Cerebral hemodynamics during orthostatic stress assessed by nonlinear modeling

2006 ◽  
Vol 101 (1) ◽  
pp. 354-366 ◽  
Author(s):  
Georgios D. Mitsis ◽  
Rong Zhang ◽  
Benjamin D. Levine ◽  
Vasilis Z. Marmarelis
Keyword(s):  
Cerebral Blood Flow Velocity ◽  
Lower Body Negative Pressure ◽  
Nonlinear Modeling ◽  
Cerebral Hemodynamics ◽  
Cerebral Hypoperfusion ◽  
Orthostatic Stress ◽  
Cerebrovascular Reserve ◽  
Vasomotor Reactivity ◽  
Arterial Blood ◽  
Cerebral Vasomotor Reactivity

The effects of orthostatic stress, induced by lower body negative pressure (LBNP), on cerebral hemodynamics were examined in a nonlinear context. Spontaneous fluctuations of beat-to-beat mean arterial blood pressure (MABP) in the finger, mean cerebral blood flow velocity (MCBFV) in the middle cerebral artery, as well as breath-by-breath end-tidal CO2 concentration (PetCO2) were measured continuously in 10 healthy subjects under resting conditions and during graded LBNP to presyncope. A two-input nonlinear Laguerre-Volterra network model was employed to study the dynamic effects of MABP and PetCO2 changes, as well as their nonlinear interactions, on MCBFV variations in the very low (VLF; below 0.04 Hz), low (LF; 0.04–0.15 Hz), and high frequency (HF; 0.15–0.30 Hz) ranges. Dynamic cerebral autoregulation was described by the model terms corresponding to MABP, whereas cerebral vasomotor reactivity was described by the model PetCO2 terms. The nonlinear model terms reduced the output prediction normalized mean square error substantially (by 15–20%) and had a prominent effect in the VLF range, both under resting conditions and during LBNP. Whereas MABP fluctuations dominated in the HF range and played a significant role in the VLF and LF ranges, changes in PetCO2 accounted for a considerable fraction of the VLF and LF MCBFV variations, especially at high LBNP levels. The magnitude of the linear and nonlinear MABP-MCBFV Volterra kernels increased substantially above −30 mmHg LBNP in the VLF range, implying impaired dynamic autoregulation. In contrast, the magnitude of the PetCO2-MCBFV kernels reduced during LBNP at all frequencies, suggesting attenuated cerebral vasomotor reactivity under dynamic conditions. We speculate that these changes may reflect a progressively reduced cerebrovascular reserve to compensate for the increasingly unstable systemic circulation during orthostatic stress that could ultimately lead to cerebral hypoperfusion and syncope.

Cerebral hypoperfusion modifies the respiratory chemoreflex during orthostatic stress

2013 ◽  
Vol 125 (1) ◽  
pp. 37-44 ◽  
Author(s):  
Shigehiko Ogoh ◽  
Hidehiro Nakahara ◽  
Kazunobu Okazaki ◽  
Damian M. Bailey ◽  
Tadayoshi Miyamoto
Keyword(s):  
Lower Body Negative Pressure ◽  
Minute Ventilation ◽  
Regression Line ◽  
Cerebral Hypoperfusion ◽  
Orthostatic Stress ◽  
Respiratory Chemoreflex ◽  
Underlying Mechanisms ◽  
End Tidal ◽  
Induced Changes ◽  
The Relationship

