A comparison of transcranial Doppler and cerebral blood flow studies to assess cerebral vasoreactivity

Long-term cognitive and neurovascular changes after carotid endarterectomy

BACKGROUND

Carotid endarterectomy (CEA) has been associated with both cognitive decline and improvement, but the underlying neurovascular mechanisms are unclear. The aim of this study was to investigate the relationship between neurovascular indices and cognitive changes after CEA.

METHODS

We studied 55 patients with severe (≥70%) symptomatic or asymptomatic carotid stenosis before and six months after CEA. A wide array of neuropsychological tests was arranged in eight cognitive domains and cognitive functions specific to hemisphere ipsilateral to operation. Differences in cognitive performance between patients and 38 matching healthy controls were studied with linear mixed models. Neurovascular functioning and microembolic signals were assessed with transcranial Doppler ultrasound of the middle cerebral artery. Associations between neurovascular indices and cognitive change were assessed with linear regression analyses.

RESULTS

On group level, the CEA patients improved more than controls in working memory, whereas no cognitive deterioration was detected. Also on individual level, improvement was most frequently observed in working memory. Worse preoperative cerebrovascular reactivity was related with improvement in cognitive functions of the ipsilateral hemisphere. Low preoperative pulsatility index was associated with improvement in executive functioning and ipsilateral cognitive functions. Poorer preoperative blood flow velocity associated with improvement in complex attention. Microembolic signals were rare.

CONCLUSION

The present findings suggest that CEA may have beneficial long-term effects on cognition. These effects may specifically involve patients with impaired preoperative circulatory adaptive mechanisms.

Intracranial Atherosclerotic Disease: Current Concepts in Medical and Surgical Management

PURPOSE OF THE REVIEW

This article reviews the current concepts in intracranial atherosclerotic disease (ICAD) as a common etiology of ischemic stroke; pathophysiologic mechanisms of ischemic stroke; diagnostic evaluation; and therapeutic modalities, including maximal medical therapy (MMT), percutaneous transluminal angioplasty and stenting (PTAS), and bypass surgery.

RECENT FINDINGS

Data from recent studies demonstrate that proper patient selection and timing of procedure and standardized PTAS techniques by experienced operators resulted in acceptably low periprocedural adverse events for patients who failed MMT.

SUMMARY

ICAD is a common cause of ischemic stroke. Complex pathology and high rates of recurrent and disabling ischemic strokes despite currently available treatments make ICAD the most challenging to treat of all ischemic stroke etiologies. Randomized trials previously showed that MMT, which involves the use of combinations of antiplatelet medications, targeted control of hypertension and serum low-density lipoprotein cholesterol, and adequate management of body weight through lifestyle modification, was superior to PTAS in decreasing rates of recurrent ischemic strokes from symptomatic ICAD. MMT performed better than expected, while periprocedural complications were significantly higher than expected in PTAS. Meanwhile, high rates of recurrent ischemic stroke despite MMT remain a great challenge. New clinical evidence continues to emerge on a safer application of PTAS, which is currently offered to a subset of patients who present with recurrent ischemic strokes despite MMT.

Ubiquinol Supplementation Improves Gender-Dependent Cerebral Vasoreactivity and Ameliorates Chronic Inflammation and Endothelial Dysfunction in Patients with Mild Cognitive Impairment

Ubiquinol can protect endothelial cells from multiple mechanisms that cause endothelial damage and vascular dysfunction, thus contributing to dementia. A total of 69 participants diagnosed with mild cognitive impairment (MCI) received either 200 mg/day ubiquinol (Ub) or placebo for 1 year. Cognitive assessment of patients was performed at baseline and after 1 year of follow-up. Patients' cerebral vasoreactivity was examined using transcranial Doppler sonography, and levels of Ub and lipopolysaccharide (LPS) in plasma samples were quantified. Cell viability and necrotic cell death were determined using the microvascular endothelial cell line bEnd3. Coenzyme Q10 (CoQ) levels increased in patients supplemented for 1 year with ubiquinol versus baseline and the placebo group, although higher levels were observed in male patients. The higher cCoQ concentration in male patients improved cerebral vasoreactivity CRV and reduced inflammation, although the effect of Ub supplementation on neurological improvement was negligible in this study. Furthermore, plasma from Ub-supplemented patients improved the viability of endothelial cells, although only in T2DM and hypertensive patients. This suggests that ubiquinol supplementation could be recommended to reach a concentration of 5 μg/mL in plasma in MCI patients as a complement to conventional treatment.

Impaired Cerebral Hemodynamics and Frailty in Patients with Cardiovascular Disease

Background

Recent studies suggest that impaired cerebrovascular reactivity (CVR), a marker of cerebral microvascular damage, is associated with a higher risk of stroke, cognitive decline, and mortality. We tested whether abnormal cerebrovascular status is associated with late-life frailty among men with pre-existing cardiovascular disease.

Methods

A subset of 327 men (mean age at baseline 56.7 ± 6.5 years) who previously participated in the Bezafibrate Infarction Prevention (BIP) trial (1990-1997) and then in the BIP Neurocognitive Study underwent a neurovascular evaluation 14.6 ± 1.9 years after baseline (T1) and were evaluated for frailty 19.9 ± 1.0 years after baseline (T2). CVR was measured at T1 using the breath-holding index and carotid large-vessel disease using ultrasound. Frailty status was measured at T2 according to the physical phenotype developed by Fried. Patients were categorized into CVR tertiles with cutoff points at ≤0.57, 0.58-0.94, and ≥0.95 and also as normal or impaired (<0.69) CVR. We assessed the change in the odds of being in the advanced rank of frailty status (normal, prefrail, and frail) using ordered logistic regression.

Results

After adjustment, the estimated OR (95% confidence intervals) for increasing frailty in the lower tertile was 1.94 (1.09-3.46) and in the middle tertile 1.24 (0.70-2.19), compared with the higher CVR tertile. The estimated OR for increasing frailty for patients with impaired vs. normal CVR was 1.76 (1.11-2.80).

Conclusions

These findings provide support that cerebral microvascular dysfunction among patients with pre-existing cardiovascular disease is related to prefrailty and frailty and suggest an added value of assessing the cerebral vascular functional status for identifying patients at-risk of developing frailty.

Evaluation of cerebrovascular reactivity in chronic hepatitis C patients using transcranial color Doppler

Hepatitis C viral (HCV) infection is associated with systemic inflammation and metabolic complications that might predispose patients to atherosclerosis, including cerebrovascular atherosclerosis. The aim of this study was to assess cerebrovascular reactivity in patients with chronic hepatitis C. Seventeen patients with chronic hepatitis C infection, as well as 11 healthy blood donors in the control group, were assessed for cerebrovascular reactivity according to the well-established breath-holding test that uses the transcranial color Doppler for measurement of blood flow velocity. Results obtained during the breath-holding revealed significantly lower average peak systolic (AvPS start, P = 0.018), end-diastolic (AvED start, P = 0.031) and mean velocity values at the very beginning of the breath-holding procedure (AvmeanV start, P = 0.02), as well as a lower mean peak systolic velocity at the end of the breath-holding test (AvPS max, P = 0.02) in the hepatitis C group. Vascular reactivity values, calculated as the breath-holding index, were also significantly lower (P = 0.045) in the hepatitis C group. In conclusion, the results of this study suggest an association between chronic HCV infection and altered cerebrovascular reactivity which may ultimately have an unfavorable effect on cerebrovascular hemodynamics and lead to increased risk of cerebrovascular diseases.

Technology Development for Simultaneous Wearable Monitoring of Cerebral Hemodynamics and Blood Pressure

For many cerebrovascular diseases both blood pressure (BP) and hemodynamic changes are important clinical variables. In this paper, we describe the development of a novel approach to noninvasively and simultaneously monitor cerebral hemodynamics, BP, and other important parameters at high temporal resolution (250 Hz sampling rate). In this approach, cerebral hemodynamics are acquired using near infrared spectroscopy based sensors and algorithms, whereas continuous BP is acquired by superficial temporal artery tonometry with pulse transit time based drift correction. The sensors, monitoring system, and data analysis algorithms used in the prototype for this approach are reported in detail in this paper. Preliminary performance tests demonstrated that we were able to simultaneously and noninvasively record and reveal cerebral hemodynamics and BP during people's daily activity. As examples, we report dynamic cerebral hemodynamic and BP fluctuations during postural changes and micturition. These preliminary results demonstrate the feasibility of our approach, and its unique power in catching hemodynamics and BP fluctuations during transient symptoms (such as syncope) and revealing the dynamic features of related events.

