mode and the radiated mode. The change in the transmission coefficient T is given by the following formula [Nicholas Lagakos, JH Cole, and JA Bucaro, "Microbend fiber-optic sensor," Appl. Opt. 26, 2171-2180 (1987)]:

[0050] (6)

[0051] where k f is the force constant, A p is the cross-sectional area, ∆P is the change in pressure applied to the microbend fiber, and ∆X is the displacement of the fiber deformation amplitude X. The critical mechanical spacing Λ in a microbend sensor is given by:

[0052] (7)

[0053] Where a is the core radius of the optical fiber, n is the refractive index of the core, and NA is the numerical aperture. The change in the transmission coefficient T in equation (6) can be rewritten as:

[0054] (8)

[0055] (9)

[0056] (10)

[0057] Where S Nrepresents the system sensitivity when N airbag units are used in the system, while S1 represents the system sensitivity when a single airbag unit is used. ΔT / ΔX represents the sensitivity of the microbend fiber sensor. It can be clearly seen from equations (8)-(10) that the sensitivity of the proposed system depends largely on the number of airbag units N and the sensitivity of the fiber sensor ΔT / ΔX.

[0058] The larger the sensitivity ΔT / ΔX of the slightly bent optical fiber sensor, the greater the overall system sensitivity S N In addition, using fewer airbag units in the airbag combination will result in a higher system sensitivity S N In order to improve the overall system sensitivity S N , the sensitivity ΔT / ΔX of the microbend fiber sensor can be increased and the number of airbag units used can be reduced. When equation (7) is satisfied, the sensitivity ΔT / ΔX of the microbend fiber sensor reaches the maximum. We can calibrate and calculate the patient's weight according to equations (8)-(10). The vibration force caused by heartbeat and breathing is a periodic signal, which does not affect the measurement of weight after averaging. In addition, the vibration caused by heartbeat and breathing will modulate the change of the transmission coefficient T according to equation (8). By demodulating the output signal, the heart rate (HR) and respiratory rate (RR) can be obtained. In the proposed system, a single airbag unit 45 is mainly used for HR and RR measurement, and N airbag units are used for BW measurement. In the proposed system, different N can be selected to make the system have different sensitivities, so that HR, RR and BW can be measured simultaneously. It solves the problem that the current airbag mattress cannot measure HR, RR and BW simultaneously. This simple and direct technology not only allows BW, HR and RR to be measured simultaneously, but also allows bedridden patients to lie on the mattress continuously.

[0059] Equation (9)

[0060]

[0061] is the most important formula we have derived and is applicable to both single-mode and multimode fibers.

[0062] We define the normalized system sensitivity

[0063] (11)

[0064] According to equation (11), we can change the sensitivity of the system by choosing different N.

[0065] To seal the sensor, the larger opening of the upper cover is covered with an elastic rubber (1 mm thickness, Shore hardness 80), while the smaller opening is connected to a four-way connector through a tube 34 to form a closed space. Pressure changes in this space cause the elastic rubber to deform, thereby moving the movable microbender, thereby changing the distance between the two microbenders. A section of multimode optical fiber is clamped between these microbenders. The initial bending degree of the sensing optical fiber can be changed by adjusting the pitch of the spiral structure between the upper and lower cover structures. Pressure changes in the closed space cause changes in the bending of the optical fiber, resulting in changes in the light transmission coefficient through this section of optical fiber. By measuring the changes in the light transmission coefficient at the receiving end and performing algorithm analysis, parameters such as heart rate (HR), respiratory rate (RR) and body weight can be extracted.

[0066] To evaluate the functionality of the proposed system, we performed several experiments to verify its proof of concept. We used an ultra-bright diode with a 90 nm bandwidth as the light source and an optical power meter with a resolution of 0.01 dB for power measurement. In addition, we utilized a digital pressure gauge with a resolution of 0.01 kPa and an electronic scale for characterization.

[0067] In our experimental setup, the optimal spacing of the microbender (Λc) relative to the optical fiber was theoretically determined to be 2.3 mm. However, for cost-effectiveness and rapid prototyping considerations, in our experiments, we used a spacing of Λ = 3 mm. It is worth noting that our goal in this study is not to develop an extremely sensitive microbend fiber sensor, but to demonstrate a new balloon microbend fiber sensor system with adjustable system sensitivity for simultaneous measurement of body weight (BW), heart rate (HR), and respiratory rate (RR).

[0068] Microbend fiber is a multimode fiber with a diameter of 100 microns. All input and output fibers are standard single-mode or multimode communication fibers. For fiber connections between single-mode and multimode fibers, we use fusion splicing and use a protective tube to protect the joint. For SMS structures, we achieve low insertion loss, ranging from about 1.53 dB to 3.76 dB.

[0069] Figure 4 This is a typical curve of the relationship between the system light transmission coefficient and pressure. Figure 4 The analysis shows that within the range of about 5 kPa, the system sensitivity is 16.18% / kPa and the R square is 0.97.