The respiratory chemoreflex is known to be modified during orthostatic stress although the underlying mechanisms remain to be established. To determine the potential role of cerebral hypoperfusion, we examined the relationship between changes in MCA Vmean (middle cerebral artery mean blood velocity) and V̇E (pulmonary minute ventilation) from supine control to LBNP (lower body negative pressure; −45mmHg) at different CO2 levels (0, 3.5 and 5% CO2). The regression line of the linear relationship between V̇E and PETCO2 (end-tidal CO2) shifted leftwards during orthostatic stress without any change in sensitivity (1.36±0.27 l/min per mmHg at supine to 1.06±0.21 l/min per mmHg during LBNP; P=0.087). In contrast, the relationship between MCA Vmean and PETCO2 was not shifted by LBNP-induced changes in PETCO2. However, changes in V̇E from rest to LBNP were more related to changes in MCA Vmean than changes in PETCO2. These findings demonstrate for the first time that postural reductions in CBF (cerebral blood flow) modified the central respiratory chemoreflex by moving its operating point. An orthostatically induced decrease in CBF probably attenuated the ‘washout’ of CO2 from the brain causing hyperpnoea following activation of the central chemoreflex.

scholarly journals Aging augments renal vasoconstrictor response to orthostatic stress in humans

2015 ◽  
Vol 309 (12) ◽  
pp. R1474-R1478 ◽  
Author(s):  
Christine M. Clark ◽  
Kevin D. Monahan ◽  
Rachel C. Drew
Keyword(s):  
Blood Flow ◽  
Healthy Aging ◽  
Lower Body Negative Pressure ◽  
Systemic Circulation ◽  
Young Group ◽  
Orthostatic Stress ◽  
Renal Vasoconstriction ◽  
Arterial Blood ◽  
Vasoconstrictor Response ◽  
Renal Vascular

The ability of the human body to maintain arterial blood pressure (BP) during orthostatic stress is determined by several reflex neural mechanisms. Renal vasoconstriction progressively increases during graded elevations in lower body negative pressure (LBNP). This sympathetically mediated response redistributes blood flow to the systemic circulation to maintain BP. However, how healthy aging affects the renal vasoconstrictor response to LBNP is unknown. Therefore, 10 young (25 ± 1 yr; means ± SE) and 10 older (66 ± 2 yr) subjects underwent graded LBNP (−15 and −30 mmHg) while beat-to-beat renal blood flow velocity (RBFV; Doppler ultrasound), arterial BP (Finometer), and heart rate (HR; electrocardiogram) were recorded. Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as mean BP/RBFV. All baseline cardiovascular variables were similar between groups, except diastolic BP was higher in older subjects ( P < 0.05). Increases in RVR during LBNP were greater in the older group compared with the young group (older: −15 mmHg Δ10 ± 3%, −30 mmHg Δ20 ± 5%; young: −15 mmHg Δ2 ± 2%, −30 mmHg Δ6 ± 2%; P < 0.05). RBFV tended to decrease more ( P = 0.10) and mean BP tended to decrease less ( P = 0.09) during LBNP in the older group compared with the young group. Systolic and diastolic BP, pulse pressure, and HR responses to LBNP were similar between groups. These findings suggest that aging augments the renal vasoconstrictor response to orthostatic stress in humans.

scholarly journals Lack of correlation between cerebral vasomotor reactivity and dynamic cerebral autoregulation during stepwise increases in inspired CO2 concentration

2016 ◽  
Vol 120 (12) ◽  
pp. 1434-1441 ◽  
Author(s):  
Sung-Moon Jeong ◽  
Seon-Ok Kim ◽  
Darren S. DeLorey ◽  
Tony G. Babb ◽  
Benjamin D. Levine ◽  
...  
Keyword(s):  
Transfer Function ◽  
Cerebral Autoregulation ◽  
Function Analysis ◽  
Low Frequency ◽  
Frequency Range ◽  
Vasomotor Reactivity ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Cerebral Vasomotor Reactivity ◽  
Dynamic Cerebral Autoregulation

