China
Africa
Explore chapters and articles related to this topic
Are We Built to Stand?
Published in Robert Bridger, A Guide to Active Working in the Modern Office, 2019
In extreme cases, some people may experience “orthostatic hypotension” (a sudden drop in blood pressure) when moving from a seated to a standing position. The symptoms are dizziness or light-headedness when standing up which occurs as a result of abnormal blood pressure regulation. Normally, when people stand, gravity causes blood to pool in the veins of the legs and trunk. This pooling lowers the blood pressure and the amount of blood available for the heart to pump to the brain. People with low blood pressure (90/60mmHg or lower) may be more likely to experience these symptoms when standing up and the symptoms normally subside in 10 minutes. In extreme cases, “fainters” may be at risk within 10 to 30 minutes of standing.
Designing for Lower Torso and Leg Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
GCS and other new wearable compressive devices are used as treatment for several other health conditions. Orthostatic hypotension (positional low blood pressure) occurs after getting up from lying down or sitting. It can manifest as lightheadedness and is often associated with decreased blood return to the heart. Granberry, Abel, and Holschuh (2017) developed a dynamic, mobile, and active knit compression garment incorporating smart materials to treat orthostatic hypotension.
Syncope: Physiology, Pathophysiology and Aeromedical Implications
Published in Anthony N. Nicholson, The Neurosciences and the Practice of Aviation Medicine, 2017
David A. Low, Christopher J. Mathias
For pilots and other air personnel, the most relevant major group of syncope to consider is autonomic (neurally) mediated syncope, previously referred to by a variety of names, including reflex and neurocardiogenic. The other two major groups of syncope, cardiac and orthostatic hypotension (with neurogenic or non-neurogenic causes), are less likely in young and usually physically fit individuals, as their incidence increases with age and comorbidity. Individuals with autonomic failure syndromes (such as multiple system atrophy and pure autonomic failure) regularly experience orthostatic hypotension (see Figure 13.5a) and at times syncope due to their inability to increasing sympathetic nerve activity when needed, as a result of central or peripheral autonomic damage. Cardiac syncope is associated with an arrhythmia or structural disease and is characterized by the suddenness of its onset and the lack of warning symptoms of cerebral hypoperfusion. An exception is the volume depletion subtype of orthostatic hypotension syncope, where excessive dehydration through sweating and/or blood loss, for example, could provoke a syncopal event in a pilot.
Baroreflex control model for cardiovascular system subjected to postural changes under normal and orthostatic conditions
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
V. L. Resmi, R. G. Sriya, N. Selvaganesan
OI refers to a medical condition where the HR cannot be controlled by poor baroreflex efferent innervation of the heart. This is observed commonly in elderly and astronauts. This is modelled by changing the baroreflex paramter which inturen loses the ability to make the pressure to nominal value. Figure 8 show the simulated results for the effect of orthostatic hypotension and hypertension condition on MAP and HR. At t = 60 sec a postural change from supine to standing is introduced along with reduced sympathetic gain. Due to the abnormalities in the vascular baroreceptors which happens due to postflight, age, local tumor growth, brain stem stroke etc., the MAP and HR cannot attain its steady state value which leads to orthostatic hypotension as shown in Figure 8. At t = 200 sec, postural change from standing to supine is introduced along with change in parasympathetic baroreflex gain. Due to the poor control of parasympathetic nerve system, a higher pressure and lower heartrate is observed which leads to orthostatic hypertension.
Tests for the identification of reflex syncope mechanism
Published in Expert Review of Medical Devices, 2023
Michele Brignole, Giulia Rivasi, Artur Fedorowski, Marcus Ståhlberg, Antonella Groppelli, Andrea Ungar
Hypotensive episodes, which can be detected on office BP measurements or ABPM, include: Orthostatic hypotension, defined as a systolic BP fall ≥20 mmHg and/or diastolic fall ≥10 mmHg or standing systolic BP <90 mmHg within 3 min of active standing [2]. It should be mentioned that orthostatic hypotension, especially the delayed form, may precede reflex syncope, which is then called a ‘complex syncope’ mechanism [5]. Consequently, the presyncopal (or pre-reflex) phase is characterized by a period of hemodynamic instability (i.e. hypotensive susceptibility), which eventually leads to a fully developed reflex syncope in the mechanism of abrupt vasodilation mainly in the venous splanchnic zone (i.e. vasodepression) [13].Post-prandial hypotension, defined as a systolic BP fall >20 mmHg during or immediately after meals on ABPM [35,36]Systolic BP drops on ABPM: recent data from a large multicentre comparison between syncope patients and matched controls indicate that one or more episodes of daytime systolic BP <90 mm Hg on ABPM permit a diagnosis of hypotensive susceptibility in reflex syncope with 91% specificity and 32% sensitivity (OR 4.6, P < 0.001), while two or more daytime SBP drops <100 mmHg achieved 84% specificity and 40% sensitivity (OR 3.5, P < 0.001) [37]. The results were confirmed in a validation cohort. A correlation with symptoms was not available, but it might be supposed that such SBP drops represent a marker of hypotensive susceptibility, that may potentially evoke a reflex syncope in the presence of specific triggers or circumstances.