Characterization and processing of novel neck photoplethysmography signals for cardiorespiratory monitoring

Epilepsy is a neurological disorder causing serious brain seizures that severely affect the patients' quality of life. Sudden unexpected death in epilepsy (SUDEP), for which no evident decease reason is found after post-mortem examination, is a common cause of mortality. The mechanisms leading to SUDEP are uncertain, but, centrally mediated apneic respiratory dysfunction, inducing dangerous hypoxemia, plays a key role. Continuous physiological monitoring appears as the only reliable solution for SUDEP prevention. However, current seizure-detection systems do not show enough sensitivity and present a high number of intolerable false alarms. A wearable system capable of measuring several physiological signals from the same body location, could efficiently overcome these limitations. In this framework, a neck wearable apnea detection device (WADD), sensing airflow through tracheal sounds, was designed. Despite the promising performance, it is still necessary to integrate an oximeter sensor into the system, to measure oxygen saturation in blood (SpO2) from neck photoplethysmography (PPG) signals, and hence, support the apnea detection decision. The neck is a novel PPG measurement site that has not yet been thoroughly explored, due to numerous challenges. This research work aims to characterize neck PPG signals, in order to fully exploit this alternative pulse oximetry location, for precise cardiorespiratory biomarkers monitoring. In this thesis, neck PPG signals were recorded, for the first time in literature, in a series of experiments under different artifacts and respiratory conditions. Morphological and spectral characteristics were analyzed in order to identify potential singularities of the signals. The most common neck PPG artifacts critically corrupting the signal quality, and other breathing states of interest, were thoroughly characterized in terms of the most discriminative features. An algorithm was further developed to differentiate artifacts from clean PPG signals. Both, the proposed characterization and classification model can be useful tools for researchers to denoise neck PPG signals and exploit them in a variety of clinical contexts. In addition to that, it was demonstrated that the neck also offered the possibility, unlike other body parts, to extract the Jugular Venous Pulse (JVP) non-invasively. Overall, the thesis showed how the neck could be an optimum location for multi-modal monitoring in the context of diseases affecting respiration, since it not only allows the sensing of airflow related signals, but also, the breathing frequency component of the PPG appeared more prominent than in the standard finger location. In this context, this property enabled the extraction of relevant features to develop a promising algorithm for apnea detection in near-real time. These findings could be of great importance for SUDEP prevention, facilitating the investigation of the mechanisms and risk factors associated to it, and ultimately reduce epilepsy mortality.Open Acces

Contactless digital tachometer using microcontroller

Tachometer is a device that used for counting or for the measuring purpose of the number of revolutions (that is the total number rotations made by the device in unit of measuring time) of an object in unit time. It is expressed in the unit of RPS or RPM, the model uses a set of infrared transducer receiver to count the RPM pulses, and the Arduino microcontroller is used for the implementation of the project. The individual pulses are counted by the microcontroller to give the final output of the RPM

A prospective observational study on newborn resuscitation in a high-resource setting

