Posture-induced changes in the vessels of the head and neck: evaluation using conventional supine CT and upright CT

Neuraxial biomechanics, fluid dynamics, and myodural regulation: rethinking management of hypermobility and CNS disorders

Individuals with joint hypermobility and the Ehlers-Danlos Syndromes (EDS) are disproportionately affected by neuraxial dysfunction and Central Nervous System (CNS) disorders: such as Spontaneous Intracranial Hypotension (SIH) due to spinal cerebrospinal fluid (CSF) leaks, Upper Cervical Instability (UCI; including craniocervical or atlantoaxial instability (CCI/AAI)), Occult Tethered Cord Syndrome (TCS), Chiari Malformation (CM) and Idiopathic Intracranial Hypertension (IIH). The neuraxis comprises the parts of the nervous system (brain, nerves, spinal cord) along the craniospinal axis of the body. Neuraxial tissue includes all tissue structures that comprise, support, sheath, and connect along the neuraxis and peripheral nerves. Altered mechanical loading or vascular supply of neural structures can adversely impact neural health and conductivity, with local and remote effects on inflammation, venous congestion, and muscle control. With EDS characterized by altered structure of the connective tissues found throughout the body including the neural system, altered mechanical properties of the central nervous system (CNS) and its surrounding tissue structures are important considerations in the development and diagnostics of these CNS disorders, as well as response to therapeutic interventions. Experts have identified a need for neuraxial curriculum in medical education and hypermobility-adapted treatment approaches in pain management, neurosurgery, anesthesiology, hematology, gastrointestinal surgery, dermatology, cardiology, dentistry, gastroenterology, allergy/immunology, physical therapy, primary care, radiology and emergency medicine. This paper reviews the interactions between neuraxial biomechanics and pathology related to CNS disorders seen commonly with EDS. First, we provide a concise synthesis of the literature on neuraxial kinematics and fluid dynamics. We then discuss the interplay of these biomechanics and their involvement in clinically-relevant diagnoses and overlapping symptom presentations, modeling physiological reasoning to highlight knowledge gaps, support clinical decision-making, improve multidisciplinary management of hypermobility-associated complexity, and add weight to the call for medical education reform.

Treatment of thoracic outlet syndrome to relieve chronic migraine

Prior case reports have suggested that treating thoracic outlet syndrome (TOS) may relieve intractable migraine headaches, but there has been no case series large enough to show when underlying TOS should be suspected as a contributor to migraine burden. This observational followed by questionnaire study was performed in an outpatient neurology practice to identify clinical features of patients with migraine in which TOS contributed to migraine burden. We report the clinical features of 50 consecutive patients (48 women, 2 men, age = 43.9+/12.7 years) who were treated for chronic migraine and TOS (20 migraine with aura, 28 migraine without aura, two hemiplegic migraines). Headaches had become chronic within 1 year of onset in 21 patients (42%) with characteristics as follows (percentages are based on known data): greater severity ipsilateral to TOS limb pain (38/50=76%), presence of limb swelling (32/48=67%), and worsened by recumbency (32/38=84%). Thirty-two patients eventually needed surgery, which included percutaneous transluminal venoplasty, 1st rib removal, scalenectomy, pectoralis minor tenotomy, and/or vein patching. The mean improvement of headaches on the treated side was 72 ± 26.7%; 12 patients experienced complete resolution of headaches after treatment of TOS (follow-up 7.2 ± 5.2 months). Questionnaire responders reported significant reductions in headache days (18.3 ± 8.6 to 11.1 ± 10.8 days/month, p < 0.0016), severity (7.8+/2.5 to 5.4 ± 2.9, p < 0.00079), and need for emergency care (3.6 ± 4.0 to 0.71 ± 1.3 visits/year, p < 0.0029). Chronic migraines can be important manifestations of TOS. Early transition to a chronic state, lateralized limb pain, and headaches worsened by recumbency are clues to the contribution of TOS pathology. Addressing the TOS contribution to migraine can significantly reduce migraine headache burden.

