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Starling resistor

Anita Kovács, Tamás Németh, Angéla Csomor, Tímea Novák, Ferenc Kövér, Erika Vörös
The signs and pathomechanism of Miyazaki syndrome is presented through the case of a young female patient. The patient underwent placement of a ventriculoperitoneal (VP) shunt with a pressure-adjustable valve for communicating hydrocephalus years before presenting to our department with the complaints of constant headache and unsteady gait. On the basis of the clinical picture and her history, plain and contrast-enhanced cranial and whole spine magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) examinations were performed, with the scans revealing signs indicative of cerebrospinal fluid (CSF) hypotension typical of Miyazaki syndrome...
May 15, 2018: World Neurosurgery
Kaixian Zhu, Ramon Farre, Ira Katz, Sébastien Hardy, Pierre Escourrou
The upper airway (UA) in humans is commonly modeled as a Starling resistor. However, negative effort dependence (NED) observed in some patients with obstructive sleep apnea (OSA) contradicts predictions based on the Starling resistor model in which inspiratory flow is independent of inspiratory driving pressure when flow is limited. In a respiratory bench model consisting of a collapsible tube and an active lung model (ASL5000), inspiratory flow characteristics were investigated in relation to upstream, downstream and extra-luminal pressures (denoted as Pus, Pds and Pout, respectively) by varying inspiratory effort (muscle pressure) from -1 to -20 cmH2 O in the active lung...
April 19, 2018: Journal of Applied Physiology
A L Gregory, A Agarwal, J Lasenby
We present a novel application of rotors in geometric algebra to represent the change of curvature tensor that is used in shell theory as part of the constitutive law. We introduce a new decomposition of the change of curvature tensor, which has explicit terms for changes of curvature due to initial curvature combined with strain, and changes in rotation over the surface. We use this decomposition to perform a scaling analysis of the relative importance of bending and stretching in flexible tubes undergoing self-excited oscillations...
November 2017: Royal Society Open Science
Dermot J Kelly, Sinéad M Farrell
More than 26 million Americans suffer with cataracts, and with 3.6 million cataract extractions performed annually in the United States, it is the most common surgical procedure. The integrity of the delicate structures of the eye that mediate vision is dependent on the intraocular pressure (IOP). Yet, IOP acts to compress the vessels within the globe-akin to a Starling resistor-and is a key component that determines the ocular perfusion pressure, defined as the difference between arterial pressure and IOP...
May 2018: Anesthesia and Analgesia
Camille Rolland-Debord, Capucine Morelot-Panzini, Thomas Similowski, Roberto Duranti, Pierantonio Laveneziana
Exercise induces release of cytokines and increase of circulating natural killers (NK) lymphocyte during strong activation of respiratory muscles. We hypothesised that non-fatiguing respiratory muscle loading during exercise causes an increase in NK cells and in metabolic stress indices. Heart rate (HR), ventilation (VE), oesophageal pressure (Pes), oxygen consumption (VO2), dyspnoea and leg effort were measured in eight healthy humans (five men and three women, average age of 31 ± 4 years and body weight of 68 ± 10 kg), performing an incremental exercise testing on a cycle ergometer under control condition and expiratory flow limitation (FL) achieved by putting a Starling resistor...
December 2017: Pflügers Archiv: European Journal of Physiology
Roberto DE Simone, Angelo Ranieri, Vincenzo Bonavita
Two critical functions for the control of intracranial fluids dynamics are carried on the venous side of the perfusion circuit: the first is the avoidance of cortical veins collapse during the physiological increases of cerebrospinal fluid (CSF) pressure in which they are immersed. The second, is the generation of an abrupt venous pressure drop at the confluence of the cortical veins with the dural sinuses that is required to allow a CSF outflow rate balanced with its production. There is evidence that both of these effects are ensured by a Starling resistor mechanism (a fluid dynamic construct that governs the flow in collapsible tubes exposed to variable external pressure) acting at the confluence of cortical veins in the dural sinus...
March 2017: Panminerva Medica
Kaveh Barami
Understanding the altered physiology following cerebrospinal fluid (CSF) diversion in the setting of adult hydrocephalus is important for optimizing patient care and avoiding complications. There is mounting evidence that the cerebral venous system plays a major role in intracranial pressure (ICP) dynamics especially when one takes into account the effects of postural changes, atmospheric pressure, and gravity on the craniospinal axis as a whole. An evolved mechanism acting at the cortical bridging veins, known as the "Starling resistor," prevents overdrainage of cranial venous blood with upright positioning...
