(Stroke. 1995;26:1014-1019.)
© 1995 American Heart Association, Inc.
Articles |
Comparison of Static and Dynamic Cerebral Autoregulation Measurements
From the Departments of Neurological Surgery (F.P.T., A.M.L., R.A., D.W.N.) and Anesthesiology (A.M.L.), University of Washington, Harborview Medical Center (Seattle).
Correspondence to David W. Newell, Harborview Medical Center, 325 Ninth Ave, ZA-86, Seattle, WA 98104.
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Abstract |
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 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
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Background and Purpose Cerebral autoregulation can be evaluated by measuring relative blood flow changes in response to a steady-state change in the blood pressure (static method) or during the response to a rapid change in blood pressure (dynamic method). The purpose of this study was to compare the results of the two methods in humans with both intact and impaired autoregulatory capacity.
Methods Using intraoperative transcranial Doppler sonography recordings from both middle cerebral arteries, we determined static and dynamic autoregulatory responses in 10 normal subjects undergoing elective surgical procedures. The changes in cerebrovascular resistance were estimated from the changes in cerebral blood flow velocity and arterial blood pressure in response to manipulations of blood pressure. Static autoregulation was determined by analyzing the response to a phenylephrine-induced rise in blood pressure, whereas rapid deflation of a blood pressure cuff around one thigh served as a stimulus for testing dynamic autoregulation. Both measurements were performed in patients with intact autoregulation during propofol anesthesia and again in the same patients after autoregulation had been impaired by administration of high-dose isoflurane.
Results There was a significant reduction in autoregulatory capacity after the administration of high-dose isoflurane, which could be demonstrated using static (P<.0001) and dynamic (P<.0001) methods. The correlation between static or steady-state and dynamic autoregulation measurements was highly significant (r=.93, P<.0001).
Conclusions These data show that in normal human subjects measurement of dynamic autoregulation yields similar results as static testing of intact and pharmacologically impaired autoregulation.
Key Words: autoregulation • blood flow velocity • cerebral blood flow • ultrasonics
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Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Cerebral autoregulation (CA) refers to the ability in the brain to maintain constant blood flow despite changes in cerebral perfusion pressure.1 2 3 In the past, evaluation of CA was performed under steady-state conditions: a measurement of cerebral blood flow (CBF) is obtained first at a constant baseline arterial blood pressure (ABP) and constant CBF, followed by another (steady-state) measurement that is taken after the autoregulatory response to a manipulation of ABP has been completed. We have termed this method "static" autoregulation testing. If the blood flow changes significantly with either an increase or a decrease in ABP, CA is said to be impaired. If blood flow is maintained at or near the baseline level, despite a change in ABP, CA is said to be intact.1 2 3 This method to evaluate CA requires time-consuming and/or invasive procedures such as the Kety-Schmidt technique4 or 133Xe measurements5 and manipulations of the blood pressure using vasoactive medications.
Aaslid et al6 introduced a noninvasive method using transcranial Doppler ultrasonography (TCD) to evaluate CA in humans. This "dynamic" approach uses the rapid drops in ABP caused by the release of thigh blood pressure cuffs as an autoregulatory stimulus and compares ABP and CBF velocity (CBFV) during the autoregulatory process. The validity of this method was questioned at the time because of the use of CBFV instead of CBF,7 but the method has subsequently been validated.8 9 10 It has also been shown recently by comparison of TCD with CBF measurements according to the Fick principle that TCD is valid for static, or steady-state, measurements of CA.11
Static measurements evaluate the overall effect (efficiency) of the autoregulatory action, ie, the change in cerebrovascular resistance (CVR) in response to the manipulation of ABP, but they do not address the time in which this change in CVR is achieved (its "latency"). Measurement of the dynamic response, however, yields information about the latency as well, which may be relevant in certain clinical conditions including head injury. Preliminary data (Aaslid et al, unpublished data, 1994) suggest that progressive impairment in autoregulation first affects the latency and then the efficiency of the autoregulatory response. However, we are aware of no clinical study that systematically compares static and dynamic autoregulation in the same individuals.
Therefore, our study investigated whether both methods correlate in patients with normal autoregulation and whether they show differences if autoregulation is impaired. Using TCD and ABP recordings, we studied both dynamic and static autoregulatory responses with intact autoregulation during propofol anesthesia and then again during high-dose isoflurane anesthesia. Isoflurane is known to impair CA in a dose-dependent manner,12 13 14 15 whereas intravenous agents like propofol have little or no effect on CA.14 16 Static and dynamic measurements of intact and impaired autoregulation were performed and analyzed to compare the results of the two measurement techniques.
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Ten adults (8 men and 2 women of physical status grade 1 or 2 according to the American Society of Anesthesiology) undergoing elective orthopedic surgery took part in the trial. The study was approved by the University of Washington Human Subject Review Committee, and written informed consent was obtained from each subject. A history or signs of cerebrovascular or cardiac disease and the use of psychoactive drugs were the exclusion criteria for the study. Anesthesia was induced with 2 to 2.5 mg/kg propofol, 3 µg/kg fentanyl, and 0.1 mg/kg vecuronium and was maintained with 50% nitrous oxide in oxygen and 2 µg/kg per hour of fentanyl infusion in addition to either propofol or isoflurane. Additional doses of vecuronium were given as needed.
