Pulse oximeters are used in operating rooms and recovery rooms as a monitoring device for oxygen in the respiratory system of the patient. The advantage of pulse oximeters over other methods of oxygen monitoring is that they are easy to use and they are non-invasive, which means it is not necessary break the skin to extract blood for information to be obtained. The standard for the measurement of partial pressure of CO2 and O2 is an arterial blood gas analysis (ABG). However routine monitoring using this method on a continuous basis is impractical since it is slow, painful and invasive. Measuring carbon dioxide is critical to preventing ailments such as carbon dioxide poisoning or hypoxia. The problem is, currently there is no known effective non-invasive method for accurately measuring carbon dioxide in the body to properly assess the adequacy of ventilation. The objective of this study was to experimentally use spectroscopy in the visible spectrum and the principles of operation of a pulse oximeter to incorporate a method of non-invasive real-time carbon dioxide monitoring that is as quick and easy to use.

Although steady progress has been made towards the development of a wearable pulse oximeter to aid in remote physiological status monitoring (RPSM) and triage operations, the ability to extract accurate physiological data from a forehead pulse oximeter during extended periods of activity and in the presence of pressure disturbances acting on the sensor remains a significant challenge. This research was undertaken to assess whether the attachment method used to secure a pulse oximeter sensor affects arterial oxygen saturation (SpO2) and heart rate (HR) accuracy during motion. Additionally, two sensor housings were prototyped to assess whether isolating the sensor from external pressure disturbances could improve SpO2 and HR accuracy. The research revealed that measurement accuracy during walking is significantly affected by the choice of an attachment method. Specifically, the research indicated that an elastic band providing a contact pressure of 60 mmHg can result in decreased measurement error and improved reliability. Furthermore, the research validated that the two isolating housings we have investigated improve SpO2 and HR errors significantly at pressures as high as 1200 mmHg (160 kPa) compared to current commercial housings. This information may be helpful in the design of a more robust pulse oximeter sensor for use in RPSM.

Pulse oximeters are low-cost, easy to use, and effective at detecting hypoxemia (low blood oxygen levels), a common complication of bronchiolitis, asthma, and pneumonia, the leading infectious cause of death in children worldwide. However, pulse oximeters are often unavailable in lowincome settings, and if available, often underused, yet little research investigates why. In this thesis, I examine pulse oximeter implementation in low-income settings, focusing on Kenyan hospitals as a case study, and using a mixed-methods approach. I conducted a systematic literature review, examining how pulse oximeter use with children at admission to hospital impacts health outcomes; I then conducted quantitative analyses of 28,000 children admitted to seven Kenyan hospitals to determine with which children pulse oximeters are used, and pulse oximetry's impact on treatment provision; these analyses informed the qualitative research component, for which I conducted interviews with 30 healthcare workers (HCWs) and staff in 14 Kenyan hospitals and employed theoretical frameworks to determine how HCWs decide whether to use pulse oximeters, and the barriers to pulse oximetry. I found that pulse oximeter use varies substantially between and within Kenyan hospitals over time. After adjusting for case-mix and signs of illness severity, HCWs were most likely to use pulse oximeters with children with a very high respiratory rate, indrawing and/or who were not alert; children who obtained a pulse oximeter reading were more likely to be prescribed oxygen than if a pulse oximeter was not used; and children with a reading below 90% were more likely to be prescribed oxygen than those with higher readings, suggesting that HCW decision-making is influenced by international and national guidelines. However, HCWs sometimes cannot use pulse oximeters when they intend to, because of insufficient pulse oximeter availability, largely due to inefficient and confusing procurement processes and repair delays. Furthermore, HCWs sometimes use pulse oximeters incorrectly or misinterpret their results, because of insufficient training. Pulse oximeter promotion programme planners can use the recommendations I provide to effectively target barriers to pulse oximeter uptake in low-income settings. Increased pulse oximetry implementation could enable early detection of hypoxemia, improving accurate diagnosis, and supporting prompt, effective treatment, which could help reduce mortality in children needing oxygen, in line with Sustainable Development Goal 3.

"Non-invasive remote physiological monitoring of soldiers on the battlefield has the potential to provide fast, accurate status assessments that are key to improving the survivability of critical injuries. The development of WPI’s wearable wireless pulse oximeter, designed for field-based applications, has allowed for the optimization of important hardware features such as physical size and power management. However, software-based digital signal processing (DSP) methods are still required to perform physiological assessments. This research evaluated DSP methods that were capable of providing arterial oxygen saturation (SpO2), heart rate (HR), heart rate variability (HRV), and respiration rate (RR) measurements derived from data acquired using a single optical sensor. In vivo experiments were conducted to evaluate the accuracies of the processing methods across ranges of physiological conditions. Of the algorithms assessed, 13 SpO2 methods, 1 HR method, 6 HRV indices, and 4 RR methods were identified that provided clinically acceptable measurement accuracies and could potentially be employed in a wearable pulse oximeter."