The impact of body position on neurofluid dynamics: present insights and advancements in imaging

The intricate neurofluid dynamics and balance is essential in preserving the structural and functional integrity of the brain. Key among these forces are: hemodynamics, such as heartbeat-driven arterial and venous blood flow, and hydrodynamics, such as cerebrospinal fluid (CSF) circulation. The delicate interplay between these dynamics is crucial for maintaining optimal homeostasis within the brain. Currently, the widely accepted framework for understanding brain functions is the Monro-Kellie's doctrine, which posits a constant sum of intracranial CSF, blood flow and brain tissue volumes. However, in recent decades, there has been a growing interest in exploring the dynamic interplay between these elements and the impact of external factors, such as daily changes in body position. CSF circulation in particular plays a crucial role in the context of neurodegeneration and dementia, since its dysfunction has been associated with impaired clearance mechanisms and accumulation of toxic substances. Despite the implementation of various invasive and non-invasive imaging techniques to investigate the intracranial hemodynamic or hydrodynamic properties, a comprehensive understanding of how all these elements interact and are influenced by body position remains wanted. Establishing a comprehensive overview of this topic is therefore crucial and could pave the way for alternative care approaches. In this review, we aim to summarize the existing understanding of intracranial hemodynamic and hydrodynamic properties, fundamental for brain homeostasis, along with factors known to influence their equilibrium. Special attention will be devoted to elucidating the effects of body position shifts, given their significance and remaining ambiguities. Furthermore, we will explore recent advancements in imaging techniques utilized for real time and non-invasive measurements of dynamic body fluid properties in-vivo.

Retrospective analysis of treatment-positioning accuracy and dose error in boron neutron capture therapy using a sitting-position treatment system for head and neck cancer

The neutron beam in boron neutron capture therapy (BNCT) exhibits poor directionality and significantly decreasing neutron flux with increasing distance. Therefore, the treatment site must be close to the irradiation aperture. Some patients with head and neck cancer may benefit from a sitting-position setup. The study aim was to evaluate the treatment-positioning accuracy and dose error in sitting patients receiving BNCT. Thirty-two patients with head and neck cancer who underwent sitting-position BNCT at Southern Tohoku BNCT Research Center were included in the study. Horizontal (ΔX) and vertical (ΔY) errors were defined as the displacement between the treatment planning system (TPS) digital reconstructed radiograph and the pre-treatment X-ray image. Using in-house software, image matching was performed. The beam-axial directional (ΔZ) error was compared with the parameters entered into the TPS and the actual pre-treatment measured values. The translational-position error was reflected in the TPS's patient coordinate system with respect to the reference plan. Re-dose calculations were performed to evaluate the effect of positional error on tumor and normal-tissue doses. The [ΔX, ΔY, ΔZ] DRR-CR mean ± 1SD were - 0.40 ± 2.0, 0.30 ± 2.3, and - 1.4 ± 1.5 mm, respectively. The Dmean and D98% tumor-dose errors were 1.22 % ± 1.44 % and 0.99 % ± 1.63 %, respectively. The D2% pharyngeal and oral mucosal-dose errors were 0.98 % ± 1.91 % and 1.21 % ± 1.78 %, respectively. The tumor- and normal-tissue dose errors were typically < 5 %. High-precision treatment was feasible in sitting-positioned BNCT.

Absorption pharmacokinetics and feasibility of intranasal dexmedetomidine in patients under general anaesthesia

BACKGROUND

The use of intranasal dexmedetomidine is hampered by a limited understanding of its absorption pharmacokinetics.

METHODS

We examined the pharmacokinetics and feasibility of intranasal dexmedetomidine administered in the supine position to adult patients undergoing general anaesthesia. Twenty-eight patients between 35 and 80 years of age, ASA 1-3 and weight between 50 and 100 kg, who underwent elective unilateral total hip or knee arthroplasty under general anaesthesia were recruited. All patients received 100 μg of intranasal dexmedetomidine after anaesthesia induction. Six venous blood samples (at 0, 5, 15, 45, 60, 240 min timepoints from dexmedetomidine administration) were collected from each patient and dexmedetomidine plasma concentrations were measured. Concentration-time profiles after nasal administration were pooled with earlier data from a population analysis of intravenous dexmedetomidine (n = 202) in order to estimate absorption parameters using nonlinear mixed effects. Peak concentration (CMAX) and time (TMAX) were estimated using simulation (n = 1000) with parameter estimates and their associated variability.

RESULTS

There were 28 adult patients with a mean (SD) age of 66 (8) years and weight of 83 (10) kg. The mean weight-adjusted dose of dexmedetomidine was 1.22 (0.15) μg kg-1. CMAX 0.273 μg L-1 was achieved at 98 min after intranasal administration (TMAX). The relative bioavailability of dexmedetomidine was 80% (95% CI 75-91%). The absorption half-time (TABS = 120 min; 95% CI 90-147 min) was slower than that in previous pharmacokinetic studies on adult patients. Perioperative haemodynamics of all patients remained stable.

