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"= = = Photoplethysmogram = = =
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" A photoplethysmogram (PPG) is an optically obtained plethysmogram that can be used to detect blood volume changes in the microvascular bed of tissue. A PPG is often obtained by using a pulse oximeter which illuminates the skin and measures changes in light absorption. A conventional pulse oximeter monitors the perfusion of blood to the dermis and subcutaneous tissue of the skin.
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" With each cardiac cycle the heart pumps blood to the periphery. Even though this pressure pulse is somewhat damped by the time it reaches the skin, it is enough to distend the arteries and arterioles in the subcutaneous tissue. If the pulse oximeter is attached without compressing the skin, a pressure pulse can also be seen from the venous plexus, as a small secondary peak.
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" The change in volume caused by the pressure pulse is detected by illuminating the skin with the light from a light-emitting diode (LED) and then measuring the amount of light either transmitted or reflected to a photodiode. Each cardiac cycle appears as a peak, as seen in the figure. Because blood flow to the skin can be modulated by multiple other physiological systems, the PPG can also be used to monitor breathing, hypovolemia, and other circulatory conditions. Additionally, the shape of the PPG waveform differs from subject to subject, and varies with the location and manner in which the pulse oximeter is attached.
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" While pulse oximeters are a commonly used medical device, the PPG derived from them is rarely displayed and is nominally only processed to determine heart rate. PPGs can be obtained from transmissive absorption (as at the finger tip) or reflection (as on the forehead).
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" In outpatient settings, pulse oximeters are commonly worn on the finger. However, in cases of shock, hypothermia, etc. blood flow to the periphery can be reduced, resulting in a PPG without a discernible cardiac pulse. In this case, a PPG can be obtained from a pulse oximeter on the head, with the most common sites being the ear, nasal septum, and forehead. PPG can also be configured as multi-site photoplethysmography (MPPG), e.g. making simultaneous measurements from the right and left ear lobes, index fingers and great toes, and offering further opportunities for the assessment of patients with suspected peripheral arterial disease, autonomic dysfunction, endothelial dysfunction, and arterial stiffness. MPPG also offers significant potential for data mining, e.g. using deep learning, as well as a range of other innovative pulse wave analysis techniques.
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" PPGs can also be obtained from the following parts:
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" Motion artifacts have been shown to be a limiting factor preventing accurate readings during exercise and free living conditions.
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" Because the skin is so richly perfused, it is relatively easy to detect the pulsatile component of the cardiac cycle. The DC component of the signal is attributable to the bulk absorption of the skin tissue, while the AC component is directly attributable to variation in blood volume in the skin caused by the pressure pulse of the cardiac cycle.
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" The height of AC component of the photoplethysmogram is proportional to the pulse pressure, the difference between the systolic and diastolic pressure in the arteries. As seen in the figure showing premature ventricular contractions (PVCs), the PPG pulse for the cardiac cycle with the PVC results in lower amplitude blood pressure and a PPG. Ventricular tachycardia and ventricular fibrillation can also be detected.
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" Respiration affects the cardiac cycle by varying the intrapleural pressure, the pressure between the thoracic wall and the lungs. Since the heart resides in the thoracic cavity between the lungs, the partial pressure of inhaling and exhaling greatly influence the pressure on the vena cava and the filling of the right atrium. This effect is often referred to as normal sinus arrhythmia.
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" During inspiration, intrapleural pressure decreases by up to 4 mm Hg, which distends the right atrium, allowing for faster filling from the vena cava, increasing ventricular preload, but decreasing stroke volume. Conversely during expiration, the heart is compressed, decreasing cardiac efficiency and increasing stroke volume. When the frequency and depth of respiration increases, the venous return increases, leading to increased cardiac output.
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" Anesthesiologists must often judge subjectively whether a patient is sufficiently anesthetized for surgery. As seen in the figure, if a patient is not sufficiently anesthetized, the sympathetic nervous system response to an incision can generate an immediate response in the amplitude of the PPG.
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" Shamir, Eidelman, et al. studied the interaction between inspiration and removal of 10% of a patient’s blood volume for blood banking before surgery. They found that blood loss could be detected both from the photoplethysmogram from a pulse oximeter and an arterial catheter. Patients showed a decrease in the cardiac pulse amplitude caused by reduced cardiac preload during exhalation when the heart is being compressed.
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" The FDA reportedly provided clearance to a photoplethysmography-based cuffless blood pressure monitor in August 2019.
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" While photoplethysmography commonly requires some form of contact with the human skin (e.g., ear, finger), remote photoplethysmography allows to determine physiological processes such as blood flow without skin contact. This is achieved by using face video to analyze subtle momentary changes in the subject's skin color which are not detectable to the human eye. Such camera-based measurement of blood oxygen levels provides a contactless alternative to conventional photoplethysmography. For instance, it can be used to monitor the heart rate of newborn babies.