After intubation of the trachea, ventilation was adjusted to provide constant normocapnia as determined by repeated blood gas sampling. A phenylephrine infusion was maintained and titrated to keep the mean blood pressure between 70 to 80 mm Hg before steady-state testing. The first series of tests was performed during infusion of 180 to 200 µg/kg per minute of propofol. Then propofol was stopped, and isoflurane was given to maintain a steady-state end-tidal concentration of 1.3% to 1.6%. At least 30 minutes was allowed to elapse after the propofol infusion had been discontinued, and 15 minutes of unchanged end-tidal isoflurane concentration was permitted before the second series of testing started.
In addition to routine monitoring including invasive ABP measurement, both middle cerebral arteries (MCAs) were identified by TCD according to standard criteria.17 The transducers were then fixed in place with a custom-designed frame, and CBFV was continuously monitored at the depth of the best signal (44 to 50 mm) with TCD equipment (Multidop X, DWL) that provided simultaneous display and recording of ABP and CBFVs.
Static CA was tested by slow continuous infusion of
phenylephrine to induce an increase in mean ABP of
approximately 20 mm Hg (to not more than 110 mm Hg) while ABP and
CBFV were continuously recorded. Static autoregulation (sCA) was
calculated as the percentage change in estimated cerebrovascular
resistance (CVRe) in relation to the change in ABP over the
entire period of time needed for an ABP increase from baseline (1) to
the higher level (2). Estimating CVRe as
CVRe=ABP/CBFV, we calculated static CA as
sCA=(%
CVRe/%ABP)x100% with
%CVRe=(CVRe2-CVRe1)/CVRe1
and %ABP=(ABP2-ABP1)/ABP1.
Thus, static CA values are expressed as a percentage of full autoregulatory capacity. A change in CVR that would fully compensate for the drop in ABP would yield a static CA of 100%, and no change in CVR would yield a static CA of 0%.
Dynamic CA was assessed as previously reported6 with the induction of a rapid-step decrease in ABP and comparison of the temporal courses of the return of ABP and CBFV to baseline. The ABP drop was achieved with the sudden release of a large blood pressure cuff around one thigh, which had been inflated to 30 mm Hg above the systolic ABP for 3 minutes. To test dynamic CA at the same ABP range as static CA, phenylephrine was titrated to maintain ABP at the upper level of the previous steady-state measurement (ie, at 90 to 100 mm Hg). Only steep drops in ABP of more than 15 mm Hg from this level were considered to be a sufficient stimulus. ABP normally remains lowered for approximately 20 seconds before gradually returning to its initial level. CBFV, in contrast, returns more rapidly to its initial level, depending on the autoregulatory ability.6
The CBFV and ABP values after the cuff release are used to calculate an
autoregulatory index that reflects the change in CVR per second in
relation to the change in ABP. Triggered at the moment of the cuff
release and based on the actual ABP curve of the following 30 seconds,
a hypothetical CBFV curve without autoregulation is calculated by
computer for this time span. This curve assumes that the CBFV passively
follows the course of the ABP, ie, that the percentage changes in CBFV
are equal to those of the ABP. If then, for example, the actual CBFV
curve from a given test fit this computer model perfectly, the
autoregulatory index would be 0. Nine other different computer models
of possible CBFV curves are calculated as well, each assuming a higher
degree of autoregulatory capacity (see "Appendix"). Each model
curve is compared to the actual CBFV recordings for the best fit (ie,
the lowest standard error of the mean of the differences between the
actual and each hypothetical curve at each of the 30 seconds after the
cuff release). The chosen model that best fits the actual CBFV curve is
superimposed onto the actual CBFV curve on the screen for visual
control of the fit (see Fig 2
).
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Higher autoregulatory values indicate increasingly better dynamic CA. For example, under resting conditions (light propofol anesthesia) our subjects had a mean autoregulatory index of about 5 (4.8±1.0, mean±SD).
All calculations were performed off-line using the time-averaged mean velocities of the maximum velocity outlines of the Doppler spectrum and mean ABP. Values for each MCA were analyzed separately. Data were analyzed using Student's t test and simple regression analysis and are shown as mean±SD.
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Results |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Demographic data and results for heart rate, PCO2, baseline ABP, and velocities after induction of anesthesia are presented in Table 1
. Table 2 shows the ABP, CBFV, and
autoregulatory data with intact autoregulation under propofol
anesthesia (top) and impaired autoregulation under isoflurane
anesthesia (bottom). No significant difference in baseline variables,
including PCO2, was noted between the
two test series other than a significant increase in CBFV from 38 cm/s
under propofol anesthesia to 51 cm/s under isoflurane anesthesia
(P<.0001).
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Static Autoregulation
During testing of static CA, phenylephrine
raised ABP in both series by a mean of 24±4 mm Hg, without a
significant difference between the two test series. Typical examples of
individual subjects for ABP and CBFV recordings during static testing
with intact (propofol) and impaired (isoflurane) autoregulatory
capacity are shown in Fig 1. Characteristically, with
propofol the rise in ABP showed only little effect on CBFV, whereas
high-dose isoflurane often produced a pressure-passive change in CBFV.
The mean reduction in static CA from 85±20% to 37±30% was
significant (P<.0001), although autoregulation was
preserved to a variable degree in some individuals.
