Design of an Apnea Monitoring Device for Preterm Babies

doi:10.21203/rs.3.rs-3954451/v1

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Design of an Apnea Monitoring Device for Preterm Babies

https://doi.org/10.21203/rs.3.rs-3954451/v1

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Apnea, a medical condition characterized by the cessation of breath for more than 15–20 seconds, is a significant health concern affecting an estimated 936 million people globally, with a more significant number being children. In preterm babies, sleep apnea can be a more prevalent issue due to their underdeveloped airways and breathing mechanisms. This condition leaves preterm infants susceptible to complications such as cognitive impairment and cerebral palsy. In Ghana, there is a lack of stand-alone apnea monitoring devices. Given that between 1–5% of children are born with obstructive sleep apnea, the need for such devices is essential. In response to this need, we applied frugal engineering principles to design a user-friendly prototype of an apnea monitor for early detection. The design comprises four central units: a power supply unit, a signal acquisition unit, a processing unit, and a display unit. The system obtains breathing signals from the thoracic region using respiratory and pressure sensors that measure and record the thoracic effort during breathing. These signals are then amplified by an operational amplifier (LM324) and processed by an ATMEGA328p microcontroller programmed using the Arduino IDE. The output is subsequently displayed on a liquid-crystal display (LCD) screen. The device was tested on an adult male with over 90% accuracy in detecting apnea. The outcome indicated the potential of the device to contribute to the early detection and management of apnea, thereby mitigating its associated health risks.

detection of apnea

preterm babies

cessation of breath

apnea monitoring devices

From the first to the thirty-eighth week of pregnancy, expectant mothers are the primary source of oxygen and nutrients for their unborn children[1]. This period, known as the gestation period, requires the utmost care to ensure the survival and healthy development of the fetus. One of the critical parameters monitored during pregnancy is oxygen saturation. Optimal oxygen saturation levels in the mother indicate a healthy environment for the baby's growth and development. However, various conditions can disrupt the typical gestation period of 38 weeks, leading to premature birth.

Premature babies, born before the completion of the entire gestation period, often require specialized care in an incubator. Continuous monitoring of the baby's oxygen saturation levels becomes crucial to ensure their well-being and proper development.

Prematurity is a significant factor in neonatal disorders. In recent times, prematurity contributes to three-quarters of the mortality of infants and half of the neonate's mental disorders. Premature death is an alarming global situation and contributes to 29% of the top five causes of neonatal mortality. Other causes of mortality among infants include congenital anomalies, neonatal tetanus, neonatal infections, asphyxia, and diarrheal diseases [2], [3]. One other major cause of premature death, in addition to those above, is sleep apnea.

Apnea is the cessation of breath for more than 15–20 seconds. There are three types of apnea: obstructive, central, and mixed. Obstructive sleep apnea (OSA) is a prevalent form of sleep apnea that arises when the relaxation of throat muscles obstructs airflow into the lungs. Central sleep apnea (CSA) is when the brain fails to transmit appropriate signals to the muscles responsible for regulating breathing. Mixed sleep apnea combines obstructive and central sleep apnea features, making it more challenging to diagnose and treat. Preterm infants are prone to obstructive apnea due to underdeveloped lungs [4]. In treating the condition, most hospitals in Ghana revive the babies using the traditional method: rubbing the back, changing the sleeping position, and bagging.

Problem identification

Sleep apnea affects up to 40% of men and 25% of women worldwide. In Ghana, the prevalence of sleep apnea is not well known due to a lack of research and increased awareness. However, among the African population, up to 30% may have moderate to severe sleep apnea, of which preterm babies are a part. Apnea can lead to various health problems in children and preterm babies, including growth restriction, developmental delays, and impaired cognitive function [5]. Ongoing sleep apnea can raise the risk of chronic conditions such as obesity, diabetes, and heart disease. Long-term exposure to breathing difficulties during sleep can affect the ability to concentrate, learn, and remember things [6]. Therefore, this condition must be detected and treated to avoid potential health challenges. From research, it was observed that, as far as monitoring of apnea was concerned, most of the hospitals in Ghana do not have devices that detect apnea directly in preterm babies.

Patient monitors, pulse oximeters, BP monitors, and ECGs summed up in an incubator are used. The devices monitor and detect the episode indirectly; however, they are inefficient as they only detect it after the child has stopped breathing. Aside from the inefficiency, rural hospitals lack adequate funds to afford efficient devices to monitor apnea, which results in a high rate of infant mortality. Also, the few hospitals with a few devices need more specialists to operate them appropriately.