CONCLUSIONS

Administration of intranasal dexmedetomidine in the supine position during general anaesthesia is feasible with good bioavailability. This administration method has slower absorption when compared to awake patients in upright position, with consequent concentrations attained after TMAX for several hours.

Cerebral venous pressures, sinus trans-stenosis gradients, and intracranial pressures are dramatically augmented by head position

BACKGROUND

Cerebral venous pressures, sinus trans-stenosis gradients, and intracranial pressures are thought to be influenced by head position.

OBJECTIVE

To investigate the intracranial manifestations of these changes in patients with cerebral venous outflow disorders (CVD).

METHODS

A retrospective chart review was conducted on 22 consecutive adult patients who underwent diagnostic cerebral venography with rotational internal jugular vein (IJV) venography and superior sagittal sinus (SSS) pressure measurements in multiple head positions. Data on venous sinus pressures, IJV pressures, and lumbar puncture (LP) opening pressures (OP) were collected and analyzed.

RESULTS

The study found that 21 (96%) patients experienced increases in SSS pressures with head rotation, with a mean increase of 25.4%. Intracranial trans-stenosis gradients showed significant variability with head position. Additionally, LP OP measurements increased by an average of 44.3% with head rotation. Dynamic IJV stenosis was observed in all patients during rotational testing.

CONCLUSION

Head position significantly affects cerebral venous pressures, trans-stenosis gradients, and intracranial pressures in patients with CVD or intracranial hypertension. These findings highlight the need for dynamic venography in the diagnostic evaluation of these conditions to better understand their pathophysiology and improve treatment strategies.

Upright CT-based evaluation of the effects of posture on skull-base reconstruction after endoscopic endonasal surgery

Cerebrospinal fluid (CSF) leakage is a common complication associated with endoscopic endonasal skull-base surgery (EESBS). Postoperative mobilization-associated postural changes are considered to cause CSF leakage. However, no study has demonstrated a robust relationship between postural changes and CSF leakage. We used upright computed tomography (CT) to clarify the effects of postural changes on the reconstructed skull base (RSB) after EESBS. Thirty patients who underwent EESBS at our institution were prospectively included, and their upright and supine CTs were compared to measure morphological changes in the RSB. Patient clinical data were also collected from medical charts and surgical videos, and their relationships with morphological changes were assessed. In upright CTs, the RSB shifted intracranially by 0.94 (0.0-2.9) mm on average. This shift was larger in cases with lesions extending to the sphenoid sinus, dural defects, intraoperative pulsation of the RSB, and large bone windows. The direction of the change was opposite to intuitive movement driven by gravity because of reduced intracranial pressure in the sitting position. Thus, these shifts can be directly associated with postoperative CSF leakage caused by reconstruction material displacement. Skull-base reconstruction and postoperative postural management accounting for these morphological changes may be necessary for preventing CSF leakage.

No influence of steady-state postural changes on cerebrovascular compliance in humans

The aim of this study was to determine the effect of posture changes on vascular compliance in intracranial (brain) versus extracranial vascular beds (forearm). Eighteen young adults (nine females) performed a supine-to-seated-to-standing protocol involving 5 min of rest in each position. Continuous blood pressure, middle cerebral artery (MCA) blood velocity, and brachial artery blood velocity were recorded at each posture. Three to five consecutive steady-state cardiac cycles at each posture were analyzed by a four-element lumped parameter modified Windkessel model to calculate vascular compliance. Mean arterial pressure (MAP) increased from supine to seated (76(9) vs. 81(12) mmHg; P = 0.006) and from supine to standing (76(9) vs. 82(13) mmHg; P = 0.034). Mean blood flow was greater in the MCA relative to the forearm (forearm: 40(5) mL·min-1, MCA: 224(17) mL·min-1; main effect P < 0.001). Conversely, vascular resistance (forearm: 3.25(0.50) mmHg-1·mL·min-1, brain: 0.36(0.04) mmHg-1·mL·min-1; main effect P < 0.001) and compliance (forearm: 0.010(0.001) mL·min-1·mmHg-1, brain: 0.005(0.001) mL·min-1·mmHg-1; main effect P = 0.001) were greater in the forearm compared to the brain. Significant main effects of posture were observed with decreasing values in upright positions for mean blood flow (P = 0.001) in both vascular beds, but not for resistance (P = 0.163) or compliance (P = 0.385). There were no significant interaction effects between vascular bed and posture for mean flow (P = 0.057), resistance (P = 0.258), or compliance (P = 0.329). This study provides evidence that under steady-state conditions, posture does not affect cerebrovascular compliance.