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Dynamic Autoregulation
Typical recordings of dynamic autoregulation testings of
individual subjects are displayed in Fig 2
. The mean
drop in ABP that was induced by the cuff release was 20±4 mm Hg
(range, 15 to 28 mm Hg; a drop of less than 15 mm Hg was not
acceptable and occurred in three subjects, all of whom demonstrated
major drops after repetition of the test). Similar to static CA, the
dynamic response showed a clear impairment with isoflurane. The
autoregulatory index dropped from 4.8±1.0 with propofol to 2.3±1.3
with isoflurane (P<.0001). There were only two subjects
(patients 3 and 10 in Tables 1 and 2) in whom dynamic CA was not
markedly reduced by high-dose isoflurane. These individuals also
demonstrated little or no impairment during static testing.
Interestingly, those two subjects were the youngest. There was no other
characteristic variable that distinguished these subjects from the
others.
Simple regression analysis comparing all corresponding static and
dynamic data shows a good correlation between static and dynamic CA
(r=.93, P<.0001; Fig 3).
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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We have shown that static, or steady-state, and dynamic tests of autoregulation yield similar results in normal anesthetized adults with intact or impaired autoregulation, thus demonstrating a good correlation between both methods.
Before we discuss the theoretical and clinical implications of our findings, several methodological aspects of the study require discussion. First, patient selection and concomitant drug administration, as well as the circumstances of surgery, may have had an influence on the results. We chose a sample of relatively young patients undergoing elective surgery without any evidence of cerebrovascular or cardiac disease to minimize the chance of preexisting abnormalities or possible inhomogeneity. We did not randomize the anesthesia sequence of the study because we wanted to verify that patients studied had intact autoregulation at the outset. We also tried to avoid testing during peaks of surgical stimulation; however, there still may have been differences in CBFV from surgical stimulation, since sensory stimulation in the periphery is associated with an increase in CBF in the contralateral hemisphere.18 Data analysis from our bilateral recordings, however, did not reveal marked side-to-side differences. Moreover, we also allowed a period of stable velocity before proceeding with the study.
Second, the concomitant drugs that were used during the induction and maintenance of anesthesia and to maintain or raise ABP are very unlikely to affect any aspect of CA. Fentanyl19 and nitrous oxide12 are not known to cause impairment of autoregulation. Additionally, if these agents had an effect on CA, one would expect this to affect both static and dynamic CA, although a differential effect could theoretically occur. Phenylephrine, which was used not only to raise ABP for static testing but also to maintain it in the respective desired range, could interfere with CA measurements if it had a direct vasoconstrictive effect on cerebral resistance vessels or the MCA. It was shown, however, by 133Xe CBF measurements that intracarotid application of epinephrine or norepinephrine does not influence regional CBF in humans, nor do these drugs change the diameter of the larger arteries as shown by angiography.20 In another study it was demonstrated that phenylephrine is able to increase CBF after hemorrhage during isoflurane anesthesia in rats, again suggesting that there is no relevant vasoconstriction of cerebral resistance vessels.21
The use of TCD for CBF measurements also must be addressed. A constant diameter of the insonated vessel, ie, the MCA, is required during the autoregulation test to interpret relative changes in CBFV as relative CBF changes.7 There is, however, considerable evidence that the MCA diameter remains practically constant during different autoregulation tests. It has been demonstrated by simultaneous comparison of CBFV measurements of cerebral arterial inflow and venous return9 and also by direct correlation with electromagnetic flowmetry8 10 that MCA velocity measurements during dynamic autoregulation reflect relative changes in blood flow. Moreover, it has been demonstrated recently that CBF measurements using xenon washout and the Fick principle11 correlated closely with changes in CBFV. Additional evidence for this assumption is derived from experiments in which direct visualization of the MCA during craniotomy revealed no significant change in vessel caliber during changes in ABP.22 The TCD method therefore appears to be a valid tool to evaluate both dynamic and static CA.
Static and dynamic testing of autoregulation may assess some different aspects of the cerebral response to changes in ABP. Autoregulation has been found to be a complex phenomenon, showing heterogeneity in its site and time course of action.23 24 25 Since metabolic, myogenic, and possibly endothelium-related mechanisms may be involved,2 3 24 26 27 28 several factors may vary depending on the challenging stimulus, the vessel tone, or the degree of impairment of CA. During static testing, our stimulus consisted of an increase in ABP, which should induce vasoconstriction of the resistance vessels to account for the autoregulatory response. During dynamic testing, ABP is lowered, which should lead to vasodilation of the arterioles. Vasoconstriction and vasodilation, however, could depend on different mechanisms of action, which could vary individually or could be affected to a different extent if autoregulation is impaired. Even if the underlying mechanism was the same, it could be hypothesized that the abilities to dilate or constrict the cerebral arterioles may show some normal variability within individuals, which could lead to a less exact correlation if the two methods were compared at intact autoregulation alone.
The vascular tone at the time of testing may affect the autoregulatory response. Aaslid et al6 have shown that hypocapnia (leading to an increase in vascular tone) enhances dynamic CA, whereas hypercapnia (causing a decrease in vascular tone) reduces the autoregulatory response. Improvement of impaired static CA with hyperventilation has been reported in patients with focal brain lesions, suggesting that the efficiency of static CA also depends on vascular tone.29 Isoflurane has some intrinsic vasodilatory effect on cerebral arterioles, whereas propofol has vasoconstrictive properties.30 31 32 This is the reason for the significant difference in CBFV between the propofol and the isoflurane series. Therefore, it is likely that the vascular tone differed between both series.
