| 1. |
- Holmgren, Madelene, et al.
(författare)
-
Prediction of cerebral perfusion pressure during carotid surgery : A computational fluid dynamics approach
- 2022
-
Ingår i: Clinical Biomechanics. - : Elsevier BV. - 0268-0033 .- 1879-1271. ; 100
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Maintaining cerebral perfusion pressure in the brain when a carotid artery is closed during vascular surgery is critical for avoiding intraoperative hypoperfusion and risk of ischemic stroke. Here we propose and evaluate a method based on computational fluid dynamics for predicting patient-specific cerebral perfusion pressures at carotid clamping during carotid endarterectomy.Methods: The study consisted of 22 patients with symptomatic carotid stenosis who underwent carotid endarterectomy (73 ± 5 years, 59–80 years, 17 men). The geometry of the circle of Willis was obtained preoperatively from computed tomography angiography and corresponding flow rates from four-dimensional flow magnetic resonance imaging. The patients were also classified as having a present or absent ipsilateral posterior communicating artery based on computed tomography angiography. The predicted mean stump pressures from computational fluid dynamics were compared with intraoperatively measured stump pressures from carotid endarterectomy.Findings: On group level, there was no difference between the predicted and measured stump pressures (−0.5 ± 13 mmHg, P = 0.86) and the pressures were correlated (r = 0.44, P = 0.039). Omitting two outliers, the correlation increased to r = 0.78 (P < 0.001) (−1.4 ± 8.0 mmHg, P = 0.45). Patients with a present ipsilateral posterior communicating artery (n = 8) had a higher measured stump pressure than those with an absent artery (n = 12) (P < 0.001).Interpretation: The stump pressure agreement indicates that the computational fluid dynamics approach was promising in predicting cerebral perfusion pressures during carotid clamping, which may prove useful in the preoperative planning of vascular interventions.
|
|
| 2. |
|
|
| 3. |
- Holmlund, Petter, 1988-
(författare)
-
Fluid dynamic principles for analysis of intracranial pressure control : application towards space medicine and hydrocephalus
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intracranial pressure (ICP) is an important component of the fluid dynamic environment of the brain and plays a central role with regards to the maintenance of normal cerebral blood flow and neuronal function. However, many regulatory mechanisms controlling the ICP are still poorly understood. One major gap in knowledge in this regard is the mechanism behind the postural/gravitational control of ICP. This is partly due to the fact that most ICP investigations are performed with the patients in a supine or recumbent position. Since most people spend 16 hours a day in an upright position, understanding these mechanics is highly motivated. Also spurring research on this topic is the increasing number of reports of the spaceflight-associated neuro-ocular syndrome (SANS) found in astronauts after prolonged exposure to weightlessness (i.e. microgravity), where evidence suggests that a disrupted balance between ICP and intraocular pressure (IOP) may be an underlying cause. Understanding how ICP is regulated with respect to posture could therefore provide important insight into the alterations introduced by microgravity, where postural effects are removed, and how to improve the safety of astronauts who are susceptible to this syndrome. Here on earth, disturbances in the ICP or cerebrospinal fluid (CSF) dynamics are associated with the development of chronic neurological diseases. One particular disease of interest is communicating hydrocephalus, where the cerebral ventricles are enlarged despite the absence of macroscopic CSF flow obstructions. A common finding in these patients is that of altered pulsatile flow in the CSF. The overall aim of this thesis was to utilize fluid dynamic principles to describe and validate potential regulatory mechanisms behind postural changes in ICP and causes of ventriculomegaly. The thesis is based on four scientific papers (paper I—IV).A postural dependency of the IOP-ICP pressure difference was verified by simultaneous measurements of ICP (assessed through lumbar puncture) and IOP (measured with an Applanation Resonance Tonometer) (paper I). Based on these measurements, a 24-hour average of the IOP-ICP pressure difference at the level of the eye was estimated for the state of microgravity, predicting a reduced pressure difference in space compared with that on earth.A hypothesis where postural changes in ICP are described by hydrostatic effects in the venous system, and where these effects are altered by the collapse of the internal jugular veins (IJVs) in more upright positions, was evaluated (paper II and III). Using ultrasound data, it was shown that the venous hydrostatic pressure gradient was balanced by viscous pressure losses in the collapsed IJVs to uphold a near atmospheric pressure at the level of the neck in the upright posture (paper II). A full evaluation of the hypothesis was then performed, based on simultaneous assessment of ICP, central venous pressure (through a PICC-line) and venous collapse in 7 postures of upper-body tilt in healthy volunteers (paper III).The proposed description could accurately predict the general changes seen in the measured ICP for all investigated postures (mean difference: -0.03±2.7 mmHg or -4.0±360 Pa).Pulsatile CSF flow-induced pressure differences between the ventricles and subarachnoid space were evaluated as a source for ventriculomegaly in communicating hydrocephalus (paper IV). The pressure distributions resulting from the pulsatile CSF flow were calculated using computational fluid dynamics based on MRI data. The estimated pressures revealed a net pressure difference (mean: 0.001±0.003 mmHg or 0.2±0.4 Pa, p=0.03) between the ventricles and the subarachnoid space, over the cardiac cycle, with higher pressure in the third and lateral ventricles.In conclusion, the results of this thesis support venous hydrostatics and jugular venous collapse as key governing factors in the postural/gravitational control of ICP. Furthermore, a postural dependency of the IOP-ICP pressure difference was demonstrated, providing a potential explanation for how an imbalance between the pressure of the eye and brain can be introduced in microgravity. Computational fluid dynamic analysis revealed that the altered pulsations in communicating hydrocephalus generate a pressure gradient within the CSF system. However, the gradient was small and additional effects are probably needed to explain the ventriculomegaly in these patients.
