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The chapters of this book have covered a wide range of topics in Photoplethysmography (PPG), from basic theory and technology to signal analysis, including a wide range of PPG applications for clinical and consumer use, etc. Owing to its practicality and ease of use, the interest in PPG-based technologies such as wearables continuous to grow year-on-year. The use of PPG for the monitoring of our health and wellbeing has been the corner stone and the main motivator for many of its applications. However, over the years researchers have gone beyond such applications and have explored the utilization of PPG in new directions such as biometrics. This is a subject of major interest as it impacts greatly our daily lives and the security of our private information, and hence it was deemed necessary to contribute parts of this last chapter and inform the readers of all the current efforts made in using PPG as a biometric indicator. Also, as it can be distilled from all the chapters in this book, there is still room for more basic understanding of the origin of the PPG and its relation to various pathophysiological phenomena. Contributors of this book have described and hailed the successes and the potential of the PPG, but at the same time have highlighted the need for more research and better understanding of the signal. Hence, another trend of the recent years, by many PPG research communities, is the return to basic PPG research. Such research can be accomplished by building the right tools and processes which will enable the further understanding of the PPG. Clearly the more we understand the PPG the better we can use it in specific applications. For example, throughout the book there were references for the need of better and more detailed understanding of the light–tissue interactions in PPG in multiple wavelengths (not just red, near-infrared, and green), in both transmission and reflection sensor topologies. Also, there were references for the need of standardization in PPG processes, such as data acquisition, waveform analysis, etc. Hence, it was deemed necessary to share with the readers some of the latest efforts in research in creating custom made phantoms and simulators for PPG, which could aid in the better understanding and utilization of the signal. This being the last chapter, it is also most fitting to offer some final thoughts in the potential future directions of this most exciting vascular optics technology.

Predicted to be 12 TM segment proteins, members of this family transport the reduced form of ascorbic acid (while the oxidized form may be handled by members of the SLC2 family (GLUT1/SLC2A1, GLUT3/SLC2A3 and GLUT4/SLC2A4). phloretin is considered a non-selective inhibitor of these transporters, with an affinity in the micromolar range [1].

In the current case series, three male patients aged 19–21 years, all participating in basketball activities during their competitive season, were evaluated and classified with patella tendinopathy...

Objective— Macrophages express 3 Akt (protein kinase B) isoforms, Akt1, Akt2, and Akt3, which display isoform-specific functions but may be redundant in terms of Akt survival signaling. We hypothesize that loss of 2 Akt isoforms in macrophages will suppress their ability to survive and modulate the development of atherosclerosis. Approach and Results— To test this hypothesis, we reconstituted male Ldlr −/− mice with double Akt2/Akt3 knockout hematopoietic cells expressing only the Akt1 isoform (Akt1 only ). There were no differences in body weight and plasma lipid levels between the groups after 8 weeks of the Western diet; however, Akt1 only → Ldlr −/− mice developed smaller (57.6% reduction) atherosclerotic lesions with more apoptotic macrophages than control mice transplanted with WT (wild type) cells. Next, male and female Ldlr −/− mice were reconstituted with double Akt1/Akt2 knockout hematopoietic cells expressing the Akt3 isoform (Akt3 only ). Female and male Akt3 only → Ldlr −/− recipients had significantly smaller (61% and 41%, respectively) lesions than the control WT→ Ldlr −/− mice. Loss of 2 Akt isoforms in hematopoietic cells resulted in markedly diminished levels of white blood cells, B cells, and monocytes and compromised viability of monocytes and peritoneal macrophages compared with WT cells. In response to lipopolysaccharides, macrophages with a single Akt isoform expressed low levels of inflammatory cytokines; however, Akt1 only macrophages were distinct in expressing high levels of antiapoptotic Il10 compared with WT and Akt3 only cells. Conclusions— Loss of 2 Akt isoforms in hematopoietic cells, preserving only a single Akt1 or Akt3 isoform, markedly compromises monocyte and macrophage viability and diminishes early atherosclerosis in Ldlr −/− mice.

