Quantification of neurovascular compliance with retrospectively gated phase-contrast MRI.

OBJECTIVE: Neurovascular compliance (NVC) is the change in the brain's arterial tree blood volume, ΔV, divided by the change in intra-vascular blood pressure, ΔP, during the cardiac cycle. The primary aim of this work was to evaluate the performance of MRI measurement of NVC obtained from time-resolved measurements of internal carotid artery (ICA) and vertebral artery (VA) flow rates. A secondary aim was to explore whether NVC could be estimated from common carotid (CCA) flow in conjunction with prior knowledge of mean ICA and VA fractional flow rates, given the small cross-section of ICA and VA in some populations, in particular small children. METHODS: ΔV was quantified from the blood flow rate measured at the ICA and VA for actual NVC derivation. It was further estimated from individually measured CCA flow rate and mean flow fractions ICA/CCA and VA/CCA (which could alternatively be obtained from literature data), to yield estimated NVC. Time-resolved blood flow rate in CCA, ICA and VA was obtained via retrospectively-gated 2D PC-MRI at 1.5 T in healthy subjects (N = 16, 8 women, mean age 36 ± 13 years). ΔP was determined via a brachial pressure measurement. RESULTS: Actual and estimated mean NVC were 27 ± 15 and 38 ± 15 µL/mmHg, respectively, and the two measurements were strongly correlated (r = 0.80; p = 0.0002) with test-retest intra-class correlation coefficients of 0.964 and 0.899. CONCLUSION: Both methods yielded excellent retest precision. In spite of a large bias, actual and estimated NVC were strongly correlated.

Assessment of Cerebral Arterial Flow Volume Changes with Carotid Vertebral Artery Duplex Doppler Ultrasound in Young-Middle-aged Subclinical Hashimoto Thyroiditis Patients.

OBJECTIVES: To demonstrate cerebral arterial flow volume changes during the hypothyroid, euthyroid, and hyperthyroid phases and comparing between laboratory findings and cerebral arterial flow changes with carotid-vertebral duplex Doppler ultrasound (CVA-DUSG) in subclinical Hashimoto thyroiditis (HT) patients. METHODS: According to the TSH level, 3 groups were constructed between patient cases. Group 1 (n=29) was the subclinical hyperthyroid group. In this group, the TSH level was between 0.0005 and 0.3 IU/ml. Group 2 (n=175) was the euthyroid group. TSH level in this group was between 0.3 and 4.2 IU/ml. Group 3 (n=76) was the subclinical hypothyroid group. In this group, the TSH level was above 4.2 IU/ml. The control-group (group 4) (n=71) included healthy people. In this group, the TSH level was between 0.3 and 4.2 IU/ml. After obtaining at least three consecutive waves from the bilateral internal cerebral artery and bilateral vertebral artery, volume flows were calculated using CVA-DUSG. Volume flows were calculated as peak systolic velocity + end diastolic velocity/2 × mean arterial diameter. The mean ICA(Internal Carotid Artery) and VA(Vertebral Artery) diameter was measured per ICA and VA. Total cerebral artery flow volume was defined as right ICA + right VA flow volume and left ICA + left VA flow volume. We also demonstrated topographic cerebral artery blood flow changes. Total ICA flow volume was used to assess the anterior part of the brain, total VA flow volume was used to evaluate the posterior part of the brain, right ICA + right VA flow volume was used to assess the right part of the brain, and left ICA + left VA flow volume was used to verify the left part of the brain. RESULTS: There were significant differences between RVA(Right Vertebral Artery) flow volume, LICA (Left Internal Carotid Artery) flow volume, total flow volume, TSH, and T3 and T4 levels in all groups according to the Dunn's multiple comparison test.(p<0.001) Mean TSH level was 0.03 (0.005-0.06) IU/ml in group 1, 2.8 (1.8-3.97) IU/ml in group 2, 7.32 (6.14-9.93) IU/ml in group 3, and 1.76 (1.17-2.49) IU/ml in the control group. The mean T3 level was 4.18 (3.55-5.38) in group 1, 2.88 (2.63-3.16) in group 2, 2.82 (2.49-3.15) in group 3, 3.14 (2.92-3.15) in the control group. The mean T4 level was 1.92 (1.29-2.5) in group 1, 1.16(1.03-1.31) in group 2, 1.01 (0.91-1.16) in group 3, 1.12 (0.97-1.30) in the control group (group 4). Mean total flow volume was 793 (745-898) ml/min in group 1, 742 (684.25-822.5) ml/min in group 2, 747 (692-824) ml/min in group 3, and 700 (673-675) ml/min in the control group. We also demonstrated topographic cerebral arterial volume flow changes with CVA-DUSG. There was a significant difference among all groups in the right and anterior parts of the brain (p < 0.001), and there was a significant difference between groups 1 and 4 in the left part of the brain (p = 0.009). CONCLUSION: This study demonstrated that total cerebral arterial volume flow increased in the hyperthyroid phase of subclinical HT cases without any internal carotid and vertebral artery diameter changes compared with the euthyroid and hypothyroid phases of subclinical HT and healthy cases. We also verified topographic cerebral arterial blood flow changes in subclinical HT cases with a real-time, easily applicable modality (CVA-DUSG) that does not include X-ray or contrast agents. There was a significant difference between all groups in the right and anterior parts of the brain and there was a significant difference between groups 1 and 4 in the left part of the brain.