The overall correlation between the two methods was good despite these considerations, suggesting that the different aspects of autoregulation respond similarly in intact as well as in severely pharmacologically impaired autoregulatory capacity. Autoregulation, however, is not an "all or none" phenomenon.25 33 34 35 Since the ability to autoregulate was almost abolished by the selected dose of isoflurane in most of our patients, the possibility remains that some aspect of autoregulation is affected first if minor impairment occurs. It seems likely, for example, that dynamic CA is initially more reduced than static CA if impairment of the autoregulatory process affects first the latency of CA and then its efficiency. Furthermore, our study cannot answer whether different mechanisms of impairment of autoregulation (eg, intracranial pathology) would lead to different results or whether the correlation would be as close in elderly subjects.
For clinical purposes, however, it seems to be fair to assume that dynamic testing reflects most aspects of the autoregulatory response correctly. Thus, evaluation of dynamic CA by TCD may be useful for patient management. A variety of pathological conditions including brain trauma, subarachnoid hemorrhage, and focal ischemia affect the autoregulatory abilities to a variable extent.25 33 34 35 Since in severely impaired CA the brain is obviously no longer protected from the effects of both hyperperfusion and hypotension, and the effect of important drugs (eg, mannitol36 ) might be dependent on intact CA, routine assessment of CA may add useful information in severe cerebral disease. Further studies are needed to determine the role of autoregulation testing in the clinical management of patients with conditions that lead to CA impairment.
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Acknowledgments |
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This work was supported through clinical investigator development award IK-015969, National Institutes of Health grant IP-50 NS-30305-01 (D.W.N.), and a grant of the Freunde und Förderer des Klinikum Großhadern e.V. (F.P.T.). The authors would like to thank all the volunteers for their participation in the study.
The effect of the cerebral autoregulation on mean velocity (mV) was approximated by a second-order linear differential equation set with state variables x1 and x2, which were assumed to be equal to 0 during the control period. After the step in ABP, these equations were solved by the computer in steps of 100 milliseconds (sampling rate, f=10 Hz) by the algorithm
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where dP is the normalized change in mean arterial blood
pressure (MABP) from its control value (cABP), including the effect of
the critical closing pressure (CCP), which was assumed to be constant
at 12 mm Hg in the present study. (This parameter can later be
estimated individually.) MABP was obtained by filtering the pulsatile
ABP at 0.5 Hz. cVmca is control velocity in the MCA. The control values
were obtained as explained in "Methods." This mathematical model
was characterized by three parameters: T, the time constant; D, the
damping factor; and K, the autoregulatory dynamic gain. These
parameters were related to the dynamic autoregulatory index and to the
dynamic rate of regulation as shown in Table 3. Figure 4 illustrates
autoregulatory responses according to the
model.
Received December 27, 1994; revision received March 3, 1995; accepted March 3, 1995.
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 M. Czosnyka, P. Smielewski, A. Lavinio, J. D. Pickard, and R. Panerai An Assessment of Dynamic Autoregulation from Spontaneous Fluctuations of Cerebral Blood Flow Velocity: A Comparison of Two Models, Index of Autoregulation and Mean Flow Index Anesth. Analg., January 1, 2008; 106(1): 234 - 239. [Abstract] [Full Text] [PDF]
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I. K. Moppett and J. G. Hardman Development and Validation of an Integrated Computational Model of Cerebral Blood Flow and Oxygenation Anesth. Analg., October 1, 2007; 105(4): 1094 - 1103. [Abstract] [Full Text] [PDF]
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G. F. A. Jansen, A. Krins, B. Basnyat, J. A. Odoom, and C. Ince Role of the altitude level on cerebral autoregulation in residents at high altitude J Appl Physiol, August 1, 2007; 103(2): 518 - 523. [Abstract] [Full Text] [PDF]
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E. L. Sammons, N. J. Samani, S. M. Smith, W. E. Rathbone, S. Bentley, J. F. Potter, and R. B. Panerai Influence of noninvasive peripheral arterial blood pressure measurements on assessment of dynamic cerebral autoregulation J Appl Physiol, July 1, 2007; 103(1): 369 - 375. [Abstract] [Full Text] [PDF]
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 Y.-S. Kim, R. Krogh-Madsen, P. Rasmussen, P. Plomgaard, S. Ogoh, N. H. Secher, and J. J. van Lieshout Effects of hyperglycemia on the cerebrovascular response to rhythmic handgrip exercise Am J Physiol Heart Circ Physiol, July 1, 2007; 293(1): H467 - H473. [Abstract] [Full Text] [PDF]
