Dynamic pressure-flow relationships of brain blood flow in the monkey

Early, Calvin B.; Dewey, Richard C.; Pieper, Heinz P.; Hunt, William E.

doi:10.3171/jns.1974.41.5.0590

Cited by 43 publications

(21 citation statements)

References 10 publications

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“…However, when dynamic measurement techniques are used, such as electromagnetic flowmetry or ultrasound Doppler, the limitations of this concept become manifest. 1,2 Dynamically, flow may stop at pressure levels significantly higher than zero. The arterial blood pressure (ABP) level at which flow stops is defined as the critical closing pressure (CCP) [1][2][3] or, in cardiac literature, the zero-flow pressure (P fϭ0 ).…”

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confidence: 99%

“…1,2 Dynamically, flow may stop at pressure levels significantly higher than zero. The arterial blood pressure (ABP) level at which flow stops is defined as the critical closing pressure (CCP) [1][2][3] or, in cardiac literature, the zero-flow pressure (P fϭ0 ). 4 Above the CCP, an approximately linear slope, sometimes referred to as the inverse flow resistance, defines the relation between pressure and flow, when these variables are plotted as an x-y function 1,2 ( Figure 1).…”

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confidence: 99%

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Dynamic Pressure–Flow Velocity Relationships in the Human Cerebral Circulation

Aaslid

Lash

Bardy

et al. 2003

Stroke

112

133

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Background and Purpose-The pressure-flow velocity relationship in the cerebral circulation is characterized by the critical closing pressure (CCP), which is the pressure at which flow ceases, and the linear slope of a plot between pressure and flow velocity. It has been suggested, but not validated, that CCP can be determined from arterial blood pressure (ABP) and transcranial Doppler (TCD) recordings during the cardiac cycle. We studied a group of patients in whom ventricular fibrillation (VF) was induced. The time interval before defibrillation enabled calculation of CCP from data in which flow approached zero. These estimates were compared with values calculated before and after fibrillation and during regular heartbeats. Methods-TCD velocities and ABP in the radial artery were recorded before, during, and after 28 episodes of VF in 13 patients. CCPs were calculated by 3 different methods: (1) linear extrapolation from data during VF (gold standard); (2) linear extrapolation from normal heartbeat data; and (3) first harmonic Fourier filtering of normal heartbeat data. Results-The CCP during VF calculated from long diastoles was 32.9Ϯ11 mm Hg (meanϮSD). The regular heartbeat estimate was 6.0Ϯ4.3 mm Hg lower (PϽ0.05). The CCP estimate with the use of a Fourier filter was 1.4Ϯ3.9 mm Hg (PϭNS) lower than during VF. During hyperemia after defibrillation, the CCP decreased by 13.3 mm Hg, while velocity increased by 63%. The decrease in CCP could explain half of the increase in flow velocity during hyperemia. Conclusions-CCP can be accurately estimated from regular heartbeat data and is an important factor in regulation of the cerebral circulation. Key Words: cerebrovascular circulation Ⅲ ultrasonography, Doppler, transcranial Ⅲ vasoreactivity T he classic concept defining cerebrovascular tone is cerebral vascular resistance. This concept was developed from cerebral blood flow (CBF) determinations with the use of indicator methods such as nitrous oxide or 133 Xe. Basically this concept assumes that perfusion pressure and flow are linearly and proportionally related. It follows that flow stops only when the perfusion pressure is zero. However, when dynamic measurement techniques are used, such as electromagnetic flowmetry or ultrasound Doppler, the limitations of this concept become manifest. 1,2 Dynamically, flow may stop at pressure levels significantly higher than zero. The arterial blood pressure (ABP) level at which flow stops is defined as the critical closing pressure (CCP) 1-3 or, in cardiac literature, the zero-flow pressure (P fϭ0 ). 4 Above the CCP, an approximately linear slope, sometimes referred to as the inverse flow resistance, defines the relation between pressure and flow, when these variables are plotted as an x-y function 1,2 ( Figure 1). It follows that flow is linearly (but not proportionally) related to pressure and that it can be regulated by changes in both CCP (the x intercept) and slope. The pressure-flow relation is mainly a function of the peripheral resistance cerebral vascular bed. It...