Pre-manipulative cervical spine testing and sustained rotation do not influence intracranial hemodynamics: an observational study with transcranial Doppler ultrasound.

INTRODUCTION: Manual joint mobilization and manipulation are recommended therapeutic interventions for people with neck pain. High-velocity thrust and sustained techniques have an uncertain association with serious arterial trauma. The validity of pre-manipulative tests of the cervical spine is often questioned, and the understanding of the effect of head/neck position on blood flow is still incomplete. Most of the evidence concerning hemodynamics in this area relates to extracranial flow (vertebral and carotid artery). Less is understood about the effects on intracranial flow while performing pre-manipulative tests and sustained positions like end of range cervical rotation mobilization. The aim of the study was to assess the influence of commonly used evaluation and treatment positions on intracranial hemodynamic parameters. METHOD: A randomized, cross-over observational study using ultrasonography on healthy subjects (n = 19) was conducted to measure hemodynamic parameters (peak systolic velocity and end diastolic maximum) of intracranial arterial systems. Two test positions (sustained pre-manipulative thrust C0-1 and sustained cervical end of range rotation) were compared with a sham position for each test position. RESULTS: :Neither the sequence of tests performed nor an independent variable (the two positions) had a significant effect (p < 0.05) on peak systolic velocity (PSV) or end diastolic maximum (EDM). DISCUSSION: No effects from commonly used assessment and treatment of neck positions on hemodynamic parameters were found. This is consistent with previous studies. Further study is indicated on people with symptoms and known pathologies.

Comparison of carotid and vertebral artery doppler measurements in supine and sitting positions.

Background: Carotid and vertebral Doppler ultrasonography (USG) is the primary diagnostic tool for the detection of extra cranial atherosclerotic disease and measurement of posterior fossa blood flow volume. The examination is performed while the patient lies on supine position. However, in daily practice we occasionally encounter patients who are not able to lie down on supine position for different reasons, such as kyphosis, severe dyspnea, or severe back pain. Aim: We aimed to compare the doppler spectral measurements of carotid and vertebral arteries obtained in supine and sitting positions. Patients and Methods: Fifty-three patients were recorded in the first group, to whom carotid and vertebral (CV) Doppler Ultrasound examination was initially performed while sitting, and another 52 patients were examined as the second group where initial measurements were done in a supine position. Peak systolic velocity (PSV), end diastolic velocity (ED) from each vessel, internal carotid artery (ICA)/common carotid artery (CCA) ratio, and volume flow of vertebral artery (VA) were measured in supine and sitting positions. Also, another 83 patients with a complaint of vertigo were included in the third group but only VA measurements were compared. Results: In the first group, there was a difference between sitting and supine positions in right ICA diastolic, right and left VA diastolic, and left CCA diastolic velocities (P < 0.05). In the second group, there was a difference in sitting and supine positions in right CCA systolic, right CCA diastolic, and left CCA diastolic velocities (P < 0.05). In the third group, there was a difference in sitting and supine positions in right and left VA diastolic velocities, left VA volume flow, and total VA volume flow (P < 0.05). A strong correlation was detected between supine and sitting positions regarding right and left ICA stenoses. Alterations in waveforms were noted in three patients' unilateral VAs, in supine and sitting positions. Conclusion: Our results suggest that CV doppler examinations may be performed in the sitting positions. Examination in the sitting position may be helpful in recognizing pre-steal and retrograde flows.

Effects of electrical muscle stimulation on cerebral blood flow.

