Colleen M. Douville

Effects of the Valsalva Maneuver on Cerebral Circulation in Healthy Adults: A Transcranial Doppler Study

BACKGROUND AND PURPOSE Knowledge is limited about the effects of the Valsalva maneuver on cerebral circulation because of the poor temporal resolution of traditional cerebral blood flow measurements. The purpose of this study was to investigate changes in cerebral blood flow during the Valsalva maneuver and to explore its potential use for the evaluation of cerebral autoregulation. METHODS Using transcranial Doppler ultrasonography, we simultaneously recorded systemic arterial blood pressure in the radial artery and flow velocities in both middle cerebral arteries in 10 healthy adults during the Valsalva maneuver. Goslings pulsatility index was calculated for all phases of the Valsalva maneuver. Autoregulatory capacities were estimated from the change in cerebrovascular resistance (flow velocity in relationship to blood pressure) during phase II and changes in the velocity-pressure relationship in phase IV relative to phase I. RESULTS The characteristic changes in blood pressure (phases I to IV) were seen in all subjects, accompanying distinct changes in cerebral blood flow velocity. The relative changes in mean velocity during phases II and IV were significantly greater than those in mean blood pressure. Compared with the baseline value, velocity decreased by 35% in phase IIa, then rose by 56.5% in phase IV (corresponding changes in blood pressure were -10.2% and +29.8%, respectively). During phase II, the pulsatility and cerebrovascular resistance decreased by 19.9%. The increase in cerebral blood flow velocity in phase IV was significantly higher than in phase I (P < .0004), and there was no corresponding significant difference in blood pressure. CONCLUSIONS These results demonstrated that in healthy humans the Valsalva maneuver causes characteristic changes in systemic blood pressure as well as in flow velocity in the middle cerebral artery, reflecting the sympathetic and cerebral autoregulatory responses, respectively. Analysis of these changes may provide an estimate of autoregulatory capacity.

Evaluation of Impaired Cerebral Autoregulation by the Valsalva Maneuver

BACKGROUND AND PURPOSE Transcranial Doppler sonography has recently been used to describe cerebral hemodynamics during the Valsalva maneuver in normal human subjects. Since some changes in flow velocity during the Valsalva maneuver seem to reflect the brains autoregulatory response to a decrease in cerebral perfusion pressure during the strain, we hypothesized that this method could identify vascular territories with impaired autoregulatory capacity. METHODS Eight patients with unilateral (n=7) or bilateral (n=1) severe obstruction of the internal carotid artery and impaired vascular responses to the CO2 reactivity test and to dynamic autoregulation testing were studied. We compared changes in flow velocities and blood pressures during defined phases of the Valsalva maneuver in the patients with the results in a group of 17 normal volunteers. We defined two indices to evaluate autoregulatory capacity based on the response to the Valsalva maneuver. RESULTS During the Valsalva maneuver, changes in flow velocity in the middle cerebral arteries ipsilateral to the lesions showed characteristic abnormalities compared with the normal pattern. Autoregulatory indices of these vessels as defined by the Valsalva maneuver were significantly different from those with normal vascular reactivity to CO2 (P<.0001). There were good correlations between an index based on the changes in flow velocity and blood pressure in phase II and the results of the CO2 test (r=.78; P<.0001) or those of dynamic autoregulatory testing (r=.6; P<.0001). CONCLUSIONS Vascular territories with severely impaired vasomotor reactivity due to carotid obstruction can be identified by transcranial Doppler sonography by their pattern of flow velocity changes if their autoregulatory capacity is challenged during the Valsalva maneuver.

Practice Standards for Transcranial Doppler (TCD) Ultrasound. Part II. Clinical Indications and Expected Outcomes

Transcranial Doppler (TCD) is a physiological ultrasound test with established safety and efficacy. Although imaging devices may be used to depict intracranial flow superimposed on structural visualization, the end‐result provided by imaging duplex or nonimaging TCD is sampling physiological flow variables through the spectral waveform assessment.