|
|
| 4. |
- Holmlund, Petter, 1988-, et al.
(författare)
-
Mathematical modelling of the CSF system : effects of microstructures and posture on optic nerve subarachnoid space dynamics
- 2022
-
Ingår i: Fluids and Barriers of the CNS. - : BioMed Central. - 2045-8118. ; 19:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The pressure difference between the eye and brain in upright postures may be affected by compartmentalization of the optic nerve subarachnoid space (ONSAS). Both pressure and deformation will depend on the microstructures of the ONSAS, and most likely also on ocular glymphatic clearance. Studying these factors could yield important knowledge regarding the translaminar pressure difference, which is suspected to play a role in normal-tension glaucoma.Methods: A compartment model coupling the ONSAS with the craniospinal CSF system was used to investigate the effects of microstructures on the pressure transfer through the ONSAS during a posture change from supine to upright body postures. ONSAS distensibility was based on MRI measurements. We also included ocular glymphatic flow to investigate how local pressure gradients alter this flow with changes in posture.Results: A compartmentalization of the ONSAS occurred in the upright posture, with ONSAS porosity (degree of microstructural content) affecting the ONSAS pressure (varying the supine/baseline porosity from 1.0 to 0.75 yielded pressures between − 5.3 and − 2 mmHg). Restricting the minimum computed porosity (occurring in upright postures) to 0.3 prevented compartmentalization, and the ONSAS pressure could equilibrate with subarachnoid space pressure (− 6.5 mmHg) in ≤ 1 h. The ocular glymphatics analysis predicted that substantial intraocular-CSF flows could occur without substantial changes in the ONSAS pressure. The flow entering the ONSAS in supine position (both from the intraocular system and from the cranial subarachnoid space) exited the ONSAS through the optic nerve sheath, while in upright postures the flow through the ONSAS was redirected towards the cranial subarachnoid space.Conclusions: Microstructures affect pressure transmission along the ONSAS, potentially contributing to ONSAS compartmentalization in upright postures. Different pathways for ocular glymphatic flow were predicted for different postures.
|
|
| 5. |
- Holmlund, Petter, 1988-, et al.
(författare)
-
Posture-dependent collapse of the optic nerve subarachnoid space : A combined MRI and modeling study
- 2021
-
Ingår i: Investigative Ophthalmology and Visual Science. - : Association for Research in Vision and Ophthalmology. - 0146-0404 .- 1552-5783. ; 62:4
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: We hypothesize that a collapse of the optic nerve subarachnoid space (ONSAS) in the upright posture may protect the eyes from large translamina cribrosa pressure differences (TLCPD) believed to play a role in various optic nerve diseases (e.g., glaucoma). In this study, we combined magnetic resonance imaging (MRI) and mathematical modeling to investigate this potential ONSAS collapse and its effects on the TLCPD.METHODS: First, we performed MRI on six healthy volunteers in 6° head-down tilt (HDT) and 13° head-up tilt (HUT) to assess changes in ONSAS volume (measured from the eye to the optic canal) with changes in posture. The volume change reflects optic nerve sheath (ONS) distensibility. Second, we used the MRI data and mathematical modeling to simulate ONSAS pressure and the potential ONSAS collapse in a 90° upright posture.RESULTS: The MRI showed a 33% decrease in ONSAS volume from the HDT to HUT (P < 0.001). In the upright posture, the simulations predicted an ONSAS collapse 25 mm behind lamina cribrosa, disrupting the pressure communication between the ONSAS and the intracranial subarachnoid space. The collapse reduced the simulated postural increase in TLCPD by roughly 1 mm Hg, although this reduction was highly sensitive to ONS distensibility, varying between 0 and 4.8 mm Hg when varying the distensibility by ± 1 SD.CONCLUSIONS: The ONSAS volume along the optic nerve is posture dependent. The simulations supported the hypothesized ONSAS collapse in the upright posture and showed that even small changes in ONS stiffness/distensibility may affect the TLCPD.
|
|
| 6. |
|
|
| 7. |
- Kristiansen, Martin, et al.