Therefore, a cost-effective, user-friendly, and efficient apnea monitoring device is needed to monitor, detect, and diagnose this condition.

The project's objective was to engineer a device capable of monitoring sleep apnea in preterm infants and notifying users of an ongoing episode via an alert system. This led to the development of a design that could be executed through three primary sections: signal acquisition, signal amplification, and the output and alarm system. The design was shaped by the data gathered from a survey during the research phase. Multiple concepts were evaluated using decision matrices to identify the optimal concept that aligns with the design objectives, product specifications, and customer requirements. The block diagram in Fig. 1 illustrates the comprehensive design mechanism of the sleep apnea monitor. It delineates the compartments of the device's operation and the interrelationships between each stage. This comprehensive approach ensures the device's effectiveness in monitoring and alerting users to sleep apnea episodes in preterm infants.

Signal Acquisition

A contact means of detecting breathing action was used. This was done using a pressure sensor that measures and records thoracic effort from breathing. This uses the respiratory sensor to detect breathing signals from preterm babies. Breathing is ascertained by the rhythmic movements of the diaphragm, which result in the expansion and relaxation of the chest. The respiration sensor picks up these motions as analog signals for processing.

The pressure sensor was attached to a strap, an anti-bacterial biocompatible cloth meant to be wrapped around the thoracic region of the preterm to detect thoracic movements as breathing takes place. The length of the strap was influenced by literature. Signals are recorded as the diaphragm contracts and relaxes continually when the baby breathes in and out.

Signal Processing

The processing of analog signals begins when the analog signals from the respiration sensor are fed into the input of the amplification sub-unit., an operational Amplifier (LM324). The LM324 IC is a low-power quad-operational amplifier with four independent operational amplifiers. Its stability and bandwidth characterize it. It is engineered to function across a broad spectrum of voltages, utilizing a single power supply. This versatility makes it a valuable component for our applications. Figure 2 shows the LM324 Operational Amplifier Pinout.

Source: https://microcontrollerslab.com/lm324-op-amp-pinout-datasheet-applications-features-datasheet/

This amplifier is used to amplify the weak bio-signals from the human body. The amplified signals are then fed into the analog input of the processor (ATMEGA328P chip). The option to use the ATMEGA328P is due to its smaller size, compactness, high performance, cost-effectiveness, and low power consumption. The ATMEGA328P is programmed using Arduino IDE to process the sensor readings into breathing patterns (inspiration and expiration). The chip is also programmed to signal a buzzer to buzz when no thoracic movement is recorded for 10 seconds or more.

Display and alert System

The project's primary objective is to design and implement a device that processes signals related to chest movements, thereby facilitating the investigation of an apnea detection system. This innovative device functions by recording the pressure values associated with the movement of the chest during respiration. These recorded pressure values are then displayed on an output screen in real-time, providing a visual representation of the ongoing breathing processes. This feature allows immediate and continuous monitoring of the subject's respiratory patterns.

One of the key features of this device is an integrated alarm system. This alarm is programmed to activate if the device does not record any breathing processes for 10 seconds. This feature serves as an immediate alert system for potential apneic spells, enhancing the safety and reliability of the device. The display is specifically programmed to represent an apneic spell when it occurs visually. This visual cue and the alarm ensure that any apnea occurrence is promptly communicated to the user. Figure 3 shows the circuit diagram of the device designed using Proteus.

Design Specification

The design specifications for our project were informed by data gathered from an online survey of medical practitioners and experts on the incidence of apneic spells in preterm infants. The primary criterion for the design was its working accuracy, which was set to exceed 85%. This means that if a preterm infant ceases to breathe, resulting in no observable chest movement, the device should be able to detect and notify the occurrence of an apnea spell at least 85% of the time. Safety was another critical specification, requiring the device to score at least 95% on a percentile scale. This safety score encompasses environmental and user safety because the device is intended for preterm infants. Comfort was also a significant consideration, as polysomnography's gold standard for apnea detection and monitoring can be uncomfortable for preterm infants due to the numerous body leads used. As such, the comfort index of our device was targeted to be greater than 80%. Budget constraints were also factored into the design process to design the device at a cost of less than GHS 500.00. This budget constraint influenced the choice of components used in the design. The device's weight was another stakeholder requirement, with a target of less than 200 grams set to ensure the device's portability. Finally, we aimed for five operational steps in the device's use to ensure user-friendliness and convenience. This comprehensive approach to design, informed by expert input and user needs, guided the development of an accurate, safe, comfortable, affordable, portable, and user-friendly device. The specification is summarized in Table 1.