Asymmetric Dynamic Cerebral Autoregulatory Response to Cyclic Stimuli

Background and Purpose— Dynamic cerebral autoregulation has been shown to be fast and effective, but it is not well known if the mechanism is symmetric, that is to say, it acts with equal compensatory action to upward as compared with downward abrupt changes in arterial blood pressure (ABP). Methods— Fourteen patients with head injuries and 10 normal subjects had bilateral transcranial Doppler and continuous ABP recording. Cyclic ABP stimuli were generated by large thigh cuffs, which were rapidly inflated above systolic pressure for 15 seconds alternating with 15 seconds of deflation. At least 8 such cycles were ensemble-averaged and the dynamic autoregulatory gain (AGup and AGdn) was estimated separately for upward and downward changes in ABP. The results were compared with the autoregulation index using conventional leg cuff releases. Results— In normal subjects, AGdn was 0.74±0.18 and AGup was 0.77±0.17 (mean±SD); the difference was insignificant. The correlation between AGdn and AGup, however, was weak (r=0.24). In the patients with head injury, AGdn was 0.30±0.21 and AGup was 1.27±0.76, the difference being highly significant (P<0.001). There was a negative relationship between AGdn and AGup (r=−0.33). Autoregulation index correlated well with AGdn (r=0.79) and weakly negatively with AGup (r=−0.47). Conclusions— A strongly asymmetric dynamic response of the cerebral autoregulation was seen the majority of patients with head injury. It might also have been present, albeit to a lesser degree, in the normal subjects. The findings suggest that nonlinear effects may be present in the operation of the cerebral autoregulation mechanism.

Transcranial doppler grading criteria for basilar artery vasospasm

OBJECTIVE:Transcranial Doppler (TCD) criteria for basilar artery (BA) vasospasm are poorly defined, and grading criteria for vertebrobasilar vasospasm are unavailable. The purpose of the present study was to define TCD grading criteria for BA vasospasm on the basis of the absolute flow velocities and the intracranial to extracranial flow velocity ratios for the posterior circulation, and to improve the sensitivity and specificity of TCD for diagnosis of BA vasospasm. METHODS:One hundred twenty-three patients with aneurysmal subarachnoid hemorrhage underwent 144 cerebral arteriograms with views of the BA during the acute phase of vasospasm (Days 3–14 after hemorrhage). BA diameters were measured and compared with diameters obtained from baseline arteriograms. Both BA and extracranial vertebral artery flow velocities were measured by TCD within 4 hours before the arteriogram. RESULTS:The velocity ratio between the BA and the extracranial vertebral arteries (VA) strongly correlated with the degree of BA narrowing (r2 = 0.648; P < 0.0001). A ratio higher than 2.0 was associated with 73% sensitivity and 80% specificity for BA vasospasm. A ratio higher than 2.5 with BA velocity greater than 85 cm/s was associated with 86% sensitivity and 97% specificity for BA narrowing of more than 25%. A BA/VA ratio higher than 3.0 with BA velocities higher than 85 cm/s was associated with 92% sensitivity and 97% specificity for BA narrowing of more than 50%. CONCLUSION:The BA/VA ratio improves the sensitivity and specificity of TCD detection of BA vasospasm. On the basis of the BA/VA ratio and BA mean velocities, we suggest new TCD grading criteria for BA vasospasm.

Time course for autoregulation recovery following severe traumatic brain injury

OBJECT The aim of the present study was to evaluate the time course for cerebral autoregulation (AR) recovery following severe traumatic brain injury (TBI). METHODS Thirty-six patients (27 males and 9 females, mean +/- SEM age 33 +/- 15.1 years) with severe TBI underwent serial dynamic AR studies with leg cuff deflation as a stimulus, until recovery of the AR responses was measured. RESULTS The AR was impaired (AR index < 2.8) in 30 (83%) of 36 patients on Days 3-5 after injury, and in 19 individuals (53%) impairments were found on Days 9-11 after the injury. Nine (25%) of 36 patients exhibited a poor AR response (AR index < 1) on postinjury Days 12-14, which eventually recovered on Days 15-23. Fifty-eight percent of the patients with a Glasgow Coma Scale score of 3-5, 50% of those with diffuse brain injury, 54% of those with elevated intracranial pressure, and 40% of those with poor outcome had no AR recovery in the first 11 days after injury. CONCLUSIONS Autoregulation recovery after severe TBI can be delayed, and failure to recover during the 2nd week after injury occurs mainly in patients with a lower Glasgow Coma Scale score, diffuse brain injury, elevated ICP, or unfavorable outcome. The finding suggests that perfusion pressure management should be considered in some of the patients for a period of at least 2 weeks.