Cerebral vasomotor reactivity (CVMR) and dynamic cerebral autoregulation (CA) are measured extensively in clinical and research studies. However, the relationship between these measurements of cerebrovascular function is not well understood. In this study, we measured changes in cerebral blood flow velocity (CBFV) and arterial blood pressure (BP) in response to stepwise increases in inspired CO2 concentrations of 3 and 6% to assess CVMR and dynamic CA in 13 healthy young adults [2 women, 32 ± 9 (SD) yr]. CVMR was assessed as percentage changes in CBFV (CVMRCBFV) or cerebrovascular conductance index (CVCi, CVMRCVCi) in response to hypercapnia. Dynamic CA was estimated by performing transfer function analysis between spontaneous oscillations in BP and CBFV. Steady-state CBFV and CVCi both increased exponentially during hypercapnia; CVMRCBFV and CVMRCVCi were greater at 6% (3.85 ± 0.90 and 2.45 ± 0.79%/mmHg) than at 3% CO2 (2.09 ± 1.47 and 0.21 ± 1.56%/mmHg, P = 0.009 and 0.005, respectively). Furthermore, CVMRCBFV was greater than CVMRCVCi during either 3 or 6% CO2 ( P = 0.017 and P < 0.001, respectively). Transfer function gain and coherence increased in the very low frequency range (0.02-0.07 Hz), and phase decreased in the low-frequency range (0.07–0.20 Hz) when breathing 6%, but not 3% CO2. There were no correlations between the measurements of CVMR and dynamic CA. These findings demonstrated influences of inspired CO2 concentrations on assessment of CVMR and dynamic CA. The lack of correlation between CVMR and dynamic CA suggests that cerebrovascular responses to changes in arterial CO2 and BP are mediated by distinct regulatory mechanisms.

Changes in cerebral oxygenation and blood flow during LBNP in spinal cord-injured individuals

2001 ◽  
Vol 91 (5) ◽  
pp. 2199-2204 ◽  
Author(s):  
Sibrand Houtman ◽  
Jorge M. Serrador ◽  
Willy N. J. M. Colier ◽  
Derek W. Strijbos ◽  
Kevin Shoemaker ◽  
...  
Keyword(s):  
Spinal Cord ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cerebral Oxygenation ◽  
Cerebral Blood Flow Velocity ◽  
Lower Body Negative Pressure ◽  
Systemic Circulation ◽  
Orthostatic Stress ◽  
Cerebrovascular Regulation ◽  
Spinal Cord Injured

Spinal cord-injured (SCI) individuals, having a sympathetic nervous system lesion, experience hypotension during sitting and standing. Surprisingly, they experience few syncopal events. This suggests adaptations in cerebrovascular regulation. Therefore, changes in systemic circulation, cerebral blood flow, and oxygenation in eight SCI individuals were compared with eight able-bodied (AB) individuals. Systemic circulation was manipulated by lower body negative pressure at several levels down to −60 mmHg. At each level, we measured steady-state blood pressure, changes in cerebral blood velocity with transcranial Doppler, and cerebral oxygenation using near-infrared spectroscopy. We found that mean arterial pressure decreased significantly in SCI but not in AB individuals, in accordance with the sympathetic impairment in the SCI group. Cerebral blood flow velocity decreased during orthostatic stress in both groups, but this decrease was significantly greater in SCI individuals. Cerebral oxygenation decreased in both groups, with a tendency to a greater decrease in SCI individuals. Thus present data do not support an advantageous mechanism during orthostatic stress in the cerebrovascular regulation of SCI individuals.

QUANTITATIVE NON-STATIONARY ASSESSMENT OF CEREBRAL HEMODYNAMICS BY EMPIRICAL MODE DECOMPOSITION OF CEREBRAL DOPPLER FLOW VELOCITY

2013 ◽  
Vol 05 (01) ◽  
pp. 1350002 ◽  
Author(s):  
CHIA-CHI CHANG ◽  
HUNG-YI HSU ◽  
TZU-CHIEN HSIAO
Keyword(s):  
Energy Density ◽  
Flow Velocity ◽  
Empirical Mode Decomposition ◽  
Cerebral Blood Flow Velocity ◽  
Ensemble Empirical Mode Decomposition ◽  
Cerebral Hemodynamics ◽  
Intrinsic Mode Functions ◽  
Dynamic Regulation ◽  
Arterial Blood ◽  
Mode Decomposition

