Transcranial Doppler cerebrovascular reactivity: Thresholds for clinical significance in cerebrovascular disease.

BACKGROUND AND PURPOSE: Thresholds for abnormal transcranial Doppler cerebrovascular reactivity (CVR) studies are poorly understood, especially for patients with cerebrovascular disease. Using a real-world cohort with cerebral arterial stenosis, we sought to describe a clinically significant threshold for carbon dioxide reactivity (CO2R) and vasomotor range (VMR). METHODS: CVR studies were performed during conditions of breathing room air normally, breathing 8% carbon dioxide air mixture, and hyperventilation. The mean and standard deviation (SD) of CO2R and VMR were calculated for the unaffected side in patients with unilateral stenosis; a deviation of 2 SDs below the mean was chosen as the threshold for abnormal. Receiver operating characteristic (ROC) curves for both sides for patients with unilateral and bilateral stenosis were evaluated for sensitivity (Sn) and specificity (Sp). RESULTS: A total of 133 consecutive CVR studies were performed on 62 patients with stenosis with mean±SD age 55±16 years. Comorbidities included hypertension (60%), diabetes (15%), stroke (40%), and smoking (35%). In patients with unilateral stenosis, mean±SD CO2R for the unaffected side was 1.86±0.53%, defining abnormal CO2R as <0.80%. Mean±SD CO2R for the affected side was 1.27±0.90%. The CO2R threshold predicted abnormal acetazolamide single-photon emission computed tomography (SPECT) (Sn = .73, Sp = .79), CT/MRI perfusion abnormality (Sn = .42, Sp = .77), infarction on MRI (Sn = .45, Sp = .76), and pressure-dependent exam (Sn = .50, Sp = .76). For the unaffected side, mean±SD VMR was 39.5±15.8%, defining abnormal VMR as <7.9%. For the affected side, mean±SD VMR was 26.5±17.8%. The VMR threshold predicted abnormal acetazolamide SPECT (Sn = .46, Sp = .94), infarction on MRI (Sn = .27, Sp = .94), and pressure-dependent exam (Sn = .31, Sp = .90). CONCLUSIONS: In patients with multiple vascular risk factors, a reasonable threshold for clinically significant abnormal CO2R is <0.80% and VMR is <7.9%. Noninvasive CVR may aid in diagnosing and risk stratifying patients with stenosis.

Use of Transcranial Doppler as a Biomarker of CAR T Cell-Related Neurotoxicity.

Background and Objectives: To examine the relationship between transcranial Doppler (TCD) mean flow velocity (MFV) and the severity and temporal onset of neurotoxicity after chimeric antigen receptor (CAR) T-cell therapy in patients with relapsed lymphoma. Methods: We identified a cohort of 165 patients with relapsed or refractory B-cell lymphoma who received CAR T-cell therapy. TCDs were performed at baseline, treatment day 5, and throughout hospitalization based on development of neurologic symptoms. We assessed the percent change in velocity from baseline in each of the 6 major supratentorial arteries and the relationship of these values to development and timing of neurotoxicity. Results: Our cohort was 30% female with an average age of 60 years. Of patients with TCDs performed, 63% developed neurotoxicity, and 32% had severe neurotoxicity. The median time of neurotoxicity onset was day 7. Higher maximum percent change in MFV across all vessels was significantly associated with likelihood of developing neurotoxicity (p = 0.0002) and associated with severe neurotoxicity (p = 0.0421). We found that with increased percent change in MFV, the strength of correlation between day of TCD velocity change and day of neurotoxicity onset increased. There was no single vessel in which increase in MFV was associated with neurotoxicity. Discussion: Our study demonstrates an association between increase in TCD MFV and the development of neurotoxicity, as well as timing of neurotoxicity onset. We believe that TCD ultrasound may be used as a bedside functional biomarker in CAR T-cell patients and may guide immunologic interventions to manage toxicity in this complex patient group.

Transcranial-Doppler-Measured Vasospasm Severity is Associated with Delayed Cerebral Infarction After Subarachnoid Hemorrhage.