BACKGROUND: Electrical muscle stimulation (EMS) induces involuntary muscle contraction. Several studies have suggested that EMS has the potential to be an alternative method of voluntary exercise; however, its effects on cerebral blood flow (CBF) when applied to large lower limb muscles are poorly understood. Thus, the purpose of this study was to examine the effects of EMS on CBF, focusing on whether the effects differ between the internal carotid (ICA) and vertebral (VA) arteries. METHODS: The participants performed the experiments under EMS and control (rest) conditions in a randomized crossover design. The ICA and VA blood flow were measured before and during EMS or control. Heart rate, blood pressure, minute ventilation, oxygen uptake, and end-tidal partial pressure of carbon dioxide (PETCO2) were monitored and measured as well. RESULTS: The ICA blood flow increased during EMS [Pre: 330 ± 69 mL min-1; EMS: 371 ± 81 mL min-1, P = 0.001, effect size (Cohen's d) = 0.55]. In contrast, the VA blood flow did not change during EMS (Pre: 125 ± 47 mL min-1; EMS: 130 ± 45 mL min-1, P = 0.26, effect size = 0.12). In the EMS condition, there was a significant positive linear correlation between ΔPETCO2 and ΔICA blood flow (R = 0.74, P = 0.02). No relationships were observed between ΔPETCO2 and ΔVA blood flow (linear: R = - 0.17, P = 0.66; quadratic: R = 0.43, P = 0.55). CONCLUSIONS: The present results indicate that EMS increased ICA blood flow but not VA blood flow, suggesting that the effects of EMS on cerebral perfusion differ between anterior and posterior cerebral circulation, primarily due to the differences in cerebrovascular response to CO2.

Resistance, but not endurance exercise training, induces changes in cerebrovascular function in healthy young subjects.

It is generally considered that regular exercise maintains brain health and reduces the risk of cerebrovascular diseases such as stroke and dementia. Since the benefits of different "types" of exercise are unclear, we sought to compare the impacts of endurance and resistance training on cerebrovascular function. In a randomized and crossover design, 68 young healthy adults were recruited to participate in 3 mo of resistance and endurance training. Cerebral hemodynamics through the internal carotid, vertebral, middle and posterior cerebral arteries were measured using Duplex ultrasound and transcranial Doppler at rest and during acute exercise, dynamic autoregulation, and cerebrovascular reactivity (to hypercapnia). Following resistance, but not endurance training, middle cerebral artery velocity and pulsatility index significantly decreased (P < 0.01 and P = 0.02, respectively), whereas mean arterial pressure and indices of cerebrovascular resistance in the middle, posterior, and internal carotid arteries all increased (P < 0.05). Cerebrovascular resistance indices in response to acute exercise and hypercapnia also significantly increased following resistance (P = 0.02), but not endurance training. Our findings, which were consistent across multiple domains of cerebrovascular function, suggest that episodic increases in arterial pressure associated with resistance training may increase cerebrovascular resistance. The implications of long-term resistance training on brain health require future study, especially in populations with pre-existing cerebral hypoperfusion and/or hypotension.NEW & NOTEWORTHY Three months of endurance exercise did not elicit adaptation in any domain of cerebrovascular function in young healthy inactive volunteers. However, resistance training induced decreased pulsatility in the extracranial arteries and increased indices of cerebrovascular resistance in cerebral arteries. This increase in cerebrovascular resistance, apparent at baseline and in response to both hypercapnia and acute exercise, may reflect a protective response in the face of changes in arterial pressure during resistance exercise.

Bilateral regional extracranial blood flow regulation to hypoxia and unilateral duplex ultrasound measurement error.

