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      Orthostatic Intolerance in Older Persons: Etiology and Countermeasures

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          Abstract

          Orthostatic challenge produced by upright posture may lead to syncope if the cardiovascular system is unable to maintain adequate brain perfusion. This review outlines orthostatic intolerance related to the aging process, long-term bedrest confinement, drugs, and disease. Aging-associated illness or injury due to falls often leads to hospitalization. Older patients spend up to 83% of hospital admission lying in bed and thus the consequences of bedrest confinement such as physiological deconditioning, functional decline, and orthostatic intolerance represent a central challenge in the care of the vulnerable older population. This review examines current scientific knowledge regarding orthostatic intolerance and how it comes about and provides a framework for understanding of (patho-) physiological concepts of cardiovascular (in-) stability in ambulatory and bedrest confined senior citizens as well as in individuals with disease conditions [e.g., orthostatic intolerance in patients with diabetes mellitus, multiple sclerosis, Parkinson's, spinal cord injury (SCI)] or those on multiple medications (polypharmacy). Understanding these aspects, along with cardio-postural interactions, is particularly important as blood pressure destabilization leading to orthostatic intolerance affects 3–4% of the general population, and in 4 out of 10 cases the exact cause remains elusive. Reviewed also are countermeasures to orthostatic intolerance such as exercise, water drinking, mental arithmetic, cognitive training, and respiration training in SCI patients. We speculate that optimally applied countermeasures such as mental challenge maintain sympathetic activity, and improve venous return, stroke volume, and consequently, blood pressure during upright standing. Finally, this paper emphasizes the importance of an active life style in old age and why early re-mobilization following bedrest confinement or bedrest is crucial in preventing orthostatic intolerance, falls and falls-related injuries in older persons.

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          Most cited references 141

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          From space to Earth: advances in human physiology from 20 years of bed rest studies (1986-2006).

          Bed rest studies of the past 20 years are reviewed. Head-down bed rest (HDBR) has proved its usefulness as a reliable simulation model for the most physiological effects of spaceflight. As well as continuing to search for better understanding of the physiological changes induced, these studies focused mostly on identifying effective countermeasures with encouraging but limited success. HDBR is characterised by immobilization, inactivity, confinement and elimination of Gz gravitational stimuli, such as posture change and direction, which affect body sensors and responses. These induce upward fluid shift, unloading the body's upright weight, absence of work against gravity, reduced energy requirements and reduction in overall sensory stimulation. The upward fluid shift by acting on central volume receptors induces a 10-15% reduction in plasma volume which leads to a now well-documented set of cardiovascular changes including changes in cardiac performance and baroreflex sensitivity that are identical to those in space. Calcium excretion is increased from the beginning of bed rest leading to a sustained negative calcium balance. Calcium absorption is reduced. Body weight, muscle mass, muscle strength is reduced, as is the resistance of muscle to insulin. Bone density, stiffness of bones of the lower limbs and spinal cord and bone architecture are altered. Circadian rhythms may shift and are dampened. Ways to improve the process of evaluating countermeasures--exercise (aerobic, resistive, vibration), nutritional and pharmacological--are proposed. Artificial gravity requires systematic evaluation. This review points to clinical applications of BR research revealing the crucial role of gravity to health.
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            SGLT2 inhibition--a novel strategy for diabetes treatment.

            Inhibiting sodium-glucose co-transporters (SGLTs), which have a key role in the reabsorption of glucose in the kidney, has been proposed as a novel therapeutic strategy for diabetes. Genetic mutations in the kidney-specific SGLT2 isoform that result in benign renal glycosuria, as well as preclinical and clinical studies with SGLT2 inhibitors in type 2 diabetes, support the potential of this approach. These investigations indicate that elevating renal glucose excretion by suppressing SGLT2 can reduce plasma glucose levels, as well as decrease weight. Although data from ongoing Phase III trials of these agents are needed to more fully assess safety, results suggest that the beneficial effects of SGLT2 inhibition might be achieved without exerting significant side effects--an advantage over many current diabetes medications. This article discusses the role of SGLT2 in glucose homeostasis and the evidence available so far on the therapeutic potential of blocking these transporters in the treatment of diabetes.
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              Postural stability and associated physiological factors in a population of aged persons.

              A battery of 13 visual, vestibular, sensorimotor, and balance tests was administered to 95 elderly persons (mean age 82.7 years) to examine the relationships between specific sensorimotor functions and measures of postural stability. When subjects stood on a firm surface, increased body sway was associated with poor tactile sensitivity and poor joint position sense. When subjects stood on a compliant surface (which reduced peripheral sensation) with their eyes open, increased body sway was associated with poor visual acuity and contrast sensitivity, reduced vibration sense, and decreased ankle dorsiflexion strength as well as reduced joint position sense. Increased body sway with eyes closed on the compliant surface was associated with poor tactile sensation, reduced quadriceps and ankle dorsiflexion strength, and increased reaction time. Poor performance in two clinical measures of postural stability was associated with reduced sensation in the lower limbs as measured by joint position sense, tactile sensitivity and vibration sense, reduced quadriceps and ankle dorsiflexion strength, and slow reaction times. The prevalence of vestibular impairments was high in this group, but vestibular function was not significantly associated with sway under any of the test conditions. The results suggest that reduced sensation, muscle weakness in the legs, and increased reaction time are all important factors associated with postural instability. An analysis of the percentage increases in sway under conditions where visual and peripheral sensation systems are removed or diminished, compared with sway under optimal conditions, indicated that peripheral sensation is the most important sensory system in the maintenance of static postural stability.
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                Author and article information

                Contributors
                Journal
                Front Physiol
                Front Physiol
                Front. Physiol.
                Frontiers in Physiology
                Frontiers Media S.A.
                1664-042X
                09 November 2017
                2017
                : 8
                Affiliations
                1Gravitational Physiology and Medicine Research Unit, Institute of Physiology, Medical University of Graz , Graz, Austria
                2Department of Biomedical Physiology and Kinesiology, Simon Fraser University , Burnaby, BC, Canada
                3Department of Medicine/Physiology, University of Fribourg , Fribourg, Switzerland
                Author notes

                Edited by: Ovidiu Constantin Baltatu, Anhembi Morumbi University, Brazil

                Reviewed by: Noman Naseer, Air University, Pakistan; Alexander V. Ovechkin, University of Louisville, United States

                *Correspondence: Nandu Goswami nandu.goswami@ 123456medunigraz.at

                This article was submitted to Integrative Physiology, a section of the journal Frontiers in Physiology

                Article
                10.3389/fphys.2017.00803
                5677785
                Copyright © 2017 Goswami, Blaber, Hinghofer-Szalkay and Montani.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                Page count
                Figures: 1, Tables: 0, Equations: 0, References: 158, Pages: 14, Words: 12593
                Categories
                Physiology
                Review

                Anatomy & Physiology

                falls, exercise, mental arithmetic, water drinking, aging, syncope

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