BACKGROUND: Angiographic vasospasm after aneurysmal subarachnoid hemorrhage (aSAH) is associated with delayed cerebral ischemia (DCI)-related cerebral infarction (radiological DCI) and worsened neurological outcome. Transcranial Doppler (TCD) measurements of cerebral blood flow velocity are commonly used after aSAH to screen for vasospasm; however, their association with cerebral infarction is not well characterized. We sought to determine whether time-varying TCD-measured vasospasm severity is associated with cerebral infarction and investigate the performance characteristics of different time/severity cutoffs for predicting cerebral infarction. METHODS: We conducted a retrospective single-center cohort study of consecutive adult patients with aSAH with at least one TCD study between 2011 and 2020. The primary outcome was radiological DCI, defined as a cerebral infarction developing at least 2 days after any surgical or endovascular intervention without an alternative cause. Cox proportional hazards models were used to examine associations between time-varying vasospasm severity and radiological DCI. Optimal TCD-based time/severity thresholds for predicting radiological DCI were then determined. RESULTS: Of 262 patients with aSAH who underwent TCD studies, 27 (10%) developed radiological DCI. Patients with radiological DCI had higher modified Fisher scale scores and trended toward earlier onset of vasospasm. Adjusted for age, Hunt and Hess scores, and modified Fisher scale scores, the worst-vessel vasospasm severity was associated with radiological DCI (adjusted hazard ratio 1.7 [95% confidence interval 1.1-2.4]). Vasospasm severity within a specific vessel was associated with risk of delayed infarction in the territory supplied by that vessel. Optimal discrimination of patients with radiological DCI was achieved with thresholds of mild vasospasm on days 4-5 or moderate vasospasm on days 6-9, with negative predictive values greater than 90% and positive predictive values near 20%. CONCLUSIONS: TCD-measured vasospasm severity is associated with radiological DCI after aSAH. An early, mild TCD-based vasospasm severity threshold had a high negative predictive value, supporting its role as a screening tool to identify at-risk patients.

Integrated STEM and poultry science curriculum to increase agricultural literacy.

The shortage of graduates pursuing careers in the poultry industry is linked to a low awareness and lack of interest. Increasing agricultural literacy could promote engagement in future poultry science opportunities. We developed an integrated STEM curriculum within a poultry science context to assess the program's impact on students' agricultural literacy development. The Elementary Education Gain Grow (E.G.G.) program consists of 5 online modules, an interactive notebook, a simulation game, and a team project. In fall 2019, 480 Indiana 4th and 5th grade students enrolled in the pilot program. A 14-point poultry content-based questionnaire was administered online to students prior to program engagement, between online and team project activities, and at program completion. Student content scores (n = 111; 23.13% response rate) increased from 7.99 (SD = 1.85) preprogram to 9.76 (SD = 2.44) post online modules (P < 0.05; Cohen's d = 0.82) and remained constant throughout the remainder of the program. Student notebook responses (n = 172; 35.83% response rate) provided qualitative data of their self-reported agricultural literacy gains and revealed patterns of increased agricultural literacy relating to the program's learning objectives. These results support the program's ability to increase student agricultural literacy. Teacher feedback (n = 9; 69.2% response rate) suggests that teachers agreed with the program's effectiveness, with qualitative responses highlighting individual experiences. Our pilot program findings support the use of an integrated STEM and poultry science elementary curriculum to increase student agricultural literacy as well as demonstrate the effectiveness of the program as an educational resource.

Validation of diffuse correlation spectroscopy measures of critical closing pressure against transcranial Doppler ultrasound in stroke patients.

SIGNIFICANCE: Intracranial pressure (ICP), variability in perfusion, and resulting ischemia are leading causes of secondary brain injury in patients treated in the neurointensive care unit. Continuous, accurate monitoring of cerebral blood flow (CBF) and ICP guide intervention and ultimately reduce morbidity and mortality. Currently, only invasive tools are used to monitor patients at high risk for intracranial hypertension. AIM: Diffuse correlation spectroscopy (DCS), a noninvasive near-infrared optical technique, is emerging as a possible method for continuous monitoring of CBF and critical closing pressure (CrCP or zero-flow pressure), a parameter directly related to ICP. APPROACH: We optimized DCS hardware and algorithms for the quantification of CrCP. Toward its clinical translation, we validated the DCS estimates of cerebral blood flow index (CBFi) and CrCP in ischemic stroke patients with respect to simultaneously acquired transcranial Doppler ultrasound (TCD) cerebral blood flow velocity (CBFV) and CrCP. RESULTS: We found CrCP derived from DCS and TCD were highly linearly correlated (ipsilateral R2 = 0.77, p = 9 × 10 - 7; contralateral R2 = 0.83, p = 7 × 10 - 8). We found weaker correlations between CBFi and CBFV (ipsilateral R2 = 0.25, p = 0.03; contralateral R2 = 0.48, p = 1 × 10 - 3) probably due to the different vasculature measured. CONCLUSION: Our results suggest DCS is a valid alternative to TCD for continuous monitoring of CrCP.

Dynamic Cerebral Autoregulation Post Endovascular Thrombectomy in Acute Ischemic Stroke.