September 2016: Neurosurgical Focus
William H Morgan, Martin L Hazelton, Dao-Yi Yu
Retinal vein pulsation was first noted soon after the invention of the ophthalmoscope 170 years ago and was seen to change with cerebrospinal fluid pressure (CSFP) variation in the 1920s. The classical explanation for vein pulsation was that the cardiac cycle induced systolic peak in intraocular pressure (IOP) tended to intermittently collapse the retinal vein close to its exit in the central optic disk, causing pulsation to be counter-phase to IOP. Recently, improved ophthalmodynamometry and video recording techniques have allowed us to explore the fundamentals of retinal vein pulsation...
November 2016: Progress in Retinal and Eye Research
Seshadri Raju, Orla Kirk, Micah Davis, Jake Olivier
BACKGROUND: The concept of "critical" stenosis at which there is a sharp reduction in forward flow is derived from arterial disease. The critical element in venous stenoses is upstream pressure, not downstream flow. Many venous symptoms and microvascular injury are related to venous hypertension. We studied the effect of venous stenosis on upstream pressure using a mechanical model and with clinical measurements after stenting of iliac vein segments (common and external). METHODS: The experimental model consisted of a Starling Resistor - Penrose tubing enclosed in a pressurized plastic chamber to simulate abdominal venous flow...
January 2014: Journal of Vascular Surgery. Venous and Lymphatic Disorders
Kaveh Barami, Sandeep Sood
Loss of cerebrospinal fluid (CSF) occurs commonly in daily neurosurgical practice. Understanding the altered physiology following CSF loss is important for optimization of patient care and avoidance of complications. There is overwhelming evidence now that the cerebral venous system plays a major role in intracranial pressure (ICP) dynamics especially when one takes into account the effects of postural changes, atmospheric pressure, and gravity on the craniospinal axis as a whole. The CSF and cerebral venous compartments are tightly coupled in two important ways...
April 2016: Child's Nervous System: ChNS: Official Journal of the International Society for Pediatric Neurosurgery
L O Müller, E F Toro, E M Haacke, D Utriainen
BACKGROUND: The presence of abnormal anatomy and flow in neck veins has been recently linked to neurological diseases. The precise impact of extra-cranial abnormalities such as stenoses remains unexplored. METHODS: Pressure and velocity fields in the full cardiovascular system are computed by means of a global mathematical model that accounts for the relationship between pulsating cerebral blood flow and intracranial pressure. RESULTS: Our model predicts that extra-cranial strictures cause increased pressure in the cerebral venous system...
June 2016: Phlebology
Kaixian Zhu, Gabriel Roisman, Sami Aouf, Pierre Escourrou
STUDY OBJECTIVES: This study challenged on a bench-test the efficacy of auto-titrating positive airway pressure (APAP) devices for obstructive sleep disordered breathing treatment and evaluated the accuracy of the device reports. METHODS: Our bench consisted of an active lung simulator and a Starling resistor. Eleven commercially available APAP devices were evaluated on their reactions to single-type SDB sequences (obstructive apnea and hypopnea, central apnea, and snoring), and to a long general breathing scenario (5...
July 2015: Journal of Clinical Sleep Medicine: JCSM: Official Publication of the American Academy of Sleep Medicine
R Stodtmeister
BACKGROUND: The ocular perfusion pressure (PP) is presently calculated by subtracting the intraocular pressure (IOP) from the mean ophthalmic artery pressure. In recent years papers have been published in which it has been shown that the pressure in the central retinal vein (CRV) may be higher than the IOP in half the glaucoma patients resulting in a lower perfusion pressure in the retina and in the prelaminar layer of the optic nerve head. OBJECTIVES: A review of these papers is given in which the pulsation of the CRV was assessed or in which the pressure in the CRV has been measured on comparing glaucoma patients and control subjects...
February 2015: Klinische Monatsblätter Für Augenheilkunde
Daniel de Sousa Michels, Amanda da Mota Silveira Rodrigues, Márcio Nakanishi, André Luiz Lopes Sampaio, Alessandra Ramos Venosa
Numerous studies have reported an association between nasal obstruction and obstructive sleep apnea syndrome (OSAS), but the precise nature of this relationship remains to be clarified. This paper aimed to summarize data and theories on the role of the nose in the pathophysiology of sleep apnea as well as to discuss the benefits of surgical and medical nasal treatments. A number of pathophysiological mechanisms can potentially explain the role of nasal pathology in OSAS. These include the Starling resistor model, the unstable oral airway, the nasal ventilatory reflex, and the role of nitric oxide (NO)...