Dynamic regulation of cerebral circulation involves complex interaction between cardiovascular, respiratory, and autonomic nervous systems. Evaluating cerebral hemodynamics by using traditional statistic- and linear-based methods would underestimate or miss important information. Complementary ensemble empirical mode decomposition (CEEMD) has great capability of adaptive feature extraction from non-linear and non-stationary data without distortion. This study applied CEEMD for assessment of cerebral hemodynamics in response to physiologic challenges including paced 6-cycle breathing, hyperventilation, 7% CO2 breathing and head-up tilting test in twelve healthy subjects. Intrinsic mode functions (IMFs) were extracted from arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) signals, and was quantified by logarithmic averaged period and logarithmic energy density. The IMFs were able to show characteristics of ABP and CBFV waveform morphology in beat-to-beat timescale and in long-term trend scale. The changes in averaged period and energy density derived from IMFs were helpful for qualitative and quantitative assessment of ABP and CBFV responses to physiologic challenges. CEEMD is a promising method for assessing non-stationary components of systemic and cerebral hemodynamics.

scholarly journals Chronic physical activity mitigates cerebral hypoperfusion during central hypovolemia in elderly humans

2010 ◽  
Vol 298 (3) ◽  
pp. H1029-H1037 ◽  
Author(s):  
Kevin Formes ◽  
Peizhen Zhang ◽  
Nancy Tierney ◽  
Frederick Schaller ◽  
Xiangrong Shi
Keyword(s):  
Lower Body Negative Pressure ◽  
Arterial Blood Flow ◽  
Cerebral Hypoperfusion ◽  
Active Lifestyle ◽  
Physically Active ◽  
Healthy Elderly ◽  
Arterial Blood ◽  
Intrinsic Mechanism ◽  
Transfer Function Gain ◽  
Elderly Humans

This study sought to test the hypothesis that orthostasis-induced cerebral hypoperfusion would be less severe in physically active elderly humans (ACT group) than in sedentary elderly humans (SED group). The peak O2 uptake of 10 SED (67.1 ± 1.4 yr) and 9 ACT (68.0 ± 1.1 yr) volunteers was determined by a graded cycling exercise test (22.1 ± 1.2 vs 35.8 ± 1.3 ml·min−1·kg−1, P < 0.01). Baseline mean arterial pressure (MAP; tonometry) and middle cerebral arterial blood flow velocity ( VMCA; transcranial Doppler) were similar between the groups (SED vs. ACT group: 91 ± 3 vs. 87 ± 3 mmHg and 54.9 ± 2.3 vs. 57.8 ± 3.2 cm/s, respectively), whereas heart rate was higher and stroke volume (bioimpedance) was smaller in the SED group than in the ACT group. Central hypovolemia during graded lower body negative pressure (LBNP) was larger ( P < 0.01) in the ACT group than in the SED group. However, the slope of VMCA/LBNP was smaller ( P < 0.05) in the ACT group (0.159 ± 0.016 cm/s/Torr) than in the SED group (0.211 ± 0.008 cm/s/Torr). During LBNP, the SED group had a greater augmentation of cerebral vasomotor tone ( P < 0.05) and hypocapnia ( P < 0.001) compared with the ACT group. Baseline MAP variability and VMCA variability were significantly smaller in the SED group than in the ACT group, i.e., 0.49 ± 0.07 vs. 1.04 ± 0.16 (mmHg)2 and 1.06 ± 0.19 vs. 4.24 ± 1.59 (cm/s)2, respectively. However, transfer function gain, coherence, and phase between MAP and VMCA signals (Welch spectral estimator) from 0.08–0.18 Hz were not different between SED (1.41 ± 0.18 cm·s−1·mmHg−1, 0.63 ± 0.06 units, and 38.03 ± 6.57°) and ACT (1.65 ± 0.44 cm·s−1·mmHg−1, 0.56 ± 0.05 units, and 48.55 ± 11.84°) groups. We conclude that a physically active lifestyle improves the intrinsic mechanism of cerebral autoregulation and helps mitigate cerebral hypoperfusion during central hypovolemia in healthy elderly adults.