Ultrasound mapping of soft tissue vascular anatomy proximal to the larynx: a prospective cohort study

BACKGROUND

Bleeding incidents during percutaneous dilatational tracheostomy are concerning, and most cases occur in patients with unrecognized and unanticipated anatomical variations in the vascular anatomy. However, the extent of this variation remains unclear. To address this knowledge gap, our study aimed to comprehensively map laryngeal vascular anatomy in a cohort of adult patients.

METHODS

Ultrasound assessments of the soft tissue in the neck were performed, spanning from the thyroid cartilage to the third tracheal ring and extending 2 cm laterally on both sidesperformed. We subdivided this area into 12 zones comprising four medial and eight lateral sections. A pre-planned form was used to document the presence of arteries or veins in each zone. The results are reported as odds ratios, 95% CIs, and corresponding P values.

RESULTS

Five-hundred patients were enrolled from August 14, 2023, to November 13, 2023, at the University Hospital of Padua. Arteries and veins were identified in all investigated zones (varying from a minimum of 1.0%-46.4%). The presence of invessels progressively increased from the cricothyroid membrane to the third tracheal ring and from the midline to the paramedian laryngeal area.

CONCLUSIONS

Given the prevalence of arteries and veins, particularly in areas where tracheostomies are commonly performed, we strongly advocate for routine ultrasound assessments before such procedures are performed.

Exploration of postural effects on the external jugular and diploic venous system using upright computed tomography scanning

PURPOSE

Few studies have investigated the influence of posture on the external jugular and diploic venous systems in the head and cranial region. In this study, we aimed to investigate the effects of posture on these systems using upright computed tomography (CT) scanning.

METHODS

This study retrospectively analysed an upright CT dataset from a previous prospective study. In each patient, the diameters of the vessels in three external jugular tributaries and four diploic veins were measured using CT digital subtraction venography in both supine and sitting positions.

RESULTS

Amongst the 20 cases in the original dataset, we eventually investigated 19 cases due to motion artifacts in 1 case. Compared with the supine position, most of the external jugular tributaries collapsed, and the average size significantly decreased in the sitting position (decreased by 22-49% on average). In contrast, most of the diploic veins, except the occipital diploic veins, tended to increase or remain unchanged (increased by 12-101% on average) in size in the sitting position compared with the supine position. However, the changes in the veins associated with this positional shift were not uniform; in approximately 5-30% of the cases, depending on each vein, an opposite trend was observed.

CONCLUSION

Compared to the supine position, the contribution of external jugular tributaries to head venous drainage decreased in the sitting position, whilst most diploic veins maintained their contribution. These results could enhance our understanding of the physiology and pathophysiology of the head region in upright and sitting positions.

Position- and posture-dependent vascular imaging-a scoping review

OBJECTIVES

Position- and posture-dependent deformation of the vascular system is a relatively unexplored field. The goal of this scoping review was to create an overview of existing vascular imaging modalities in different body positions and postures and address the subsequent changes in vascular anatomy.

METHODS

Scopus, Medline, and Cochrane were searched for literature published between January 1, 2000, and June 30, 2022, incorporating the following categories: image modality, anatomy, orientation, and outcomes.

RESULTS

Out of 2446 screened articles, we included 108. The majority of papers used ultrasound (US, n = 74) in different body positions and postures with diameter and cross-sectional area (CSA) as outcome measures. Magnetic resonance imaging (n = 22) and computed tomography (n = 8) were less frequently used but allowed for investigation of other geometrical measures such as vessel curvature and length. The venous system proved more sensitive to postural changes than the arterial system, which was seen as increasing diameters of veins below the level of the heart when going from supine to prone to standing positions, and vice versa.

CONCLUSIONS

The influence of body positions and postures on vasculature was predominantly explored with US for vessel diameter and CSA. Posture-induced deformation and additional geometrical features that may be of interest for the (endovascular) treatment of vascular pathologies have been limitedly reported, such as length and curvature of an atherosclerotic popliteal artery during bending of the knee after stent placement. The most important clinical implications of positional changes are found in diagnosis, surgical planning, and follow-up after stent placement.