The development of the endovascular thrombectomy (EVT) technique has revolutionized acute stroke management for patients with large vessel occlusions (LVOs). The impact of successful recanalization using an EVT on autoregulatory profiles is unknown. A more complete understanding of cerebral autoregulation in the context of EVT may assist with post-procedure hemodynamic optimization to prevent complications. We examined cerebral autoregulation in 107 patients with an LVO in the anterior circulation (proximal middle cerebral artery (M1/2) and internal cerebral artery (ICA) terminus) who had been treated using an EVT. Dynamic cerebral autoregulation was assessed at multiple time points, ranging from less than 24 hours to 5 days following last seen well (LSW) time, using transcranial Doppler ultrasound recordings and transfer function analysis. Complete (Thrombolysis in Cerebral Infarction (TICI) 3) recanalization was associated with a more favorable autoregulation profile compared with TICI 2b or poorer recanalization (p < 0.05), which is an effect that was present after accounting for differences in the infarct volumes. Less effective autoregulation in the first 24 h following the LSW time was associated with increased rates of parenchymal hematoma types 1 and 2 hemorrhagic transformations (PH1-PH2). These data suggest that patients with incomplete recanalization and poor autoregulation (especially within the first 24 h post-LSW time) may warrant closer blood pressure monitoring and control in the first few days post ictus.

Clinical Predictors of Neurotoxicity After Chimeric Antigen Receptor T-Cell Therapy.

Importance: Chimeric antigen receptor (CAR) T-cell therapy for relapsed or refractory hematologic malignant neoplasm causes severe neurologic adverse events ranging from encephalopathy and aphasia to cerebral edema and death. The cause of neurotoxicity is incompletely understood, and its unpredictability is a reason for prolonged hospitalization after CAR T-cell infusion. Objective: To identify clinical and laboratory parameters predictive of neurotoxicity and to develop a prognostic score associated with its risk. Design, Setting, and Participants: This single-center diagnostic/prognostic accuracy study was conducted at Brigham and Women's Hospital/Dana Farber Cancer Institute from April 2015 to February 2020. A consecutive sample of all patients undergoing CAR T-cell therapy with axicabtagene ciloleucel for relapsed or refractory lymphoma were assessed for inclusion (n = 213). Patients who had previously received CAR T cells or who were treated for mantle cell lymphoma were excluded (n = 9). Patients were followed up for a minimum of 30 days from the date of CAR T-cell infusion. Main Outcomes and Measures: The primary outcomes were measures of performance (accuracy, sensitivity, specificity, area under the curve) of a diagnostic tool to predict the occurrence of CAR-associated neurotoxicity, as graded by the Common Terminology Criteria for Adverse Events criteria. Results: Two hundred four patients (127 men [62.2%]; mean [SD] age, 60.0 [12.1] years) were included in the analysis, of which 126 (61.8%) comprised a derivation cohort and 78 (38.2%), an internal validation cohort. Seventy-three patients (57.9%) in the derivation cohort and 45 patients (57.7%) in the validation cohort experienced neurotoxicity. Clinical and laboratory values obtained early in admission were used to develop a multivariable score that can predict the subsequent development of neurotoxicity; when tested on an internal validation cohort, this score had an area under the curve of 74%, an accuracy of 77%, a sensitivity of 82%, and a specificity of 70% (positive:negative likelihood ratio, 2.71:0.26). Conclusions and Relevance: The score developed in this study may help predict which patients are likely to experience CAR T-cell-associated neurotoxicity. The score can be used for triaging and resource allocation and may allow a large proportion of patients to be discharged from the hospital early.

Microembolic Signals Detected by Transcranial Doppler Predict Future Stroke and Poor Outcomes.

BACKGROUND AND PURPOSE: Although transcranial Doppler detects microembolic signals (MES) in numerous settings, the practical significance of such findings remains unclear. METHODS: Clinical information from ischemic stroke or transient ischemic attack patients (n = 248) who underwent embolic monitoring from January 2015 to December 2018 was obtained. RESULTS: MES were found in 15% of studies and ischemic recurrence was seen in 11% of patients (over 7 ± 6 days). Patients with MES had more lacunes than those without MES (1 ± 3 vs. 1 ± 2, P = .016), were more likely to have ischemic recurrence (37% vs. 6%, P < .001), undergo a future revascularization procedure (26% vs. 10%, P = .005), have a longer length of stay (9 vs. 4 days, P = .043), and have worse functional disability at discharge (modified Rankin Scale 3-6, 66% vs. 34%, P < .001). After controlling for several relevant cofactors, patients with MES were more likely to have ischemic recurrence (HR 4.90, 95% CI 2.16-11.09, P < .001), worse functional disability (OR 3.31, 95% CI 1.22-8.99, P = .019), and longer length of stays (ß = .202, P < .001). CONCLUSIONS: MES may help to risk stratify patients as their presence is associated with ischemic recurrence and worse outcomes.