Impact of fluid challenge increase in cardiac output on the relationship between systemic and cerebral hemodynamics in severe sepsis compared to brain injury and controls

Background

Cognitive dysfunction and delirium after ICU are frequent and may partially result from brain ischemia episodes. We hypothesized that systemic inflammation (severe sepsis or septic shock) modifies the control of brain circulation and the relation between systemic and cerebral hemodynamic after a positive response to fluid challenge (FC).

Methods

Three groups of patients were studied if they increased stroke volume (SV) > 10% after 250 or 500 ml of crystalloids: control group: patients free of comorbidity anesthetized for orthopedic surgery; sepsis group: patients with severe sepsis or septic shock (classic definition); brain injury (BI) group: trauma brain jury or hemorrhagic stroke with no detectable systemic inflammation. The measurements before and after FC were mean arterial blood pressure (MAP) (radial catheter); SV and cardiac output (CO; transesophageal Doppler); bilateral middle cerebral artery (MCAv) velocity with peak systolic (PSV) and end diastolic (EDV) values (transcranial Doppler); end-tidal CO₂. The role of MAP increase was investigated by an arbitrarily threshold increase of 5%, called responder in CO and MAP (RR). The remaining patients were call responders in CO and non-responders in MAP (RnR). Nonparametric tests were used for statistical analysis.

Results

Among the 86 screened patients, 66 have completed the protocol: 17 in control group; 38 in sepsis group; and 11 in BI group. All patients increased SV > 10% after FC. Only the sepsis group increased MAP [+ 12 (2–25%), p < 0.05] with a significant increase in PSV and EDV [(17 (3–30)% and 17 (12–42)%, respectively (p < 0.05)], which did not change in the two other groups. The septic RR or RnR had similar variations in MCAv after FC. The baseline MAP < or > baseline median MAP had similar MCAv.

Conclusions

After a FC-induced increase in SV, MCAv (PSV and EDV) increased only in septic group, mostly independently from MAP increase and from baseline MAP level. Cerebral perfusion becomes passively dependent on systemic blood flow, suggesting a modification of the control of cerebrovascular tone in sepsis-induced systemic inflammation. This information has been considered in the clinical management of septic patients.

Electronic supplementary material

The online version of this article (10.1186/s13613-018-0419-1) contains supplementary material, which is available to authorized users.

Transcranial Doppler Monitoring of Intracranial Pressure Plateau Waves

Background

Transcranial Doppler (TCD) has been used to estimate ICP noninvasively (nICP); however, its accuracy varies depending on different types of intracranial hypertension. Given the high specificity of TCD to detect cerebrovascular events, this study aimed to compare four TCD-based nICP methods during plateau waves of ICP.

Methods

A total of 36 plateau waves were identified in 27 patients (traumatic brain injury) with TCD, ICP, and ABP simultaneous recordings. The nICP methods were based on: (1) interaction between flow velocity (FV) and ABP using a “black-box” mathematical model (nICP_BB); (2) diastolic FV (nICP_FV_d); (3) critical closing pressure (nICP_CrCP), and (4) pulsatility index (nICP_PI). Analyses focused on relative changes in time domain between ICP and noninvasive estimators during plateau waves and the magnitude of changes (∆ between baseline and plateau) in real ICP and its estimators. A ROC analysis for an ICP threshold of 35 mmHg was performed.

Results

In time domain, nICP_PI, nICP_BB, and nICP_CrCP presented similar correlations: 0.80 ± 0.24, 0.78 ± 0.15, and 0.78 ± 0.30, respectively. nICP_FV_d presented a weaker correlation (R = 0.62 ± 0.46). Correlations between ∆ICP and ∆nICP were better represented by nICP_CrCP and BB, R = 0.48, 0.44 (p < 0.05), respectively. nICP_FV_dand PI presented nonsignificant ∆ correlations. ROC analysis showed moderate to good areas under the curve for all methods: nICP_BB, 0.82; nICP_FV_d, 0.77; nICP_CrCP, 0.79; and nICP_PI, 0.81.

Conclusions

Changes of ICP in time domain during plateau waves were replicated by nICP methods with strong correlations. In addition, the methods presented high performance for detection of intracranial hypertension. However, absolute accuracy for noninvasive ICP assessment using TCD is still low and requires further improvement.

Analysis of Fluctuation in Cerebral Venous Oxygenation Using MR Imaging: Quantitative Evaluation of Vasomotor Function of Arterioles

Purpose:

Cerebral arteriolar vasomotor function plays an important role in brain health. Since respiratory changes in the partial arterial pressure of CO₂ (PaCO₂) cause arterioles to vasodilate or vasoconstrict, resting-state arteriolar vasomotion results in the fluctuation of venous blood oxygenation, which can be monitored by observing magnetic resonance (MR) signals. Focusing on the superior sagittal sinus as the largest cerebral vein, we developed a method to elucidate the respiratory fluctuation of cerebral venous oxygenation that may reflect the vasomotor function.

Methods:

Single slices of varying thickness (7–15 mm) taken perpendicular to the superior sagittal sinus of five volunteers were imaged by spin-echo echo-planar imaging using a 1.5-T MR system. The time series of the signal intensity at the superior sagittal sinus was Fourier-transformed, and the spectral fluctuation intensity (SFI) at respiratory frequency was obtained. The amplitude of the respiratory fluctuation in the cerebral venous oxygenation was calculated from the gradient of the relation between the SFI and the average signal intensity, which increased proportionally with an increase in slice thickness. The amplitude of the fluctuation in cerebral venous oxygenation at low (<0.1 Hz) and cardiac pulsation frequencies was also calculated for comparison with the respiratory fluctuation.

Results:

The amplitude of respiratory fluctuation in the cerebral venous oxygenation was quantified as 1.2%, demonstrating the validity of our method via the highest significant correlation (r = 0.82) in the plot of SFI and average signal intensities; the correlations at low and cardiac pulsation frequencies were 0.60 and 0.63, respectively.

Conclusion:

We have successfully demonstrated cerebral venous oxygenation fluctuation at respiratory frequencies in the resting state. This fluctuation was non-invasively evaluated as 1.2%, representing the control value for the arteriolar vasomotor function of a healthy human.

Influence of Human Jaw Movement on Cerebral Blood Flow

Temporal changes in cerebral blood flow induced by jaw movement have yet to be investigated. To assess the influence of pattern and intensity of muscle contraction during jaw movement on task-induced change in cerebral blood flow, we performed bilateral transcranial Doppler ultrasound examination during clenching, gum chewing, and tooth tapping in healthy volunteers. A random-effects model analysis revealed a significant increase in middle cerebral artery blood flow velocity during clenching (high muscle activity) and gum chewing (moderate muscle activity), compared with the preceding rest period; however, such an increase was not detected during tooth tapping (low muscle activity). Cerebral blood flow was greater on the working side during the intensive isometric contraction of the masseter muscle in clenching. These results suggest that task-induced change in cerebral blood flow during jaw movement is influenced by the change in peripheral circulation evoked by muscle contraction.

Neurosonology and noninvasive imaging of the carotid arteries

In this chapter, we review imaging of the extracranial carotid arteries and the indications for noninvasive carotid artery evaluation, measuring the degree of arterial stenosis and plaque morphology. We also analyze the types of noninvasive imaging, including carotid duplex ultrasound, transcranial Doppler, magnetic resonance angiography, and computer tomography angiography. We look at each of these modalities, briefly discussing techniques, benefits, limitations, and sources of error. Furthermore, we discuss the apparent accuracy and the need for multimodality imaging. Finally, an imaging algorithm for the evaluation of the extracranial carotid arteries is proposed, which is in routine use at our hospital.