NEW FINDINGS: What is the central question of this study? Is blood flow regulation to hypoxia different between the internal carotid arteries (ICAs) and vertebral arteries (VAs), and what is the measurement error in unilateral extracranial artery assessments compared to bilateral? What is the main finding and its importance? ICA and VA blood flow regulation to hypoxia is comparable when factoring for vessel type and vessel side. Compared to bilateral assessment, vessels assessed unilaterally had individual measurement errors of up to 37%. Assessing the vessel with the larger resting blood flow, not the left or right vessel, reduces unilateral measurement error. ABSTRACT: Whether blood flow regulation to hypoxia is similar between left and right internal carotid arteries (ICAs) and vertebral arteries (VAs) is unclear. Extracranial blood flow is regularly calculated by doubling a unilateral assessment; however, lateral artery differences may lead to measurement error. This study aimed to determine extracranial blood flow regulation to hypoxia when factoring for vessel type (ICAs or VAs) and vessel side (left or right) effects, and to investigate unilateral assessment measurement error compared to bilateral assessment. In a repeated-measures crossover design, extracranial arteries of 44 participants were assessed bilaterally by duplex ultrasound during 90 min of normoxic and poikilocapnic hypoxic (12.0% fraction of inspired oxygen) conditions. Linear mixed model analyses revealed no Condition × Vessel Type × Vessel Side interaction for blood flow, vessel diameter and flow velocity (all P > 0.05) indicating left and right ICA and VA blood flow regulation to hypoxia was similar. Bilateral hypoxic reactivity was comparable (ICAs, 1.4 (1.0) vs. VAs, 1.7 (1.1) Δ%·Δ SpO2-1 ; P = 0.12). Compared to bilateral assessment, unilateral mean measurement error of the relative blood flow response to hypoxia was up to 5%, but individual errors reached 37% and were greatest in ICAs and VAs with the smaller resting blood flow due to a ratio-scaling problem. In conclusion, left and right ICA and VA regulation to hypoxia is comparable when factoring for vessel type and vessel side. Assessing the ICA and VA vessels with the larger resting blood flow, not the left or right vessel, reduces unilateral measurement error.

Hourly staircase sprinting exercise "snacks" improve femoral artery shear patterns but not flow-mediated dilation or cerebrovascular regulation: a pilot study.

Healthy males (n = 10; age: 24 ± 4 years; body mass index: 24 ± 2 kg·m-2) completed 2 randomized conditions separated by ≥48 h involving 6-8.5 h of sitting with ("stair snacks") and without (sedentary) hourly staircase sprint interval exercise (∼14-20 s each). Resting blood flow and shear rates were measured in the femoral artery, internal carotid artery, and vertebral artery (Duplex ultrasound). Flow-mediated dilation (FMD) was quantified as an index of peripheral endothelial function in the femoral artery. Neurovascular coupling (NVC; regional blood flow response to local increases in cerebral metabolism) was assessed in the posterior cerebral artery (transcranial Doppler ultrasound). Femoral artery hemodynamics were higher following the active trial with no change in the sedentary trial, including blood flow (+32 ± 23% vs. -10 ± 28%; P = 0.015 and P = 0.253, respectively), vascular conductance (+32 ± 27% vs. -15 ± 26%; P = 0.012 and P = 0.098, respectively), and mean shear rate (+17 ± 8% vs. -8 ± 28%; P = 0.004 and P = 0.310, respectively). The change in FMD was not different within or between conditions (P = 0.184). Global cerebral blood flow (CBF), conductance, shear patterns, and NVC were not different within or between conditions (all P > 0.05). Overall, exercise "stair snacks" improve femoral artery blood flow and shear patterns but not peripheral (e.g., FMD) or cerebral (e.g., CBF and NVC) vascular function following prolonged sitting. The study was registered at ClinicalTrials.gov (NCT03374436). Novelty: Breaking up 8.5 h of sitting with hourly staircase sprinting exercise "snacks" improves resting femoral artery shear patterns but not FMD. Cerebral blood flow and neurovascular coupling were unaltered following 6 h of sitting with and without hourly exercise breaks.

The Hemodynamic Response of the Vertebral Artery to 3 Time Durations of the Static Stretching Exercise in the End Position of Contralateral Cervical Rotation.

OBJECTIVES: To evaluate the effect of 3 different time durations of sustained end-range cervical rotation during static stretching exercises on the hemodynamics of the vertebral artery. METHODS: This observational study used Doppler ultrasonography to measure the average vertebral artery hemodynamics at the sustained end-range cervical rotation after 3 time durations of static stretching exercise: 10 seconds, 30 seconds, and 60 seconds. The sustained end-range cervical rotation was applied to 30 asymptomatic male participants. RESULTS: The peak systolic velocity 35.2 ± 6.9 cm/s and the end systolic velocity 12.7 ± 1.6 cm/s reduced significantly, while resistive index 0.74 ± 0.03 increased after 60 seconds of sustained end-range contralateral cervical rotation by 39.1%, 32.4%, and 8.8%, respectively, compared with the neutral position. There were no significant differences found between peak systolic velocity and resistive index after a stretching duration of 60 and 30 seconds. Similarly, there were no notable changes in end systolic velocity when comparing 10 seconds with 30 seconds. CONCLUSION: The static stretching exercise using sustained end-range cervical rotation for 60 seconds induced marked changes in the hemodynamics of the vertebral artery.