[0070] To explore Figure 1To show the relationship between body weight and output power in the system, we used a body weight simulator. Following the guidelines of the International Electrotechnical Commission [International Electrotechnical Commission. Medical electrical equipment-part2 particular requirements for safety of electrically operated hospital beds. IEC 60601-2-52:2009], water in a water storage container was used to simulate the weight of a human body, where the weight was distributed proportionally to three areas: 45% to the torso, 25% to the hips, and 30% to the legs. We used 20 airbag units, each with a diameter of 7.5 cm and a length of 80 cm. The relationship between body weight and normalized output power is approximately linear, and the system sensitivity S 20 It is 1.527% / kg. Figure 5 The measured system light transmission coefficient versus body weight is shown. From the calibration curve

[0071] Weight (kg) = (0.5701-ΔT) / 0.01527

[0072] It can be obtained that the measurement accuracy of the system is less than 4%. If a nonlinear regression calibration curve is used, the measurement accuracy of the system can be less than 2%.

[0073] Next, its ability to measure small changes in body weight, heart rate, and respiratory rate was evaluated. First, the power change was observed when the initial 40 kg body weight was increased by 1 kg using a combination of 20 balloon units. The average power change recorded was 0.05 dB, an order of magnitude that can be easily detected by most commercial optical power meters. This corresponds to a pressure change of about 0.04 kPa measured by the digital manometer, which is also the change caused by the breathing effort of a volunteer. This robustness and accuracy in measuring weight fluctuations makes the system particularly beneficial for patients with renal failure or kidney disease. These people often require dialysis to eliminate excess body fluid, which usually ranges from 2 to 10 kg, in order to maintain their dry weight.

[0074] The next experiments focused on measuring the heart rate (HR) and respiratory rate (RR). For this purpose, both a single airbag unit (which was 451 located under the volunteer's shoulder) and all 20 airbag units were used. The output signals were transmitted via Bluetooth to the terminal laptop 13 at a sampling frequency of 50 Hz. Using our algorithm [Y. Zhang, Z. Chen, HI Hee, Noninvasive measurement of heart rate and respiratory rate for perioperative infants, J. Lightwave Technol. 37 (2019) 2807–2814.] in the laptop 13, the HR and RR signals can be extracted and the results reported subsequently.

[0075] To validate the HR measurement, a medical multi-parameter monitor (IOCARE, PM-900 monitor) was used, while RR was counted manually by our staff as a reference. The test subjects were asked to remain quiet to minimize the interference of background noise. During the experiment, the reference monitor, manual counting, and sensor system simultaneously acquired output results.

[0076] A total of 11 participants, including 8 men and 3 women, took part in the HR and RR experiments. The tests were performed with the participants in the common supine position, simulating the situation of a typical patient in bed. Figure 6 Screenshots showing the original waveform (acquired within 12 seconds), filtered breathing waveform (acquired within 12 seconds), and BCG waveform (acquired within 6 seconds) of a volunteer: (a) N=20; (b) N=1

[0077] exist Figure 6 In (a), the heartbeat signal in the raw data is somewhat blurred because all 20 airbag units are used at the same time. Figure 6 In (b), the heartbeat becomes clearly discernible within the respiratory modulation curve when only a single unit is used. This improvement is attributed to the significant increase in system sensitivity when a single balloon unit is used. In fact, according to equation (9), the system sensitivity of a single balloon unit is approximately 20 times that when all balloon units (N=20) are used.

[0078] In addition, Figure 6In (b), the volunteer's breathing rate can be estimated to be (60 * 3 / 12) = 15 times per minute (bpm). In addition, there are about 7.5 peaks that occur at almost equal intervals, synchronized with the volunteer's heartbeat. The approximate calculation of HR results in (60*7.5 / 6) = 75 bpm (slightly different from the algorithm's result of 76 bpm). These results demonstrate the sensor's ability to detect weak cardiac force oscillations.

[0079] It is noteworthy that the heart rate measurements obtained by our proposed system are very close to those recorded by the medical device, demonstrating the reliability of our sensor's performance. In addition, the respiratory rate was counted manually and compared, and the measured results were very close to the actual values. The maximum error observed was only 3 bpm for the respiratory rate and 5 bpm for the heart rate measurement. The mean error and standard deviation of the heart rate were 0.39 bpm and 0.70 bpm, respectively. Similarly, the mean error and standard deviation of the respiratory rate were 0.4 bpm and 0.77 bpm, respectively. These values ​​are within the acceptable range specified by the standards. The error analysis highlights the potential of the sensor to accurately measure vital signs with high precision.

[0080] Through a series of experiments, we successfully verified the working mechanism of the proposed system and confirmed its feasibility. The system was effectively demonstrated to be used to simultaneously measure body weight (BW), heart rate (HR), and respiratory rate (RR) in bed. Through in-depth analysis and experiments, we have a clear understanding of its functional mechanism.