2014: International Journal of Otolaryngology
J P Jamison, M T Stewart
Simulation of disorders of respiratory mechanics shown by spirometry provides insight into the pathophysiology of disease but some clinically important disorders have not been simulated and none have been formally evaluated for education. We have designed simple mechanical devices which, along with existing simulators, enable all the main dysfunctions which have diagnostic value in spirometry to be simulated and clearly explained with visual and haptic feedback. We modelled the airways as Starling resistors by a clearly visible mechanical action to simulate intra- and extra-thoracic obstruction...
October 2015: Advances in Health Sciences Education: Theory and Practice
Andrew Wellman, Pedro R Genta, Robert L Owens, Bradley A Edwards, Scott A Sands, Stephen H Loring, David P White, Andrew C Jackson, Ole F Pedersen, James P Butler
The human pharyngeal airway during sleep is conventionally modeled as a Starling resistor. However, inspiratory flow often decreases with increasing effort (negative effort dependence, NED) rather than remaining fixed as predicted by the Starling resistor model. In this study, we tested a major prediction of the Starling resistor model--that the resistance of the airway upstream from the site of collapse remains fixed during flow limitation. During flow limitation in 24 patients with sleep apnea, resistance at several points along the pharyngeal airway was measured using a pressure catheter with multiple sensors...
December 15, 2014: Journal of Applied Physiology
Peter S Stewart, Oliver E Jensen, Alexander J E Foss
PURPOSE: There is no easy way to estimate the intracranial pressure (ICP) noninvasively. The retinal vein can exhibit large amplitude oscillations at the level of the lamina cribrosa under certain circumstances. The aims of this study were to develop a theoretical understanding of the conditions required to establish this vigorous oscillatory behavior and to determine whether observations of it could lead to a noninvasive estimate of the ICP. METHODS: A mathematical model was constructed in which the central retinal vein was modeled as 2 Starling resistors in series, 1 located in the eye and the other in the cerebrospinal fluid (CSF) space, separated by a region where it was not collapsible, corresponding to its course within the optic nerve itself...
October 2014: Investigative Ophthalmology & Visual Science
Lucas O Müller, Eleuterio F Toro
Here we extend the global, closed-loop, mathematical model for the cardiovascular system in Müller and Toro (2014) to account for fundamental mechanisms affecting cerebral venous haemodynamics: the interaction between intracranial pressure and cerebral vasculature and the Starling-resistor like behaviour of intracranial veins. Computational results are compared with flow measurements obtained from Magnetic Resonance Imaging (MRI), showing overall satisfactory agreement. The role played by each model component in shaping cerebral venous flow waveforms is investigated...
October 17, 2014: Journal of Biomechanics
Pedro R Genta, Robert L Owens, Bradley A Edwards, Scott A Sands, Danny J Eckert, James P Butler, Stephen H Loring, Atul Malhotra, Andrew C Jackson, David P White, Andrew Wellman
The upper airway is often modeled as a Starling resistor, which predicts that flow is independent of inspiratory effort during flow limitation. However, while some obstructive sleep apnea (OSA) patients exhibit flat, Starling resistor-like flow limitation, others demonstrate considerable negative effort dependence (NED), defined as the percent reduction in flow from peak to mid-inspiration. We hypothesized that the variability in NED could be due to differences in phasic pharyngeal muscle activation between individuals...
September 15, 2014: Respiratory Physiology & Neurobiology
Robert L Owens, Bradley A Edwards, Scott A Sands, James P Butler, Danny J Eckert, David P White, Atul Malhotra, Andrew Wellman
The upper airway is often modeled as a classical Starling resistor, featuring a constant inspiratory airflow, or plateau, over a range of downstream pressures. However, airflow tracings from clinical sleep studies often show an initial peak before the plateau. To conform to the Starling model, the initial peak must be of small magnitude or dismissed as a transient. We developed a method to simulate fast or slow inspirations through the human upper airway, to test the hypothesis that this initial peak is a transient...
April 15, 2014: Journal of Applied Physiology
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