scholarly journals Cerebral Vasomotor Reactivity during Hypo- and Hypercapnia in Sedentary Elderly and Masters Athletes

2013 ◽  
Vol 33 (8) ◽  
pp. 1190-1196 ◽  
Author(s):  
Yong-Sheng Zhu ◽  
Takashi Tarumi ◽  
Benjamin Y Tseng ◽  
Dean M Palmer ◽  
Benjamin D Levine ◽  
...  
Keyword(s):  
Exercise Training ◽  
Aerobic Exercise ◽  
Aerobic Exercise Training ◽  
Vasomotor Reactivity ◽  
Arterial Blood ◽  
Cerebrovascular Function ◽  
Age Related ◽  
Masters Athletes ◽  
Cerebral Vasomotor Reactivity ◽  
The Impact

Physical activity may influence cerebrovascular function. The objective of this study was to determine the impact of life-long aerobic exercise training on cerebral vasomotor reactivity (CVMR) to changes in end-tidal CO2 (EtCO2) in older adults. Eleven sedentary young (SY, 27 ± 5 years), 10 sedentary elderly (SE, 72 ± 4 years), and 11 Masters athletes (MA, 72 ± 6 years) underwent the measurements of cerebral blood flow velocity (CBFV), arterial blood pressure, and EtCO2 during hypocapnic hyperventilation and hypercapnic rebreathing. Baseline CBFV was lower in SE and MA than in SY while no difference was observed between SE and MA. During hypocapnia, CVMR was lower in SE and MA compared with SY (1.87 ± 0.42 and 1.47 ± 0.21 vs. 2.18 ± 0.28 CBFV%/mm Hg, P < 0.05) while being lowest in MA among all groups ( P < 0.05). In response to hypercapnia, SE and MA exhibited greater CVMR than SY (6.00 ± 0.94 and 6.67 ± 1.09 vs. 3.70 ± 1.08 CBFV1%/mm Hg, P < 0.05) while no difference was observed between SE and MA. A negative linear correlation between hypo- and hypercapnic CVMR ( R2 = 0.37, P < 0.001) was observed across all groups. Advanced age was associated with lower resting CBFV and lower hypocapnic but greater hypercapnic CVMR. However, life-long aerobic exercise training appears to have minimal effects on these age-related differences in cerebral hemodynamics.

scholarly journals The cerebrovascular response to lower-body negative pressure vs. head-up tilt

2017 ◽  
Vol 122 (4) ◽  
pp. 877-883 ◽  
Author(s):  
Anne-Sophie G. T. Bronzwaer ◽  
Jasper Verbree ◽  
Wim J. Stok ◽  
Mat J. A. P. Daemen ◽  
Mark A. van Buchem ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Negative Pressure ◽  
Cerebral Blood Flow Velocity ◽  
Lower Body Negative Pressure ◽  
Orthostatic Stress ◽  
Lower Body ◽  
Head Up Tilt ◽  
End Tidal ◽  
Pronounced Reduction

Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (−50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBF v) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT ( P ≤ 0.020). Mean CBF v initially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller ( P ≤ 0.029) during LBNP. The reduction in end-tidal Pco2 partial pressure (PetCO2) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT ( P = 0.008). We consider the larger decrease in CBF v during HUT vs. LBNP attributable to the pronounced reduction in PetCO2 and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality. NEW & NOTEWORTHY Lower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco2 together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stress.

scholarly journals Transcranial doppler methods in the assessment of cerebral vasomotor reactivity

2020 ◽  
Vol 73 (1-2) ◽  
pp. 21-28
Author(s):  
Aleksandra Lucic-Prokin ◽  
Petar Slankamenac ◽  
Pavle Kovacevic
Keyword(s):  
Transcranial Doppler ◽  
Cerebral Hemodynamics ◽  
Physiological Data ◽  
Invasive Approach ◽  
Arterial Perfusion ◽  
Advantages And Disadvantages ◽  
Non Invasive ◽  
Vasomotor Reactivity ◽  
Cerebral Vasomotor Reactivity ◽  
Ischemic Events