(författare)
-
Optic nerve subarachnoid space posture dependency : an MRI study in subjects with normal tension glaucoma and healthy controls
- 2023
-
Ingår i: Investigative Ophthalmology and Visual Science. - 0146-0404 .- 1552-5783. ; 64:15
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: The purpose of this study was to examine the differences of optic nerve subarachnoid space (ONSAS) volume in patients with normal tension glaucoma (NTG) and healthy controls in different body positions.Methods: Eight patients with NTG and seven healthy controls underwent magnetic resonance imaging (MRI) examinations in head up tilt (HUT) +11 degrees and head down tilt (HDT) -5 degrees positions according to a randomized protocol determining the starting position. The ONSAS volume in both body positions was measured and compared between the two groups. The results were analyzed using a generalized linear model.Results: Between HDT and HUT, the postural ONSAS volume change was dependent on starting position (P < 0.001) and group (P = 0.003, NTG versus healthy). A subgroup analysis of those that were randomized to HUT examination first, coming directly from an upright position, showed that the patients with NTG had significantly larger positional ONSAS volume changes compared to the healthy controls; 121 ± 22 µL vs. 65 ± 37 µL (P = 0.049). Analysis of the ONSAS volume distribution showed different profiles for patients with NTG and healthy controls.Conclusions: There was a significant difference in ONSAS volume change between patients with NTG and healthy subjects when subjected to posture changes, specifically when going from upright to head-down posture. This indicates that patients with NTG had been exposed to a lower ONSAS pressure when they came from the upright posture, which suggests an increased translaminar pressure difference in upright position. This may support the theory that NTG has a dysfunction in an occlusion mechanism of the optic nerve sheath that could cause abnormally negative ONSAS pressures in upright posture.
|
|
| 8. |
- Nilsson, Daniel, et al.
(författare)
-
Patient-specific brain arteries molded as a flexible phantom model using 3D printed water-soluble resin
- 2022
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Visualizing medical images from patients as physical 3D models (phantom models) have many roles in the medical field, from education to preclinical preparation and clinical research. However, current phantom models are generally generic, expensive, and time-consuming to fabricate. Thus, there is a need for a cost- and time-efficient pipeline from medical imaging to patient-specific phantom models. In this work, we present a method for creating complex 3D sacrificial molds using an off-the-shelf water-soluble resin and a low-cost desktop 3D printer. This enables us to recreate parts of the cerebral arterial tree as a full-scale phantom model (10×6×410×6×4 cm) in transparent silicone rubber (polydimethylsiloxane, PDMS) from computed tomography angiography images (CTA). We analyzed the model with magnetic resonance imaging (MRI) and compared it with the patient data. The results show good agreement and smooth surfaces for the arteries. We also evaluate our method by looking at its capability to reproduce 1 mm channels and sharp corners. We found that round shapes are well reproduced, whereas sharp features show some divergence. Our method can fabricate a patient-specific phantom model with less than 2 h of total labor time and at a low fabrication cost.
|
|
| 9. |
- Vikström, Axel, et al.
(författare)
-
Establishing the distribution of cerebrovascular resistance using computational fluid dynamics and 4D flow MRI
- 2024
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 14:1
-
Tidskriftsartikel (refereegranskat)abstract
- Cerebrovascular resistance (CVR) regulates blood flow in the brain, but little is known about the vascular resistances of the individual cerebral territories. We present a method to calculate these resistances and investigate how CVR varies in the hemodynamically disturbed brain. We included 48 patients with stroke/TIA (29 with symptomatic carotid stenosis). By combining flow rate (4D flow MRI) and structural computed tomography angiography (CTA) data with computational fluid dynamics (CFD) we computed the perfusion pressures out from the circle of Willis, with which CVR of the MCA, ACA, and PCA territories was estimated. 56 controls were included for comparison of total CVR (tCVR). CVR were 33.8 ± 10.5, 59.0 ± 30.6, and 77.8 ± 21.3 mmHg s/ml for the MCA, ACA, and PCA territories. We found no differences in tCVR between patients, 9.3 ± 1.9 mmHg s/ml, and controls, 9.3 ± 2.0 mmHg s/ml (p = 0.88), nor in territorial CVR in the carotid stenosis patients between ipsilateral and contralateral hemispheres. Territorial resistance associated inversely to territorial brain volume (p < 0.001). These resistances may work as reference values when modelling blood flow in the circle of Willis, and the method can be used when there is need for subject-specific analysis.
|
|
| 10. |
|
|
