Effect of cerebral venous congestion on the pressure-volume index in the evaluation of intracranial pressure dynamics

Venous sinus stenting improves cerebral autoregulation in a patient with venous sinus stenosis: a case report

BACKGROUND

Venous sinus stenosis (VSS) is a type of cerebral venous vascular disease. Cerebral autoregulation is an indicator of cerebral arterial function. The cerebral circulatory system is composed of the venous system and arterial system. Impaired venous function may affect arterial function. Thus, cerebral venous stenosis may influence cerebral autoregulation.

CASE PRESENTATION

In this case, a 50-year-old woman with transient blindness and headache was admitted to the hospital. The patient was diagnosed with VSS. A stent was placed at the stenosis. The stent released the intravenous pressure and remitted the patient's symptoms. Measurements of dynamic cerebral autoregulation (dCA) were performed at 3 time points: before stenting, after stenting, and 3 months later. The dCA gradually improved after stenting.

CONCLUSION

VSS may have an influence on cerebral autoregulation, and effective treatment improves cerebral autoregulation in patients with VSS.

Perispinal Delivery of CNS Drugs

Perispinal injection is a novel emerging method of drug delivery to the central nervous system (CNS). Physiological barriers prevent macromolecules from efficiently penetrating into the CNS after systemic administration. Perispinal injection is designed to use the cerebrospinal venous system (CSVS) to enhance delivery of drugs to the CNS. It delivers a substance into the anatomic area posterior to the ligamentum flavum, an anatomic region drained by the external vertebral venous plexus (EVVP), a division of the CSVS. Blood within the EVVP communicates with the deeper venous plexuses of the CSVS. The anatomical basis for this method originates in the detailed studies of the CSVS published in 1819 by the French anatomist Gilbert Breschet. By the turn of the century, Breschet's findings were nearly forgotten, until rediscovered by American anatomist Oscar Batson in 1940. Batson confirmed the unique, linear, bidirectional and retrograde flow of blood between the spinal and cerebral divisions of the CSVS, made possible by the absence of venous valves. Recently, additional supporting evidence was discovered in the publications of American neurologist Corning. Analysis suggests that Corning's famous first use of cocaine for spinal anesthesia in 1885 was in fact based on Breschet's anatomical findings, and accomplished by perispinal injection. The therapeutic potential of perispinal injection for CNS disorders is highlighted by the rapid neurological improvement in patients with otherwise intractable neuroinflammatory disorders that may ensue following perispinal etanercept administration. Perispinal delivery merits intense investigation as a new method of enhanced delivery of macromolecules to the CNS and related structures.

Space headache on Earth: Head-down-tilted bed rest studies simulating outer-space microgravity

Background

Headache is a common symptom during space travel, both isolated and as part of space motion syndrome. Head-down-tilted bed rest (HDTBR) studies are used to simulate outer space microgravity on Earth, and allow countermeasure interventions such as artificial gravity and training protocols, aimed at restoring microgravity-induced physiological changes.

Objectives

The objectives of this article are to assess headache incidence and characteristics during HDTBR, and to evaluate the effects of countermeasures.

Methods

In a randomized cross-over design by the European Space Agency (ESA), 22 healthy male subjects, without primary headache history, underwent three periods of –6-degree HDTBR. In two of these episodes countermeasure protocols were added, with either centrifugation or aerobic exercise training protocols. Headache occurrence and characteristics were daily assessed using a specially designed questionnaire.

Results

In total 14/22 (63.6%) subjects reported a headache during ≥1 of the three HDTBR periods, in 12/14 (85.7%) non-specific, and two of 14 (14.4%) migraine. The occurrence of headache did not differ between HDTBR with and without countermeasures: 12/22 (54.5%) subjects vs. eight of 22 (36.4%) subjects; p = 0.20; 13/109 (11.9%) headache days vs. 36/213 (16.9%) headache days; p = 0.24). During countermeasures headaches were, however, more often mild ( p = 0.03) and had fewer associated symptoms ( p = 0.008).

Conclusions

Simulated microgravity during HDTBR induces headache episodes, mostly on the first day. Countermeasures are useful in reducing headache severity and associated symptoms. Reversible, microgravity-induced cephalic fluid shift may cause headache, also on Earth. HDTBR can be used to study space headache on Earth.

Space Headache: A New Secondary Headache

Headache is a common, but rarely voiced, complaint during space flights, usually attributed to space motion sickness (SMS). We used a specifically designed questionnaire based on the criteria of the International Classification of Headache Disorders, 2nd edn (ICHD-II). Of the 16 male and one female astronauts who participated in the survey, 12 (71%) reported having experienced at least one headache episode while in space, whereas they had not suffered from headache when on earth. There were in total 21 space headache episodes, of moderate to severe intensity in 71%. In two astronauts (12%) the headache and associated symptoms would match the ICHD-II criteria for migraine and in three (18%) astronauts for tension-type headache; in 12 (70%) astronauts the headache was non-specific. The vast majority of headache episodes (76%) were not associated with symptoms of SMS. We conclude that space flights may trigger headaches without other SMS symptoms in otherwise ‘super-healthy’ male subjects. We propose to classify space headache as a separate entity among the secondary headaches attributed to disorders of homeostasis.