Objective: The aim of this study was to evaluate the capability of features extracted from photoplethysmography (PPG) based Pulse Rate Variability (PRV) to classify hypertensive, normotensive and hypotensive events, and to estimate mean arterial, systolic and diastolic blood pressure in critically ill patients. Methods: Time-domain, frequency-domain and non-linear indices from PRV were extracted from 5-min and 1-min segments obtained from PPG signals. These features were filtered using machine learning algorithms in order to obtain the optimal combination for the classification of hypertensive, hypotensive and normotensive events, and for the estimation of blood pressure. Results: 5-min segments allowed for an improved performance in both classification and estimation tasks. Classification of blood pressure states showed around 70% accuracy and around 75% specificity. The sensitivity, precision and F1 scores were around 50%. In estimating mean arterial, systolic, and diastolic blood pressure, mean absolute errors as low as 2.55 ± 0.78 mmHg, 4.74 ± 2.33 mmHg, and 1.78 ± 0.14 mmHg were obtained, respectively. Bland-Altman analysis and Wilcoxon rank sum tests showed good agreement between real and estimated values, especially for mean and diastolic arterial blood pressures. Conclusion: PRV-based features could be used for the classification of blood pressure states and the estimation of blood pressure values, although including additional features from the PPG waveform could improve the results. Significance: PRV contains information related to blood pressure, which may aid in the continuous, noninvasive, non-intrusive estimation of blood pressure and detection of hypertensive and hypotensive events in critically ill subjects.

Heart rate variability (HRV) utilizes the electrocardiogram (ECG) and has been widely studied as a non-invasive indicator of cardiac autonomic activity. Pulse rate variability (PRV) utilizes photoplethysmography (PPG) and recently has been used as a surrogate for HRV. Several studies have found that PRV is not entirely valid as an estimation of HRV and that several physiological factors, including the pulse transit time (PTT) and blood pressure (BP) changes, may affect PRV differently than HRV. This study aimed to assess the relationship between PRV and HRV under different BP states: hypotension, normotension, and hypertension. Using the MIMIC III database, 5 min segments of PPG and ECG signals were used to extract PRV and HRV, respectively. Several time-domain, frequency-domain, and nonlinear indices were obtained from these signals. Bland–Altman analysis, correlation analysis, and Friedman rank sum tests were used to compare HRV and PRV in each state, and PRV and HRV indices were compared among BP states using Kruskal–Wallis tests. The findings indicated that there were differences between PRV and HRV, especially in short-term and nonlinear indices, and although PRV and HRV were altered in a similar manner when there was a change in BP, PRV seemed to be more sensitive to these changes.