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M. Ichinose, S. Koga, N. Fujii, N. Kondo, and T. Nishiyasu Modulation of the spontaneous beat-to-beat fluctuations in peripheral vascular resistance during activation of muscle metaboreflex Am J Physiol Heart Circ Physiol, July 1, 2007; 293(1): H416 - H424. [Abstract] [Full Text] [PDF]
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 P. N. Ainslie, C. Murrell, K. Peebles, M. Swart, M. A. Skinner, M. J. A. Williams, and R. D. Taylor Early morning impairment in cerebral autoregulation and cerebrovascular CO2 reactivity in healthy humans: relation to endothelial function Exp Physiol, July 1, 2007; 92(4): 769 - 777. [Abstract] [Full Text] [PDF]
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 R. Aaslid, M. Blaha, G. Sviri, C. M. Douville, and D. W. Newell Asymmetric Dynamic Cerebral Autoregulatory Response to Cyclic Stimuli Stroke, May 1, 2007; 38(5): 1465 - 1469. [Abstract] [Full Text] [PDF]
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 N. Tontisirin, S. L. Muangman, P. Suz, C. Pihoker, D. Fisk, A. Moore, A. M. Lam, and M. S. Vavilala Early Childhood Gender Differences in Anterior and Posterior Cerebral Blood Flow Velocity and Autoregulation Pediatrics, March 1, 2007; 119(3): e610 - e615. [Abstract] [Full Text] [PDF]
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L. A. Steiner and P. J. D. Andrews Monitoring the injured brain: ICP and CBF Br. J. Anaesth., July 1, 2006; 97(1): 26 - 38. [Abstract] [Full Text] [PDF]
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R. B. Panerai, M. Moody, P. J. Eames, and J. F. Potter Cerebral blood flow velocity during mental activation: interpretation with different models of the passive pressure-velocity relationship J Appl Physiol, December 1, 2005; 99(6): 2352 - 2362. [Abstract] [Full Text] [PDF]
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R. V. Immink, G. A. van Montfrans, J. Stam, J. M. Karemaker, M. Diamant, and J. J. van Lieshout Dynamic Cerebral Autoregulation in Acute Lacunar and Middle Cerebral Artery Territory Ischemic Stroke Stroke, December 1, 2005; 36(12): 2595 - 2600. [Abstract] [Full Text] [PDF]
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 F. A. Sorond, R. Khavari, J. M. Serrador, and L. A. Lipsitz Regional Cerebral Autoregulation During Orthostatic Stress: Age-Related Differences J. Gerontol. A Biol. Sci. Med. Sci., November 1, 2005; 60(11): 1484 - 1487. [Abstract] [Full Text] [PDF]
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M. S. Olufsen, J. T. Ottesen, H. T. Tran, L. M. Ellwein, L. A. Lipsitz, and V. Novak Blood pressure and blood flow variation during postural change from sitting to standing: model development and validation J Appl Physiol, October 1, 2005; 99(4): 1523 - 1537. [Abstract] [Full Text] [PDF]
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R. B. Panerai, M. Moody, P. J. Eames, and J. F. Potter Dynamic cerebral autoregulation during brain activation paradigms Am J Physiol Heart Circ Physiol, September 1, 2005; 289(3): H1202 - H1208. [Abstract] [Full Text] [PDF]
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S. Preisman, R. Marks, O. Nahtomi-Shick, and A. Sidi Preservation of static and dynamic cerebral autoregulation after mild hypothermic cardiopulmonary bypass Br. J. Anaesth., August 1, 2005; 95(2): 207 - 211. [Abstract] [Full Text] [PDF]
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M. Reinhard, M. Roth, B. Guschlbauer, A. Harloff, J. Timmer, M. Czosnyka, and A. Hetzel Dynamic Cerebral Autoregulation in Acute Ischemic Stroke Assessed From Spontaneous Blood Pressure Fluctuations Stroke, August 1, 2005; 36(8): 1684 - 1689. [Abstract] [Full Text] [PDF]
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T. J. McCulloch, T. W. Boesel, and A. M. Lam The Effect of Hypocapnia on the Autoregulation of Cerebral Blood Flow During Administration of Isoflurane Anesth. Analg., May 1, 2005; 100(5): 1463 - 1467. [Abstract] [Full Text] [PDF]
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A. Van Osta, J.-J. Moraine, C. Melot, H. Mairbaurl, M. Maggiorini, and R. Naeije Effects of High Altitude Exposure on Cerebral Hemodynamics in Normal Subjects Stroke, March 1, 2005; 36(3): 557 - 560. [Abstract] [Full Text] [PDF]
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S. Ogoh, M. K. Dalsgaard, C. C. Yoshiga, E. A. Dawson, D. M. Keller, P. B. Raven, and N. H. Secher Dynamic cerebral autoregulation during exhaustive exercise in humans Am J Physiol Heart Circ Physiol, March 1, 2005; 288(3): H1461 - H1467. [Abstract] [Full Text] [PDF]
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 J. Kolodjaschna, F. Berisha, S. Lung, H. Schima, E. Polska, and L. Schmetterer Comparison of the Autoregulatory Mechanisms between Middle Cerebral Artery and Ophthalmic Artery after Thigh Cuff Deflation in Healthy Subjects Invest. Ophthalmol. Vis. Sci., February 1, 2005; 46(2): 636 - 640. [Abstract] [Full Text] [PDF]