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" Remote photoplethysmography can also be performed by digital holography, which is sensitive to the phase of light waves, and hence can reveal sub-micron out-of-plane motion. In particular, wide-field imaging of pulsatile motion induced by blood flow can be measured on the thumb by digital holography. The results are comparable to blood pulse monitored by plethysmoraphy during an occlusion-reperfusion experiment . A major advantage of this system is that no physical contact with the studied tissue surface area is required.
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" A refinement of this technique, holographic laser Doppler imaging, enables non-invasive retinal and choroidal blood flow pulse wave monitoring .
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" In laser Doppler holography of the eye fundus, the choroid constitutes the predominant contribution to the high frequency laser Doppler signal. It is however possible to circumvent its influence by subtracting the spatially averaged baseline signal, and achieve high temporal resolution and full-field imaging capability of pulsatile blood flow.
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"= = = Nucleus ambiguus = = =
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" The nucleus ambiguus (literally ""ambiguous nucleus"") is a group of large motor neurons, situated deep in the medullary reticular formation named by Jacob Clarke. The nucleus ambiguus contains the cell bodies of neurons that innervate the muscles of the soft palate, pharynx, and larynx which are associated with speech and swallowing. As well as motor neurons, the nucleus ambiguus contains preganglionic parasympathetic neurons which innervate postganglionic parasympathetic neurons in the heart.
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" It is a region of histologically disparate cells located just dorsal (posterior) to the inferior olivary nucleus in the lateral portion of the upper (rostral) medulla. It receives upper motor neuron innervation directly via the corticobulbar tract.
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" This nucleus gives rise to the branchial efferent motor fibers of the vagus nerve (CN X) terminating in the laryngeal, pharyngeal muscles, and musculus uvulae; as well as to the efferent motor fibers of the glossopharyngeal nerve (CN IX) terminating in the stylopharyngeus muscle.
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" The nucleus ambiguus controls the motor innervation of ipsilateral muscles of the soft palate, pharynx, larynx and upper esophagus. Lesions of nucleus ambiguus results in nasal speech, dysphagia, dysphonia, and deviation of the uvula toward the contralateral side. Preganglionic parasympathetics to the heart also flow through the external formation of the nucleus.
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" The muscles supplied by the vagus (included with this is the cranial root of the accessory nerve), such as levator veli palatini, are also necessary to swallow properly through integration by the nucleus of the solitary tract. The vagus also supplies the upper part of the esophagus, and other parts of the pharynx and larynx.
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" As well as motor neurons, the nucleus ambiguus in its ""external formation"" contains cholinergic preganglionic parasympathetic neurons for the heart. These neurons are cardioinhibitory. This cardioinhibitory effect is one of the means by which quick changes in blood pressure are achieved by the central nervous system (the primary means being changes in sympathetic nervous system activity, which constricts arterioles and makes the heart pump faster and harder). That is, through integrated and antagonistic system with sympathetic outflow from the vasomotor center of the brainstem, the parasympathetic outflow arising from the nucleus ambiguus and dorsal motor nucleus of the vagus nerve acts to decrease cardiac activity in response to fast increases in blood pressure. The external formation of the nucleus ambiguus also sends bronchoconstrictor fibers to the bronchopulmonary system, which can produce reflexive decreases in pulmonary bronchial airflow. The pathophysiologic relevance of this system, which may act in concert with the cardioinhibitory system, is poorly understood, but likely plays a role in bronchospastic diseases like COPD/emphysema (in which inhaled anticholinergic medications such as Spiriva/tiotropium or ipratropium are standard-of-care treatment) and asthma, particularly for exercise-related asthma exacerbations, which may have a component of autonomic dysregulation.
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"= = = Arthur Waley = = =
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" Arthur David Waley (born Arthur David Schloss, 19 August 188927 June 1966) was an English orientalist and sinologist who achieved both popular and scholarly acclaim for his translations of Chinese and Japanese poetry. Among his honours were the CBE in 1952, the Queen's Gold Medal for Poetry in 1953, and he was invested as a Companion of Honour in 1956.
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" Although highly learned, Waley avoided academic posts and most often wrote for a general audience. He chose not to be a specialist but to translate a wide and personal range of classical literature. Starting in the 1910s and continuing steadily almost until his death in 1966, these translations started with poetry, such as ""A Hundred and Seventy Chinese Poems"" (1918) and ""Japanese Poetry: The Uta"" (1919), then an equally wide range of novels, such as ""The Tale of Genji"" (1925–26), an 11th-century Japanese work, and ""Monkey"", from 16th-century China. Waley also presented and translated Chinese philosophy, wrote biographies of literary figures, and maintained a lifelong interest in both Asian and Western paintings.