Neurological toxicities associated with chimeric antigen receptor T-cell therapy.

Chimeric antigen receptor T cell therapy has become an important tool in the treatment of relapsed and refractory malignancy; however, it is associated with significant neurological toxicity. We characterized the neurological toxicity associated with chimeric antigen receptor T-cell therapy in a consecutive series of 100 patients up to 2 months post transfusion, 28 of whom were obtained from chart review and the others by prospective observation. The underlying neoplasms were lymphoma (74%), myeloma (14%), leukaemia (10%), and sarcoma (2%). The median age of the cohort was 64.5 years old and 39% of patients were female. The most commonly occurring neurological symptoms were encephalopathy (57%), headache (42%), tremor (38%), aphasia (35%) and focal weakness (11%). Focal neurological deficits are frequently observed after chimeric antigen receptor T-cell therapy and are associated with regional EEG abnormalities, FDG-PET hypometabolism, and elevated velocities on transcranial Doppler ultrasound. In contrast, structural imaging was typically normal. As this form of treatment is more widely adopted, recognition of the frequently encountered symptoms will be of increasing importance for the neurologists and oncologists caring for this growing patient population.

Pathophysiologic differences in cerebral autoregulation after subarachnoid hemorrhage.

OBJECTIVE: To understand the physiologic basis of impaired cerebral autoregulation in subarachnoid hemorrhage (SAH) and its relationship to neurologic outcomes. METHODS: The cohort included 121 patients with nontraumatic SAH admitted to a neurointensive critical care unit from March 2010 to May 2015. Vasospasm was ascertained from digital subtraction angiography and delayed cerebral ischemia (DCI) was defined as new cerebral infarction on high-resolution CT. Cerebral blood flow and beat-by-beat pressure were recorded daily on days 2-4 after admission. Autoregulatory capacity was quantified from pressure flow relation via projection pursuit regression. The main outcome was early alterations in autoregulatory mechanisms as they relate to vasospasm and DCI. RESULTS: Forty-three patients developed only vasospasm, 9 only DCI, and 14 both. Autoregulatory capacity correctly predicted DCI in 86% of training cohort patients, generalizing to 80% of the patients who were not included in the original model. Patients who developed DCI had a distinct autoregulatory profile compared to patients who did not develop secondary complications or those who developed only vasospasm. The rate of decrease in flow was significantly steeper in response to transient reductions in pressure. The rate of increase in flow was markedly lower, suggesting a diminished ability to increase flow despite transient increases in pressure. CONCLUSIONS: The extent and nature of impairment in autoregulation accurately predicts neurologic complications on an individual patient level, and suggests potentially differential impairments in underlying physiologic mechanisms. A better understanding of these can lead to targeted interventions to mitigate neurologic morbidity.

Deferoxamine, Cerebrovascular Hemodynamics, and Vascular Aging: Potential Role for Hypoxia-Inducible Transcription Factor-1-Regulated Pathways.

BACKGROUND AND PURPOSE: Iron chelation therapy is emerging as a novel neuroprotective strategy. The mechanisms of neuroprotection are diverse and include both neuronal and vascular pathways. We sought to examine the effect of iron chelation on cerebrovascular function in healthy aging and to explore whether hypoxia-inducible transcription factor-1 activation may be temporally correlated with vascular changes. METHODS: We assessed cerebrovascular function (autoregulation, vasoreactivity, and neurovascular coupling) and serum concentrations of vascular endothelial growth factor and erythropoietin, as representative measures of hypoxia-inducible transcription factor-1 activation, during 6 hours of deferoxamine infusion in 24 young and 24 older healthy volunteers in a randomized, blinded, placebo-controlled cross-over study design. Cerebrovascular function was assessed using the transcranial Doppler ultrasound. Vascular endothelial growth factor and erythropoietin serum protein assays were conducted using the Meso Scale Discovery platform. RESULTS: Deferoxamine elicited a strong age- and time-dependent increase in the plasma concentrations of erythropoietin and vascular endothelial growth factor, which persisted ≤3 hours post infusion (age effect P=0.04; treatment×time P<0.01). Deferoxamine infusion also resulted in a significant time- and age-dependent improvement in cerebral vasoreactivity (treatment×time P<0.01; age P<0.01) and cerebral autoregulation (gain: age×time×treatment P=0.04). CONCLUSIONS: Deferoxamine infusion improved cerebrovascular function, particularly in older individuals. The temporal association between improved cerebrovascular function and increased serum vascular endothelial growth factor and erythropoietin concentrations is supportive of shared hypoxia-inducible transcription factor-1-regulated pathways. Therefore, pharmacological activation of hypoxia-inducible transcription factor-1 to enhance cerebrovascular function may be a promising neuroprotective strategy in acute and chronic ischemic syndromes, especially in elderly patients. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT013655104.

