Venous collapse regulates intracranial pressure in upright body positions

Holmlund, Petter; Eklund, Anders; Koskinen, Lars‐Owe D.; Johansson, Elias; Sundström, Nina; Malm, Jan; Qvarlander, Sara

doi:10.1152/ajpregu.00291.2017

Cited by 55 publications

(63 citation statements)

References 33 publications

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Section: Discussionsupporting

confidence: 91%

“…Of note, venous pressure has been shown by Holmlund et al to be predictive of changes in intracranial pressure with increases in venous CSA correlating with increases in intracranial pressure [25]. Moreover, Holmlund et al also showed increases in venous CSA as well as central venous pressure as tilt angle increased from sitting to supine which is again consistent with our results [25]. These ndings are, however, tempered by one study that showed that measured ICP and central venous pressure both decreased during acute (<1 minute) episodes of zero G in parabolic ight, which differs from ndings of increased central venous pressure during HDT [26].…”

Section: Discussionmentioning

confidence: 94%

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Quantification of Arterial, Venous, and Cerebrospinal Fluid Flow Dynamics by Magnetic Resonance Imaging Under Simulated Micro-Gravity Conditions: A Prospective Cohort Study

Zahid

Martin

Collins

et al. 2020

Preprint

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Abstract Background: Astronauts undergoing long-duration spaceflight are exposed to numerous health risks, including Spaceflight-Associated Neuro-Ocular Syndrome (SANS), a spectrum of ophthalmic changes that can result in permanent loss of visual acuity. The etiology of SANS is not well understood but is thought to involve changes in cerebrovascular flow dynamics in response to microgravity. There is a paucity of knowledge in this area; in particular, cerebrospinal fluid (CSF) flow dynamics have not been well characterized under microgravity conditions. Our study was designed to determine the effect of simulated microgravity (head-down tilt [HDT]) on cerebrovascular flow dynamics. We hypothesized that under microgravity conditions simulated by HDT, increased pressure in the intracranial space would alter intracranial CSF and venous flow dynamics by causing: 1) increased venous pressure reflected by increased venous cross-sectional area; and 2) a decrease in cardiac-related pulsatile CSF flow.Methods: In a prospective cohort study, we measured flow in major cerebral arteries, veins, and CSF spaces in fifteen healthy volunteers using phase contrast magnetic resonance (PCMR) before and during 15° HDT.Results: We found a significant increase in venous cross-sectional area with HDT (p=0.005), indicating increased venous pressure, along with a decrease in all CSF flow variables [systolic peak flow (p=0.009), and peak-to-peak pulse amplitude (p=0.001)]. Arterial average flow (p=0.04), systolic peak flow (p=0.04), and peak-to-peak pulse amplitude (p=0.02) all also significantly decreased.Conclusions: These results collectively demonstrate that acute application of 15° HDT caused a reduction in CSF flow variables (systolic peak flow and peak-to-peak pulse amplitude), coupled with an increase in venous CSA suggesting increased venous pressure with HDT.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 94%

Quantification of Arterial, Venous, and Cerebrospinal Fluid Flow Dynamics by Magnetic Resonance Imaging Under Simulated Micro-Gravity Conditions: A Prospective Cohort Study

Zahid

Martin

Collins

et al. 2020

Preprint

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“…The significant dilation of the jugular vein, which we observed during head-down tilts (Figure 10B), is a frequent finding during venous pooling in the head [46,47]. Orthostatic gradients associated with head-up posture frequently induce the collapse of the jugular vein [5,48]; in contrast, head-up rotations in the alligator produced variable changes in the jugular luminal area, including increases in luminal area. One cause of the largerthan-expected jugular luminal areas during head-up rotations may be the unusual patterns of heart rate observed during thisstudy (see below), but it may also reflect the nature of the cephalic venous system in alligators.…”

Section: Discussionmentioning

confidence: 70%

The Influence of Gravitational Gradients on the American Alligator (Alligator mississippiensis)