CLINICAL RELEVANCE STATEMENT

This scoping review presents the current state and opportunities of position- and posture-dependent imaging of vascular structures using various imaging modalities that are relevant in the fields of clinical diagnosis, surgical planning, and follow-up after stent placement.

KEY POINTS

• The influence of body positions and postures on the vasculature was predominantly investigated with US for vessel diameter and cross-sectional area. • Research into geometrical deformation, such as vessel length and curvature adaptation, that may be of interest for the (endovascular) treatment of vascular pathologies is limited in different positions and postures. • The most important clinical implications of postural changes are found in diagnosis, surgical planning, and follow-up after stent placement.

Differential Assessment of Internal Jugular Vein Stenosis in Patients Undergoing CT and MRI with Contrast

OBJECTIVE

Internal Jugular Vein Stenosis (IJVS) is hypothesized to play a role in the pathogenesis of diverse neurological diseases. We sought to evaluate differences in IJVS assessment between CT and MRI in a retrospective patient cohort.

METHODS

We included consecutive patients who had both MRI of the brain and CT of the head and neck with contrast from 1 June 2021 to 30 June 2022 within the same admission. The degree of IJVS was categorized into five grades (0-IV).

RESULTS

A total of 35 patients with a total of 70 internal jugular (IJ) veins were included in our analysis. There was fair intermodality agreement in stenosis grades (κ = 0.220, 95% C.I. = [0.029, 0.410]), though categorical stenosis grades were significantly discordant between imaging modalities, with higher grades more frequent in MRI (χ2 = 27.378, p = 0.002). On CT-based imaging, Grade III or IV stenoses were noted in 17/70 (24.2%) IJs, whereas on MRI-based imaging, Grade III or IV stenoses were found in 40/70 (57.1%) IJs. Among veins with Grade I-IV IJVS, MRI stenosis estimates were significantly higher than CT stenosis estimates (77.0%, 95% C.I. [35.9-55.2%] vs. 45.6%, 95% C.I. [35.9-55.2%], p < 0.001).

CONCLUSION

MRI with contrast overestimates the degree of IJVS compared to CT with contrast. Consideration of this discrepancy should be considered in diagnosis and treatment planning in patients with potential IJVS-related symptoms.

Fetal head-down posture may explain the rapid brain evolution in humans and other primates: An interpretative review

Evolutionary cerebrovascular consequences of upside-down postural verticality of the anthropoid fetus have been largely overlooked in the literature. This working hypothesis-based report provides a literature interpretation from an aspect that the rapid evolution of the human brain has been promoted by fetal head-down position due to maternal upright and semi-upright posture. Habitual vertical torso posture is a feature not only of humans, but also of monkeys and non-human apes that spend considerable time in a sitting position. Consequently, the head-down position of the fetus may have caused physiological craniovascular hypertension that stimulated expansion of the intracranial vessels and acted as an epigenetic physiological stress, which enhanced neurogenesis and eventually, along with other selective pressures, led to the progressive growth of the anthropoid brain and its organization. This article collaterally opens a new insight into the conundrum of high cephalopelvic proportions (i.e., the tight fit between the pelvic birth canal and fetal head) in phylogenetically distant lineages of monkeys, lesser apes, and humans. Low cephalopelvic proportions in non-human great apes could be accounted for by their energetically efficient horizontal nest-sleeping and consequently by their larger body mass compared to monkeys and lesser apes that sleep upright. One can further hypothesize that brain size varies in anthropoids according to the degree of exposure of the fetus to postural verticality. The supporting evidence for this postulation includes a finding that in fossil hominins cerebral blood flow rate increased faster than brain volume. This testable hypothesis opens a perspective for research on fetal postural cerebral hemodynamics.

Impact of ischemic heart disease and cardiac rehabilitation on cerebrovascular compliance