Bakgrunn: Omkring åtte prosent av verdens nyfødte har behov for pustehjelp for å klare overgangen fra intra- til ekstrauterint liv. Nøyaktig forekomst er usikker og varierer antagelig mellom ulike settinger, men resuscitering av nyfødte er likevel en av de vanligste akuttbehandlinger i sykehus rundt om i verden. Internasjonale retningslinjer for nyfødtresuscitering skal sikre lik og optimal behandling av syke nyfødte. Imidlertid er kunnskapsgrunnlaget for internasjonale retningslinjer mangelfullt, og baserer seg i stor grad på prekliniske studier uten sikker forankring i den kliniske hverdagen. Pustestøtte ansees som det viktigste tiltaket, og retningslinjer presiserer at overtrykksventilering bør starte innen ett minutt fra fødsel hos barn som ikke puster selv. Lav hjertefrekvens kan indikere behov for pustestøtte, og ved eventuelle tiltak vil rask bedring i hjertefrekvens indikere at behandlingen er effektiv. Retningslinjer anbefaler derfor tidlig vurdering av barnets hjertefrekvens, og at hjertefrekvens overvåkes under resuscitering ved hjelp av pulsoksymetri (PO) eller elektrokardiografi (EKG). Likevel finnes det lite kunnskap om hva som faktisk er normal hjertefrekvens de første minuttene etter fødsel, og man vet ikke hvilken metode som mest effektivt overvåker barnets hjertefrekvens under resuscitering. T-stykke ventilator er blitt et vanlig apparat for å gi luftveisstøtte til nyfødte. Forskning på bruk av disse apparatene under resuscitering i hovedsak utprøvd på premature nyfødte. Resultater fra forskning på nyfødtresuscitering danner et viktig grunnlag for videre utvikling av evidensbaserte anbefalinger. Mål: Mål for dette prosjektet var å i) studere forekomst av, karakteristika ved, og utfall av nyfødtresuscitering på kort sikt i en høyressurs setting, ii) studere etterlevelsen av retningslinjer for nyfødtresuscitering og undersøke hvor effektivt PO og EKG er til å overvåke hjertefrekvens under resuscitering, iii) beskrive normal hjertefrekvens hos friske nyfødte etter vaginal forløsning og sen avnavling, og iv) beskrive hvilke trykk og volum som leveres ved overtrykksventilering av ikke-pustende nyfødte til termin, når man bruker en T-stykke ventilator. Metode: Denne sammenstillingen bygger på fire prospektive observasjonsstudier. Alle studiene er utført ved Stavanger Universitetssjukehus. Studie I benyttet seg av rapporteringsskjema og videofilming over 12 måneder for å registrere og analysere tiltak ved nyfødtresuscitering. Vi registrerte forekomst av overtrykksventilering, kontinuerlig positivt luftveistrykk (CPAP), intubasjon, hjertekompresjoner og intravenøs administrasjon av adrenalin. Utfall etter resuscitering ble hentet fra elektroniske pasientjournaler. I studie II brukte vi videofilmer fra resuscitering av ikke-pustende barn ≥ 34 gestasjonsuker sammen med PO og/eller EKG-signal fra pasientmonitor. Vi målte tid fra fødsel til vurdering av hjerterytme og tid til oppstart av overtrykksventilering. Videre målte vi tid til pålitelig signal fra PO og EKG. I studie III målte vi hjertefrekvens de første fem minuttene etter fødsel hos friske, vaginalforløste terminbarn med sen avnavling, ved hjelp av en nyutviklet hjertefrekvensmåler med tørrelektrode-EKG (NeoBeat). Vi brukte ‘locally estimated scatterplot smoothing’ for å beregne og tegne percentiler. I studie IV brukte vi en ventilasjonsmonitor for å måle og analysere venilasjonsparametre under overtrykksventilering av terminbarn etter fødsel med T-stykke ventilator som var innstilt etter internasjonale anbefalinger (30/5 cmH2O). Vi analyserte de første 100 innblåsingene i hver resuscitering, og delte dem inn i tidlig (1.-20. innblåsing) og sen (21.-100. innblåsing) fase. Vi brukte ‘general estimating equations’ for å analysere assosiasjoner mellom tidalvolum og topptrykk, innblåsingstid og ventilasjonsfrekvens. Resultat: I studie I inkluderte vi 4693 nyfødte. Av disse ble 291 (6.2%) behandlet med pustehjelp eller annen støtte umiddelbart etter fødsel. Antall nyfødte som ble behandlet med overtrykksventilering, CPAP, intubasjon, brystkompresjoner og intravenøs administrasjon av adrenalin var henholdsvis 170 (3.6%), 121 (2.6%), 19 (0.4%), ti (0.2%), og tre (0.1%). Median (IQR) varighet av overtrykksventilasjon var 106 (54-221) sekunder. 