Prospective Study on Noninvasive Assessment of Intracranial Pressure in Traumatic Brain-Injured Patients: Comparison of Four Methods

Elevation of intracranial pressure (ICP) may occur in many diseases, and therefore the ability to measure it noninvasively would be useful. Flow velocity signals from transcranial Doppler (TCD) have been used to estimate ICP; however, the relative accuracy of these methods is unclear. This study aimed to compare four previously described TCD-based methods with directly measured ICP in a prospective cohort of traumatic brain-injured patients. Noninvasive ICP (nICP) was obtained using the following methods: 1) a mathematical "black-box" model based on interaction between TCD and arterial blood pressure (nICP_BB); 2) based on diastolic flow velocity (nICP_FVd); 3) based on critical closing pressure (nICP_CrCP); and 4) based on TCD-derived pulsatility index (nICP_PI). In time domain, for recordings including spontaneous changes in ICP greater than 7 mm Hg, nICP_PI showed the best correlation with measured ICP (R = 0.61). Considering every TCD recording as an independent event, nICP_BB generally showed to be the best estimator of measured ICP (R = 0.39; p < 0.05; 95% confidence interval [CI] = 9.94 mm Hg; area under the curve [AUC] = 0.66; p < 0.05). For nICP_FVd, although it presented similar correlation coefficient to nICP_BB and marginally better AUC (0.70; p < 0.05), it demonstrated a greater 95% CI for prediction of ICP (14.62 mm Hg). nICP_CrCP presented a moderate correlation coefficient (R = 0.35; p < 0.05) and similar 95% CI to nICP_BB (9.19 mm Hg), but failed to distinguish between normal and raised ICP (AUC = 0.64; p > 0.05). nICP_PI was not related to measured ICP using any of the above statistical indicators. We also introduced a new estimator (nICP_Av) based on the average of three methods (nICP_BB, nICP_FVd, and nICP_CrCP), which overall presented improved statistical indicators (R = 0.47; p < 0.05; 95% CI = 9.17 mm Hg; AUC = 0.73; p < 0.05). nICP_PI appeared to reflect changes in ICP in time most accurately. nICP_BB was the best estimator for ICP "as a number." nICP_Av demonstrated to improve the accuracy of measured ICP estimation.

Cerebral blood flow change during volatile induction in large-dose sevoflurane versus intravenous propofol induction: transcranial Doppler study

Background

The impact of volatile induction using large-dose sevoflurane (VI-S) on cerebral blood flow has not been well investigated. The present study compared the changes in cerebral blood flow of middle cerebral artery using transcranial Doppler (TCD) during VI-S and conventional induction using propofol.

Methods

Patients undergoing elective lumbar discectomy were randomly allocated to receive either sevoflurane (8%, Group VI-S, n = 11) or target-controlled infusion of propofol (effect site concentration, 3.0 µg/ml; Group P, n = 11) for induction of anesthesia. The following data were recorded before and at 1, 2, and 3 min after commencement of anesthetic induction (T0, T1, T2, and T3, respectively): mean velocity of the middle cerebral artery (V_MCA) by TCD, mean blood pressure (MBP), heart rate, bispectral index score (BIS) and end-tidal CO₂ (ETCO₂). Changes in V_MCA and MBP from their values at T0 (ΔV_MCA and ΔMBP) at T1, T2, and T3 were also determined.

Results

BISs at T1, T2 and T3 were significantly less than that at T0 in both groups (P < 0.05). ΔVMCA in Group VI-S at T2 and T3 (18.1% and 12.4%, respectively) were significantly greater than those in Group P (-7.6% and -19.8%, P = 0.006 and P < 0.001, respectively), whereas ETCO₂ and ΔMBP showed no significant intergroup difference.

Conclusions

VI-S using large-dose sevoflurane increases cerebral blood flow resulting in luxury cerebral flow-metabolism mismatch, while conventional propofol induction maintains cerebral flow-metabolism coupling. This mismatch in VI-S may have to be considered in clinical application of VI-S.

Cerebral vasomotor reactivity: steady-state versus transient changes in carbon dioxide tension

New Findings

What is the central question of this study?

The relationship between changes in cerebral blood flow and arterial carbon dioxide tension is used to assess cerebrovascular function. Hypercapnia is generally evoked by two methods, i.e. steady-state and transient increases in carbon dioxide tension. In some cases, the hypercapnia is immediately preceded by a period of hypocapnia. It is unknown whether the cerebrovascular response differs between these methods and whether a period of hypocapnia blunts the subsequent response to hypercapnia.

What is the main finding and its importance?

The cerebrovascular response is similar between steady-state and transient hypercapnia. However, hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.

Cerebral vasomotor reactivity (CVMR) to changes in arterial carbon dioxide tension () is assessed during steady-state or transient changes in . This study tested the following two hypotheses: (i) that CVMR during steady-state changes differs from that during transient changes in ; and (ii) that CVMR during rebreathing-induced hypercapnia would be blunted when preceded by a period of hyperventilation. For each hypothesis, end-tidal carbon dioxide tension () middle cerebral artery blood velocity (CBFV), cerebrovascular conductance index (CVCI; CBFV/mean arterial pressure) and CVMR (slope of the linear regression between changes in CBFV and CVCI versus) were assessed in eight individuals. To address the first hypothesis, measurements were made during the following two conditions (randomized): (i) steady-state increases in of 5 and 10 Torr above baseline; and (ii) rebreathing-induced transient breath-by-breath increases in . The linear regression for CBFV versus (P = 0.65) and CVCI versus (P = 0.44) was similar between methods; however, individual variability in CBFV or CVCI responses existed among subjects. To address the second hypothesis, the same measurements were made during the following two conditions (randomized): (i) immediately following a brief period of hypocapnia induced by hyperventilation for 1 min followed by rebreathing; and (ii) during rebreathing only. The slope of the linear regression for CBFV versus (P < 0.01) and CVCI versus (P < 0.01) was reduced during hyperventilation plus rebreathing relative to rebreathing only. These results indicate that cerebral vasomotor reactivity to changes in is similar regardless of the employed methodology to induce changes in and that hyperventilation-induced hypocapnia attenuates the cerebral vasodilatory responses during a subsequent period of rebreathing-induced hypercapnia.

Cerebral vasoreactivity: impact of heat stress and lower body negative pressure

OBJECTIVE

Cerebrovascular reactivity represents the capacity of the cerebral circulation to raise blood flow in the face of increased demand, and may be reduced in some clinical and physiological conditions. We tested the hypothesis that the hypercapnia-induced increase in cerebral perfusion is attenuated during heat stress (HS) compared to normothermia (NT), and this response is further reduced during the combined challenges of HS and lower body negative pressure (LBNP).

METHODS

Ten healthy individuals (9 men) undertook rebreathing-induced hypercapnia during NT, HS, and HS + 20 mmHg LBNP (HSLBNP), while cerebral perfusion was indexed from middle cerebral artery blood velocity (MCA V mean). Cerebrovascular responses were calculated from the slope of the change in MCA V mean and cerebral vascular conductance (CVCi) relative to the increase in end tidal carbon dioxide ([Formula: see text]) during rebreathing.

RESULTS

MCA V mean was similar in HS (55 ± 19 cm s(-1)) and HSLBNP (52 ± 16 cm s(-1)), and both values were reduced relative to NT (66 ± 20 cm s(-1)), yet the rise in MCA V mean per Torr increase in [Formula: see text] during rebreathing was similar in each condition (NT: 2.5 ± 0.6 cm s(-1) Torr(-1); HS: 2.4 ± 0.8 cm s(-1) Torr(-1); HSLBNP: 2.1 ± 1.1 cm s(-1) Torr(-1)). Likewise, the rate of increase in CVCi was not different between conditions (NT: 2.1 ± 0.65 cm s(-1 )mmHg(-1)100 Torr(-1); HS: 2.4 ± 0.8 cm s(-1) mmHg(-1) 100 Torr(-1); HSLBNP: 2.0 ± 1.0 cm s(-1) mmHg(-1) 100 Torr(-1)).

INTERPRETATIONS

These data indicate that cerebrovascular reactivity is not compromised during whole-body heat stress alone or when combined with mild orthostatic stress relative to normothermic conditions.

Dynamic cerebral autoregulation is acutely impaired during maximal apnoea in trained divers

Aims

To examine whether dynamic cerebral autoregulation is acutely impaired during maximal voluntary apnoea in trained divers.