Table 1

Specification Table
METRIC	TARGET VALUE
People able to use	preterm
Efficiency of device	> 85%
Weight	< 200 grams
Production cost	<GHC300
Internal parts enclose	100%
Lifespan of a 9v battery	4 weeks
Steps to operate	< 5
Biocompatibility	> 95 percent

Conceptualization

The system's functional structure and the creation of the concept were both influenced by these criteria. The decision matrix was used to evaluate several concepts to find the best one that met the design objective, specification, and customer requirement. The sub-functional units of the design were simulated in virtual models. The design employs four central sub-functional units. These are the signal acquisition, signal processing display, and alarm system. The morphological chart analyzed the various concepts that could be deployed to achieve each sub-function.

Decision Matrix

The decision matrix shown in Fig. 4 was used to ascertain the various components that could be used and how each component performs against the design criteria set out by the customers alongside the design specification.

The proposed final design sketch and circuit diagram were developed using Computer-Aided Design (CAD) and Proteus software, respectively. During the developmental phase of the design process, several changes were made based on the design criteria set out by our device stakeholders. A design prototype was built using the components that proved to be most suitable from the decision matrix, and using the 3D printer, the casing was printed, as shown in Fig. 6.

The prototype was tested on an adult male. This is because the device was unable to be ethically cleared to be tested on its targeted users (preterm babies). The testing was carried out by wrapping the straps interfaced with the FSR sensor around the subject's thoracic region. When the subject began to breathe, the FSR sensor picked chest movements and displayed them as pressure readings on the LCD screen. The breathing processes, inhalation, and exhalation were also displayed on the output screen. The subject was then asked to hold his breath for at least 10 seconds. After 10 seconds of holding breath, the buzzer went off, signaling the occurrence of an apneic spell. This was also accompanied by the display of "apnea occurring" on the output screen. Figure 5 describes the operational steps of the device, Fig. 7 shows the soldered components on a circuit board, Fig. 8 represents a rendered 3D CAD of the device, Fig. 9 shows the exploded view of the design showing the assembly parts, and Fig. 10 shows a displayed warning indicating apnea occurring.

S. H. Choi[7] concluded that premature infants exhibit immature respiratory organs, which results in a notable decline in cerebral oxygenation during episodes of apnea, particularly when accompanied by reduced peripheral oxygen saturation (SpO2). Therefore, monitoring the breathing process in preterm infants is vital.

The utilization of indirect monitoring methods for detecting apnea in premature infants often yields delayed responses, making it challenging to initiate resuscitation promptly. A more effective approach involves using a combination of ECG and pulse oximeter to accurately detect apnea by analyzing the reduction in blood oxygen concentration and subsequent decrease in saturated partial pressure of oxygen (SPO2). This approach can detect apnea and associated hypoxia. To assess its efficacy, we compared it to ventilation/apnea (V/A) monitoring, which detects the cessation of breathing and depletion of available oxygen in the blood. The pulse oximeter promptly detects the decline in SPO2 and triggers a signal. Additionally, the decrease in SPO2 affects muscle activity, which can be observed through appropriate ECG leads connected to the infant for heart activity monitoring.

The system design utilizes the thoracic cavity's motion to monitor the inhalation and exhalation process in preterm infants. This is achieved by employing a force sensor connected to a strap wrapped around the chest area of the infant.

The chest circumference of a preterm infant typically falls within the range of 15.24cm to 31.7cm. During deep inspiration, the movement of the chest increases within a range of 1.5cm to 7cm [8].

The dynamic fluctuations in the dimensions of the thoracic region during the respiratory cycle generate a mechanical force that acts upon the force sensor. Subsequently, the microcontroller transduces the force into pressure measurements, which are then visually presented on the LCD, representing inhalation and exhalation patterns. In the absence of any force applied to the force sensor resulting from alterations in the dimensions of the thoracic region for 10 seconds, the system is designed to activate an alarm. This alarm serves as a notification to healthcare providers about the potential occurrence of an apnea episode. Additionally, for visual identification of an apneic event, the LCD is programmed to exhibit the message "apnea occurring." These features ensure that the detection method employed in this design is direct and timely, providing immediate and accurate identification of apnea episodes.