63% av de resusciterte nyfødte ≥34 gestasjonsuker ble igjen hos foreldre etter resusciteringen. I studie II analyserte vi resusciteringer av 104 nyfødte som ikke pustet etter fødsel. I bare 35% av tilfellene ble hjertefrekvens vurdert (ved palpasjon eller auskultasjon) og overtrykksventilering startet innen 60 sekunder etter fødsel. Tiden fra fødsel til vurdering av hjertefrekvens og oppstart av overtrykksventilering var henholdsvis 70 (47-118) og 78 (42-118) sekunder. Tiden fra fødsel til pålitelig registrering av hjertefrekvens fra PO og EKG var henholdsvis 348 (217-524) og 174 (105-227) sekunder (p<0.001). Tiden fra PO måler eller EKG elektroder ble festet på barnet og til pålitelig registrering av hjertefrekvens var henholdsvis 199 (77-352) og 16 (11-22) sekunder (p<0.001). I studie III målte vi hjertefrekvens etter fødsel hos 898 friske nyfødte terminbarn. Hjertefrekvensen økte raskt fra 123 (98-147) slag per minutt ved 5 sekunders alder til 175 (157-189) slag per minutt ved 61 sekunders alder. I studie IV analyserte vi venilasjonsparametre under resuscitering av 129 nyfødte terminbarn. Topptrykket var 30 (28-31) mbar i tidlig fase og 30 (27-31) mbar i sen fase. Tidalvolum var 4.5 (1.6-7.8) ml/kg i tidlig fase og 5.7 (2.2-9.8) ml/kg i sen fase. Innblåsingstid på mer enn 0.41 sekunder i tidlig fase og 0.50 sekunder i sen fase var assosiert med de høyeste tidalvolumene. Ventilasjonsfrekvens på mer enn 32 innblåsinger per minutt i tidlig fase og 41 innblåsinger i per minutt i sen fase var assosiert med reduserte tidalvolum. Konklusjon: Nyfødtresuscitering forekom hyppig i denne høyressurs-settingen. De fleste nyfødte responderte raskt på luftveisstøtte. Etterlevelsen av gjeldende retningslinjer var dårlig. Under resuscitering av nyfødte ble pålitelig overvåkning av hjertefrekvens etablert raskere med EKG enn med PO. Vi har presentert percentiler for normal hjertefrekvens etter fødsel hos friske vaginalforløste terminbarn etter sen avnavling. Når man ventilerte nyfødte terminbarn ved hjelp av en T-stykke ventilator ble det levert stabile topptrykk, men det var vesentlig variasjon i tidalvolum. Innblåsingstid på omtrent 0.5 sekunder og ventilasjonsfrekvens på 30-40 innblåsinger i minuttet var assosiert med det høyeste tidalvolumet.Background: An estimated eight percent of newborns globally need respiratory support at birth to make the transition from intra- to extra uterine life. Although these estimates are uncertain, and presumably vary between settings, newborn resuscitation remains one of the most commonly occurring emergencies in the hospital. Resuscitation guidelines should ensure optimal treatment of compromised newborns; however, there is a general lack of evidence to support the different treatment recommendations. Existing knowledge is in large part derived from pre-clinical studies, and the transferability to real-world resuscitations is uncertain. Guidelines highlight support of breathing as the single most important task during newborn resuscitation, and positive pressure ventilation (PPV) should be initiated within the first minute of life in apnoeic newborns. Furthermore, guidelines acknowledge the newborn heart rate as an important factor to guide resuscitative interventions, and recommend continuous heart rate monitoring during resuscitation by either pulse oximetry (PO) or electrocardiography (ECG). However, there is limited data on the normal heart rate in healthy newborns, and the optimal method for monitoring heart rate during newborn resuscitation remains unknown. The flow driven T-piece resuscitator is a widely used device for respiratory support at birth. However, research into its ventilation performance during resuscitation is limited to premature newborns. Studies on newborn resuscitations provide important feedback to support the process of evolving evidence based resuscitation guidelines. Aim: The aim of this thesis was to i) study the incidence, characteristics and short-term outcomes in newborn resuscitation in a high-resource setting, ii) study compliance with resuscitation algorithms and efficacy of PO versus ECG as heart rate monitoring during resuscitation, iii) describe the normal heart rate in vaginally delivered healthy term newborns after delayed cord clamping, and iv) describe delivered pressures and tidal volumes during positive pressure ventilation of apnoeic term newborns with a T-piece resuscitator. Method: This thesis consists of four prospective observational studies. All studies were conducted at Stavanger University Hospital in Norway. Study I