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Thalamocortical network: a core structure for integrative multimodal vestibular functions.
Brandt, T, Dieterich, M
Current opinion in neurology. 2019;(1):154-164
Abstract
PURPOSE OF REVIEW To apply the concept of nonreflexive sensorimotor and cognitive vestibular functions and disturbances to the current view of separate right and left thalamocortical systems. RECENT FINDINGS The neuronal modules for sensorimotor and cognitive functions are organized in so-called provincial hubs with intracommunity connections that interact task-dependently via connector hubs. Thalamic subnuclei may serve not only as provincial hubs but also in higher order nuclei as connector hubs. Thus, in addition to its function as a cortical relay station of sensory input, the human thalamus can be seen as an integrative hub for brain networks of higher multisensory vestibular function. Imaging studies on the functional connectivity have revealed a dominance of the right side in right-handers at the upper brainstem and thalamus. A connectivity-based parcellation study has confirmed the asymmetrical organization (i.e., cortical dominance) of the parieto-insular vestibular cortex, an area surrounded by other vestibular cortical areas with symmetrical (nondominant) organization. Notably, imaging techniques have shown that there are no crossings of the vestibular pathways in between the thalamic nuclei complexes. Central vestibular syndromes caused by lesions within the thalamocortical network rarely manifest with rotational vertigo. This can be explained and mathematically simulated by the specific coding of unilateral vestibular dysfunction within different cell systems, the angular velocity cell system (rotational vertigo in lower brainstem lesions) in contrast to the head direction cell system (directional disorientation and swaying vertigo in thalamocortical lesions). SUMMARY The structural and functional separation of the two thalamic nuclei complexes allowed a lateralization of the right and left hemispheric functions to develop. Furthermore, it made possible the simultaneous performance of sensorimotor and cognitive tasks, which require different spatial reference systems in opposite hemispheres, for example, egocentric manipulation of objects (handedness) and allocentric orientation of the self in the environment by the multisensory vestibular system.
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Associations of prolonged standing with musculoskeletal symptoms-A systematic review of laboratory studies.
Coenen, P, Parry, S, Willenberg, L, Shi, JW, Romero, L, Blackwood, DM, Healy, GN, Dunstan, DW, Straker, LM
Gait & posture. 2017;:310-318
Abstract
While prolonged standing has shown to be detrimentally associated with musculoskeletal symptoms, exposure limits and underlying mechanisms are not well understood. We systematically reviewed evidence from laboratory studies on musculoskeletal symptom development during prolonged (≥20min) uninterrupted standing, quantified acute dose-response associations and described underlying mechanisms. Peer-reviewed articles were systematically searched for. Data from included articles were tabulated, and dose-response associations were statistically pooled. A linear interpolation of pooled dose-response associations was performed to estimate the duration of prolonged standing associated with musculoskeletal symptoms with a clinically relevant intensity of ≥9 (out of 100). We included 26 articles (from 25 studies with 591 participants), of which the majority examined associations of prolonged standing with low back and lower extremity symptoms. Evidence on other (e.g., upper limb) symptoms was limited and inconsistent. Pooled dose-response associations showed that clinically relevant levels of low back symptoms were reached after 71min of prolonged standing, with this shortened to 42min in those considered pain developers. Regarding standing-related low back symptoms, consistent evidence was found for postural mechanisms (i.e., trunk flexion and lumbar curvature), but not for mechanisms of muscle fatigue and/or variation in movement. Blood pooling was the most consistently reported mechanism for standing-related lower extremity symptoms. Evidence suggests a detrimental association of prolonged standing with low back and lower extremity symptoms. To avoid musculoskeletal symptoms (without having a-priori knowledge on whether someone will develop symptoms or not), dose-response evidence from this study suggests a recommendation to refrain from standing for prolonged periods >40min. Interventions should also focus on underlying pain mechanisms.
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3.
Prolonged sitting leg vasculopathy: contributing factors and clinical implications.
Padilla, J, Fadel, PJ
American journal of physiology. Heart and circulatory physiology. 2017;(4):H722-H728
Abstract
Atherosclerotic peripheral artery disease primarily manifests in the medium- to large-sized conduit arteries of the lower extremities. However, the factors underlying this increased vulnerability of leg macrovasculature to disease are largely unidentified. On the basis of recent studies, we propose that excessive time spent in the sitting position and the ensuing reduction in leg blood flow-induced shear stress cause endothelial cell dysfunction, a key predisposing factor to peripheral artery disease. In particular, this review summarizes the findings from laboratory-based sitting studies revealing acute leg vascular dysfunction with prolonged sitting in young healthy subjects, discusses the primary physiological mechanisms and the potential long-term implications of such leg vasculopathy with repeated exposure to prolonged sitting, as well as identifies strategies that may be effective at evading it.
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Why is excessive sitting a health risk?