Marcus Tullius Cicero (106–43 bce) rose to prominence in the state during the final decades of the Roman Republic. Blessed with a goodly measure of natural ability, an extraordinary amount of self-discipline, and a remarkably broad and deep education not only in rhetoric but also in philosophy and the other noble arts, Cicero employed his oratorical skill to establish himself in the courts and on the Rostra as Rome’s finest orator. He was elected to the state’s chief political offices at the youngest possible age, and during the final months of his consulship (63 bce), he foiled a plot by L. Sergius Catilina to overthrow the government. His decisive action in that affair was the source of great glory and pride in having saved the state, but also of great pain and heartache, for some five years later he was forced into exile for his part in the summary execution of Catilinarian co-conspirators who were also Roman citizens. Following his return to Rome, he found himself at loggerheads with members of the so-called “First Triumvirate,” a situation that resulted for him in something like a forced retirement from political activity. A decade later, in the wake of Julius Caesar’s victory in the civil war and subsequent dictatorship, Cicero was placed in a similar situation. During both these occasions (namely, the mid-50s and mid-40s bce), he channeled his energies in the direction of his other great love, i.e., contemplation, study, and writing. Remarkably, these two periods saw him produce nearly a score of treatises, including his most important and influential rhetorical writings, wherein he enunciated his deeply-held conviction that eloquent speech (coupled with reason) was a chief civilizing factor in human society—a glue that binds and builds well-ordered communities when employed responsibly by its most expert practitioners. Following the assassination of Caesar and the emergence of Marcus Antonius as a force who appeared to be aiming to secure his own dictatorial powers, Cicero once again took up the mantle of the Republic, hoping for its restoration. He opposed Antonius and his actions by writing and delivering to the Senate and people a series of speeches known as the Philippics. But on the brink of success, young Caesar Octavianus allied himself with Antonius, and Cicero’s name found a prominent place on the list of those proscribed: his head and hands, severed by Antonius’s henchmen, were gruesomely displayed on the speaker’s platform in the Roman forum. See the separate Oxford Bibliographies article in Classics Cicero for a general and more comprehensive bibliography of Cicero and his other works. Other Oxford Bibliographies articles that may be of interest include Greek Rhetoric, Latin Rhetoric, and Rhetoric.

This paper introduces a novel technique for the development of custom polydimethylsiloxane (PDMS) vessels for use in phantom technologies. The method involves continuous dip coating of commercial silicone tubes with rapid curation in a single controlled process. The technique accommodates the production of different vessel diameters, wall thicknesses (56 µm-80 µm) and mechanical properties. Clear phantoms were fabricated to compare the commercial silicone tubes against the customs vessels. A pulsatile fluidic pump (BDCLabs, CO, USA) driven by a computer controlled linear motor generated the pulsatile flow through the phantom. The resulting flow profile, using the custom vessels, simulates human blood flow and the detected contact PPG signal from the phantom closely resembles the morphology of in vivo PPG waveforms with signal-to-noise ratios of 38.16 dB and 40.59 dB, compared to the closest commercially-available tubing at 5.38 dB and 10.59 dB for the red and infrared wavelengths respectively. The rigidity and thick walls of commercial silicone tubes impede the expansion of the tubing under systolic pressure. This technique eliminates this common limitation in phantom development.

Introduction: Heart Rate Variability (HRV) and Pulse Rate Variability (PRV), are non-invasive techniques for monitoring changes in the cardiac cycle. Both techniques have been used for assessing the autonomic activity. Although highly correlated in healthy subjects, differences in HRV and PRV have been observed under various physiological conditions. The reasons for their disparities in assessing the degree of autonomic activity remains unknown.\ud \ud Methods: To investigate the differences between HRV and PRV, a whole-body cold exposure (CE) study was conducted on 20 healthy volunteers (11 male and 9 female, 30.3 ± 10.4 years old), where PRV indices were measured from red photoplethysmography signals acquired from central (ear canal, ear lobe) and peripheral sites (finger and toe), and HRV indices from the ECG signal. PRV and HRV indices were used to assess the effects of CE upon the autonomic control in peripheral and core vasculature, and on the relationship between HRV and PRV. The hypotheses underlying the experiment were that PRV from central vasculature is less affected by CE than PRV from the peripheries, and that PRV from peripheral and central vasculature differ with HRV to a different extent, especially during CE.\ud \ud Results: Most of the PRV time-domain and Poincaré plot indices increased during cold exposure. Frequency-domain parameters also showed differences except for relative-power frequency-domain parameters, which remained unchanged. HRV-derived parameters showed a similar behavior but were less affected than PRV. When PRV and HRV parameters were compared, time-domain, absolute-power frequency-domain, and non-linear indices showed differences among stages from most of the locations. Bland-Altman analysis showed that the relationship between HRV and PRV was affected by CE, and that it recovered faster in the core vasculature after CE. \ud \ud Conclusion: PRV responds to cold exposure differently to HRV, especially in peripheral sites such as the finger and the toe, and may have different information not available in HRV due to its non-localized nature. Hence, multi-site PRV shows promise for assessing the autonomic activity on different body locations and under different circumstances, which could allow for further understanding of the localized responses of the autonomic nervous system.