The respiratory sensor (FSR) used has a slight noise margin; thus, sensing the chest movements surrounding noise (artifact) affected the readings. These were considered during the programming of the sensor; hence, the threshold resistance for detecting a chest movement was set to 100 ohms.

The simulation of the final circuit in Proteus software revealed the nature of the signals picked up by the FSR. This confirmed the literature that bio-signals are weak and need to be amplified. Therefore, an operational Amplifier (LM324) was used to amplify the bio-signals retrieved from the subject.

The alarm system made use of Audio/Visual recognition. This ensures that healthcare attendants are well notified of the incidence of an apneic spell.

Testing the device several times showed that its accuracy depended on the battery's voltage. The device was made to run on a 9v DC power supply. Any power lesser than that will cause a decrease in the efficiency and accuracy of the device. It was realized that the major setback in the device in the face of low voltage was false alarms. This was due to the voltage divider that stepped down the 9v to 5v for the ATMEGA 328P chip.

The system was specifically engineered to operate on a 9V battery, eliminating the need for an external power source. The primary objective of this design was to create an independent apnea detection system capable of real-time monitoring and identification of apnea episodes in preterm infants, enabling prompt medical interventions. This objective has been accomplished.

However, there are certain limitations to consider, along with potential areas for improvement. One such enhancement involves integrating the system with Internet of Things (IoT) technology, allowing it to transmit apnea attack notifications to healthcare providers via mobile devices. Additionally, leveraging IoT capabilities allows the system to store patients' breathing records in a cloud-based platform. This stored data can be retrieved and utilized for medical diagnosis of other health issues, extending the system's utility beyond apnea detection.

Upon acknowledging the breathing challenges of preterm infants, an engineering methodology was employed to fabricate a cost-effective and user-friendly prototype for early apnea detection. The design encompasses a power supply, signal acquisition, processing, and display units. The operational logic of the system was elucidated via a flow chart. Experimental design testing was conducted on an adult male, yielding results corresponding to the designated objectives. Nevertheless, opportunities for improvement persist. Recommendations and suggestions were articulated to guide future investigations and advancements in this project.

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable

Availability of data and materials

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

Competing interests

No, I declare that the authors have no competing interests as defined by BMC, or other interests that might be perceived to influence the results and/or discussion reported in this paper.

Funding

Not Applicable

Authors' contributions

SBS performed the functional analysis, assisted with the circuit design, and discussion of results, and was a major contributor to writing the manuscript. MKK assisted with the circuit design, conducted a literature review, and wrote the manuscript. FCW designed the 3D model printed the model, and assisted with assembling the device. ACA assisted with the questionnaire design and assembly of the device. EO assisted with the soldering of components and testing of sensors. FKD designed the flow chart and decision matrix. DKA Assisted with Assembly of device.

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Slowik JM, Sankari A, Collen JF. Obstructive Sleep Apnea, StatPearls [Internet], Dec. 2022, Accessed: Feb. 04, 2024. [Online]. Available: https://www.ncbi.nlm.nih.gov/books/NBK459252/.
Sarfo FS, et al. Prevalence and Predictors of Sleep Apnea Risk among Ghanaian Stroke Survivors. J Stroke Cerebrovasc Dis. Jul. 2017;26(7):1602. 10.1016/J.JSTROKECEREBROVASDIS.2017.02.027.
Hall MH et al. Feb., Association between sleep duration and mortality is mediated by markers of inflammation and health in older adults: The health, aging and body composition study, Sleep, vol. 38, no. 2, pp. 189–195, 2015, 10.5665/SLEEP.4394.
Choi SH, Lee J, Nam SK, Jun YH. Cerebral Oxygenation during Apnea in Preterm Infants: Effects of Accompanying Peripheral Oxygen Desaturation. Neonatal Med. Feb. 2021;28(1):14–21. 10.5385/NM.2021.28.1.14.
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No competing interests reported.

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You are reading this latest preprint version

Design of an Apnea Monitoring Device for Preterm Babies

Status:

Version 1

Abstract

Figures

INTRODUCTION

Problem identification

MATERIALS AND METHODS

Signal Acquisition

Signal Processing

Source: https://microcontrollerslab.com/lm324-op-amp-pinout-datasheet-applications-features-datasheet/

Display and alert System

Design Specification

Conceptualization

Decision Matrix

RESULTS

DISCUSSION

CONCLUSION

Declarations

Ethics approval and consent to participate

Consent for publication

Availability of data and materials

Competing interests

Funding

Authors' contributions

References

Additional Declarations

Status:

Version 1