Methods

Mean arterial pressure (MAP), cerebral blood flow-velocity (CBFV) and end-tidal partial pressures of O₂ and CO₂ (PETO₂ and PETCO₂) were measured in eleven trained, male apnoea divers (28±2 yr; 182±2 cm, 76±7 kg) during maximal “dry” breath holding. Dynamic cerebral autoregulation was assessed by determining the strength of phase synchronisation between MAP and CBFV during maximal apnoea.

Results

The strength of phase synchronisation between MAP and CBFV increased from rest until the end of maximal voluntary apnoea (P<0.05), suggesting that dynamic cerebral autoregulation had weakened by the apnoea breakpoint. The magnitude of impairment in dynamic cerebral autoregulation was strongly, and positively related to the rise in PETCO₂ observed during maximal breath holding (R² = 0.67, P<0.05). Interestingly, the impairment in dynamic cerebral autoregulation was not related to the fall in PETO₂ induced by apnoea (R² = 0.01, P = 0.75).

Conclusions

This study is the first to report that dynamic cerebral autoregulation is acutely impaired in trained divers performing maximal voluntary apnoea. Furthermore, our data suggest that the impaired autoregulatory response is related to the change in PETCO₂, but not PETO₂, during maximal apnoea in trained divers.

Neurosonological Examination: A Non-Invasive Approach for the Detection of Cerebrovascular Impairment in AD

There has been a growing interest in vascular impairment associated with Alzheimer’s disease (AD). This interest was stimulated by the findings of higher incidence of vascular risk factors in AD. Signs of vascular impairment were investigated notably in the field of imaging methods. Our aim was to explore ultrasonographic studies of extra- and intracranial vessels in patients with AD and mild cognitive impairment (MCI) and define implications for diagnosis, treatment, and prevention of the disease. The most frequently studied parameters with extracranial ultrasound are intima-media thickness in common carotid artery, carotid atherosclerosis, and total cerebral blood flow. The transcranial ultrasound concentrates mostly on flow velocities, pulsatility indices, cerebrovascular reserve capacity, and cerebral microembolization. Studies suggest that there is morphological and functional impairment of cerebral circulation in AD compared to healthy subjects. Ultrasound as a non-invasive method could be potentially useful in identifying individuals in a higher risk of progression of cognitive decline.

Aneurysmal subarachnoid hemorrhage models: do they need a fix?

The discovery of tissue plasminogen activator to treat acute stroke is a success story of research on preventing brain injury following transient cerebral ischemia (TGI). That this discovery depended upon development of embolic animal model reiterates that proper stroke modeling is the key to develop new treatments. In contrast to TGI, despite extensive research, prevention or treatment of brain injury following aneurysmal subarachnoid hemorrhage (aSAH) has not been achieved. A lack of adequate aSAH disease model may have contributed to this failure. TGI is an important component of aSAH and shares mechanism of injury with it. We hypothesized that modifying aSAH model using experience acquired from TGI modeling may facilitate development of treatment for aSAH and its complications. This review focuses on similarities and dissimilarities between TGI and aSAH, discusses the existing TGI and aSAH animal models, and presents a modified aSAH model which effectively mimics the disease and has a potential of becoming a better resource for studying the brain injury mechanisms and developing a treatment.

The Effects of Involuntary Respiratory Contractions on Cerebral Blood Flow during Maximal Apnoea in Trained Divers

The effects of involuntary respiratory contractions on the cerebral blood flow response to maximal apnoea is presently unclear. We hypothesised that while respiratory contractions may augment left ventricular stroke volume, cardiac output and ultimately cerebral blood flow during the struggle phase, these contractions would simultaneously cause marked ‘respiratory’ variability in blood flow to the brain. Respiratory, cardiovascular and cerebrovascular parameters were measured in ten trained, male apnoea divers during maximal ‘dry’ breath holding. Intrathoracic pressure was estimated via oesophageal pressure. Left ventricular stroke volume, cardiac output and mean arterial pressure were monitored using finger photoplethysmography, and cerebral blood flow velocity was obtained using transcranial ultrasound. The increasingly negative inspiratory intrathoracic pressure swings of the struggle phase significantly influenced the rise in left ventricular stroke volume (R² = 0.63, P<0.05), thereby contributing to the increase in cerebral blood flow velocity throughout this phase of apnoea. However, these contractions also caused marked respiratory variability in left ventricular stroke volume, cardiac output, mean arterial pressure and cerebral blood flow velocity during the struggle phase (R² = 0.99, P<0.05). Interestingly, the magnitude of respiratory variability in cerebral blood flow velocity was inversely correlated with struggle phase duration (R² = 0.71, P<0.05). This study confirms the hypothesis that, on the one hand, involuntary respiratory contractions facilitate cerebral haemodynamics during the struggle phase while, on the other, these contractions produce marked respiratory variability in blood flow to the brain. In addition, our findings indicate that such variability in cerebral blood flow negatively impacts on struggle phase duration, and thus impairs breath holding performance.

Hyperperfusion syndrome after carotid endarterectomy and carotid stenting

BACKGROUND

Hyperperfusion syndrome (HS) is a relatively rare but possibly serious complication of carotid revascularization procedures. Impaired cerebral autoregulation and postrevascularization changes in cerebral blood flow are the main mechanisms involved in the development of HS. Most up-to-date studies addressing this issue are retrospective and tend to concentrate on carotid endarterectomy (CEA), neglecting carotid stenting (CAS). Our aim was to compare the frequency of clinical signs of HS and hyperperfusion detected by transcranial Doppler (TCD) in patients undergoing CAS or CEA due to carotid stenosis.

METHODS

In this prospective observational study, we evaluated 61 patients scheduled for routine CAS or CEA. Each patient was examined by a neurologist before and after the revascularization procedure to assess the clinical status. Severe headache, ocular or facial pain, confusion, visual disturbances, epileptic seizures or any focal deficits not caused by cerebral ischemia were considered clinical signs of HS. Peak systolic velocity (PSV), end-diastolic velocity, mean velocity (MV), and pulsatility index were measured by TCD once before and twice after the intervention (within 6 h after and 2-5 days after the procedure). Hyperperfusion was defined as a >100% increase in the middle cerebral artery (MCA) blood velocity, evaluated separately for PSV and MV after the procedure compared with the baseline value. Cerebrovascular reactivity (CVR) was evaluated with a TCD acetazolamide test before the intervention.

RESULTS

CAS (n = 33) and CEA (n = 28) patients were included in the study. There was no difference between the groups in the frequency of clinical signs of HS (21.2 vs. 21.4%) and ratio of TCD hyperperfusion (12.1 vs. 14.3%). In the CAS group, ipsilateral MCA velocity significantly increased directly after the intervention and 2-5 days later, while it increased in the CEA group only 2-5 days after the intervention. The sensitivity and specificity of hyperperfusion, defined by MV, for HS signs were 38.5 and 93.8%, respectively, whereas those defined by PSV were 30.8 and 89.6%, respectively. The sensitivity and specificity of impaired CVR (<25%) for HS signs were 63.6 and 73.5%, respectively.

CONCLUSIONS

There is no difference in the frequency of HS clinical signs and hyperperfusion detected by TCD between patients after CAE and CAS. Clinical signs suggested HS does not always correspond with TCD hyperperfusion. However, both the CVR test and TCD measurements of MCA velocity can help identify patients at high risk for HS.

Moderate correlation between breath-holding and CO(2) inhalation/hyperventilation methods for transcranial doppler evaluation of cerebral vasoreactivity

BACKGROUND

Both CO(2) inhalation followed by hyperventilation and breath-holding have been utilized to measure cerebral vasomotor reactivity (VMR) but their correlation has been poorly studied and understood.

METHODS

A retrospective study was conducted in 143 subjects (62.6 ± 15.8 years old, 64% men) with transcranial Doppler ultrasonography measurement of mean flow velocity (MFV) at baseline, after 30 seconds of breath-holding, and after CO(2) inhalation followed by hyperventilation, in the left and right middle cerebral artery. Breath-holding index (BHI) was calculated as the percentage of MFV increase from baseline per second of apnea. CO(2) inhalation/hyperventilation index (CO(2) /HV) was calculated as the percentage of MFV difference between CO(2) inhalation and hyperventilation.