Heart rate variability (HRV) is a noninvasive marker of cardiac autonomic activity and has been used in different circumstances to assess the autonomic responses of the body. Pulse rate variability (PRV), a similar variable obtained from pulse waves, has been used in recent years as a valid surrogate of HRV. However, the effect that localized changes in autonomic activity have in the relationship between HRV and PRV has not been entirely understood. In this study, a whole-body cold exposure protocol was performed to generate localized changes in autonomic activity, and HRV and PRV from different body sites were obtained. PRV measured from the earlobe and the finger was shown to differ from HRV, and the correlation between these variables was affected by the cold. Also, it was found that PRV from the finger was more affected by cold exposure than PRV from the earlobe. In conclusion, PRV is affected differently to HRV when localized changes in autonomic activity occur. Hence, PRV should not be considered as a valid surrogate of HRV under certain circumstances.Clinical Relevance - This indicates that pulse rate variability is affected differently to heart rate variability when autonomic activity is modified and suggests that pulse rate variability is not always a valid surrogate of heart rate variability.

The aim of this study was to investigate the effect of emitter-detector separation distance and arterial depth in reflectance photoplethysmography (PPG), utilizing a homogenous pulsatile phantom that exhibits the broad optical absorbance and scattering properties of human tissue. The developed phantom comprised of embedded silicone arteries (outer diameter = 4 mm) that were arranged parallel to one another at nine increasing depths (3.2 mm to 24.4 mm). A pulsatile pump (Harvard Apparatus, MA, USA) circulated a blood imitating fluid through the vessels at the desired heart rate (60 bpm) and stroke volume (5 Lmin-1). The PPG sensor’s emitter and detector were isolated on a translation bridge to provide a computer-controlled separation distance between them. Recordings were taken at each vessel depth for emitter-detector separation distances from 2 mm to 8 mm in 0.1 mm steps. The optimum separation distance between the emitter and detector for vessels between depths of 3.2 mm and 10.5 mm was between 3.7 and 4.3 mm, suggesting that the maximum penetration of IR (930 nm) light in a homogenous pulsatile phantom is no greater than 10.5 mm.

Currently there exists little knowledge or work in phantoms for the in-vitro evaluation of photoplethysmography (PPG), and its&rsquo, relationship with vascular mechanics. Such phantoms are needed to provide robust, basic scientific knowledge, which will underpin the current efforts in developing new PPG technologies for measuring or estimating blood pressure, blood flow and arterial stiffness, to name but a few. This work describes the design, fabrication and evaluation of finger tissue-simulating pulsatile phantoms with integrated custom vessels. A novel technique has been developed to produce custom polydimethylsiloxane (PDMS) vessels by a continuous dip-coating process. This process can accommodate the production of different sized vessel diameters (1400&ndash, 2500 &micro, m) and wall thicknesses (56&ndash, 80 &micro, m). These vessels were embedded into a mould with a solution of PDMS and India ink surrounding them. A pulsatile pump experimental rig was set up to test the phantoms, where flow rate (1&ndash, 12 L&middot, min&minus, 1), heart rate (40&ndash, 120 bpm), and total resistance (0&ndash, 100% resistance clamps) could be controlled on demand. The resulting flow profiles approximates human blood flow, and the detected contact PPG signal (red and infrared) from the phantom closely resembles the morphology of in-vivo PPG waveforms with signal-to-noise ratios of 38.16 and 40.59 dB, for the red and infrared wavelengths, respectively. The progress made by this phantom development will help in obtaining new knowledge in the behaviour of PPG&rsquo, s under differing flow conditions, optical tissue properties and differing vessel stiffness.