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confidence: 99%

Dynamic Pressure–Flow Velocity Relationships in the Human Cerebral Circulation

Aaslid

Lash

Bardy

et al. 2003

Stroke

112

133

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“…[2][3][4][5][6][7] When large pneumatic cuffs placed around both thighs are inflated above systolic pressure for Ն2 minutes and then suddenly released, a sharp drop in ABP is usually observed, lasting Ϸ10 seconds before returning to its original level. A simultaneous drop in cerebral blood flow velocity (CBFV), usually estimated with Doppler ultrasound, 8 accompanies the fall in ABP.…”

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confidence: 99%

Assessment of the Thigh Cuff Technique for Measurement of Dynamic Cerebral Autoregulation

Mahony

Panerai

Deverson

et al. 2000

Stroke

108

113

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Background and Purpose-Dynamic methods of measuring cerebral autoregulation have become an accepted alternative to static evaluation. This article aims to describe a set of data collected from healthy volunteers by a dynamic method, the purpose being to qualify and quantify expected results for those who may be designing a study using this technique. Methods-Cerebral blood flow velocity (CBFV) (measured by transcranial Doppler) and arterial blood pressure (Finapres) were recorded in 16 normal subjects before, during, and after the induction of a blood pressure drop (release of bilateral thigh cuffs). This procedure was repeated 6 times for each subject. A mathematical model was applied to the data to generate an autoregulatory index (ARI) with values between 0 and 9. Results-The ARI values for this sample population follow a normal distribution, with a meanϮSD of 4.98Ϯ1.06 (nϭ15).Analysis of the cumulative mean ARI values of all subjects showed an exponential-type convergence of ARI toward the sample mean as the number of test iterations increased. The population average blood pressure drop on thigh cuff release was 26.4Ϯ7.1 mm Hg (nϭ16), occurring in 4.6Ϯ1.7 seconds. The corresponding population average drop for CBFV was 15.6Ϯ5.8 cm/s, taking 2.5Ϯ1.0 seconds. No significant trend was noted in the measurements as the number of test iterations increased. The correlation between the predicted and actual CBFV, having a mean value of 0.76Ϯ0.19, showed evidence of a nonlinear relationship to ARI values. Significant correlation was also found between ARI and (1) arterial blood pressure before cuff release and (2)

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“…The inflow pressure at which flow reaches zero is called the critical closing pressure (CrCP) [3, 4]. Dewey et al [5 ]and Early et al [6 ]demonstrated in monkeys that CrCP is the primary variable affecting cerebral blood flow. They also identified vasomotor tone and ICP as the main determinants of CrCP.…”

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confidence: 99%

Comparison of Critical Closing Pressures Extracted from Carotid Tonometry and Finger Plethysmography

et al. 2005

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Background: The reliability of critical closing pressure (CrCP) estimates derived from peripheral blood pressure (BP) measurements is unclear. We attempted to evaluate the influences of peripheral circulation on determining CrCP. Methods: Twenty-five young healthy volunteers were studied. BP waves were obtained with plethysmography (Portapres) and carotid applanatory tonometry, respectively, for analysis. Transcranial Doppler was used to monitor cerebral flow velocity. Using linear regression analysis, beat-to-beat CrCP was calculated at rest, during voluntary hyperventilation and during 5% CO₂ inhalation. Results: Twenty of 25 participants demonstrating satisfactory tonometric tracings for both tests were included in the analysis. The systolic BP measured using plethysmography was higher than that derived from tonometry (139.4 ± 24.7 vs. 105.5 ± 29.6, p < 0.001). CrCP values derived from tonometry were all positive and higher than CrCP values derived from plethysmography (62.9 ± 19.9 vs. 11.1 ± 17.8, p < 0.001). The changes in CrCP induced by 5% CO₂ inhalation and hyperventilation had a correlation between two BP monitoring methods (r = 0.52, p = 0.001). Conclusions: Pressure waveform is an important determinant in calculating CrCP by linear regression analysis. The relative changes in CrCP induced by hemodynamic challenges remained a relevant indicator of cerebrovascular regulation regardless of the methods used for non-invasive BP recording.

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Dynamic pressure-flow relationships of brain blood flow in the monkey

Cited by 43 publications

References 10 publications

Dynamic Pressure–Flow Velocity Relationships in the Human Cerebral Circulation

Dynamic Pressure–Flow Velocity Relationships in the Human Cerebral Circulation

Assessment of the Thigh Cuff Technique for Measurement of Dynamic Cerebral Autoregulation

Comparison of Critical Closing Pressures Extracted from Carotid Tonometry and Finger Plethysmography

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