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L. A. Lipsitz, M. Gagnon, M. Vyas, I. Iloputaife, D. K. Kiely, F. Sorond, J. Serrador, D. M. Cheng, V. Babikian, and L. A. Cupples Antihypertensive Therapy Increases Cerebral Blood Flow and Carotid Distensibility in Hypertensive Elderly Subjects Hypertension, February 1, 2005; 45(2): 216 - 221. [Abstract] [Full Text] [PDF]
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J. M. Serrador, F. A. Sorond, M. Vyas, M. Gagnon, I. D. Iloputaife, and L. A. Lipsitz Cerebral pressure-flow relations in hypertensive elderly humans: transfer gain in different frequency domains J Appl Physiol, January 1, 2005; 98(1): 151 - 159. [Abstract] [Full Text] [PDF]
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I. K. Moppett and R. P. Mahajan Transcranial Doppler ultrasonography in anaesthesia and intensive care Br. J. Anaesth., November 1, 2004; 93(5): 710 - 724. [Full Text] [PDF]
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 R. V. Immink, B.-J. H. van den Born, G. A. van Montfrans, R. P. Koopmans, J. M. Karemaker, and J. J. van Lieshout Impaired Cerebral Autoregulation in Patients With Malignant Hypertension Circulation, October 12, 2004; 110(15): 2241 - 2245. [Abstract] [Full Text] [PDF]
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M. R. Edwards, D. L. Devitt, and R. L. Hughson Two-breath CO2 test detects altered dynamic cerebrovascular autoregulation and CO2 responsiveness with changes in arterial PCO2 Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2004; 287(3): R627 - R632. [Abstract] [Full Text] [PDF]
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D. D. O'Leary, J. K. Shoemaker, M. R. Edwards, and R. L. Hughson Spontaneous beat-by-beat fluctuations of total peripheral and cerebrovascular resistance in response to tilt Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2004; 287(3): R670 - R679. [Abstract] [Full Text] [PDF]
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K. Moller, T. Qvist, F. Tofteng, C. Sahl, S. Sonderkaer, T. Dethloff, G. M. Knudsen, and F. S. Larsen Cerebral Blood Flow and Metabolism During Infusion of Norepinephrine and Propofol in Patients With Bacterial Meningitis Stroke, June 1, 2004; 35(6): 1333 - 1339. [Abstract] [Full Text] [PDF]
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C. Haubrich, A. Wendt, R.R. Diehl, and C. Klotzsch Dynamic Autoregulation Testing in the Posterior Cerebral Artery Stroke, April 1, 2004; 35(4): 848 - 852. [Abstract] [Full Text] [PDF]
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H S Markus Cerebral perfusion and stroke J. Neurol. Neurosurg. Psychiatry, March 1, 2004; 75(3): 353 - 361. [Abstract] [Full Text] [PDF]
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 E. Neri, C. Sassi, L. Barabesi, M. Massetti, G. Pula, D. Buklas, R. Tassi, and P. Giomarelli Cerebral autoregulation after hypothermic circulatory arrest in operations on the aortic arch Ann. Thorac. Surg., January 1, 2004; 77(1): 72 - 79. [Abstract] [Full Text] [PDF]
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 G.ón Albina, L.ía Fernandez Cisneros, R.én Laiño, U. L Nobo, D. Ortega, E. Schwarz, L. Barja, R. Lagos, A. Giniger, and S.án F Ameriso Transcranial Doppler monitoring during head upright tilt table testing in patients with suspected neurocardiogenic syncope Europace, January 1, 2004; 6(1): 63 - 69. [Abstract] [Full Text] [PDF]
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L. A. Steiner, J. P. Coles, A. J. Johnston, D. A. Chatfield, P. Smielewski, T. D. Fryer, F. I. Aigbirhio, J. C. Clark, J. D. Pickard, D. K. Menon, et al. Assessment of Cerebrovascular Autoregulation in Head-Injured Patients: A Validation Study Stroke, October 1, 2003; 34(10): 2404 - 2409. [Abstract] [Full Text] [PDF]
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C. Haubrich, W. Kruska, R.R. Diehl, W. Moller-Hartmann, and C. Klotzsch Dynamic Autoregulation Testing in Patients With Middle Cerebral Artery Stenosis Stroke, August 1, 2003; 34(8): 1881 - 1885. [Abstract] [Full Text] [PDF]
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B. J. Carey, R. B. Panerai, and J. F. Potter Effect of Aging on Dynamic Cerebral Autoregulation During Head-Up Tilt Stroke, August 1, 2003; 34(8): 1871 - 1875. [Abstract] [Full Text] [PDF]
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A. J. Johnston, M. Czosnyka, D. Georgiadis, R.W. Baumgartner, S. Schwarz, D.H. Evans, and S. Schwab Measuring Cerebral Autoregulation in Stroke Patients * Response Stroke, June 1, 2003; 34 (6): e39 - e40. [Full Text] [PDF]
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M. S. Vavilala, L. A. Lee, M. Lee, A. Graham, E. Visco, and A. M. Lam Cerebral autoregulation in children during sevoflurane anaesthesia{dagger} Br. J. Anaesth., May 1, 2003; 90(5): 636 - 641. [Abstract] [Full Text] [PDF]
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M. Muller, O. Bianchi, S. Erulku, C. Stock, and K. Schwerdtfeger Changes in Linear Dynamics of Cerebrovascular System After Severe Traumatic Brain Injury Stroke, May 1, 2003; 34(5): 1197 - 1202. [Abstract] [Full Text] [PDF]