Pesola, AJ, Pekkonen, M, Finni, T
Duodecim; laaketieteellinen aikakauskirja. 2016;(21):1964-71
Abstract
Increased epidemiological evidence over the past few years has shown excessive sitting to be a health risk even if recommendations for physical activity are fulfilled. Sitting is an independent health risk for two reasons: sitting and physical activity exhibit poor correlation, and an increase in physical activity does not contribute to all mechanisms underlying the health risks of sitting. During sitting, muscular passivity increases insulin resistance and influences the transport and oxidation of fatty acids in muscular tissue, and acute exercise is not sufficient to restore all changes. Accordingly, adequate everyday physical activity seems to be important for maintaining the signaling pathways affecting insulin sensitivity.
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[A PARADIGM SHIFT IN THE PERCEPTION OF HEALTH MAINTENANCE FROM INCREASING PHYSICAL ACTIVITY TO DECREASING PHYSICAL INACTIVITY].
Rotman, D, Constantini, N
Harefuah. 2016;(6):374-7, 385, 384
Abstract
Modern man spends most of his waking hours (50-70%) in one form or another of sedentary behavior, defined as activity conducted in a sitting or reclining position involving low energy expenditure. The remaining waking hours are spent performing low intensity physical activity (25-45%) and medium-high intensity physical activity (less than 5%): Despite this distribution, medical research has focused on the impact of increasing medium-high intensity physical activity and many health organizations' recommendations are in accordance. In recent years, research conducted has begun to examine the effect inactivity has on health and has shown that excess sedentary behaviour is an independent risk factor for a wide range of medical problems such as obesity, metabolic syndrome, poor cardiovascular health profile, diabetes mellitus, and possibly cancer. Although the higher risk brought on by sedentary behaviour is partially reduced by increasing medium-high intensity physical activity, it is not completely neutralized. One way to diminish the harm caused by long hours of sitting is to take short breaks during periods of prolonged sitting in order to walk. According to these findings, it is worthwhile to recommend reducing the hours spent in sedentary behaviour, or at least to take frequent short breaks ("activity snacks") during periods of prolonged sitting to get up and walk around.
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The placenta: a multifaceted, transient organ.
Burton, GJ, Fowden, AL
Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 2015;(1663):20140066
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Abstract
The placenta is arguably the most important organ of the body, but paradoxically the most poorly understood. During its transient existence, it performs actions that are later taken on by diverse separate organs, including the lungs, liver, gut, kidneys and endocrine glands. Its principal function is to supply the fetus, and in particular, the fetal brain, with oxygen and nutrients. The placenta is structurally adapted to achieve this, possessing a large surface area for exchange and a thin interhaemal membrane separating the maternal and fetal circulations. In addition, it adopts other strategies that are key to facilitating transfer, including remodelling of the maternal uterine arteries that supply the placenta to ensure optimal perfusion. Furthermore, placental hormones have profound effects on maternal metabolism, initially building up her energy reserves and then releasing these to support fetal growth in later pregnancy and lactation post-natally. Bipedalism has posed unique haemodynamic challenges to the placental circulation, as pressure applied to the vena cava by the pregnant uterus may compromise venous return to the heart. These challenges, along with the immune interactions involved in maternal arterial remodelling, may explain complications of pregnancy that are almost unique to the human, including pre-eclampsia. Such complications may represent a trade-off against the provision for a large fetal brain.
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[Rhabdomyolysis after radical nephrectomy in the lateral decubitus position: report of 2 cases].
Shibamori, K, Yamamoto, T, Matsuki, M, Matsuda, Y, Kato, S, Takei, F, Yanase, M
Nihon Hinyokika Gakkai zasshi. The japanese journal of urology. 2014;(4):218-23
Abstract
Rhabdomyolysis is a rare perioperative complication, however, potentially lead to fatal outcome. We experienced 2 cases of rhabdomyolysis after radical nephrectomy and nephroureterectomy in the lateral decubitus position. (Case 1) A 40-years old man was seen in our hospital because of asymptomatic grosshematuria. Computed tomography revealed right renal pelvic cancer, cT3N0M0. Right radical nephroureterectomy, lymph node dissection, partial cystectomy was underwent, and the operation was finished without any trouble. At the post-operative day 1, serum creatinine level was elevated to the point of 4.2 mg/dl, and serum creatine kinase was 1,945 IU/l. Continuous hemodiafiltration (CHDF) was done at intensive-care unit (ICU), and serum creatinine and creatine kinase level were decreased. At the post-operative day 1, urine myoglobin level was prominently elevated (2,943.7 ng/ml), so we diagnosed acute renal failure due to rhabdomyolysis. (Case 2) A 40-years old man was incidentally pointed out of right renal tumor that was seen as renal cell carcinoma, cT1aN0M0. Open partial nephrectomy was underwent, and there was no trouble during the operation. After recovering from anesthesia, the patient felt left thigh pain strongly. Serum creatine kinase was 888 IU/L after the operation. At the postoperative day 1, serum creatine kinase level was markedly increased (31,138 IU/L). Serum creatinine level was 1.34 mg/dl. Urine and serum myoglobin level was prominently elevated (89,000 ng/ml and 8,634 ng/ml, respectively). We diagnosed it rhabdomyolysis, and he received large amount of fluid intravenously at intensive-care unit. Serum creatine kinase was peak out at the post-operative day 3 (20,709 IU/L), and hemodialysis was not performed.
