The use of transcranial Doppler (TCD) ultrasound for the assessment of cerebral blood flow velocity (CBFV) provides an indication of cerebral blood flow assuming the diameter of the insonated vessel remains constant. Studies using TCD have traditionally described cerebrovascular hemodynamics with respect to CBFV and cerebrovascular resistance (CVRi); however, a more complete assessment of the cerebral circulation can be gleaned from the analysis of within beat characteristic of the TCD velocity waveform for the determination of cerebrovascular tone. Therefore, the general purpose of the presented studies was to assess CBFV responses and within beat characteristic for the description of cerebrovascular hemodynamics after long duration spaceflight, with sustained orthostasis, in response to changes in the partial pressure of end tidal carbon dioxide (PETCO2), and with NG stimulation. After long duration spaceflight, cerebrovascular autoregulation was found to be impaired along with a reduction in cerebrovascular CO2 reactivity (Study 1). Additionally, critical closing pressure (CrCP) was found to be increased suggesting potential remodelling of the cerebrovasculature contributing to an increase in cerebrovascular tone (Study 2). With sustained orthostasis, CBFV was found to progressively decrease and to be related to reductions in PETCO2 and increases in CrCP suggesting the contribution of changes in cerebrovascular tone leading to the development of syncope (Study 4). The CBFV reduction with the progression towards syncope was also associated with changes in waveform morphology such that the dicrotic notch point was less than the end diastolic value (Study 3). Mathematical modelling (RCKL) was used to further assess changes in cerebrovascular hemodynamics for physiological interpretation of changes in CBFV waveform morphology and found that the amplitude of the dicrotic notch and the calculation of the augmentation index were both significantly related to vascular compliance before and after stimulation with NG (Study 5). The use of quantitative assessments of common carotid artery (CCA) blood flow as an indicator of cerebral blood flow suggested the dilation of the middle cerebral artery (MCA) with NG (Study 5 and 6) and changes in MCA diameter with acute alterations in PETCO2 (Study 6). CCA and MCA velocity wave morphology were assessed showing that with changes in PETCO2, changes in CBFV velocity wave were not reflected in the CCA trace (Study 7). In addition, further assessment of the CBFV velocity trace and the calculation of CrCP and the augmentation index suggested that with changes in PETCO2 cerebrovascular compliance and cerebrovascular tension, both thought to be components of cerebrovascular tone, change independently (Study 7). Combined, the results of the presented studies suggest that changes in cerebrovascular hemodynamics can be determined from alterations in the CBFV velocity waveform morphology. However, further work is required to determine how these variations relate to specific components of cerebrovascular tone, including alterations in cerebrovascular compliance and vascular tension, and how these variables change with acute and chronic alterations in cerebrovascular hemodynamics.

We investigated an emerging brain-computer interface (BCI) modality, namely, transcranial Doppler ultrasonography (TCD), which measures cerebral blood flow velocity. We hypothesized that a bilateral TCD-driven online BCI would be able to dichotomously classify a user’s intentions with at least 70% accuracy. To test this hypothesis, we had three objectives: (1) to develop a signal classifier that yielded high (>80%) offline accuracies; (2) to develop an online TCD-BCI system with an onscreen keyboard; and, (3) to determine the achievable online accuracy with able-bodied participants. With a weighted, forward feature selection and a Naïve Bayes classifier, sensitivity and specificity of 81.44 ± 8.35% and 82.30 ± 7.39%, respectively, were achieved in the online differentiation of two mental tasks. The average information transfer rate and throughput of the system were 0.87 bits/min and 0.35 ± 0.18 characters/min, respectively. These promising online results encourage future testing of TCD-BCI systems with the target population.

We investigated an emerging brain-computer interface (BCI) modality, namely, transcranial Doppler ultrasonography (TCD), which measures cerebral blood flow velocity. We hypothesized that a bilateral TCD-driven online BCI would be able to dichotomously classify a user’s intentions with at least 70% accuracy. To test this hypothesis, we had three objectives: (1) to develop a signal classifier that yielded high (>80%) offline accuracies; (2) to develop an online TCD-BCI system with an onscreen keyboard; and, (3) to determine the achievable online accuracy with able-bodied participants. With a weighted, forward feature selection and a Naïve Bayes classifier, sensitivity and specificity of 81.44 ± 8.35% and 82.30 ± 7.39%, respectively, were achieved in the online differentiation of two mental tasks. The average information transfer rate and throughput of the system were 0.87 bits/min and 0.35 ± 0.18 characters/min, respectively. These promising online results encourage future testing of TCD-BCI systems with the target population.