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J. J. Van Lieshout, W. Wieling, J. M. Karemaker, and N. H. Secher Syncope, cerebral perfusion, and oxygenation J Appl Physiol, March 1, 2003; 94(3): 833 - 848. [Abstract] [Full Text] [PDF]
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M. R. Edwards, Z. L. Topor, and R. L. Hughson A new two-breath technique for extracting the cerebrovascular response to arterial carbon dioxide Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2003; 284(3): R853 - R859. [Abstract] [Full Text] [PDF]
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B. Rosengarten, S. Osthaus, D. Auch, and M. Kaps Effects of Acute Hyperhomocysteinemia on the Neurovascular Coupling Mechanism in Healthy Young Adults Stroke, February 1, 2003; 34(2): 446 - 451. [Abstract] [Full Text] [PDF]
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C. W. Park, M. Sturzenegger, C. M. Douville, R. Aaslid, and D. W. Newell Autoregulatory Response and CO2 Reactivity of the Basilar Artery Stroke, January 1, 2003; 34(1): 34 - 39. [Abstract] [Full Text] [PDF]
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D. Georgiadis, S. Schwarz, D.H. Evans, S. Schwab, and R.W. Baumgartner Cerebral Autoregulation Under Moderate Hypothermia in Patients With Acute Stroke Stroke, December 1, 2002; 33(12): 3026 - 3029. [Abstract] [Full Text] [PDF]
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K. Nagase, K. Ando-Nagase, and H. Endoh To Cite or Not to Cite * Response Anesth. Analg., October 1, 2002; 95(4): 1127 - 1128. [Full Text] [PDF]
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M. R. Edwards, J. K. Shoemaker, and R. L. Hughson Dynamic modulation of cerebrovascular resistance as an index of autoregulation under tilt and controlled PETCO2 Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2002; 283(3): R653 - R662. [Abstract] [Full Text] [PDF]
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E W Lang, H M Mehdorn, N W C Dorsch, and M Czosnyka Continuous monitoring of cerebrovascular autoregulation: a validation study J. Neurol. Neurosurg. Psychiatry, May 1, 2002; 72(5): 583 - 586. [Abstract] [Full Text] [PDF]
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P J Eames, M J Blake, S L Dawson, R B Panerai, and J F Potter Dynamic cerebral autoregulation and beat to beat blood pressure control are impaired in acute ischaemic stroke J. Neurol. Neurosurg. Psychiatry, April 1, 2002; 72(4): 467 - 472. [Abstract] [Full Text] [PDF]
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H. Endoh, T. Honda, S. Ohashi, S. Hida, C. Shibue, and N. Komura The Influence of Nicardipine-, Nitroglycerin-, and Prostaglandin E1-Induced Hypotension on Cerebral Pressure Autoregulation in Adult Patients During Propofol-Fentanyl Anesthesia Anesth. Analg., January 1, 2002; 94(1): 169 - 173. [Abstract] [Full Text] [PDF]
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R. Schondorf, R. Stein, R. Roberts, J. Benoit, and W. Cupples Dynamic cerebral autoregulation is preserved in neurally mediated syncope J Appl Physiol, December 1, 2001; 91(6): 2493 - 2502. [Abstract] [Full Text] [PDF]
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R. L. Hughson, M. R. Edwards, D. D. O'Leary, and J. K. Shoemaker Critical Analysis of Cerebrovascular Autoregulation During Repeated Head-Up Tilt Stroke, October 1, 2001; 32(10): 2403 - 2408. [Abstract] [Full Text] [PDF]
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B. J. Carey, B. N. Manktelow, R. B. Panerai, and J. F. Potter Cerebral Autoregulatory Responses to Head-Up Tilt in Normal Subjects and Patients With Recurrent Vasovagal Syncope Circulation, August 21, 2001; 104(8): 898 - 902. [Abstract] [Full Text] [PDF]
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J. Sato, M. Tachibana, T. Numata, T. Nishino, and A. Konno Differences in the dynamic cerebrovascular response between stepwise up tilt and down tilt in humans Am J Physiol Heart Circ Physiol, August 1, 2001; 281(2): H774 - H783. [Abstract] [Full Text] [PDF]
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R. K. Tibble, K. J. Girling, and R. P. Mahajan A Comparison of the Transient Hyperemic Response Test and the Static Autoregulation Test to Assess Graded Impairment in Cerebral Autoregulation During Propofol, Desflurane, and Nitrous Oxide Anesthesia Anesth. Analg., July 1, 2001; 93(1): 171 - 176. [Abstract] [Full Text] [PDF]
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R. B. Panerai, S. L. Dawson, P. J. Eames, and J. F. Potter Cerebral blood flow velocity response to induced and spontaneous sudden changes in arterial blood pressure Am J Physiol Heart Circ Physiol, May 1, 2001; 280(5): H2162 - H2174. [Abstract] [Full Text] [PDF]
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B. J. Carey, P. J. Eames, M. J. Blake, R. B. Panerai, and J. F. Potter Dynamic Cerebral Autoregulation Is Unaffected by Aging Stroke, December 1, 2000; 31(12): 2895 - 2900. [Abstract] [Full Text] [PDF]
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M. Ursino, A. Ter Minassian, C. A. Lodi, and L. Beydon Cerebral hemodynamics during arterial and CO2 pressure changes: in vivo prediction by a mathematical model Am J Physiol Heart Circ Physiol, November 1, 2000; 279(5): H2439 - H2455. [Abstract] [Full Text] [PDF]