We aimed to determine the influence of ischemic heart disease (IHD) and cardiac rehabilitation (CR) on cerebrovascular compliance index (Ci). Eleven (one female) patients with IHD (mean[SD]: 61[11] yr, 29[4] kg/m2) underwent 6 mo of CR, which consisted of ≥3 sessions/wk of aerobic and resistance training (20-60 min each). Ten (three female) similarly aged controls (CON) were tested at baseline as a comparator group. Middle cerebral artery velocity (MCAv) and mean arterial pressure were monitored continuously using transcranial Doppler ultrasound and finger photoplethysmography, respectively, during a rapid sit-to-stand maneuver. A Windkessel model was used to estimate cerebrovascular Ci every five cardiac cycles for a duration of 30 s. Cerebrovascular resistance was calculated as the quotient of MAP and MCAv. Two-way ANOVAs were used to determine whether cerebrovascular variables differ during postural transitions between groups and after CR. Baseline MCAv was higher in CON versus IHD (P = 0.014) and a time × group interaction was observed (P = 0.045) where MCAv decreased more in CON after standing. Compared with the precondition, CR had no effect on MCAv (condition P = 0.950) but a main effect of time indicated that MCAv decreased from the seated position in both conditions (time P = 0.013). Baseline cerebrovascular Ci was greater in IHD versus CON (P = 0.049) and the peak cerebrovascular Ci during the transition to standing was significantly higher in IHD compared with CON (interaction P = 0.047). CR did not affect cerebrovascular compliance (P = 0.452) and no time-by-condition interaction upon standing was present (P = 0.174). Baseline cerebrovascular Ci is higher in IHD at baseline compared with CON, but 6 mo of CR did not modify the transient increase in cerebrovascular Ci during sit-to-stand maneuvers.NEW & NOTEWORTHY Post-cardiac event cognitive impairment is common and exercise-based rehabilitation may be an effective intervention to mitigate cognitive decline. Microvascular damage due to high blood pressure pulsatility entering the brain is the putative mechanism of vascular dementia. Whether patients with ischemic heart disease exhibit lower cerebrovascular compliance, and if cardiac rehabilitation can improve cerebrovascular compliance is unknown. We observed that patients with ischemic heart disease have paradoxically higher cerebrovascular compliance, which is not affected by cardiac rehabilitation.

Effects of body positions on arterial stiffness as assessed by pulse wave velocity

BACKGROUND

Assessing arterial stiffness through pulse wave velocity (PWV) usually requires participants to be in a supine position. If this position is not feasible, adjustments such as tilting the bed or bending the knees may be made. The Vicorder device also recommends tilting the upper body to prevent jugular vein interference in the recorded carotid pulse.

OBJECTIVE

To examine the impact of varying body positions on PWV.

METHODS

Seventy adults were studied in the fully supine (0°) to 40° upper body tilted-up positions with and without knee bend. Carotid-femoral PWV (cfPWV) was measured using two different testing devices (Omron VP-1000plus and Vicorder) and brachial-ankle PWV (baPWV) was measured using Omron.

RESULTS

cfPWV measured at 10° tilt-up was not different from 0° position while baPWV increased significantly from 10°. Elevations in cfPWV were 7% at 20° and 15% at 40° compared with 0° position. Knee bend did not affect cfPWV but decreased baPWV at each angle ( P  < 0.05). Jugular vein interference on the Vicorder was observed in 78% of participants in supine position, decreasing as body angle increased (7% at 30°). However, cfPWV values measured by Vicorder were consistent with those obtained by Omron even with jugular vein interference.

CONCLUSION

Arterial stiffness assessed by PWV increased gradually and significantly in semi-Fowler's position ≥20°. Knee bend decreased baPWV but did not seem to affect cfPWV. PWV should be measured in supine position if possible. If the supine posture is not tolerated, knee bend followed by a slight incline position may be recommended.

Anatomy imaging and hemodynamics research on the cerebral vein and venous sinus among individuals without cranial sinus and jugular vein diseases

In recent years, imaging technology has allowed the visualization of intracranial and extracranial vascular systems. However, compared with the cerebral arterial system, the relative lack of image information, individual differences in the anatomy of the cerebral veins and venous sinuses, and several unique structures often cause neurologists and radiologists to miss or over-diagnose. This increases the difficulty of the clinical diagnosis and treatment of cerebral venous system diseases. This review focuses on applying different imaging methods to the normal anatomical morphology of the cerebral venous system and special structural and physiological parameters, such as hemodynamics, in people without cranial sinus and jugular vein diseases and explores its clinical significance. We hope this study will reinforce the importance of studying the cerebral venous system anatomy and imaging data and will help diagnose and treat systemic diseases.

