The hydrostatic pressure indifference point underestimates orthostatic redistribution of blood in humans

Petersen, Lonnie G.; Carlsen, Jonathan Frederik; Nielsen, Michael Bachmann; Damgaard, Morten; Secher, Niels H.

doi:10.1152/japplphysiol.01175.2013

Cited by 20 publications

(32 citation statements)

References 37 publications

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“…() even achieved a slightly negative central venous pressure (−0.6 ± 0.8 mmHg) by application of 45 mmHg LBNP, which is close to normal upright values (Petersen et al . ). At head‐up tilt angles above 20–30° the internal jugular veins start to collapse and intravascular pressure approaches zero (Dawson et al .…”

Section: Discussionmentioning

confidence: 97%

“…), and a reduction in arterial feeding pressure at brain‐level due to the hydrostatic pressure gradient between the heart and the brain (Petersen et al . ). Despite similar effects on central haemodynamics, LBNP may therefore better protect cerebral perfusion compared to head elevation.…”

Section: Discussionmentioning

confidence: 97%

“…However, a limitation of head‐up tilt is the introduction of a hydrostatic pressure gradient between heart and brain, which reduces not only ICP but also arterial blood pressure at brain level (Petersen et al . ). The concurrent decrease in arterial feeding pressure decreases cerebral perfusion and oxygenation (Mehagnoul‐Schipper et al .…”

Section: Introductionmentioning

confidence: 97%

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Lower body negative pressure to safely reduce intracranial pressure

Petersen

Lawley

Lilja-Cyron

et al. 2018

The Journal of Physiology

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Key points During long‐term missions, some astronauts experience structural and functional changes of the eyes and brain which resemble signs/symptoms experienced by patients with intracranial hypertension. Weightlessness prevents the normal cerebral volume and pressure ‘unloading’ associated with upright postures on Earth, which may be part of the cerebral and ocular pathophysiology. By placing the lower body in a negative pressure device (LBNP) that pulls fluid away from cranial compartments, we simulated effects of gravity and significantly lowered pressure within the brain parenchyma and ventricle compartments. Application of incremental LBNP demonstrated a non‐linear dose–response curve, suggesting 20 mmHg LBNP as the optimal level for reducing pressure in the brain without impairing cerebral perfusion pressure. This non‐invasive method of reducing pressure in the brain holds potential as a countermeasure in space as well as having treatment potential for patients on Earth with traumatic brain injury or other pathology leading to intracranial hypertension. Abstract Patients with elevated intracranial pressure (ICP) exhibit neuro‐ocular symptoms including headache, papilloedema and loss of vision. Some of these symptoms are also present in astronauts during and after prolonged space‐flight where lack of gravitational stress prevents daily lowering of ICP associated with upright posture. Lower body negative pressure (LBNP) simulates the effects of gravity by displacing fluid caudally and we hypothesized that LBNP would lower ICP without compromising cerebral perfusion. Ten cerebrally intact volunteers were included: six ambulatory neurosurgical patients with parenchymal ICP‐sensors and four former cancer patients with Ommaya‐reservoirs to the frontal horn of a lateral ventricle. We applied LBNP while recording ICP and blood pressure while supine, and during simulated intracranial hypertension by 15° head‐down tilt. LBNP from 0 to 50 mmHg at increments of 10 mmHg lowered ICP in a non‐linear dose‐dependent fashion; when supine (n = 10), ICP was decreased from 15 ± 2 mmHg to 14 ± 4, 12 ± 5, 11 ± 4, 10 ± 3 and 9 ± 4 mmHg, respectively (P < 0.0001). Cerebral perfusion pressure (CPP), calculated as mean arterial blood pressure at midbrain level minus ICP, was unchanged (from 70 ± 12 mmHg to 67 ± 9, 69 ± 10, 70 ± 12, 72 ± 13 and 74 ± 15 mmHg; P = 0.02). A 15° head‐down tilt (n = 6) increased ICP to 26 ± 4 mmHg, while application of LBNP lowered ICP (to 21 ± 4, 20 ± 4, 18 ± 4, 17 ± 4 and 17 ± 4 mmHg; P < 0.0001) and increased CPP (P < 0.01). An LBNP of 20 mmHg may be the optimal level to lower ICP without impairing CPP to counteract spaceflight‐associated neuro‐ocular syndrome in astronauts. Furthermore, LBNP holds clinical potential as a safe, non‐invasive method for lowering ICP and improving CPP for patients with pathologically elevated ICP on Earth.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 97%

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Lower body negative pressure to safely reduce intracranial pressure

Petersen

Lawley

Lilja-Cyron

et al. 2018

The Journal of Physiology

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“…Leep and Mokri proposed 2 possible mechanisms for the syndrome of orthostatic headache without CSF leak: (1) CSF leak may be present but evade detection by current diagnostic modalities or (2) a mechanism other than CSF leak may be responsible for intracranial hypovolemia . For example, increased compliance of the lower spinal CSF space, as in a disorder of the connective tissue matrix that increases dural distensibility, would cause the hydrostatic indifference point (where venous pressure is unaffected by posture, normally located at the level of the diaphragm) to move caudally when a patient was upright and thereby reduce intracranial pressure . The 6 patients in that series had no history of skull or spine surgery, making them distinct from the current 2 patients who had the cranial vault violated by suboccipital craniectomy, performed specifically to alter CSF dynamics.…”

Section: Discussionmentioning

confidence: 99%

Orthostatic Headache After Suboccipital Craniectomy Without CSF Leak: Two Case Reports

Montenegro

Cutsforth‐Gregory

2018

Headache

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“…However, during a change in posture, the arterial blood pressure at heart level is affected less than ICP and cerebral perfusion pressure because the hydrostatic indifference point is located close to heart level (Petersen et al. ). As dynamic changes in the gravitational vector affect regional arterial pressure and ICP/cerebral perfusion pressure differently, it is possible that dynamic cerebral autoregulation is over‐ or underestimated.…”

mentioning

confidence: 99%