RESULTS

There were 75 carotid arteries with >70% stenosis or occlusion, and 18 middle cerebral arteries with >50% stenosis or occlusion. The mean BHI was 0.93 ± 0.7 and 0.89 ± 0.6, whereas the mean CO(2) /HV was 61 ± 26% and 60 ± 26%, respectively, on the right and left sides. The correlation between BHI and CO(2) /HV was moderate on the right (r = 0.33; p < 0.01) and left sides (r = 0.38; p < 0.01). Multivariate linear regression analysis indicated that age (p = 0.01) and history of stroke (p = 0.007) were associated independently with an impaired VMR on the right as measured by CO(2) /HV. No predictors for impaired VMR by CO(2) /HV on the left and by BHI on either side were found.

CONCLUSIONS

CO(2) /HV and BHI are only moderately correlated. Further studies are necessary to determine which method more accurately predicts clinical morbidity. © 2012 Wiley Periodicals, Inc. J Clin Ultrasound 2012; Published online in Wiley Online Library.

Normal pressure perfusion breakthrough after resection of arteriovenous malformation

Objectives. The syndrome of normal pressure perfusion breakthrough (NPPB) follows the surgical resection of a small fraction of cerebral arteriovenous malformations (AVM). Although intraoperative hyperemia occurs in NPPB, the relationship and temporal profile of vasomotor paralysis to NPPB are unknown. In the present study, serial transcranial Doppler (TCD) studies (static and stress) were correlated with clinic observations to determine the relationship and temporal profile of vasomotor paralysis to NPPB. Methods. Thirty-five patients underwent complete AVM removal with preservation of the normal arteries and veins. Serial TCD examinations were performed under static and stress conditions (CO(2), Diamox, or blood pressure challenge). Vasomotor paralysis was considered present when CO(2) or Diamox challenge produced less than a 10% change in flow velocity or when flow velocity changed with blood pressure over physiological ranges. Results. Two of 35 patients (6%) developed NPPB immediately after AVM resection. Results of TCD studies were consistent with vasomotor paralysis. NPPB and vasomotor paralysis abated together in both patients on postoperative day 3 to 4. In one patient, NPPB and vasomotor paralysis reoccurred on postoperative day 8 after liberalization of blood pressure control.

CONCLUSIONS

NPPB occurs in a small fraction of patients after AVM resection. The occurrence of NPPB correlates with vasomotor paralysis, and both are present immediately postoperatively and last several days. Improving vasomotor tone and clinical condition do not imply complete normalization of the cerebral circulation because NPPB and vasomotor paralysis can reoccur after liberalization of blood pressure control.

The interaction of carbon dioxide and hypoxia in the control of cerebral blood flow

Both hypoxia and carbon dioxide increase cerebral blood flow (CBF), and their effective interaction is currently thought to be additive. Our objective was to test this hypothesis. Eight healthy subjects breathed a series of progressively hypoxic gases at three levels of carbon dioxide. Middle cerebral artery velocity, as an index of CBF; partial pressures of carbon dioxide and oxygen and concentration of oxygen in arterial blood; and mean arterial blood pressure were monitored. The product of middle cerebral artery velocity and arterial concentration of oxygen was used as an index of cerebral oxygen delivery. Two-way repeated measures analyses of variance (rmANOVA) found a significant interaction of carbon dioxide and hypoxia factors for both CBF and cerebral oxygen delivery. Regression models using sigmoidal dependence on carbon dioxide and a rectangular hyperbolic dependence on hypoxia were fitted to the data to illustrate this interaction. We concluded that carbon dioxide and hypoxia act synergistically in their control of CBF so that the delivery of oxygen to the brain is enhanced during hypoxic hypercapnia and, although reduced during normoxic hypocapnia, can be restored to normal levels with progressive hypoxia.

Cerebral and myocardial blood flow responses to hypercapnia and hypoxia in humans

In humans, cerebrovascular responses to alterations in arterial Pco2 and Po2 are well documented. However, few studies have investigated human coronary vascular responses to alterations in blood gases. This study investigated the extent to which the cerebral and coronary vasculatures differ in their responses to euoxic hypercapnia and isocapnic hypoxia in healthy volunteers. Participants ( n = 15) were tested at rest on two occasions. On the first visit, middle cerebral artery blood velocity ( V̄P) was assessed using transcranial Doppler ultrasound. On the second visit, coronary sinus blood flow (CSBF) was measured using cardiac MRI. For comparison with V̄P, CSBF was normalized to the rate pressure product [an index of myocardial oxygen consumption; normalized (n)CSBF]. Both testing sessions began with 5 min of euoxic [end-tidal Po2 (PetO2) = 88 Torr] isocapnia [end-tidal Pco2 (PetCO2) = +1 Torr above resting values]. PetO2 was next held at 88 Torr, and PetCO2 was increased to 40 and 45 Torr in 5-min increments. Participants were then returned to euoxic isocapnia for 5 min, after which PetO2 was decreased from 88 to 60, 52 and 45 Torr in 5-min decrements. Changes in V̄P and nCSBF were normalized to isocapnic euoxic conditions and indexed against PetCO2 and arterial oxyhemoglobin saturation. The V̄P gain for euoxic hypercapnia (%/Torr) was significantly higher than nCSBF ( P = 0.030). Conversely, the V̄P gain for isocapnic hypoxia (%/%desaturation) was not different from nCSBF ( P = 0.518). These findings demonstrate, compared with coronary circulation, that the cerebral circulation is more sensitive to hypercapnia but similarly sensitive to hypoxia.

The cerebrovascular response to carbon dioxide in humans

Carbon dioxide (CO2) increases cerebral blood flow and arterial blood pressure. Cerebral blood flow increases not only due to the vasodilating effect of CO2 but also because of the increased perfusion pressure after autoregulation is exhausted. Our objective was to measure the responses of both middle cerebral artery velocity (MCAv) and mean arterial blood pressure (MAP) to CO2 in human subjects using Duffin-type isoxic rebreathing tests. Comparisons of isoxic hyperoxic with isoxic hypoxic tests enabled the effect of oxygen tension to be determined. During rebreathing the MCAv response to CO2 was sigmoidal below a discernible threshold CO2 tension, increasing from a hypocapnic minimum to a hypercapnic maximum. In most subjects this threshold corresponded with the CO2 tension at which MAP began to increase. Above this threshold both MCAv and MAP increased linearly with CO2 tension. The sigmoidal MCAv response was centred at a CO2 tension close to normal resting values (overall mean 36 mmHg). While hypoxia increased the hypercapnic maximum percentage increase in MCAv with CO2 (overall means from76.5 to 108%) it did not affect other sigmoid parameters. Hypoxia also did not alter the supra-threshold MCAv and MAP responses to CO2 (overall mean slopes 5.5% mmHg⁻¹ and 2.1 mmHg mmHg⁻¹, respectively), but did reduce the threshold (overall means from 51.5 to 46.8 mmHg). We concluded that in the MCAv response range below the threshold for the increase of MAP with CO2, the MCAv measurement reflects vascular reactivity to CO2 alone at a constant MAP.

Gender characteristics of cerebral hemodynamics during complex cognitive functioning

Functional Transcranial Doppler sonography (fTCD) has been applied to assess peak mean cerebral blood flow velocity (MFV) with a high temporal resolution during cognitive activation. Yet, little attention has been devoted to gender-related alterations of MFV, including spectral analysis. In healthy subjects, fTCD was used to investigate a series of cerebral hemodynamic parameters in the middle cerebral arteries (MCA) during the Trail Making Tests (TMT), a means of selective attention and complex cognitive functioning. In females, there was a frequency peak at 0.375 Hz in both MCA, and we observed a dynamic shift in hemispheric dominance during that condition. Further, after the start phase, there was an MFV decline during complex functioning for the entire sample. These novel results suggest condition-specific features of cerebral hemodynamics in females, and it adds to the notion that gender is a fundamental confounder of brain physiology.