The use of transcranial Doppler (TCD) ultrasound for the assessment of cerebral blood flow velocity (CBFV) provides an indication of cerebral blood flow assuming the diameter of the insonated vessel remains constant. Studies using TCD have traditionally described cerebrovascular hemodynamics with respect to CBFV and cerebrovascular resistance (CVRi); however, a more complete assessment of the cerebral circulation can be gleaned from the analysis of within beat characteristic of the TCD velocity waveform for the determination of cerebrovascular tone. Therefore, the general purpose of the presented studies was to assess CBFV responses and within beat characteristic for the description of cerebrovascular hemodynamics after long duration spaceflight, with sustained orthostasis, in response to changes in the partial pressure of end tidal carbon dioxide (PETCO2), and with NG stimulation. After long duration spaceflight, cerebrovascular autoregulation was found to be impaired along with a reduction in cerebrovascular CO2 reactivity (Study 1). Additionally, critical closing pressure (CrCP) was found to be increased suggesting potential remodelling of the cerebrovasculature contributing to an increase in cerebrovascular tone (Study 2). With sustained orthostasis, CBFV was found to progressively decrease and to be related to reductions in PETCO2 and increases in CrCP suggesting the contribution of changes in cerebrovascular tone leading to the development of syncope (Study 4). The CBFV reduction with the progression towards syncope was also associated with changes in waveform morphology such that the dicrotic notch point was less than the end diastolic value (Study 3). Mathematical modelling (RCKL) was used to further assess changes in cerebrovascular hemodynamics for physiological interpretation of changes in CBFV waveform morphology and found that the amplitude of the dicrotic notch and the calculation of the augmentation index were both significantly related to vascular compliance before and after stimulation with NG (Study 5). The use of quantitative assessments of common carotid artery (CCA) blood flow as an indicator of cerebral blood flow suggested the dilation of the middle cerebral artery (MCA) with NG (Study 5 and 6) and changes in MCA diameter with acute alterations in PETCO2 (Study 6). CCA and MCA velocity wave morphology were assessed showing that with changes in PETCO2, changes in CBFV velocity wave were not reflected in the CCA trace (Study 7). In addition, further assessment of the CBFV velocity trace and the calculation of CrCP and the augmentation index suggested that with changes in PETCO2 cerebrovascular compliance and cerebrovascular tension, both thought to be components of cerebrovascular tone, change independently (Study 7). Combined, the results of the presented studies suggest that changes in cerebrovascular hemodynamics can be determined from alterations in the CBFV velocity waveform morphology. However, further work is required to determine how these variations relate to specific components of cerebrovascular tone, including alterations in cerebrovascular compliance and vascular tension, and how these variables change with acute and chronic alterations in cerebrovascular hemodynamics.

Background: Stroke is a leading cause of significant physical, cognitive, and psychiatric morbidity. One risk factor for stroke is paradoxical embolization through a patent foramen ovale (PFO). In cardiac clinical practice, power M-mode Transcranial Doppler (TCD) evaluation is the gold standard for diagnosis of PFO, or right-to-left cardiac shunt (RLS). Brain micro-embolization due to diagnostic bubble contrast echocardiography may cause neurological symptoms in patients with PFO. However, the neurocognitive effects of TCD have not been studied. Objective: The purpose of this study was to evaluate cognitive outcomes in patients who undergo routine diagnostic bubble contrast TCD. The aims of the study were (1) to determine if cognitive function declines pre- to post-TCD evaluation and, (2) to assess the relationship between cognitive function and severity of the RLS measured using the Spencer Grading System. Methods: One hundred and four participants referred to Sorensen Cardiovascular Group for diagnosis of RLS were evaluated for changes in cognitive functioning at three time points. A dual baseline (pre-test and baseline test) was administered to mitigate practice effects between the first and second administrations. All pre and post-TCD comparisons were analyzed using the baseline test and post-TCD test, controlling for the effects of practice, if present. Results: Practice effects were observed for the working memory task, with significant improvement in working memory scores occurring between the first (pre-test) and second (baseline) administrations. The main effect for shunt group (no shunt vs. moderate-to-severe shunt) and the shunt group by time interactions were not significant for processing speed, attention, or working memory, adjusting for practice effects, age, and education. Migraine did not predict group status for mood or shunt variables. Conclusion: Cardiac patients with both small and large RLS did not experience a decline in processing speed, attention, or working memory ability following TCD, suggesting that TCD-induced microemboli do not result in immediate cognitive deficits in these domains. These findings support the use of TCD for routine evaluation of PFO, even in patients with severe RLS, although findings are limited to young (30s), medically healthy, predominately Caucasian individuals assessed immediately following TCD. Results do not exclude the possibility of cognitive impairment at follow-up, on other cognitive tests, or in other cognitive domains.