used incident report forms and video recordings to register and analyse resuscitative interventions during a period of 12 months. We recorded the incidence of PPV, continuous positive airway pressure (CPAP), intubation, chest compressions and intravenous administration of adrenaline. From electronic patient records we extracted short-term outcomes after resuscitation. In study II, we combined video recordings of resuscitations with PO and ECG signals from the patient monitor, to analyse guideline compliance and efficacy of heart rate monitoring in newborns ≥34 weeks of gestation receiving PPV after birth. We recorded the time from birth to initiation of PPV and time from birth to initial heart rate assessment by palpation or stethoscope. We compared time to accurate heart rate monitoring between PO and 3-lead ECG. For study III, we used a novel dry electrode ECG heart rate meter (NeoBeat, Laerdal Medical, Stavanger, Norway) to record physiological newborn heart rate in healthy vaginally born newborns after delayed cord clamping the first five minutes after birth. Heart rate centiles were drawn using a local regression model. In study IV we combined video recordings of resuscitations and a respiratory function monitor to record and analyse ventilation parameters during PPV of apnoeic term newborns after birth, using a T-piece resuscitator at standard internationally recommended settings of 30/5 cmH2O. We analysed the first 100 inflations from each resuscitation, and divided them into an early (inflation 1-20) and a late (inflation 21-100) phase. We applied general estimating equations to analyse the association between delivered tidal volumes, and peak inflating pressure, inflation time, and inflation rate. Results: Study I included 4693 newborns. Of those, 291 (6.2%) received interventions after birth. The incidence of PPV, CPAP (only), intubation, chest compressions, and intravenous administration of adrenaline were 170 (3.6%), 121 (2.6%), 19 (0.4%), ten (0.2%), and three (0.1%), respectively. Median (IQR) duration of PPV was 106 (54-221) seconds. 63% of newborns ≥34 weeks of gestation were returned to parental care immediately after resuscitation. For study II, we analysed video- and heart rate recordings of 104 resuscitations. Initial heart rate assessment (stethoscope or palpation) and initiation of PPV were achieved within 60 seconds for 35% of the resuscitated newborns. The time from birth to initial heart rate assessment and initiation of PPV was 70 (47-118) and 78 (42-118) seconds, respectively. Time from birth to provision of a reliable heart rate signal was 348 (217-524) seconds for PO, and 174 (105-227) seconds for ECG (p<0.001). Time from sensor application to a reliable heart rate signal was 199 (77-352) seconds for PO, and 16 (11-22) seconds for ECG (p<0.001). In study III, we recorded heart rates from five seconds to five minutes in 898 healthy, vaginally delivered term newborns. Following birth, the heart rate increased rapidly from 123 (98-147) beats per minute at five seconds after birth to 175 (157-189) beats per minute at 61 seconds after birth. In study IV we analysed ventilation parameters from the resuscitation of 129 term newborns. PIP was 30 (28-31) mbar in the early phase and 30 (27-31) mbar in the late phase. Tidal volume was 4.5 (1.6-7.8) ml/kg in the early phase and 5.7 (2.2-9.8) ml/kg in the late phase. Inflation times exceeding 0.41 seconds in the early phase and 0.50 seconds in the late phase were associated with the highest delivered tidal volumes. Inflation rates exceeding 32 per minute during the early phase and 41 per minute in the late phase were associated with a decrease in tidal volumes. Conclusion: The need of resuscitative interventions after birth was frequent in this high-resource setting, and most newborns responded quickly to airway support. The adherence to guidelines was poor. ECG provided a reliable heart rate signal significantly faster than PO during newborn resuscitation. We presented normal heart rate centiles in vaginally delivered term newborns after delayed cord clamping. When ventilating apnoeic newborns at birth with a T-piece resuscitator, there was a consistent delivery of PIP, however, tidal volumes varied substantially. Inflation time of approximately 0.5 seconds and rates of approximately 30-40 per minute were associated with the highest delivered tidal volumes.Doktorgradsavhandlin