[0081] A notable feature of our proposed system is the adjustable system sensitivity: one balloon unit with an inherently high sensitivity S1 is used to measure heart rate and respiration rate, while the remaining balloon combination has an inherent system sensitivity of approximately S1 / N for weight measurement. Weight measurement does not require a high system sensitivity. Our system uses adjustable system sensitivity to simultaneously measure the patient's weight, respiration rate, and heart rate, overcoming the difficulty of detecting the tiny cycle signals of respiration and heartbeat. Unlike previous methods, which used a balance tube and two sensing balloon units to address this challenge, our system avoids the reduced sensitivity associated with such methods. In addition, low-frequency signals of respiration are more easily detected in our system, circumventing the limitations encountered by previous methods. Unlike systems that eliminate the initial weight in the differential pressure sensor setup, our system has the advantage of measuring weight, heart rate, and respiration rate simultaneously.

[0082] We have invented and verified a novel vital signs monitoring system for bedridden patients. The system uses the air pressure changes in the airbags in the air mattress to simultaneously measure the patient's weight, respiratory rate, and heart rate without the patient standing up or moving in bed. The working mechanism of the proposed system has been studied and verified experimentally. This innovative solution is particularly suitable for bedridden patients. They are bedridden, unable to stand, or require continuous monitoring of dynamic physiological data. The proposed vital signs monitoring system for bedridden patients may be used in future medical systems to monitor basic vital signs of bedridden patients. It is an affordable solution and has great potential for application in home environments.

[0083] A total of 6 subjects participated in the experiment, including 4 men and 2 women. They were asked to remain quiet in bed to minimize the interference of background noise. The test was performed with the subjects in the common supine position, simulating the situation of a typical patient in bed. According to the calibration curve

[0084] Weight (kg) = (0.34557-ΔT) / 0.01477

[0085] The subject's weight can be calculated. According to our algorithm [Y. Zhang, Z. Chen, HI Hee, Noninvasive measurement of heart rate and respiratory rate for perioperative infants, J. Lightwave Technol. 37 (2019) 2807–2814.], the subject's heart rate and respiratory rate can be obtained. Table 1 shows the simultaneous measurement results of BW, HR and RR.

[0086] Table 1 Simultaneous measurement results of BW, HR and RR

[0087]

Claims

1. A fiber optic monitor capable of monitoring the vital signs of bedridden patients, characterized in that: It includes an air pump, an air valve switch, a four-way connector, an air bag, a light source, a first photodetector, a second photodetector, an optical fiber coupler, a slightly bent optical fiber sensing component, an optical power measurement module, a respiratory rate and heart rate measurement module, a microcontroller MCU module and a terminal; The air pump is connected to a four-way connector via an air valve switch, and the four-way connector is connected to the airbag and the slightly bent optical fiber sensing assembly; the slightly bent optical fiber sensing assembly is connected to the light source and the optical fiber coupler; the optical fiber coupler is connected to the first photodetector and the second photodetector; the first photodetector is connected to the optical power measurement module, and the second photodetector is connected to the respiratory rate and heart rate measurement module; the optical power measurement module and the respiratory rate and heart rate measurement module are both connected to the microcontroller MCU module; the microcontroller MCU module is connected to the terminal.

2. The optical fiber monitor capable of monitoring vital signs parameters of bedridden patients according to claim 1, characterized in that: The airbag comprises N airbag units, where N>1; the air pump inflates the airbag units through an air valve switch and a four-way connector.

3. The optical fiber monitor capable of monitoring vital signs parameters of bedridden patients according to claim 2, characterized in that: The micro-bend optical fiber sensing component is cylindrical and consists of an upper cover structure and a lower cover structure; a micro-bender with a tooth pitch and a pair of teeth is provided in the lower cover structure, and a multi-mode optical fiber is fixed on the teeth with glue; the upper cover structure and the lower cover structure are connected by a spiral buckle; and it also includes a movable micro-bender with four small columns, which are placed in the corresponding holes of the optical fiber upper cover structure and the lower cover structure for positioning.

4. The optical fiber monitor capable of monitoring vital signs parameters of bedridden patients according to claim 3, characterized in that: A first optical fiber is connected between the light source and the slightly bent optical fiber sensing assembly, and a second optical fiber is connected between the slightly bent optical fiber sensing assembly and the optical fiber coupler.

5. The optical fiber monitor capable of monitoring vital sign parameters of bedridden patients according to claim 4, characterized in that: The air pump inflates an airbag containing N unit airbags through an air valve switch and a four-way connector port; when the airbag is filled to a set pressure, the air valve is closed; at this time, the pressure acts on the optical fiber in the micro-bend optical fiber sensing component through the port of the four-way connector and causes the optical fiber to bend and deform; the light emitted by the light source is incident on the micro-bend optical fiber sensing component through a first optical fiber and passes through a second optical fiber and then a 1x2 optical fiber coupler, and the light is divided into two paths: one path is incident on a first photodetector, and the other path is incident on a second photodetector; after photoelectric conversion by the first photodetector and the second photodetector, the signals are respectively input into an optical power measurement module and a respiratory rate and heart rate measurement module; the microcontroller MCU module transmits the signals and results of the optical power measurement module and the respiratory rate and heart rate measurement module to the terminal by wire or wirelessly.

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