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" A recent evaluation called Waley ""the great transmitter of the high literary cultures of China and Japan to the English-reading general public; the ambassador from East to West in the first half of the 20th century"", and went on to say that he was ""self-taught, but reached remarkable levels of fluency, even erudition, in both languages. It was a unique achievement, possible (as he himself later noted) only in that time, and unlikely to be repeated.""
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" Arthur Waley was born Arthur David Schloss on 19 August 1889 in Tunbridge Wells, Kent, England, the son of an economist, David Frederick Schloss. He was educated at Rugby School and entered King's College, Cambridge in 1907 on a scholarship to study the Classics, but left in 1910 due to eye problems that hindered his ability to study.
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" Waley briefly worked in an export firm in an attempt to please his parents, but in 1913 he was appointed Assistant Keeper of Oriental Prints and Manuscripts at the British Museum. Waley's supervisor at the Museum was the poet and scholar Laurence Binyon, and under his nominal tutelage Waley taught himself to read Classical Chinese and Classical Japanese, partly to help catalogue the paintings in the Museum's collection. Notwithstanding his ability in reading classical literature, Waley never learned to speak either modern Mandarin Chinese or Japanese, in part because he never visited either China or Japan.
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" Waley was of Ashkenazi Jewish ancestry. He changed his surname from Schloss in 1914, when, like many others in England with German surnames, he sought to avoid the anti-German prejudice common in Britain during the First World War.
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" Waley entered into a lifelong relationship with the English ballet dancer, orientalist, dance critic, and dance researcher Beryl de Zoete, whom he met in 1918 but never married.
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" Waley left the British Museum in 1929 to devote himself fully to writing and translation, and never held a full-time job again, except for a four-year stint in the Ministry of Information during the Second World War.
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" Waley lived in Bloomsbury and had a number of friends among the Bloomsbury Group, many of whom he had met when he was an undergraduate. He was one of the earliest to recognise Ronald Firbank as an accomplished author and, together with Osbert Sitwell, provided an introduction to the first edition of Firbank's collected works.
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" Ezra Pound was instrumental in getting Waley's first translations into print in ""The Little Review"". His view of Waley's early work was mixed, however. As he wrote to Margaret Anderson, the editor of the ""Little Review"", in a letter of 2 July 1917: ""Have at last got hold of Waley's translations from Po chu I. Some of the poems are magnificent. Nearly all the translations marred by his bungling English and defective rhythm. ... I shall try to buy the best ones, and to get him to remove some of the botched places. (He is stubborn as a donkey, or a ""scholar"".)"" In his introduction to his translation of ""The Way and its Power"" Waley explains that he was careful to put meaning above style in translations where meaning would be reasonably considered of more importance to the modern western reader.
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" Waley married Alison Grant Robertson in May 1966, one month before his death on 27 June. He is buried in Highgate Cemetery.
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" Sacheverell Sitwell, who considered Waley ""the greatest scholar and the person with most understanding of all human arts"" that he had known in his lifetime, later recalled Waley's last days,
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" Waley was elected an honorary fellow of King's College, Cambridge in 1945, received the Commander of the Order of the British Empire (CBE) honor in 1952, the Queen's Gold Medal for Poetry in 1953, and the Order of the Companions of Honour (CH) in 1956.
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" Jonathan Spence wrote of Waley's translations that he
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" His many translations include ""A Hundred and Seventy Chinese Poems"" (1918), ""Japanese Poetry: The Uta"" (1919), ""The No Plays of Japan"" (1921), ""The Tale of Genji"" (published in 6 volumes from 1921–33), ""The Pillow Book of Sei Shōnagon"" (1928), The ""Kutune Shirka"" (1951), ""Monkey"" (1942, an abridged version of ""Journey to the West""), ""The Poetry and Career of Li Po"" (1959) and ""The Secret History of the Mongols and Other Pieces"" (1964). Waley received the James Tait Black Memorial Prize for his translation of ""Monkey"", and his translations of the classics, the ""Analects of Confucius"" and ""The Way and Its Power"" (Tao Te Ching), are still in print, as is his interpretive presentation of classical Chinese philosophy, ""Three Ways of Thought in Ancient China"" (1939).
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" Waley's translations of verse are widely regarded as poems in their own right, and have been included in many anthologies such as the ""Oxford Book of Modern Verse 1892–1935"", ""The Oxford Book of Twentieth Century English Verse"" and the ""Penguin Book of Contemporary Verse (1918–1960)"" under Waley's name. Many of his original translations and commentaries have been re-published as Penguin Classics and Wordsworth Classics, reaching a wide readership.
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" Despite translating many Chinese and Japanese classical texts into English, Waley never travelled to either country, or anywhere else in East Asia. In his preface to ""The Secret History of the Mongols"" he writes that he was not a master of many languages, but claims to have known Chinese and Japanese fairly well, a good deal of Ainu and Mongolian, and some Hebrew and Syriac.