Basilar Artery Vasospasm and Delayed Posterior Circulation Ischemia After Aneurysmal Subarachnoid Hemorrhage

Background and Purpose— The clinical and hemodynamic impacts of basilar artery (BA) vasospasm (VS) after aneurysmal subarachnoid hemorrhage (SAH) are ill-defined. The purpose of the present study was to evaluate the relationship between BA-VS and regional cerebral blood flow (rCBF) with posterior circulation after aneurysmal SAH. Methods— Daily transcranial Doppler (TCD) measurements of posterior and anterior circulation arteries were conducted in 162 patients with aneurysmal SAH. rCBF to the brain stem (BS) and other brain territories was assessed by multiple single-photon emission computed tomography with 99mTc ethyl cysteinate dimer single-photon emission computed tomography (ECD-SPECT) imaging during the course of VS. Results— SPECT imaging showed delayed BS hypoperfusion in 29 patients (17.9%). Of them, 23 patients (79.3%) were found to have BA-VS. Patients with very high BA flow velocities (FVs; >115 cm/s) had a 50% chance of developing delayed BS ischemia. BA-VS was found at a higher rate in patients who experienced reduced rCBF in the cerebellum (56.3%), thalamic nuclei (68.4%), and occipital lobe (81.8%). Although patients with delayed BS hypoperfusion did not present with a higher clinical grade, their clinical outcome was significantly worse (Glasgow Outcome Score after 30 days 2.48±1.16 versus 3.3±1.27; P = 0.001). Conclusions— These findings suggest for the first time that BA-VS after aneurysmal SAH is associated with hypoperfusion to BS and other posterior circulation territories. The risk for delayed BS ischemia increased significantly when TCD BA-FVs were >115 cm/s.

Autoregulatory Response and CO2 Reactivity of the Basilar Artery

Background and Purpose— Transcranial Doppler has been extensively used to measure cerebrovascular control mechanisms, including autoregulation in humans and in patients with cerebrovascular diseases. There have been sufficient reports on the measurement of normal autoregulatory response (AR) and CO2 reactivity (CR) of the middle cerebral artery (MCA) but few reports of these indices for the basilar artery (BA). We measured AR and CR in the BA in healthy volunteers to determine normal values and compared them with simultaneous measurements made in the MCA. Methods— Sixteen normal subjects were enrolled. Time-averaged mean velocities of maximum blood flow in the BA and MCA were continuously and simultaneously monitored by using transcranial Doppler along with continuous measurement of mean arterial blood pressure (MABP). Values were obtained during rest, alterations of end-tidal Paco2 (ETCO2), and acute decrease and recovery of MABP. AR was evaluated by using the thigh cuff method and graded by the standard dynamic autoregulatory index (ARI), with values between 0 and 9. CR was measured as percentage change in time-averaged mean velocity per mm Hg ETCO2. Results— The mean age of 16 subjects was 27.38±8.50 years. Average baseline values for MABP and ETCO2 were 82.29±7.10 and 42.75±3.77 mm Hg, respectively. Mean ARI was 4.62±1.26 for the BA and was 4.77±1.23 for the MCA (n=15) (P =0.598). Average CR was 2.54±0.39%/mm Hg ETCO2 for the BA and 2.51±0.29%/mm Hg ETCO2 for the MCA (n=16) (P =0.686). Conclusions— Our study demonstrates that ARI and CR values for the BA are similar to those for the MCA.