Changes in Vertebral Artery Blood Flow in Different Head Positions and Post-Cervical Manipulative Therapy.

OBJECTIVE: The objective of this study was to investigate the hemodynamics of blood flow through the V3 region of the vertebral artery contralateral to the side manipulated during different rotary head positions and post-cervical spinal manipulation. METHODS: This quasi-experimental study was performed on 25 healthy, asymptomatic participants, both male and female, between 20 and 30 years of age. Each participant presented with a C0/C1 or C1/C2 cervical facet restriction (as determined by motion palpation). Participation was voluntary, and participants had no symptoms of vertebrobasilar artery insufficiency or contraindications to cervical spinal manipulation. Doppler ultrasound was used to measure vertebral artery blood flow (V3 region) hemodynamics, contralateral side of manipulation, as close to C1/C2 region as possible in 4 positions of cervical rotation (neutral, 45°, maximum, and post-manipulation neutral). Doppler ultrasound parameters included peak systolic flow velocity, end diastolic flow velocity, mean flow velocity, vessel diameter, and flow rate. The nonparametric Friedman test was used for analysis across each head and neck position, and post manipulation. RESULTS: No clinical or statistically significant results (P > .05) were found for any of the hemodynamic parameters in any of the head positions. CONCLUSIONS: Hemodynamic measurements of the V3 region of the vertebral artery do not show significant changes in the measured head positions or following manipulation of the upper cervical spine in patients without pre-existing risk factors.

Changes in Vertebral Arterial Blood Flow During Premanipulative Tests in Participants With Upper Cervical Spine Motion Restriction.

OBJECTIVE: The purpose of the present study was to measure changes in blood flow velocity and volume flow rate (VFR) in the contralateral vertebral artery (VA) during end-range rotation and pre-manipulative hold at C1-C2 and to compare these measurements between participants with and without C1-C2 range of motion (ROM) restriction. METHODS: This research was approached as an exploratory study and designed as a parallel noninterventional controlled trial with intentionally equal allocation, for studying diagnostic tests. Fifteen women and 13 men (mean age 44) were recruited (volunteer sample) in physiotherapy clinics. No participant had any current neurologic or vertebrobasilar insufficiency symptoms. The measurements of 13 participants with a limited ROM C1-C2 and 15 with no limitation were compared. Blood flow velocity and VFR in the contralateral VA were measured using color duplex Doppler imaging in 3 neck positions: neutral, maximal rotation, and pre-manipulative hold of C1-C2. RESULTS: Pre-manipulative hold significantly (P < .01) decreased all blood flow velocity parameters and VFR, mainly in the left VA. End-range rotation showed a significant (P < .05) decrease in the peak systolic velocity in the left VA. No significant differences were found between participants grouped by the presence or absence of a C1-C2 ROM restriction. CONCLUSION: A C1-C2 rotational ROM restriction does not appear associated with change in a significantly reduced VA blood flow due to the neck position.

Changes in internal carotid and vertebral arterial wall stiffness with head movement can be detected with shear wave elastography.

Background: Safe practice is important for patients with neck pain, with the potential for injury to cervical arteries. Cervical manipulation or end range techniques/positions may place considerable strain on the arteries. Altered integrity of the arterial wall may render them more susceptible to minor trauma, particularly in the upper cervical region. Screening of blood flow velocity is limited for predicting those at risk. Examining properties of the cervical arterial wall (stiffness characteristics) and their response to head movement may provide an alternate measure of arterial susceptibility.Objectives: To investigate whether shear wave ultrasound elastography can detect any changes in internal carotid (ICA) and vertebral (VA) arterial wall stiffness in neutral compared with contralateral head rotation.Design: Observational studyMethods: Shear wave ultrasound elastography was used to measure the stiffness of the ICA and VA. Shear wave velocity (m/s), indicative of arterial stiffness, was measured in both arteries proximally (C3-4) and distally (C1-2) in neutral and contralateral head rotation as were intimal thickness (mm) and flow velocity (cm/s).Results: Thirty participants (20-62 years) were successfully imaged. The VA was stiffer than ICA and it became significantly stiffer in contralateral rotation (p = 0.05). The ICA became significantly less stiff (p = 0.01). Effects were more apparent at C1-2 but significant in the ICA only (p = 0.03). Flow velocity and intimal thickness were unchanged in rotation.Conclusions: Changes in VA and ICA arterial wall stiffness can be measured with shear wave ultrasound elastography. This measure may ultimately help identify arteries with greater vulnerability to rotational stresses.

