Critical closing pressure during experimental intracranial hypertension: comparison of three calculation methods.

: The critical closing pressure (CrCP) defines arterial blood pressure below which cerebral arteries collapse. It represents a clinically relevant parameter for the estimation of cerebrovascular tone. Although there are few methods to assess CrCP, there is no consensus which of them estimates this parameter most accurately.

Effect of Mild Hypocapnia on Critical Closing Pressure and Other Mechanoelastic Parameters of the Cerebrospinal System.

Objective: Brain arterial critical closing pressure (CrCP) has been studied in several diseases such as traumatic brain injury (TBI), subarachnoid haemorrhage, hydrocephalus, and in various physiological scenarios: intracranial hypertension, decreased cerebral perfusion pressure, hypercapnia, etc. Little or nothing so far has been demonstrated to characterise change in CrCP during mild hypocapnia.

Method: We retrospectively analysed recordings of intracranial pressure (ICP), arterial blood pressure (ABP) and blood flow velocity from 27 severe TBI patients (mean 39.

Increased ICP and Its Cerebral Haemodynamic Sequelae.

Objectives: Increased intracranial pressure (ICP) is a pathological feature of many neurological diseases; however, the local and systemic sequelae of raised ICP are incompletely understood. Using an experimental paradigm, we aimed to describe the cerebrovascular consequences of acute increases in ICP.

Materials And Methods: We assessed cerebral haemodynamics [mean arterial blood pressure (MAP), ICP, laser Doppler flowmetry (LDF), basilar artery Doppler flow velocity (Fv) and estimated vascular wall tension (WT)] in 27 basilar artery-dependent rabbits during experimental (artificial lumbar CSF infusion) intracranial hypertension.

Waveform Analysis of Intraspinal Pressure After Traumatic Spinal Cord Injury: An Observational Study (O-64).

Following a traumatic brain injury (TBI), intracranial pressure (ICP) increases, often resulting in secondary brain insults. After a spinal cord injury, here the cord may be swollen, leading to a local increase in intraspinal pressure (ISP). We hypothesised that waveform analysis methodology similar to that used for ICP after TBI may be applicable for the monitoring of patients with spinal cord injury.

The Ontogeny of Cerebrovascular Critical Closing Pressure.

Premature infants are at risk of vascular neurological insults. Hypotension and hypertension are considered injurious, but neither condition is defined with consensus. Critical closing pressure (CrCP) is the arterial blood pressure (ABP) at which cerebral blood flow ceases.

Derangement of Cerebral Blood Flow Autoregulation During Intracranial Pressure Plateau Waves as Detected by Time and Frequency-Based Methods.

Plateau waves are sudden elevations of intracranial pressure (ICP) above 40 mmHg, lasting at least 5 min, and are associated with cerebral vasodilatation. We studied the performance of several parameters for cerebral autoregulation assessment during 30 plateau waves of 24 patients with traumatic brain injury. Continuous signals were collected for ICP, arterial blood pressure (ABP) and transcranial Doppler flow velocity (FV).

Cerebral Critical Closing Pressure During Infusion Tests.

We studied possible correlations between cerebral hemodynamic indices based on critical closing pressure (CrCP) and cerebrospinal fluid (CSF) compensatory dynamics, as assessed during lumbar infusion tests. Our data consisted of 34 patients with normal-pressure hydrocephalus who undertook an infusion test, in conjunction with simultaneous transcranial Doppler ultrasonography (TCD) monitoring of blood flow velocity (FV). CrCP was calculated from the monitored signals of ICP, arterial blood pressure (ABP), and FV, whereas vascular wall tension (WT) was estimated as CrCP - ICP.

Monitoring Cerebral Autoregulation After Subarachnoid Hemorrhage.

Introduction: Delayed cerebral ischemia (DCI) is a major contributor to morbidity and mortality after subarachnoid hemorrhage (SAH). Data challenge vasospasm being the sole cause of ischemia and suggest other factors. We tested the hypothesis that early autoregulatory failure might predict DCI.