Effects of acetazolamide on the micro- and macro-vascular cerebral hemodynamics: a diffuse optical and transcranial doppler ultrasound study

Acetazolamide (ACZ) was used to stimulate the cerebral vasculature on ten healthy volunteers to assess the cerebral vasomotor reactivity (CVR). We have combined near infrared spectroscopy (NIRS), diffuse correlation spectroscopy (DCS) and transcranial Doppler (TCD) technologies to non-invasively assess CVR in real-time by measuring oxy- and deoxy-hemoglobin concentrations, using NIRS, local cerebral blood flow (CBF), using DCS, and blood flow velocity (CBFV) in the middle cerebral artery, using TCD. Robust and persistent increases in oxy-hemoglobin concentration, CBF and CBFV were observed. A significant agreement was found between macro-vascular (TCD) and micro-vascular (DCS) hemodynamics, between the NIRS and TCD data, and also within NIRS and DCS results. The relative cerebral metabolic rate of oxygen, rCMRO(2), was also determined, and no significant change was observed. Our results showed that the combined diffuse optics-ultrasound technique is viable to follow (CVR) and rCMRO(2) changes in adults, continuously, at the bed-side and in real time.

Feeling lightheaded: the role of cerebral blood flow

OBJECTIVE

The main aims of this study were a) to investigate the relationship between lightheadedness and cerebral blood flow velocity (CBFv) during hyperventilation-induced hypocapnia, and b) to investigate whether and why the relationship between lightheadedness and CBFv may change after several episodes of this sensation.

METHODS

Three hypocapnic and three normocapnic overbreathing trials were administered in a semirandomized order to healthy participants (N = 33). Each type of breathing trial was consistently paired with one odor. Afterward, participants were presented each odor once in two spontaneous breathing and in two normocapnic overbreathing trials. CBFv in the right middle cerebral artery was measured by transcranial Doppler ultrasonography (TCD). Also breathing behavior and self-reported lightheadedness were measured continuously. Each trial was followed by a symptom checklist.

RESULTS

Self-reported lightheadedness was closely related to changes in CBFv in the hypocapnic overbreathing trials. During the subsequent normocapnic trials, however, participants experienced more lightheadedness and "feeling unreal" to the odor that had previously been paired with hyperventilation-induced hypocapnia. These complaints were not accompanied by changes in end-tidal CO(2) nor in CBFv.

CONCLUSIONS

The results show that lightheadedness is associated with changes in CBFv but that after a few episodes, the underlying mechanism for this symptom may shift to perceptual-cognitive processes. These findings may help to understand why lightheadedness occurs during emotional distress and panic. In addition, altered cerebral blood flow is unlikely to play a primary precipitating role in recurrent symptoms of lightheadedness.

Delayed Migraine-Like Headache in Healthy Volunteers After a Combination of Acetazolamide and Glyceryl Trinitrate

Glyceryl trinitrate (GTN) is a pro-drug dissociating nitric oxide throughout the body. It dilates cephalic arteries without increasing cerebral blood flow (CBF). GTN induces headache in healthy volunteers and migraine attacks in migraineurs. Acetazolamide (Az) increases CBF but does not dilate cerebral arteries. The hypothesis tested here was that Az, by dilating cerebral arterioles but not arteries and thereby decreasing pulsatile stretching of the wall of the large arteries and their perivascular sensory nerves, would reduce or prevent the GTN-induced headache We tested this hypothesis in 14 healthy volunteers. In a randomized, double-blind, cross-over study, they were pretreated with Az or placebo followed on both study days by a GTN infusion of 0.5 μg kg-1 min-1 for 20 min. Headache was scored on a verbal rating scale and a headache diary was kept for 12 h. Mean blood velocity of the middle cerebral artery was measured (transcranial Doppler). Our hypothesis was disproved, as Az did not decrease GTN-induced headache. Unexpectedly but interestingly, GTN combined with Az induced more delayed headache than GTN alone. Furthermore, a migraine-like headache was observed in three volunteers, who did not develop migraine after GTN alone. The fact that a suitable pharmacological intervention may trigger migraine in individuals with no prior migraine may suggest that the ability to develop migraine without aura is a quantitative genetic trait.

Effects of heat stress on dynamic cerebral autoregulation during large fluctuations in arterial blood pressure

Impaired cerebral autoregulation during marked reductions in arterial blood pressure may contribute to heat stress-induced orthostatic intolerance. This study tested the hypothesis that passive heat stress attenuates dynamic cerebral autoregulation during pronounced swings in arterial blood pressure. Mean arterial blood pressure (MAP) and middle cerebral artery blood velocity were continuously recorded for approximately 6 min during normothermia and heat stress (core body temperature = 36.9 +/- 0.1 degrees C and 38.0 +/- 0.1 degrees C, respectively, P < 0.001) in nine healthy individuals. Swings in MAP were induced by 70-mmHg oscillatory lower body negative pressure (OLBNP) during normothermia and at a sufficient lower body negative pressure to cause similar swings in MAP during heat stress. OLBNP was applied at a very low frequency ( approximately 0.03 Hz, i.e., 15 s on-15 s off) and a low frequency ( approximately 0.1 Hz, i.e., 5 s on-5 s off). For each thermal condition, transfer gain, phase, and coherence function were calculated at both frequencies of OLBNP. During very low-frequency OLBNP, transfer function gain was reduced by heat stress (0.55 +/- 0.20 and 0.31 +/- 0.07 cm x s(-1) x mmHg(-1) during normothermia and heat stress, respectively, P = 0.02), which is reflective of improved cerebrovascular autoregulation. During low-frequency OLBNP, transfer function gain was similar between thermal conditions (1.19 +/- 0.53 and 1.01 +/- 0.20 cm x s(-1) x mmHg(-1) during normothermia and heat stress, respectively, P = 0.32). Estimates of phase and coherence were similar between thermal conditions at both frequencies of OLBNP. Contrary to our hypothesis, dynamic cerebral autoregulation during large swings in arterial blood pressure during very low-frequency (i.e., 0.03 Hz) OLBNP is improved during heat stress, but it is unchanged during low-frequency (i.e., 0.1 Hz) OLBNP.

Continuous neuromonitoring using transcranial Doppler reflects blood flow during carbon dioxide challenge in primates with global cerebral ischemia

OBJECTIVE

At present, there is no consensus on the optimal monitoring method for cerebral blood flow (CBF) in neurointensive care patients. The aim of the present study was to investigate whether continuous transcranial Doppler (TCD) monitoring with modulation of partial pressure of CO2 reflects CBF changes. This hypothesis was tested in 2 pathological settings in which cerebral ischemia can be imminent: after an episode of cerebral ischemia and during vasospasm after subarachnoid hemorrhage.

METHODS

Sixteen cynomolgus monkeys were divided into 3 groups: 1) chemoregulation in control animals to assess the physiological range of CBF regulation, 2) chemoregulation during vasospasm after subarachnoid hemorrhage, and 3) chemoregulation after transient cerebral ischemia. We surgically placed a thermal CBF probe over the cortex perfused by the right middle cerebral artery. Corresponding TCD values were acquired simultaneously while partial pressure of CO2 was changed within a range of 25 to 65 mm Hg (chemoregulation). A correlation coefficient of CBF with TCD values of greater than r equals 0.8 was considered clinically relevant.

RESULTS

CBF and CBF velocity correlated strongly after cerebral ischemia (r = 0.83, P < 0.001). Correlations were poor in chemoregulation controls (r = 0.2) and in the vasospasm group (r = 0.55).

CONCLUSION

The present study provides experimental support that, in clearly defined conditions, continuous TCD monitoring combined with chemoregulation testing may provide an estimate of CBF in the early postischemic period.