Arterial and venous cerebral blood flow responses to long-term head-down bed rest in male volunteers.

NEW FINDINGS: What is the central question of this study? A heterogeneous cerebral blood flow (CBF) response in the cerebral arteries has been demonstrated in several physiological conditions, and it might be attributable to different physiological properties. However, the whole cerebral haemodynamic response to weightlessness remains unknown. What is the main finding and its importance? Long-term head-down bed rest caused a heterogeneous CBF response between the anterior and posterior cerebral arteries and between the cerebral arteries and veins. Especially, in contrast to the anterior cerebral circulation, the posterior arterial and venous CBFs were well maintained throughout weightlessness. ABSTRACT: In this study, we investigated the whole cerebral haemodynamic response to long-term head-down bed rest (HDBR). We hypothesized that long-term exposure to weightlessness influences cerebral blood flow (CBF) or CBF distribution among cerebral arteries and veins because of the different physiological roles of each cerebral vessel. To test this hypothesis, 10 male volunteers were exposed to -6 deg HDBR for 60 days. Blood flows in the internal carotid artery, external carotid artery and vertebral artery or internal jugular vein and vertebral vein were measured using ultrasonography before and on days 30 and 57 of the HDBR. The internal carotid artery blood flow was reduced on day 30 (P = 0.019) and had returned to the baseline level by day 57. In contrast, the vertebral artery blood flow remained unaltered throughout the HDBR (P = 0.626). The internal jugular vein blood flow was reduced on day 30 (P = 0.009), whereas the vertebral vein blood flow remained unaltered (P = 0.397). These findings suggest that long-term HDBR causes a heterogeneous CBF response between the anterior and posterior cerebral circulation in the both arteries and veins. The posterior arterial and venous CBFs were well maintained throughout HDBR, and these CBF responses to HDBR were different from the anterior cerebral circulation.

Differential vasomotor responses to isocapnic hyperoxia: cerebral versus peripheral circulation.

Isocapnic hyperoxia (IH) evokes cerebral and peripheral hypoperfusion via both disturbance of redox homeostasis and reduction in nitric oxide (NO) bioavailability. However, it is not clear whether the magnitude of the vasomotor responses depends on the vessel network exposed to IH. To test the hypothesis that the magnitude of IH-induced reduction in peripheral blood flow (BF) may differ from the hypoperfusion response observed in the cerebral vascular network under oxygen-enriched conditions, nine healthy men (25 ± 3 yr, mean ± SD) underwent 10 min of IH during either saline or vitamin C (3 g) infusion, separately. Femoral artery (FA), internal carotid artery (ICA), and vertebral artery (VA) BF (Doppler ultrasound), as well as arterial oxidant (8-isoprostane), antioxidant [ascorbic acid (AA)], and NO bioavailability (nitrite) markers were simultaneously measured. IH increased 8-isoprostane levels and reduced nitrite levels; these responses were followed by a reduction in both FA BF and ICA BF, whereas VA BF did not change. Absolute and relative reductions in FA BF were greater than IH-induced changes in ICA and VA perfusion. Vitamin C infusion increased arterial AA levels and abolished the IH-induced increase in 8-isoprostane levels and reduction in nitrite levels. Whereas ICA and VA BF did not change during the vitamin C-IH trial, FA perfusion increased and reached similar levels to those observed during normoxia with saline infusion. Therefore, the magnitude of IH-induced reduction in femoral blood flow is greater than that observed in the vessel network of the brain, which might involve the determinant contribution that NO has in the regulation of peripheral vascular perfusion.

Steady-state cerebral blood flow regulation at altitude: interaction between oxygen and carbon dioxide.