In vivo non-invasive monitoring of optically resonant metal nanoparticles using multi-wavelength photoplethysmography

Nanotechnology has recently emerged as a powerful modality in many biomedical applications. In particular, several classes of nanoparticles have been employed as cancer therapy and imaging contrast agents. These particles can have architecture of varying complexity, depending on their specific application. These complex architectures are achieved by various chemical techniques usually performed in specific sequences to add complexity and functionality. One such class of nanoparticle, used in tumor treatment and as contrast agents in several optical imaging techniques, is the plasmon resonant metal nanoparticle. The most common metal used for these particles is gold because of its biocompatibility, lack of cellular toxicity, and simple surface chemistry. These particles have specific optical properties in the near infrared spectrum making them ideal for modern cancer therapy and optical imaging. Two examples of these particles are gold nanoshells and gold nanorods, both of which are highly absorptive and scattering at near infrared wavelengths. It is for this reason that they are often employed in photo thermal ablation of tumors using near infrared light. In this type of tumor treatment, the particles are injected intravenously and accumulate in the tumor. After accumulation, a near infrared laser is used to heat the particles and destroy the tumor. These gold nanoparticles must be modified with biocompatible stealthing compounds before they can be injected. This is because of the high efficiency of the body\u27s reticuloendotheial system, which will quickly eliminate materials foreign through cellular phagocytosis. Although techniques for quality control in manufacturing these nanoparticles are used to confirm proper surface modification, their in vivo behavior is very difficult to predict. It is for this reason that real time feedback in nanoparticle therapy is an urgent need and will greatly improve its efficacy. This dissertation reports the development of a non-invasive optical system capable of reporting the in vivo vascular concentration of these nanoparticles in near real time. The device, termed the pulse photometer, utilizes a technique similar to that used in pulse oximetry. This technique is photoplethysmography, which has many medical applications. One of these is determining the optical characteristics of pulsatile arterial blood, which are affected after the injection of these optically resonant particles. Several prototypes of this are presented in this dissertation. The culmination of this work is the prototype III pulse photometer capable of concurrent nanoparticle monitoring and oximetry. Final testing of this prototype revealed its ability to accurately determine the vascular optical density of gold nanorods compared to ex vivo spectrophotometry, a technique also verified in this dissertation, by statistical Bland-Altman analysis