Introduction. Transcranial Doppler is the only non-invasive neuroimaging modality in the diagnosis and monitoring of various neurovascular diseases. Apart from assessing cerebral hemodynamics of blood flow in the basal brain arteries, transcranial Doppler provides physiological data and anatomical images. Quantification analysis of vasomotor reactivity. Various transcranial Doppler methods evaluate cerebral vasomotor reactivity, providing important information on the properties of arterioles under induced hemodynamic conditions. Exogenous and endogenous vasoactive stimuli of different potency (apnea, acetazolamide, carbon dioxide, L-arginine) are most commonly used, making transcranial Doppler a prognostic indicator of future ischemic events. This article reviews principles of various transcranial Doppler methods in the evaluation of vasomotor reactivity, emphasizing their advantages and disadvantages. Transcranial Doppler in the field of reduced vasomotor reactivity. Evaluation of vasomotor reactivity has a role in the prediction of future ischemic events, evaluation of revascularization effect after carotid endarterectomy, but also in the increasingly significant choice of the right time to perform it. In recent years, transcranial Doppler methods have found application in other areas of dysfunctional cerebral hemodynamics: dementia, hypertension, migraines, and sepsis. Conclusion. Due to an excellent temporal resolution, non-invasive approach, good cost-benefit ratio, bedside monitoring, relative simplicity in terms of interpretation and performance, and portability, transcranial Doppler in vasomotor reactivity may be the ideal tool in the evaluation of cerebral hemodynamics, arterial perfusion integrity and collateral capacity.

scholarly journals Two-Tiered Response of Cardiorespiratory-Cerebrovascular Network to Orthostatic Challenge

2021 ◽  
Vol 12 ◽  
Author(s):  
Peter Mukli ◽  
Zoltan Nagy ◽  
Frigyes Samuel Racz ◽  
Istvan Portoro ◽  
Andras Hartmann ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Arterial Blood Pressure ◽  
Pearson Correlation ◽  
Transcranial Doppler Sonography ◽  
Cerebral Hemodynamics ◽  
Orthostatic Stress ◽  
Arterial Blood ◽  
Postural Changes ◽  
The Impact ◽  
Homeostatic Mechanisms

Dynamic interdependencies within and between physiological systems and subsystems are key for homeostatic mechanisms to establish an optimal state of the organism. These interactions mediate regulatory responses elicited by various perturbations, such as the high-pressure baroreflex and cerebral autoregulation, alleviating the impact of orthostatic stress on cerebral hemodynamics and oxygenation. The aim of this study was to evaluate the responsiveness of the cardiorespiratory-cerebrovascular networks by capturing linear and nonlinear interdependencies to postural changes. Ten young healthy adults participated in our study. Non-invasive measurements of arterial blood pressure (from that cardiac cycle durations were derived), breath-to-breath interval, cerebral blood flow velocity (BFV, recorded by transcranial Doppler sonography), and cerebral hemodynamics (HbT, total hemoglobin content monitored by near-infrared spectroscopy) were performed for 30-min in resting state, followed by a 1-min stand-up and a 1-min sit-down period. During preprocessing, noise was filtered and the contribution of arterial blood pressure was regressed from BFV and HbT signals. Cardiorespiratory-cerebrovascular networks were reconstructed by computing pair-wise Pearson-correlation or mutual information between the resampled signals to capture their linear and/or nonlinear interdependencies, respectively. The interdependencies between cardiac, respiratory, and cerebrovascular dynamics showed a marked weakening after standing up persisting throughout the sit-down period, which could mainly be attributed to strikingly attenuated nonlinear coupling. To summarize, we found that postural changes induced topological changes in the cardiorespiratory-cerebrovascular network. The dissolution of nonlinear networks suggests that the complexity of key homeostatic mechanisms maintaining cerebral hemodynamics and oxygenation is indeed sensitive to physiological perturbations such as orthostatic stress.

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