Dynamic cerebral autoregulation after intracerebral hemorrhage: A case-control study.

BACKGROUND: Dynamic cerebral autoregulation after intracerebral hemorrhage (ICH) remains poorly understood. We performed a case-control study to compare dynamic autoregulation between ICH patients and healthy controls. METHODS: Twenty-one patients (66 ± 15 years) with early (< 72 hours) lobar or basal ganglia ICH were prospectively studied and compared to twenty-three age-matched controls (65 ± 9 years). Continuous measures of mean flow velocity (MFV) in the middle cerebral artery and mean arterial blood pressure (MAP) were obtained over 5 min. Cerebrovascular resistance index (CVRi) was calculated as the ratio of MAP to MFV. Dynamic cerebral autoregulation was assessed using transfer function analysis of spontaneous MAP and MFV oscillations in the low (0.03-0.15 Hz) and high (0.15-0.5 Hz) frequency ranges. RESULTS: The ICH group demonstrated higher CVRi compared to controls (ipsilateral: 1.91 ± 1.01 mmHg·s·cm-1, p = 0.04; contralateral: 2.01 ± 1.24 mmHg·s·cm-1, p = 0.04; vs. control: 1.42 ± 0.45 mmHg·s·cm-1). The ICH group had higher gains than controls in the low (ipsilateral: 1.33 ± 0.58%/mmHg, p = 0.0005; contralateral: 1.47 ± 0.98%/mmHg, p = 0.004; vs. control: 0.82 ± 0.30%/mmHg) and high (ipsilateral: 2.11 ± 1.31%/mmHg, p < 0.0001; contralateral: 2.14 ± 1.49%/mmHg, p < 0.0001; vs. control: 0.66 ± 0.26%/mmHg) frequency ranges. The ICH group also had higher coherence in the contralateral hemisphere than the control (ICH contralateral: 0.53 ± 0.38, p = 0.02; vs. control: 0.38 ± 0.15) in the high frequency range. CONCLUSIONS: Patients with ICH had higher gains in a wide range of frequency ranges compared to controls. These findings suggest that dynamic cerebral autoregulation may be less effective in the early days after ICH. Further study is needed to determine the relationship between hematoma size and severity of autoregulation impairment.

Autoregulation in the posterior circulation is altered by the metabolic state of the visual cortex.

BACKGROUND AND PURPOSE: Previous studies suggest that dynamic autoregulation in the posterior cerebral artery (PCA) is less efficient compared to the middle cerebral artery (MCA). We examined the role of cerebral vasodilation caused by metabolic activation (ie, visual stimulus) on autoregulatory characteristics in the 2 vascular territories. METHODS: Blood flow velocity in the PCA and MCA and mean arterial pressure were measured continuously in 45 healthy volunteers (62+/-3 years) while seated with eyes open. Additional 20 subjects (60+/-5 years) were examined with eyes closed and open. Autoregulation was assessed using transfer function gains in both the PCA and MCA territories in the low (0.03-0.07 Hz), high (0.07-0.15 Hz), and cardiac (approximately 1 Hz) frequency ranges. RESULTS: With eyes open, gains were significantly higher in the PCA compared to the MCA in the low (PCA: 1.41+/-0.09 vs MCA: 1.18+/-0.07; P=0.003) and high (PCA: 2.06+/-0.12 vs MCA: 1.61+/-0.08; P=0.0001) frequencies. Opening eyes increased blood flow velocity and reduced cerebrovascular resistance index in the PCA but not in MCA. This vasodilation in the PCA was associated with increased gain in the low (autoregulatory) frequency, whereas MCA gain did not change (PCA: 0.89+/-0.14 vs 1.31+/-0.17, MCA: 1.24+/-0.16 vs 1.16+/-0.11; P=0.02). CONCLUSIONS: Dilation of the PCA territory during visual cortex activation resulted in increased PCA transfer function gain without changing MCA gain. Thus, impaired autoregulation in the PCA reported in previous literature is likely the result of metabolic vasodilation and not an inherent difference in the autoregulatory characteristics of the posterior circulation.