Cerebral blood flow and dynamic cerebral autoregulation during ethanol intoxication and hypercapnia

More than one-third of patients diagnosed with head injury are intoxicated with ethanol. Most clinical and animal studies have shown alcohol to have a deleterious impact in the setting of cerebrovascular trauma; however, there are also data showing neuroprotective effects in low ethanol doses. Human studies using imaging modalities suggest that small doses of alcohol produce cerebral vasodilatation and higher doses cerebral vasoconstriction. The aim of this study was to investigate the effect of ethanol intake on dynamic cerebral autoregulation and velocities in the middle cerebral arteries, and compare these changes with the effects of hypercapnia. Dynamic cerebral autoregulation and cerebral blood flow velocities were analysed before and after alcohol intake (1.1 g/kg of body weight) in six adult volunteers. Cerebral blood flow velocities in both middle cerebral arteries were monitored continuously by transcranial Doppler. A value for dynamic cerebral autoregulation was calculated from the rate of increase in middle cerebral artery velocities after a rapid-step decrease in arterial blood pressure. A sudden decrease in blood pressure was achieved by the release of previously inflated large blood pressure cuffs around the subjects thighs. Three volunteers were also tested before alcohol intake with CO(2) challenge (breathing 6% CO(2)) during the autoregulation procedure. Blood alcohol level reached 90 mg/dl approximately 60 min after ethanol ingestion. Cerebral blood velocities increased by 8% from baseline for uncorrected end-tidal (et) CO(2) and by 24% for correction to et CO(2)=40. Dynamic cerebral autoregulation measured as an autoregulation index decreased from 4.3+/-1.3 to 2.9+/-1.1 (p=0.089), which did not reach statistical significance. During hypercapnic conditions, dynamic cerebral autoregulation dropped from 4+/-0.8 to 0.9+/-0.9. In conclusion, mild alcohol intoxication caused cerebral vasodilatation with a subsequent increase in cerebral blood flow of 8-24%. Dynamic cerebral autoregulation was not found to be significantly impaired by ethanol. Hypercapnia almost completely destroys the physiological autoregulatory mechanism. A mild hyper-ventilation to etCO(2)=34-36 may be a compensatory contra-measure for ethanol-induced vasodilatation in the setting of head trauma.

Impact of Basilar Artery Vasospasm on Outcome in Patients With Severe Cerebral Vasospasm After Aneurysmal Subarachnoid Hemorrhage

Background and Purpose— The purpose of the present study was to evaluate the impact of basilar artery (BA) vasospasm on outcome in patients with severe vasospasm after aneurysmal subarachnoid hemorrhage (aSAH). Methods— Sixty-five patients with clinically suspect severe cerebral vasospasm after aSAH underwent cerebral angiography before endovascular treatment. Vasospasm severity was assessed for each patient by transcranial Doppler measurements, angiography, and 99mTc-ethylcysteinate dimer single-photon emission computed tomography (ECD-SPECT) imaging. Percentage of BA narrowing was calculated in reference to the baseline angiogram. Results— BA narrowing ≥25% was found in 23 of 65 patients, and delayed brain stem (BS) hypoperfusion, as estimated by ECD-SPECT, was found in 16. Fourteen of 23 patients with BA narrowing ≥25% experienced BS hypoperfusion, whereas only 2 of 42 patients with ≥25% BA narrowing experienced BS ischemia (P<0.001). Stepwise logistic regression after adjusting for age with Hunt and Hess grade, Fisher grade, hydrocephalus, and aneurysmal location as covariables revealed BA narrowing ≥25% and delayed BS hypoperfusion to be significantly and independently associated with unfavorable 3-month outcome (P=0.0001; odds ratio, 10.1; 95% CI, 2.5 to 40.8; and P=0.007; odds ratio, 13.8, 95% CI, 2.18 to 91.9, respectively). Conclusions— These findings suggest for the first time that BA vasospasm after aSAH is an independent and significant prognostic factor associated with poor outcome in patients with severe cerebral vasospasm requiring endovascular therapy. Further study should be done to evaluate the role of interventional therapy on outcome in patients with posterior circulation vasospasm.