Recent development of respiratory rate measurement technologies

Respiratory rate (RR) is an important physiological parameter whose abnormity has been regarded as an important indicator of serious illness. In order to make RR monitoring simple to do, reliable and accurate, many different methods have been proposed for such automatic monitoring. According to the theory of respiratory rate extraction, methods are categorized into three modalities: extracting RR from other physiological signals, RR measurement based on respiratory movements, and RR measurement based on airflow. The merits and limitations of each method are highlighted and discussed. In addition, current works are summarized to suggest key directions for the development of future RR monitoring methodologies

ARTIFICIAL INTELLIGENCE-ENABLED EDGE-CENTRIC SOLUTION FOR AUTOMATED ASSESSMENT OF SLEEP USING WEARABLES IN SMART HEALTH

ARTIFICIAL INTELLIGENCE-ENABLED EDGE-CENTRIC SOLUTION FOR AUTOMATED ASSESSMENT OF SLEEP USING WEARABLES IN SMART HEALT

Fusion enhancement for tracking of respiratory rate through intrinsic mode functions in photoplethysmography

Decline in respiratory regulation demonstrates the primary forewarning for the onset of physiological aberrations. In clinical environment, the obtrusive nature and cost of instrumentation have retarded the integration of continuous respiration monitoring for standard practice. Photoplethysmography (PPG) presents a non-invasive, optical method of assessing blood flow dynamics in peripheral vasculature. Incidentally, respiration couples as a surrogate constituent in PPG signal, justifying respiratory rate (RR) estimation. The physiological processes of respiration emerge as distinctive oscillations that are fluctuations in various parameters extracted from PPG signal. We propose a novel algorithm designed to account for intermittent diminishment of the respiration induced variabilities (RIV) by a fusion-based enhancement of wavelet synchrosqueezed spectra. We have combined the information on intrinsic mode functions (IMF) of five RIVs to enhance mutually occurring, instantaneous frequencies of the spectra. The respiration rate estimate is obtained by tracking the spectral ridges with a particle filter. We have evaluated the method with a dataset recorded from 29 young adult subjects (mean: 24.17 y, SD: 4.19 y) containing diverse, voluntary, and periodically metronome-assisted respiratory patterns. Bayesian inference on fusion-enhanced Respiration Induced Frequency Variability (RIFV) indicated MAE and RMSE of 1.764 and 3.996 BPM, respectively. The fusion approach was deemed to improve MAE and RMSE of RIFV by 0.185 BPM (95% HDI: 0.0285-0.3488, effect size: 0.548) and 0.250 BPM (95% HDI: 0.0733-0.431, effect size: 0.653), respectively, with further pronounced improvements to other RIVs. We conclude that the fusion of variability signals proves important to IMF localization in the spectral estimation of RR.acceptedVersionPeer reviewe

Towards a better understanding of the impact of heart rate on the BOLD signal: a new method for physiological noise correction and its applications

Functional magnetic resonance imaging (fMRI) based on blood oxygenation level-dependent (BOLD) contrast allows non-invasive examination of brain activity and is widely used in the neuroimaging field. The BOLD contrast mechanism reflects hemodynamic changes resulting from a complex interplay of blood flow, blood volume, and oxygen consumption. Heart rate (HR) variations are the most intriguing and less understood physiological processes affecting the BOLD signal, as they are the result of a wide variety of interacting factors. The use of the response function that best models HR-induced signal changes, called cardiac response function (CRF), is an effective method to reduce HR noise in fMRI. However, current models of physiological noise correction based on CRF, i.e. canonical and individual, either do not take into account variations in HR between subjects, and are thus inadequate for cohorts with varying HR, or require time-consuming quality control of individual physiological recordings and derived CRFs. By analyzing a large cohort of healthy individuals, the results presented in this thesis show that different HRs influence the BOLD signal and their corresponding spectra differently. A further finding is that HR plays an essential role in determining the shape of the CRF. Slower HRs produce a smoothed CRF with a single well-defined maximum, while faster HRs cause a second maximum. Taking advantage of this dependence of the CRF on HR, a novel method is proposed to model HR-induced fluctuations in the BOLD signal more accurately than current approaches of physiological noise correction. This method, called HR-based CRF, consists of two CRFs: one for HRs below 68 bpm and one for HRs above this value. HR-based CRFs can be directly applied to the fMRI data without the time-consuming task of deriving a CRF for each subject while accounting for inter-subject variability in HR response

Robust and Analytical Cardiovascular Sensing

The photoplethysmogram (PPG) is a noninvasive cardiovascular signal related to the pulsatile volume of blood in tissue. The PPG is user-friendly and has the potential to be measured remotely in a contactless manner using a regular RGB camera. In this dissertation, we study the modeling and analytics of PPG signal to facilitate its applications in both robust and remote cardiovascular sensing. In the first part of this dissertation, we study the remote photoplethysmography (rPPG) and present a robust and efficient rPPG system to extract pulse rate (PR) and pulse rate variability (PRV) from face videos. Compared with prior art, our proposed system can achieve accurate PR and PRV estimates even when the video contains significant subject motion and environmental illumination change. In the second part of the dissertation, we present a novel frequency tracking algorithm called Adaptive Multi-Trace Carving (AMTC) to address the micro signal extraction problems. AMTC enables an accurate detection and estimation of one or more subtle frequency components in a very low signal-to-noise ratio condition. In the third part of the dissertation, the relation between electrocardiogram (ECG) and PPG is studied and the waveform of ECG is inferred via the PPG signals. In order to address this cardiovascular inverse problem, a transform is proposed to map the discrete cosine transform coefficients of each PPG cycle to those of the corresponding ECG cycle. As the first work to address this biomedical inverse problem, this line of research enables a full utilization of the easy accessibility of PPG and the clinical authority of ECG for better preventive healthcare