High-altitude ascent imposes a unique cerebrovascular challenge due to two opposing blood gas chemostimuli. Specifically, hypoxia causes cerebral vasodilation, whereas respiratory-induced hypocapnia causes vasoconstriction. The conflicting nature of these two superimposed chemostimuli presents a challenge in quantifying cerebrovascular reactivity (CVR) in chronic hypoxia. During incremental ascent to 4240 m over 7 days in the Nepal Himalaya, we aimed to (a) characterize the relationship between arterial blood gas stimuli and anterior, posterior and global (g)CBF, (b) develop a novel index to quantify cerebral blood flow (CBF) in relation to conflicting steady-state chemostimuli, and (c) assess these relationships with cerebral oxygenation (rSO2). On rest days during ascent, participants underwent supine resting measures at 1045 m (baseline), 3440 m (day 3) and 4240 m (day 7). These measures included pressure of arterial (Pa)CO2, PaO2, arterial O2 saturation (SaO2; arterial blood draws), unilateral anterior, posterior and gCBF (duplex ultrasound; internal carotid artery [ICA] and vertebral artery [VA], gCBF [{ICA + VA} × 2], respectively) and rSO2 (near-infrared spectroscopy). We developed a novel stimulus index (SI), taking into account both chemostimuli (PaCO2/SaO2). Subsequently, CBF was indexed against the SI to assess steady-state cerebrovascular responsiveness (SS-CVR). When both competing chemostimuli are taken into account, (a) SS-CVR was significantly higher in ICA, VA and gCBF at 4240 m compared to lower altitudes, (b) delta SS-CVR with ascent (1045 m vs. 4240 m) was higher in ICA vs. VA, suggesting regional differences in CBF regulation, and (c) ICA SS-CVR was strongly and positively correlated (r = 0.79) with rSO2 at 4240 m.

Anatomic Considerations for Injection of the Lateral Atlanto-Axial Joint.

OBJECTIVE: We aimed to define the potential complications of intra-articular steroid injections into the lateral C1-2 articulations and safety margins to the relevant structures. METHODS: A total of 488 contrast-enhanced computed tomography angiogram (CTA) "arch to vertex" studies were retrospectively reviewed for theoretical intersection of the vertebral artery or thecal sac and distance of the named structures from the anticipated/theoretical trajectory of injection into the lateral C1-C2 joint. RESULTS: Patients were 60.4±15.8 years old and 55.5% male. In total, seven vertebral arteries and 11 thecal sac theoretical intersections were found. In cases without a direct intersection, the distance from the trajectory (range) was 0.71±0.18 (0.22-1.44) cm to the vertebral artery and 0.6±0.22 (0.14-1.8) cm to the thecal sac. CONCLUSIONS: Although injection of steroid into the lateral C1-C2 articulation for pain management has historically been reported to carry risk of severe complications due to close proximity and location variability of surrounding structures, our study quantifies the potential risk of such injections. Further, our analysis suggests that preprocedural imaging should be considered.

Effects of Head and Neck Positions on Blood Flow in the Vertebral, Internal Carotid, and Intracranial Arteries: A Systematic Review.

BACKGROUND: Manual therapy interventions targeting the neck include various positions and movements of the craniocervical region. The hemodynamic changes in various spinal positions potentially have clinical relevance. OBJECTIVES: To investigate the effects of craniocervical positions and movements on hemodynamic parameters (blood flow velocity and/or volume) of cervical and craniocervical arteries. METHODS: A search of 4 databases (PubMed, Embase, CINAHL, and Index to Chiropractic Literature) and, subsequently, a hand search of reference lists were conducted. Full-text experimental and quasi-experimental studies on the influence of cervical positions on blood flow of the vertebral, internal carotid, and basilar arteries were eligible for this review. Two independent reviewers selected and extracted the data using the double-screening method. RESULTS: Of the 1453 identified studies, 31 were included and comprised 2254 participants. Most studies mentioned no significant hemodynamic changes during maximal rotation (n = 16). A significant decrease in hemodynamics was identified for the vertebral artery, with a hemodynamic decrease in the position of maximum rotation (n = 8) and combined movement of maximum extension and maximum rotation (n = 4). A similar pattern of decreased hemodynamics was also identified for the internal carotid and intracranial arteries. Three studies focused on high-velocity thrust positioning and movement. None of the studies reported hemodynamic changes. The synthesized data suggest that in the majority of people, most positions and movements of the craniocervical region do not affect blood flow. CONCLUSION: The findings of this systematic review suggest that craniocervical positioning may not alter blood flow as much as previously expected. LEVEL OF EVIDENCE: Therapy, level 2a. J Orthop Sports Phys Ther 2019;49(10):688-697. Epub 5 Jul 2019. doi:10.2519/jospt.2019.8578.

Changes in Vertebral Artery Hemodynamics Associated With McKenzie Therapeutic Cervical Movements: An Exploration Using Duplex Ultrasound Imaging.