Cerebrospinal fluid micro-volume changes inside the spinal space affect intracranial pressure in different body positions of animals and phantom

Interpersonal differences can be observed in the human cerebrospinal fluid pressure (CSFP) in the cranium in an upright body position, varying from positive to subatmospheric values. So far, these changes have been explained by the Monroe–Kellie doctrine according to which CSFP should increase or decrease if a change in at least one of the three intracranial volumes (brain, blood, and CSF) occurs. According to our hypothesis, changes in intracranial CSFP can occur without a change in the volume of intracranial fluids. To test this hypothesis, we alternately added and removed 100 or 200 μl of fluid from the spinal CSF space of four anesthetized cats and from a phantom which, by its dimensions and biophysical characteristics, imitates the cat cerebrospinal system, subsequently comparing CSFP changes in the cranium and spinal space in both horizontal and vertical positions. The phantom was made from a rigid “cranial” part with unchangeable volume, while the “spinal” part was made of elastic material whose modulus of elasticity was in the same order of magnitude as those of spinal dura. When a fluid volume (CSF or artificial CSF) was removed from the spinal space, both lumbar and cranial CSFP pressures decreased by 2.0–2.5 cm H2O for every extracted 100 μL. On the other hand, adding fluid volume to spinal space causes an increase in both lumbar and cranial CSFP pressures of 2.6–3.0 cm H2O for every added 100 μL. Results observed in cats and phantoms did not differ significantly. The presented results on cats and a phantom suggest that changes in the spinal CSF volume significantly affect the intracranial CSFP, but regardless of whether we added or removed the CSF volume, the hydrostatic pressure difference between the measuring sites (lateral ventricle and lumbar subarachnoid space) was always constant. These results suggest that intracranial CSFP can be increased or decreased without significant changes in the volume of intracranial fluids and that intracranial CSFP changes in accordance with the law of fluid mechanics.

Cerebral venous anatomy: implications for the neurointerventionalist

Meaningful contributions to neurointerventional practice may be possible by considering the dynamic aspects of angiography in addition to fixed morphologic information. The functional approach to venous anatomy requires integration of the traditional static anatomic features of the system-deep, superficial, posterior fossa, medullary veins, venous sinuses, and outflow routes into an overall appreciation of how a classic model of drainage is altered, embryologically, or pathologically, depending on patterns of flow-visualization made possible by angiography. In this review, emphasis is placed on balance between alternative venous networks and their redundancy, and the problems which arise when these systems are lacking. The role of veins in major neurovascular diseases, such as dural arteriovenous fistulae, arteriovenous malformations, pulsatile tinnitus, and intracranial hypertension, is highlighted, and deficiencies in knowledge emphasized.

Cranial defect and pneumocephalus are associated with significant postneurosurgical positional brain shift: evaluation using upright computed tomography

Only few studies have assessed brain shift caused by positional change. This study aimed to identify factors correlated with a large postneurosurgical positional brain shift (PBS). Sixty-seven patients who underwent neurosurgical procedures had upright computed tomography (CT) scan using settings similar to those of conventional supine CT. The presence of a clinically significant PBS, defined as a brain shift of ≥ 5 mm caused by positional change, was evaluated. The clinical and radiological findings were investigated to identify factors associated with a larger PBS. As a result, twenty-one patients had a clinically significant PBS. The univariate analysis showed that supratentorial lesion location, intra-axial lesion type, craniectomy procedure, and residual intracranial air were the predictors of PBS. Based on the multivariate analysis, craniectomy procedure (p < 0.001) and residual intracranial air volume (p = 0.004) were the predictors of PBS. In a sub-analysis of post-craniectomy patients, PBS was larger in patients with supratentorial craniectomy site and parenchymal brain injury. A large craniectomy area and long interval from craniectomy were correlated with the extent of PBS. In conclusion, patients who undergo craniectomy and those with residual intracranial air can present with a large PBS. In post-craniectomy patients, the predisposing factors of a large PBS are supratentorial craniectomy, presence of parenchymal injury, large skull defect area, and long interval from craniectomy. These findings can contribute to safe mobilization among postneurosurgical patients and the risk assessment of sinking skin flap syndrome.