A near infrared spectroscopy study investigating oxygen utilisation in hydrocephalic rats

Determination of hydrocephalus and its severity is important for optimal management of the condition. We have used near infrared spectroscopy (NIRS) to assess changes in concentrations of oxygenated (O2Hb), deoxygenated (HHb), total haemoglobin (tHb) and cytochrome c oxidase (Caa3) in normal and hydrocephalic Texas (HTx) rats in response to a 5 min head down tilt and a sodium pentobarbitone (NaPB) challenge. The former was used to test vascular responses and the latter to test metabolic responses. The haemoglobin oxygenation index (HbD) was derived which provides information regarding oxygen utilisation ([HbD]=[O2Hb]-[HHb]). With the tilt challenge, a significant (P=0.001) difference was observed in [HbD] between normal (n=24) and hydrocephalic (n=14) rats (-3.50 (-6.00 to 0.00) microM cm(-1 )and 7.50 (0.75 to 14.25) microM cm(-1), respectively). In another experiment we tested the response of ten rats to NaPB administration and observed a significant difference (P=0.008) in [Caa3] between normal (n=5) and hydrocephalic (n=5) rats (-6.60 (-7.55 to -5.50) microM cm(-1 )and -2.20 (-5.60 to -1.05) microM cm(-1), respectively). Coronal sections of these ten rat brains were analysed and significant (P<0.05) relationships were found between some of the NIRS parameters and cortical thickness or lateral ventricle area measurements. Our studies demonstrate that a significant difference in cerebral oxygenation and haemodynamics can be observed between normal and hydrocephalic HTx rats using NIRS.

Cerebral Venous Infarction: The Pathophysiological Concept

Cerebral venous occlusion represents an often underdiagnosed cause for acute or slowly progressive neurological deterioration. The underlying pathophysiological basis is not well understood, but is different from those of arterial occlusion reflecting therefore different anatomical and physiological features of the cerebral venous system. Extensive collateral circulation within the cerebral venous system allows for a significant degree of compensation in the early stages of venous occlusion. Elevated cerebral venous pressure due to cerebral venous occlusion can result in a spectrum of phenomena including a dilated venous and capillary bed, development of interstitial edema, increased cerebrospinal fluid production, decreased cerebrospinal fluid absorption and rupture of venous structures (hematoma). All of these pathophysiological changes may explain the clinical observation that cerebral venous occlusion, if promptly diagnosed and adequately managed, contains reversible alterations and need not always lead to venous infarction. The present review outlines this different pathophysiological behavior of venous compared to arterial occlusion in the cerebral vasculature; special reference is given to the effect of these changes on the therapeutic impact.

Does edema formation occur in the rabbit brain exposed to head-down tilt?

Earlier studies showed that exposure to microgravity caused cephalad fluid shift, increased capillary pressure in the head, and produced facial edema and nasal congestion. In the present study, edema formation in the brain was investigated in rabbits exposed to simulated microgravity, head-down tilt (HDT), by measuring water content and histological examinations. Water content in the brain tissues of rabbits exposed to 2 and 8 days of HDT did not increase significantly compared with that of control animals. Neither vital staining using Evans blue nor immunohistochemical examination demonstrated extravasation of plasma constituents in the brain tissues of the HDT rabbits. Although marked congestion was noted in the brain, hematoxylin and eosin staining did not show edematous changes, such as distension of the perivascular and pericellular spaces and vacuolar appearance, in the tissues obtained from HDT rabbits. Transmission electron microscopy revealed that tight junctions of the capillary endothelium were intact in the HDT rabbits. These results suggest that either HDT up to 8 days does not cause brain edema in rabbits or it induces only a slight brain edema which is hard to be demonstrated by measurement of water content or histological examinations.

The impact of raised intracranial pressure on cerebral venous hemodynamics: a prospective venous transcranial Doppler ultrasonography study

OBJECT

The effect of increased intracranial pressure (ICP) on cerebral venous blood flow has been the subject of very few clinical and experimental studies. The authors assessed the usefulness of venous transcranial Doppler (TCD) ultrasonography as a noninvasive monitoring tool for predicting raised ICP.

METHODS

Serial venous TCD studies of the basal vein of Rosenthal and the straight sinus (SS) were prospectively performed in 30 control volunteers and 25 patients with raised ICP. Correlations with ICP data were calculated using a multivariate regression model. Venous blood flow velocities (BFVs) in the basal vein of Rosenthal showed, within a certain range, a linear relationship between mean ICP and maximal venous BFV (r = 0.645; p<0.002). Moreover, a linear relationship was found for maximal venous BFVs in the SS and mean ICP (r = 0.928; p<0.0003).

CONCLUSIONS

Venous TCD studies may provide an additional noninvasive monitoring tool for raised ICP and give further insights into the cerebral venous hemodynamics present during raised ICP.

Mechanisms of increased intracranial pressure in rabbits exposed to head-down tilt

Changes in intracranial pressure (ICP) resulting from head-down tilt (HDT) were studied in rabbits, and a possible role of edema formation in the change of ICP was examined. Animals were anesthetized with pentobarbital sodium and artificially ventilated. ICP was continuously monitored through a catheter inserted into the subarachnoid space. It increased depending on the tilt angle and decreased when the tilt angle was reduced. ICP elevated from 4.6 +/- 0.7 mmHg (mean +/- standard error of the mean) at horizontal prone position to 13.7 +/- 1.0 mmHg immediately after the onset of 45 degrees HDT and gradually reduced toward the pre-HDT baseline in the next 8 h. ICP decreased below the pre-HDT baseline value immediately after returning to the horizontal prone position, and gradually increased toward the baseline during the 2 h of recovery period. Histological examination (HE stain) demonstrated that exposure to 8 h of HDT did not cause remarkable edema in either the gray matter or the white matter in rabbits. Water content and specific gravity of brain tissues both were increased in the HDT group in comparison with the control group. These results suggest that edema formation plays little role in the elevation of ICP during the acute phase of HDT in rabbits.