The effects of reduced end-tidal carbon dioxide tension on cerebral blood flow during heat stress

Passive heat stress reduces arterial carbon dioxide partial pressure (P(aCO2)) as reflected by 3 to 5 Torr reductions in end-tidal carbon dioxide tension (P(ETCO2)). Heat stress also reduces cerebrovascular conductance (CBVC) by up to 30%. While is a strong regulator of CBVC, it is unlikely that the relatively small change in during heating is solely responsible for the reductions in CBVC. This study tested the hypothesis that P(aCO2), referenced by P(ETCO2), is not the sole mechanism for reductions in CBVC during heat stress. Mean arterial blood pressure (MAP), P(ETCO2), middle cerebral artery blood velocity (MCA V(mean)), and calculated CBVC (MCA V(mean)/MAP) were assessed in seven healthy individuals, during three separate conditions performed sequentially: (1) normothemia, (2) control passive heat stress and (3) passive heat stress with P(ETCO2) clamped at the normothermic level (using a computer-controlled sequential gas delivery breathing circuit). MAP was similar in the three thermal conditions (P = 0.55). Control heat stress increased internal temperature approximately 1.3 degrees C, which resulted in decreases in P(ETCO2), MCA V(mean) and calculated CBVC (P < 0.001 for all variables). During heat stress + clamp conditions internal temperature remained similar to that during the control heat stress condition (P = 0.31). Heat stress + clamp successfully restored to the normothermic level (P = 0.99) and increased MCA V(mean) (P = 0.002) and CBVC (P = 0.008) relative to control heat stress. Despite restoration of P(ETCO2), MCA V(mean) (P = 0.005) and CBVC (P = 0.03) remained reduced relative to normothermia. These results indicate that heat stress-induced reductions in , as referenced by P(ETCO2), contribute to the decrease in MCA V(mean) and CBVC; however, other factors (e.g. perhaps elevated sympathetic nerve activity) are also involved in mediating this response.

Change in cerebral perfusion after carotid angioplasty with stenting is related to cerebral vasoreactivity: a study using dynamic susceptibility-weighted contrast-enhanced MR imaging and functional MR imaging with a breath-holding paradigm

BACKGROUND AND PURPOSE

Carotid angioplasty with stent placement (CAS) is an optional treatment for significant carotid stenosis. Cerebral vasoreactivity (CVR), representing the reserve capacity of cerebral perfusion, usually decreases in patients with severe carotid stenosis. This study aimed to investigate the relationship between the baseline CVR assessed by functional MR imaging (fMRI) and the changes in cerebral blood flow (CBF) after CAS.

MATERIALS AND METHODS

Fourteen patients with at least 70% unilateral carotid stenosis underwent CAS. Baseline CVR was evaluated by fMRI a under breath-holding paradigm. CBF was assessed by dynamic susceptibility-weighted contrast-enhanced MR imaging before and 3-5 days after CAS. The lateral index (LI) was defined as (n - L) / (n + L), where n and L represent the number of activated voxels in fMRI on the normal and lesion hemispheres, respectively.

RESULTS

No subject had clinical evidence of hyperperfusion syndrome. The LI represented baseline CVR. Patients were divided into normal (LI < 0, n = 6) and impaired (LI > 0, n = 8) CVR groups. The CBF on the normal and lesion sides was calculated separately. CBF increment on the lesion side after CAS was significantly higher in the impaired CVR group than that in the normal CVR group (P = .035). There was a significantly positive correlation between CVR impairment and the CBF increment (P = .026).

CONCLUSIONS

fMRI could be a reproducible tool in evaluating CVR. After CAS, early CBF changes on the lesion side are more prominent in patients with impaired CVR. Baseline CVR might predict early CBF increase after CAS.

Acetazolamide vasoreactivity evaluated by transcranial power harmonic imaging and Doppler sonography

BACKGROUND

Cerebral vasoreactivity (CVR) in the major cerebral arteries evaluated by transcranial Doppler sonography has shown some correlation with CVR in the brain tissue measured by other neuroradiological modalities. To clarify vasoreactive differences in the brain tissue and the major cerebral arteries, we have evaluated the relationship of acetazolamide (ACZ) CVR between transcranial ultrasonic power harmonic imaging (PHI) and color Doppler sonography (CDS), in cases ofparenchymal pathology with and without occlusive vascular lesions.

MATERIALS AND METHODS

The subjects were 31 stroke patients with intraparenchymal pathologies, 15 with (occlusive group) and 16 without (non-occlusive group) occlusive carotid and/or middle cerebral artery lesions. CVR based on values before/after ACZ (angle-collected CDS velocity in the middle and posterior cerebral arteries, PHI contrast area size, peak intensity, time to peak intensity), and correlation of CVR between PHI and CDS were compared between the side with and without lesions in both groups.

FINDINGS

(a) PHI CVR tended to be more disturbed than CDS CVR. CVR side differences were not significant. (b) CVR correlations between PHI and CDS were always lower in the pathological sides.

CONCLUSIONS

CVR in brain tissue evaluated by PHI is susceptible to disturbance in comparison with CDS, due to both parenchymal and vascular occlusive pathologies.

Cerebrovascular reactivity in depressed patients without vascular risk factors

INTRODUCTION

Cerebrovascular reactivity (CVR) seems to be gaining importance as a prognostic factor for stroke risk. CVR reflects the compensatory dilatory capacity of cerebral arterioles to a dilatory stimulus; this mechanism plays an important role in maintaining a constant cerebral blood flow. Evaluating factors that influence CVR will help prevention or early detection of cerebrovascular disease (CVD). In this study we aimed to measure the CVR in vascular-risk free depressed individuals so as to evaluate the effect depression has on CVR and hence its role as a stroke risk factor.

METHODS

Using acetazolamid (ACZ) stimulation, CVR was assessed with a transcranial Doppler ultrasound in 25 non-smoking depressed patients (average age: 48.48 +/- 14.40) and in 25 healthy non-smoking controls (average age: 46.76 +/- 13.69) by calculating the difference between the maximal mean blood flow velocity at baseline and the maximal mean blood flow velocity after ACZ stimulation.

RESULTS

Basal Cerebral Blood flow in Patients was 50.6 cm/s (SD: 11.6) versus controls 52.80 cm/s (SD: 12.70) whereas after stimulation maximal blood flow velocity was 72.64 cm/s (SD: 15.75) in patients versus 80.20 cm/s (SD: 18.43) in controls. In an analysis of covariance we found that cerebrovascular reactivity was significantly reduced in the vascular-risk free depressed sample. Age had a significant influence whereas gender did not.

DISCUSSION

Major Depression appears to decrease cerebrovascular reactivity supporting the idea of increased risk for stroke in depressed patients. The mechanisms leading to this phenomenon and its subtle subgroup differences should be further investigated.

Cerebral blood flow sensitivities to CO2 measured with steady-state and modified rebreathing methods

It is well established that the ventilatory response to carbon dioxide (CO(2)) measured by modified rebreathing (Sr(VE)) is closer to that measured by the steady-state method (Ss(VE)) than is the response measured by Read's rebreathing method. It is also known that the value estimated by the steady-state method depends upon the combination of data points used to measure it. The aim of this study was to investigate if these observations were also true for cerebral blood flow (CBF), as measured by steady-state (Ss(CBF)) and modified rebreathing (Sr(CBF)) tests. Six subjects undertook two protocols: (a) steady state: PET(CO2) was held at 1.5 mm Hg above normal (isocapnia) for 10 min, then raised to three levels of hypercapnia, (8 min each; 6.5, 11.5 and 16.5 mm Hg above normal, separated by 4 min isocapnia). End-tidal PO2 was held at 300 mm Hg; (b) modified rebreathing: subjects underwent 6 min of voluntary hyperventilation to PET(CO2) approximately 20 mm Hg, and then rebreathed via a 6l bag filled with 6.5% CO(2) in O(2). We confirmed that the value for Ss(VE) depended upon the combination of data points used to calculate it, and also confirmed that Ss(VE) and Sr(VE) were similar. However, this was not the case with CBF. Estimates of Ss(CBF) were the same, regardless of the data points used in calculation, and Ss(CBF) was 89% greater than Sr(CBF) (P<0.05). We interpret these findings as consistent with the notion that the specific CO(2) stimulus differs for CBF and ventilatory control. The data also indicate that prior hypocapnia in the modified rebreathing protocol may have a persistent effect on both cerebral vessels and central ventilatory control.

Impaired rapid modulation of cerebral hemodynamics during a planning task in schizophrenia

OBJECTIVE

Patients with schizophrenia show deficits in planning, and the Stockings of Cambridge (SOC) is a task that assesses planning performance. This study was undertaken to investigate rapid changes of cerebral hemodynamics during separate phases of SOC in schizophrenia and normals by means of functional transcranial Doppler sonography (fTCD).

METHODS

We included 21 patients with chronic schizophrenia and a control group of 20 healthy subjects in the study. They underwent fTCD of the middle (MCA) and anterior cerebral arteries (ACA) during performance of SOC.