Cardiovascular Response to Posture Changes: Multiscale Modeling and in vivo Validation During Head-Up Tilt

In spite of cardiovascular system (CVS) response to posture changes have been widely studied, a number of mechanisms and their interplay in regulating central blood pressure and organs perfusion upon orthostatic stress are not yet clear. We propose a novel multiscale 1D-0D mathematical model of the human CVS to investigate the effects of passive (i.e., through head-up tilt without muscular intervention) posture changes. The model includes the main short-term regulation mechanisms and is carefully validated against literature data and in vivo measures here carried out. The model is used to study the transient and steady-state response of the CVS to tilting, the effects of the tilting rate, and the differences between tilt-up and tilt-down. Passive upright tilt led to an increase of mean arterial pressure and heart rate, and a decrease of stroke volume and cardiac output, in agreement with literature data and present in vivo experiments. Pressure and flow rate waveform analysis along the arterial tree together with mechano-energetic and oxygen consumption parameters highlighted that the whole system approaches a less stressed condition at passive upright posture than supine, with a slight unbalance of the energy supply-demand ratio. The transient dynamics is not symmetric in tilt-up and tilt-down testing, and is non-linearly affected by the tilting rate, with stronger under- and overshoots of the hemodynamic parameters as the duration of tilt is reduced. By enriching the CVS response to posture changes, the present modeling approach shows promise in a number of applications, ranging from autonomic system disorders to spaceflight deconditioning.

Cerebral blood flow, cerebrovascular reactivity and their influence on ventilatory sensitivity

NEW FINDINGS

What is the topic of this review? Cerebrovascular reactivity to CO₂ , which is a principal factor in determining ventilatory responses to CO₂ through the role reactivity plays in determining cerebral extra- and intracellular pH. What advances does it highlight? Recent animal evidence suggests central chemoreceptor vasculature may demonstrate regionally heterogeneous cerebrovascular reactivity to CO₂ , potentially as a protective mechanism against excessive CO₂ washout from the central chemoreceptors, thereby allowing ventilation to reflect the systemic acid-base balance needs (respiratory changes in P aC O 2 ) rather than solely the cerebral needs. Ventilation per se does not influence cerebrovascular reactivity independent of changes in P aC O 2 .

ABSTRACT

Alveolar ventilation and cerebral blood flow are both predominantly regulated by arterial blood gases, especially arterial P C O 2 , and so are intricately entwined. In this review, the fundamental mechanisms underlying cerebrovascular reactivity and central chemoreceptor control of breathing are covered. We discuss the interaction of cerebral blood flow and its reactivity with the control of ventilation and ventilatory responsiveness to changes in P C O 2 , as well as the lack of influence of ventilation itself on cerebrovascular reactivity. We briefly summarize the effects of arterial hypoxaemia on the relationship between ventilatory and cerebrovascular response to both P C O 2 and P O 2 . We then highlight key methodological considerations regarding the interaction of reactivity and ventilatory sensitivity, including the following: regional heterogeneity of cerebrovascular reactivity; a pharmacological approach for the reduction of cerebral blood flow; reactivity assessment techniques; the influence of mean arterial blood pressure; and sex-related differences. Finally, we discuss ventilatory and cerebrovascular control in the context of high altitude and congestive heart failure. Future research directions and pertinent questions of interest are highlighted throughout.

The relationship between cerebral blood flow and venous sinus pressure: can hyperemia induce idiopathic intracranial hypertension?

Background

It has been shown that idiopathic intracranial hypertension (IIH) in children is associated with cerebral hyperemia, which induces an increase in cerebral venous pressure. The current literature suggests venous pressure scales with blood flow in a linear fashion, however, a linear relationship would not raise the pressure high enough to induce IIH. There is, however, some evidence to suggest that this relationship could be quadratic in nature. The purpose of this paper is to characterize the relationship between cerebral blood flow and the pressure drop across the cerebral venous system.

Methods

10 CT venogram data sets were collected for this study, with 5 useable geometries created. Computational fluid dynamics (CFD) models were generated using these geometries, with 10 simulations conducted per patient. The flow rates tested ranged from 200 mL/min to 2000 mL/min. 3D pressure and velocity streamline distributions were created and analyzed for each CFD model, with pressure drops across the cerebral venous system determined. The effective and hydraulic diameters were determined at the superior sagittal sinus, transverse sinus and both proximal and distal sigmoid sinuses.

Results

A quadratic relationship between blood flow and sinus pressure was found, with correlations of 0.99 or above in all five patients. The presence of vortical blood flow was found to explain this trend, with fluid curl and pressure drop correlations being above 0.97. This suggests that the presence of high blood flow should be considered in the diagnostic workup of IIH.

Conclusions

The cerebral venous sinus blood flow and pressure response relationship are quadratic in nature, with the major cause of this being the degree of rotation induced in the flow. The elevated blood flow found in children with IIH can explain the increased ICP that is found, secondary to the increase in venous pressure that develops.