OBJECTIVE: The purpose of this study was to explore vertebral artery hemodynamic changes associated with McKenzie therapeutic cervical movements in healthy individuals. METHODS: A single-group repeated-measure design was used to examine 20 healthy participants aged 22.05 (1.69) years, mean (standard deviation). Vertebral artery volume flow, diameter, resistive index, time-averaged maximum velocity, and pulsatility index were measured using Duplex ultrasound. Vertebral artery hemodynamics were measured at cervical neutral positions then compared against vertebral artery hemodynamics measured during end-range loading and after repeated McKenzie therapeutic movements. Wilcoxon signed rank tests were used for comparisons, and standardized mean differences (SMDs) were calculated to quantify the changes in size. RESULTS: Repeated retraction with extension in a sitting position and end-range retraction with extension in supine position were significantly associated with an increase in vertebral artery volume flow, P ≤ .01, and the SMD suggests small-medium changes in size. Statistical significant vertebral artery dilation was observed in the sitting position with protraction, combined retraction with extension, and flexion, P ≤ .01, yet the SMD suggested small changes in size. End-range flexion was significantly associated with a reduction in vertebral artery pulsatility index, and the SMD suggested large changes in size. Repeated retraction with extension in supine position was significantly associated with an increase in vertebral artery time-averaged maximum velocity, yet the SMD revealed no clinically important difference. CONCLUSION: For the healthy participants in this study, McKenzie cervical movements were mostly associated with an increase in vertebral artery hemodynamics.

Stroke mechanisms and their correlation with functional outcome in medullary infarction.

PURPOSE: To study the stroke mechanism of medullary infarction (MI) and their correlation with prognosis. METHODS: We collected 81 consecutive patients with acute isolated MI including 50 patients with lateral MI (LMI), 30 with medial MI (MMI) and one with combined MI. The stroke mechanisms were defined as follows: 1. Large artery atherosclerotic occlusive disease (LAOD): with severe stenosis (>50%) or occlusion on the relevant arteries. 2. Penetrating artery disease (PAD): occlusion of penetrating arteries that arise from vertebral artery or basilar artery with no significant stenosis of the vertebro-basilar artery. 3. Dissection: angiographic findings met the criteria. 4. Cardiogenic embolism: abrupt onset with atrial fibrillation. The poor outcome was defined as a condition that includes the mRS ≥2 and/or dysphagia at one year after onset. RESULTS: There were 20 patients with PAD (40%), 18 with dissection (36.0%) and 11 with LAOD (22.0%) in LMI and 17 with PAD (56.6%), 10 with LAOD (33.3%) in MMI. LAOD and dissection compared with PAD were independently correlated with poor outcome in LMI (OR: 12.8, p = 0.029 and OR: 14.9, p = 0.035). LAOD was significantly correlated with poor outcome in MMI (OR: 13.4, p = 0.014). CONCLUSIONS: PAD was the most predominant stroke mechanism in MI and generally showed favorable outcome. Patients with LAOD and dissection showed worse outcome than those with PAD.

The age-related reduction in cerebral blood flow affects vertebral artery more than internal carotid artery blood flow.

Ageing reduces cerebral blood flow (CBF), while mean arterial pressure (MAP) becomes elevated. According to 'the selfish brain' hypothesis of hypertension, a reduction in vertebral artery blood flow (VA) leads to increased sympathetic activity and thus increases MAP. In twenty-two young (24 ± 3 years; mean ± SD) and eleven elderly (70 ± 5 years) normotensive men, duplex ultrasound evaluated whether the age-related reduction in CBF affects VA more than internal carotid artery (ICA) blood flow. Pulse-contour analysis evaluated MAP while near-infrared spectroscopy determined frontal lobe oxygenation and transcranial Doppler middle cerebral artery mean blood velocity (MCA Vmean ). During supine rest, MAP (90 ± 13 versus 78 ± 9 mmHg; P<0·001) was elevated in the older subjects while their frontal lobe oxygenation (68 ± 7% versus 77 ± 7%; P<0·001), MCA Vmean (49 ± 9 versus 60 ± 12 cm s-1 ; P = 0·016) and CBF (754 ± 112 versus 900 ± 144 ml min-1 ; P = 0·004) were low reflected in VA (138 ± 48 versus 219 ± 50 ml min-1 ; P<0·001) rather than in ICA flow (616 ± 96 versus 680 ± 120 ml min-1 ; P = 0·099). In conclusion, blood supply to the brain and its oxygenation are affected by ageing and the age-related decline in VA flow appears to be four times as large as that in ICA and could be important for the age-related increase in MAP.