RESULTS

The main finding was that healthy subjects significantly modulated the early cerebral hemodynamic response along distinct conditions of SOC, whereas we observed no significant differences in patients. Normally, there was an up-regulation of cerebral hemodynamics during mental planning, and about zero values were observed during movement execution. Patients showed lower development of the early cerebral hemodynamic response during planning of SOC.

CONCLUSIONS

The findings of this study suggest a uniform pattern of cerebral hemodynamic regulation during a planning task in schizophrenia, whereas healthy subjects modulated such a response along a planning-movement execution sequence.

SIGNIFICANCE

We provide novel evidence that modulation of cerebral hemodynamics is compromised in schizophrenia, and that fTCD constitutes a proper method to measure these alterations.

Cerebral vasomotor reactivity of patients with acute ischemic stroke: Cortical versus subcortical infarcts: An Israeli–Turkish collaborative study

BACKGROUND

Cerebral hemodynamic features of patients with different types of acute ischemic stroke are still obscure. We compared cerebral vasomotor reactivity (VMR) in acute cortical (CI) and subcortical (SI) brain infarcts.

METHODS

Acute stroke patients (within 72 h of stroke onset) underwent transcranial Doppler and the Diamox test (1 g acetazolamide IV). The percent difference between blood flow velocities in the middle cerebral arteries before and after acetazolamide was defined as VMR%. CI and SI infarcts were confirmed by computerized tomography and/or magnetic resonance imaging. Clinical status and disability were assessed by means of the National Institutes of Health Stroke Scale (NIHSS) and modified Rankin Scale (mRS) respectively.VMR% values and stroke severity and disability parameters were compared between CI and SI groups using ANOVA and Pearson's correlation (r) coefficients.

RESULTS

VMR% values of the ipsilateral side to the brain infarct in the CI group were significantly lower as compared with SI group (12.2+/-15.9% and 25.6+/-24.4% respectively, P=0.03). VMR% values in both groups were not correlated with stroke severity and disability (P<0.2).

CONCLUSIONS

Our results suggest greater vulnerability of resistance arterioles in the setting of cortical gray matter infarcts. Although gray matter VMR is physiologically higher than white matter VMR, patients with acute CI have impaired cerebral vascular reserve.

Basilar artery blood flow velocity changes in patients with panic disorder following 35% carbon dioxide challenge

PURPOSE

We compared the mean basilar artery blood flow velocity (BABFV) between patients with panic disorder and healthy subjects both at rest and immediately following carbon dioxide (CO(2)) challenge, and examined the effects of treatment on BABFV.

METHODS

Twenty four patients with panic disorder with or without agoraphobia and 12 healthy comparison subjects were studied. Visual Analog Anxiety Scale was used to evaluate the anxiogenic effect of 35% CO(2) inhalation. Mean BABFV was monitored using transcranial Doppler ultrasonography at rest and 10, 20, 30, 60, 90, 120 s after 35% CO(2) challenge both before and after four weeks treatment with paroxetine.

RESULTS

The hemodynamic response pattern of basilar artery to CO(2) inhalation was significantly different between two groups. CO(2) rapidly triggered blood flow velocity in basilar artery amongst panic patients but not in healthy comparisons. The mean time to normalization of BABFV was significantly longer in panic patients. Four weeks of treatment with paroxetine led to a significantly reduced mean BABFV after 35% CO(2) inhalation in comparison with pretreatment.

CONCLUSIONS

Patients with panic disorder had impaired cerebral regulatory mechanisms observed as a change in response characteristics in BABFV in response to CO(2) inhalation. Treatment with paroxetine reduced the increase of BABFV seen in patients after the CO(2) challenge.

Transcranial Doppler estimation of cerebral blood flow and cerebrovascular conductance during modified rebreathing

Clinical transcranial Doppler assessment of cerebral vasomotor reactivity (CVMR) uses linear regression of cerebral blood flow velocity (CBFV) vs. end-tidal CO(2) (Pet(CO(2))) under steady-state conditions. However, the cerebral blood flow (CBF)-Pet(CO(2)) relationship is nonlinear, even for moderate changes in CO(2). Moreover, CBF is increased by increases in arterial blood pressure (ABP) during hypercapnia. We used a modified rebreathing protocol to estimate CVMR during transient breath-by-breath changes in CBFV and Pet(CO(2)). Ten healthy subjects (6 men) performed 15 s of hyperventilation followed by 5 min of rebreathing, with supplemental O(2) to maintain arterial oxygen saturation constant. To minimize effects of changes in ABP on CVMR estimation, cerebrovascular conductance index (CVCi) was calculated. CBFV-Pet(CO(2)) and CVCi-Pet(CO(2)) relationships were quantified by both linear and nonlinear logistic regression. In three subjects, muscle sympathetic nerve activity was recorded. From hyperventilation to rebreathing, robust changes occurred in Pet(CO(2)) (20-61 Torr), CBFV (-44 to +104% of baseline), CVCi (-39 to +64%), and ABP (-19 to +23%) (all P < 0.01). Muscle sympathetic nerve activity increased by 446% during hypercapnia. The linear regression slope of CVCi vs. Pet(CO(2)) was less steep than that of CBFV (3 vs. 5%/Torr; P = 0.01). Logistic regression of CBF-Pet(CO(2)) (r(2) = 0.97) and CVCi-Pet(CO(2)) (r(2) = 0.93) was superior to linear regression (r(2) = 0.91, r(2) = 0.85; P = 0.01). CVMR was maximal (6-8%/Torr) for Pet(CO(2)) of 40-50 Torr. In conclusion, CBFV and CVCi responses to transient changes in Pet(CO(2)) can be described by a nonlinear logistic function, indicating that CVMR estimation varies within the range from hypocapnia to hypercapnia. Furthermore, quantification of the CVCi-Pet(CO(2)) relationship may minimize the effects of changes in ABP on the estimation of CVMR. The method developed provides insight into CVMR under transient breath-by-breath changes in CO(2).

Cerebrovascular reactivity over time course in healthy subjects

INTRODUCTION

Cerebrovascular reactivity (CVR) reflects the compensatory dilatory capacity of cerebral arterioles to a dilatory stimulus and is an important mechanism for maintaining constant cerebral blood flow. Many pathological conditions are associated with an impaired CVR thus contributing to a higher risk of cerebrovascular disease. Since an impaired CVR might contribute to a cerebrovascular disease if it lasts for a longer period of time, it is of importance to know what the time-course of CVR might be under healthy conditions.

METHODS

We investigated CVR in 33 healthy subjects on baseline and on follow-up after 1 to 3 years. CVR was determined by calculating the difference between maximal blood flow velocity after stimulation with acetazolamide and during rest. Blood flow velocities were measured by transcranial Doppler ultrasound.

RESULTS

CVR did not differ significantly in a group of healthy persons when reevaluated after 1 to 3 years. Possible influencing factors like age, gender, interval between testing, and smoking did not show a significant influence.

DISCUSSION

This is the first study to investigate within-subject-differences in healthy subjects. CVR seems to remain constant under healthy conditions. Even this short period of life-span is of importance because an altered CVR can improve under treatment within weeks. Nevertheless further studies should follow-up longer periods of time.

Simultaneous VEP and transcranial Doppler ultrasound recordings to investigate activation-flow coupling in humans

Simultaneous assessment of electrical as well as hemodynamic responses in visual stimulation tasks is a relatively new approach to investigate activation-flow coupling in humans. To investigate the relation of both signals, we compared visually evoked potentials (VEP) with evoked flow velocity responses in the posterior cerebral artery by performing different visual stimulation tasks in healthy students. Check sizes and flickering frequency of a checkerboard pattern and the radial visual field section of a dartboard pattern were varied. VEPs were expressed in amplitude differences. Hemodynamic changes were given in terms of a control system model specifying the gain, attenuation, natural frequency and rate time parameters. From the typical VEP amplitude differences, we found the early N75-P100 amplitude difference significantly correlated to the gain parameter of the hemodynamic response. Both parameters increased with higher complexity of the checkerboard pattern and increasing visual field sections, whereas they remained nearly stable in the chosen frequency range. To corroborate the hypothesis of a tight coupling, further studies have to prove if the strength of this coupling could be used in clinical conditions.