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G. F. A. Jansen, A. Krins, B. Basnyat, A. Bosch, and J. A. Odoom Cerebral Autoregulation in Subjects Adapted and Not Adapted to High Altitude Stroke, October 1, 2000; 31(10): 2314 - 2318. [Abstract] [Full Text] [PDF]
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H. Endoh, T. Honda, N. Komura, C. Shibue, I. Watanabe, and K. Shimoji The Effects of Nicardipine on Dynamic Cerebral Autoregulation in Patients Anesthetized with Propofol and Fentanyl Anesth. Analg., September 1, 2000; 91(3): 642 - 646. [Abstract] [Full Text] [PDF]
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P. J. Mahony, R. B. Panerai, S. T. Deverson, P. D. Hayes, and D. H. Evans Assessment of the Thigh Cuff Technique for Measurement of Dynamic Cerebral Autoregulation Stroke, February 1, 2000; 31(2): 476 - 480. [Abstract] [Full Text] [PDF]
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 R Y T Sung, Z D Du, C W Yu, M C Yam, and T F Fok Cerebral blood flow during vasovagal syncope induced by active standing or head up tilt Arch. Dis. Child., February 1, 2000; 82(2): 154 - 158. [Abstract] [Full Text]
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R. B. Panerai, S. L. Dawson, and J. F. Potter Linear and nonlinear analysis of human dynamic cerebral autoregulation Am J Physiol Heart Circ Physiol, September 1, 1999; 277(3): H1089 - H1099. [Abstract] [Full Text] [PDF]
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A.E. Baird, S. Warach, K. W. Muir, and D. G. Grosset Using Pathophysiology in Acute Stroke Trials Response Stroke, June 1, 1999; 30(6): 1293 - 1293. [Full Text] [PDF]
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R. B. Panerai, D. H. Evans, A. R. Naylor, A. Hetzel, K. Kempf, and S. Braune Influence of Arterial Blood Pressure on Cerebrovascular Reactivity Response Stroke, June 1, 1999; 30 (6): 1293 - 1295. [Full Text]
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A. C. Summors, A. K. Gupta, and B. F. Matta Dynamic Cerebral Autoregulation During Sevoflurane Anesthesia: A Comparison with Isoflurane Anesth. Analg., February 1, 1999; 88(2): 341 - 341. [Abstract] [Full Text] [PDF]
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R. P. Mahajan and S.-E. Ricksten The Effects of Propofol on Cerebral Blood Flow Velocity and Cerebral Oxygen Extraction During Cardiopulmonary Bypass • Response Anesth. Analg., January 1, 1999; 88(1): 231 - 232. [Full Text] [PDF]
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R. B. Panerai, R. P. White, H. S. Markus, and D. H. Evans Grading of Cerebral Dynamic Autoregulation From Spontaneous Fluctuations in Arterial Blood Pressure Stroke, November 1, 1998; 29(11): 2341 - 2346. [Abstract] [Full Text] [PDF]
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E. M. Manno, D. R. Gress, L. H. Schwamm, M. N. Diringer, and C. S. Ogilvy Effects of Induced Hypertension on Transcranial Doppler Ultrasound Velocities in Patients After Subarachnoid Hemorrhage Stroke, February 1, 1998; 29(2): 422 - 428. [Abstract] [Full Text] [PDF]
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R. Zhang, J. H. Zuckerman, C. A. Giller, and B. D. Levine Transfer function analysis of dynamic cerebral autoregulation in humans Am J Physiol Heart Circ Physiol, January 1, 1998; 274(1): H233 - H241. [Abstract] [Full Text] [PDF]
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A. P. Blaber, R. L. Bondar, F. Stein, P. T. Dunphy, P. Moradshahi, M. S. Kassam, and R. Freeman Transfer Function Analysis of Cerebral Autoregulation Dynamics in Autonomic Failure Patients Stroke, September 1, 1997; 28(9): 1686 - 1692. [Abstract] [Full Text]
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R. Schondorf, J. Benoit, and T. Wein Cerebrovascular and Cardiovascular Measurements During Neurally Mediated Syncope Induced by Head-Up Tilt Stroke, August 1, 1997; 28(8): 1564 - 1568. [Abstract] [Full Text]
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R. P. White and H. S. Markus Impaired Dynamic Cerebral Autoregulation in Carotid Artery Stenosis Stroke, July 1, 1997; 28(7): 1340 - 1344. [Abstract] [Full Text]
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S. Cencetti, G. Bandinelli, and A. Lagi Effect of Pco2 Changes Induced by Head-Upright Tilt on Transcranial Doppler Recordings Stroke, June 1, 1997; 28(6): 1195 - 1197. [Abstract] [Full Text]
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P. Smielewski, M. Czosnyka, P. Kirkpatrick, H. McEroy, H. Rutkowska, and J. D. Pickard Assessment of Cerebral Autoregulation Using Carotid Artery Compression Stroke, December 1, 1996; 27(12): 2197 - 2203. [Abstract] [Full Text]
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F. P. Tiecks, C. Douville, S. Byrd, A. M. Lam, and D. W. Newell Evaluation of Impaired Cerebral Autoregulation by the Valsalva Maneuver Stroke, July 1, 1996; 27(7): 1177 - 1182. [Abstract] [Full Text]
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