Knoche¹,

Young²,

Kondrashova³

2019

Anat Physiol

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Background Cranial fluids of vertebrae mammals are composed of arterial blood, venous blood, and cerebrospinal fluid that can be altered by orthostatic pressures; head‐down postures can elevate intracranial pressure and carotid/jugular luminal area while head up postures produce opposite effects. Previous studies on aquatic and terrestrial snakes showed cardiovascular variation while arboreal snakes showed little cardiovascular variation during orthostatic transitions. Little experimental work regarding orthostatic transitions has been done on alligators. Alligators are known to have unique blood flow patterns due to active regulation of blood flow. The purpose of this study is to investigate the effects of gravitational tilt on vessel luminal diameter and ICP in alligators. Methods Live adult alligators (n = 5, 165 – 183 cm total length) were subjected to gravitational tilts between 45° head‐up to 45° head‐down in 15° increments. Short (30 s) and long (120 s) duration tilts were performed to assess barostatic reflex and ICP using ocular ultrasonography, respectively. Vascular ultrasonography was also used to assess luminal diameter of the carotid artery and jugular vein. Instantaneous heart rate was inferred from EKG recordings throughout tilts. Results Throughout orthostatic transitions, ocular ultrasonography revealed an increase in optic nerve sheath diameter (head down tilts) and a decrease in optic nerve sheath diameter (head up tilts). Head down tilts resulted in jugular and carotid dilation while head up tilts resulted in various jugular luminal diameters and minimal change in carotid diameter. Heart rate increased at the onset of all orthostatic transitions. There was no evidence for a barostatic response. Conclusions Ocular ultrasonography was used to non‐invasively assess intracranial pressure of reptiles. There was a linear relationship between orthostatic transitions and intracranial pressure due to redistribution of CSF. Compared to previous studies, orthostatic transitions produced similar results on vessel flow and diameter. Variations of vessel flow and diameter may be attributed to unusual patters of heart rate or blood shunts in the cephalic venous system. Increases in heart rate in all rotations may be due to a fear response. Additional studies are needed to further understand the underlying regulatory mechanisms that give rise to the alligator's heart rate and blood flow patterns. Support or Funding Information Funding: The Influence of Gravitational Gradients on American Alligators (Alligator Mississippiensis) project has been funded by A.T. Still University's Masters in Biomedical Sciences program. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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“…, where p CVP−p d represents the pressure difference between CVP and dural sinus pressure due to venous flow and flow resistance. Holmlund et al [61] reported CVP in healthy controls in supine position to be 4.2 mmHg. Avasthey [62] measured venous pressure at various sites in the venous system and found a pressure increase of approximately 2.2 mmHg from the CVP (measured in the right atrium) to the internal jugular vein at the level of the ear.…”

Section: Resistance and Pressure For Outflow Into Dural Sinus Or Lympmentioning

confidence: 99%

“…Adding the pressure increases from the right atrium to the sagittal sinus we can approximate p CVP−p d = 4.2 mmHg and p d = 8.4 mmHg . It should be noted that both ICP and the dural venous pressure changes with body position [61], and that we only considered the supine position.…”

Section: Resistance and Pressure For Outflow Into Dural Sinus Or Lympmentioning

confidence: 99%

Intracranial pressure elevation alters CSF clearance pathways

Vinje

Eklund

Mardal

et al. 2020

Fluids Barriers CNS

119

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Background: Infusion testing is a common procedure to determine whether shunting will be beneficial in patients with normal pressure hydrocephalus. The method has a well-developed theoretical foundation and corresponding mathematical models that describe the CSF circulation from the choroid plexus to the arachnoid granulations. Here, we investigate to what extent the proposed glymphatic or paravascular pathway (or similar pathways) modifies the results of the traditional mathematical models. Methods: We used a compartment model to estimate pressure in the subarachnoid space and the paravascular spaces. For the arachnoid granulations, the cribriform plate and the glymphatic circulation, resistances were calculated and used to estimate pressure and flow before and during an infusion test. Finally, different variations to the model were tested to evaluate the sensitivity of selected parameters. Results: At baseline intracranial pressure (ICP), we found a very small paravascular flow directed into the subarachnoid space, while 60% of the fluid left through the arachnoid granulations and 40% left through the cribriform plate. However, during the infusion, 80% of the fluid left through the arachnoid granulations, 20% through the cribriform plate and flow in the PVS was stagnant. Resistance through the glymphatic system was computed to be 2.73 mmHg/ (mL/min), considerably lower than other fluid pathways, giving non-realistic ICP during infusion if combined with a lymphatic drainage route. Conclusions: The relative distribution of CSF flow to different clearance pathways depends on ICP, with the arachnoid granulations as the main contributor to outflow. As such, ICP increase is an important factor that should be addressed when determining the pathways of injected substances in the subarachnoid space. Our results suggest that the glymphatic resistance is too high to allow for pressure driven flow by arterial pulsations and at the same time too small to allow for a direct drainage route from PVS to cervical lymphatics.

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Venous collapse regulates intracranial pressure in upright body positions

Cited by 55 publications

References 33 publications

Quantification of Arterial, Venous, and Cerebrospinal Fluid Flow Dynamics by Magnetic Resonance Imaging Under Simulated Micro-Gravity Conditions: A Prospective Cohort Study

Quantification of Arterial, Venous, and Cerebrospinal Fluid Flow Dynamics by Magnetic Resonance Imaging Under Simulated Micro-Gravity Conditions: A Prospective Cohort Study

The Influence of Gravitational Gradients on the American Alligator (Alligator mississippiensis)

Intracranial pressure elevation alters CSF clearance pathways

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