<i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring
Photoplethysmography is an extensively-used, portable, and noninvasive technique for measuring vital parameters such as heart rate, respiration rate, and blood pressure. The deployment of this technology in veterinary medicine has been hindered by the challenges in effective transmission of light pr...
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| Format: | Article |
| Language: | English |
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MDPI AG
2020-12-01
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| Series: | Sensors |
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| Online Access: | https://www.mdpi.com/1424-8220/20/24/7335 |
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| author | Jose Manuel Valero-Sarmiento Parvez Ahmmed Alper Bozkurt |
| author_facet | Jose Manuel Valero-Sarmiento Parvez Ahmmed Alper Bozkurt |
| author_sort | Jose Manuel Valero-Sarmiento |
| collection | DOAJ |
| description | Photoplethysmography is an extensively-used, portable, and noninvasive technique for measuring vital parameters such as heart rate, respiration rate, and blood pressure. The deployment of this technology in veterinary medicine has been hindered by the challenges in effective transmission of light presented by the thick layer of skin and fur of the animal. We propose an injectable capsule system to circumvent these limitations by accessing the subcutaneous tissue to enable reliable signal acquisition even with lower light brightness. In addition to the reduction of power usage, the injection of the capsule offers a less invasive alternative to surgical implantation. Our current prototype combines two application-specific integrated circuits (ASICs) with a microcontroller and interfaces with a commercial light emitting diode (LED) and photodetector pair. These ASICs implement a signal-conditioning analog front end circuit and a frequency-shift keying (FSK) transmitter respectively. The small footprint of the ASICs is the key in the integration of the complete system inside a 40-mm long glass tube with an inner diameter of 4 mm, which enables its injection using a custom syringe similar to the ones used with microchip implants for animal identification. The recorded data is transferred wirelessly to a computer for post-processing by means of the integrated FSK transmitter and a software-defined radio. Our optimized LED duty cycle of 0.4% at a sampling rate of 200 Hz minimizes the contribution of the LED driver (only 0.8 mW including the front-end circuitry) to the total power consumption of the system. This will allow longer recording periods between the charging cycles of the batteries, which is critical given the very limited space inside the capsule. In this work, we demonstrate the wireless operation of the injectable system with a human subject holding the sensor between the fingers and the <i>in vivo</i> functionality of the subcutaneous sensing on a pilot study performed on anesthetized rat subjects. |
| first_indexed | 2024-03-10T13:54:22Z |
| format | Article |
| id | doaj.art-84d180da8e29440e9e59dee403ae731c |
| institution | Directory Open Access Journal |
| issn | 1424-8220 |
| language | English |
| last_indexed | 2024-03-10T13:54:22Z |
| publishDate | 2020-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Sensors |
| spelling | doaj.art-84d180da8e29440e9e59dee403ae731c2023-11-21T01:50:13ZengMDPI AGSensors1424-82202020-12-012024733510.3390/s20247335<i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal MonitoringJose Manuel Valero-Sarmiento0Parvez Ahmmed1Alper Bozkurt2Department of Electrical and Computer Engineering, NC State University, Raleigh, NC 27695-7911, USADepartment of Electrical and Computer Engineering, NC State University, Raleigh, NC 27695-7911, USADepartment of Electrical and Computer Engineering, NC State University, Raleigh, NC 27695-7911, USAPhotoplethysmography is an extensively-used, portable, and noninvasive technique for measuring vital parameters such as heart rate, respiration rate, and blood pressure. The deployment of this technology in veterinary medicine has been hindered by the challenges in effective transmission of light presented by the thick layer of skin and fur of the animal. We propose an injectable capsule system to circumvent these limitations by accessing the subcutaneous tissue to enable reliable signal acquisition even with lower light brightness. In addition to the reduction of power usage, the injection of the capsule offers a less invasive alternative to surgical implantation. Our current prototype combines two application-specific integrated circuits (ASICs) with a microcontroller and interfaces with a commercial light emitting diode (LED) and photodetector pair. These ASICs implement a signal-conditioning analog front end circuit and a frequency-shift keying (FSK) transmitter respectively. The small footprint of the ASICs is the key in the integration of the complete system inside a 40-mm long glass tube with an inner diameter of 4 mm, which enables its injection using a custom syringe similar to the ones used with microchip implants for animal identification. The recorded data is transferred wirelessly to a computer for post-processing by means of the integrated FSK transmitter and a software-defined radio. Our optimized LED duty cycle of 0.4% at a sampling rate of 200 Hz minimizes the contribution of the LED driver (only 0.8 mW including the front-end circuitry) to the total power consumption of the system. This will allow longer recording periods between the charging cycles of the batteries, which is critical given the very limited space inside the capsule. In this work, we demonstrate the wireless operation of the injectable system with a human subject holding the sensor between the fingers and the <i>in vivo</i> functionality of the subcutaneous sensing on a pilot study performed on anesthetized rat subjects.https://www.mdpi.com/1424-8220/20/24/7335injectablephotoplethysmographybiomedical electronicsbiophotonicsencapsulationimplant |
| spellingShingle | Jose Manuel Valero-Sarmiento Parvez Ahmmed Alper Bozkurt <i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring Sensors injectable photoplethysmography biomedical electronics biophotonics encapsulation implant |
| title | <i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring |
| title_full | <i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring |
| title_fullStr | <i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring |
| title_full_unstemmed | <i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring |
| title_short | <i>In Vivo</i> Evaluation of a Subcutaneously Injectable Implant with a Low-Power Photoplethysmography ASIC for Animal Monitoring |
| title_sort | i in vivo i evaluation of a subcutaneously injectable implant with a low power photoplethysmography asic for animal monitoring |
| topic | injectable photoplethysmography biomedical electronics biophotonics encapsulation implant |
| url | https://www.mdpi.com/1424-8220/20/24/7335 |
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