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Squatting test: A posture to study and counteract cardiovascular abnormalities associated with autonomic dysfunction.
Philips, JC, Scheen, AJ
Autonomic neuroscience : basic & clinical. 2011;(1-2):3-9
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Abstract
The squatting test is an active posture manoeuvre that imposes one of the most potent orthostatic stresses. In normal subjects, the changes in blood pressure and heart rate are transient because of appropriate baroreflex homeostasis and do not provoke symptoms. However, in various pathological conditions, both the increase in blood pressure during squatting and the decrease in blood pressure during standing may be more important and sustained, potentially leading to complaints and adverse events. Squatting has been used to evaluate patients with tetralogy of Fallot, heart transplant, dysautonomia, including diabetic cardiovascular autonomic neuropathy, and individuals prone to vasovagal syncope. Careful analysis of changes in blood pressure and heart rate during the transition from standing to squatting and from squatting to standing allows the early detection of altered vagal and/or sympathetic function. Of note squatting position has been proposed as a therapeutic means to counteract the fall in blood pressure in patients suffering from dizziness due to dysautonomia and orthostatic hypotension or presenting pre-syncope symptoms, such as soon after exercise. The aims of the present review are to analyse the haemodynamic pattern during a squatting test in various pathological situations and to describe what may be the negative and positive haemodynamic changes associated with this posture. We were especially interested in using the squatting test for the assessment of cardiovascular autonomic neuropathy associated with diabetes mellitus.
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Postural blood pressure changes and orthostatic hypotension in the elderly patient: impact of antihypertensive medications.
Hajjar, I
Drugs & aging. 2005;(1):55-68
Abstract
With age our ability to maintain haemodynamic homeostasis during position changes becomes less effective. This predisposes elderly patients to significant changes in blood pressure upon standing and orthostatic hypotension (OH). The prevalence of OH varies according to the population being studied. A range of between 5% and 60% has been reported with the lower rate in elderly individuals living in the community and higher rates in those living in an institution or in the acute-care setting. Multiple factors have been linked to OH including age, bed rest, low body mass index and medications. Although antihypertensive medications can theoretically, as a group, worsen OH, the majority of cross-sectional studies have found no association. In addition, prospective randomised trials have demonstrated an improvement in postural blood pressure (PBP) changes with antihypertensive medications. When considering the individual classes, peripheral vasodilators, specifically alpha-adrenoceptor antagonists and nondihydropyridine calcium channel antagonists, can exacerbate PBP changes and lead to OH. ACE inhibitors, angiotensin-receptor antagonists and beta-adrenoceptor antagonists with intrinsic sympathomimetic activity are less likely to worsen OH. Careful management of electrolyte disturbance can decrease the risk of developing OH with diuretic use. With the aging population, this problem will be encountered by the clinicians at a much higher rate. A detailed patient history, an accurate orthostatic blood pressure measurement and careful evaluation of the autonomic nervous system can provide clinical guidance for management of OH. In hypertensive individuals with no pre-treatment OH, the use of antihypertensive medication can be safe and lead to a low risk of developing OH. In individuals with pre-treatment OH or who develop OH while on antihypertensive medications avoidance of the classes that may exacerbate OH and a judicious use of antihypertensive classes that may improve PBP changes may be safe and adequate treatment.
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10.
Water drinking in the management of orthostatic intolerance due to orthostatic hypotension, vasovagal syncope and the postural tachycardia syndrome.
Mathias, CJ, Young, TM
European journal of neurology. 2004;(9):613-9
Abstract
Water drinking recently has been shown to raise blood pressure in normal subjects and in patients with autonomic failure who have orthostatic hypotension. However, in normal young subjects, ingestion of approximately 500 ml has no pressor effect; but in older subjects there is an increase in blood pressure. An even greater rise in blood pressure occurs in cases with autonomic failure. The possible mechanisms responsible for the pressor response to water include neural and humoral factors; fluid redistribution also needs to be considered. This review will concentrate on the water pressor response in normal subjects and different groups of patients with autonomic diseases who have orthostatic intolerance, on the mechanisms that could be involved, and on whether this pressor response may be used in the management of orthostatic hypotension, vasovagal syncope and the postural tachycardia syndrome.