The Ontogeny of Cerebrovascular Pressure Autoregulation in Premature Infants.

Our objective was to quantify cerebrovascular autoregulation as a function of gestational age (GA) and across the phases of the cardiac cycle. One hundred eighty-six premature infants, with a GA range of 23-33 weeks, were monitored using umbilical artery catheters and transcranial Doppler insonation of middle cerebral artery flow velocity (FV) for 1-h sessions over the first week of life. Autoregulation was quantified as a moving correlation coefficient between systolic arterial blood pressure (ABP) and systolic FV (Sx); mean ABP and mean FV (Mx); diastolic ABP and diastolic FV (Dx).

The Diastolic Closing Margin Is Associated with Intraventricular Hemorrhage in Premature Infants.

Premature infants are at an increased risk of intraventricular hemorrhage (IVH). The roles of hypotension and hyperemia are still debated. Critical closing pressure (CrCP) is the arterial blood pressure (ABP) at which cerebral blood flow (CBF) ceases.

Elevated Diastolic Closing Margin Is Associated with Intraventricular Hemorrhage in Premature Infants.

Objective: To determine whether the diastolic closing margin (DCM), defined as diastolic blood pressure minus critical closing pressure, is associated with the development of early severe intraventricular hemorrhage (IVH).

Study Design: A reanalysis of prospectively collected data was conducted. Premature infants (gestational age 23-31 weeks) receiving mechanical ventilation (n = 185) had ∼1-hour continuous recordings of umbilical arterial blood pressure, middle cerebral artery cerebral blood flow velocity, and PaCO2 during the first week of life.

Cerebral haemodynamics during experimental intracranial hypertension.

Intracranial hypertension is a common final pathway in many acute neurological conditions. However, the cerebral haemodynamic response to acute intracranial hypertension is poorly understood. We assessed cerebral haemodynamics (arterial blood pressure, intracranial pressure, laser Doppler flowmetry, basilar artery Doppler flow velocity, and vascular wall tension) in 27 basilar artery-dependent rabbits during experimental (artificial CSF infusion) intracranial hypertension.

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.

Intraspinal pressure and spinal cord perfusion pressure after spinal cord injury: an observational study.

Object: In contrast to intracranial pressure (ICP) in traumatic brain injury (TBI), intraspinal pressure (ISP) after traumatic spinal cord injury (TSCI) has not received the same attention in terms of waveform analysis. Based on a recently introduced technique for continuous monitoring of ISP, here the morphological characteristics of ISP are observationally described. It was hypothesized that the waveform analysis method used to assess ICP could be similarly applied to ISP.

Cerebral critical closing pressure in hydrocephalus patients undertaking infusion tests.

Objectives: Links between cerebrospinal fluid (CSF) compensation and cerebral blood flow (CBF) have been studied in many clinical scenarios. In hydrocephalus, disturbed CSF circulation seems to be a primary problem, having been linked to CBF disturbances, particularly in white matter close to surface of dilated ventricles. We studied possible correlations between cerebral haemodynamic indices using transcranial Doppler (TCD) ultrasonography and CSF compensatory dynamics assessed during infusion tests.

Ontogeny of cerebrovascular critical closing pressure.

Background: Premature infants are at risk of vascular neurologic insults. Hypotension and hypertension are considered injurious, but neither condition is defined with consensus. Cerebrovascular critical closing pressure (CrCP) is the arterial blood pressure (ABP) at which cerebral blood flow (CBF) ceases.

A noninvasive estimation of cerebral perfusion pressure using critical closing pressure.

Object: Cerebral blood flow is associated with cerebral perfusion pressure (CPP), which is clinically monitored through arterial blood pressure (ABP) and invasive measurements of intracranial pressure (ICP). Based on critical closing pressure (CrCP), the authors introduce a novel method for a noninvasive estimator of CPP (eCPP).

Methods: Data from 280 head-injured patients with ABP, ICP, and transcranial Doppler ultrasonography measurements were retrospectively examined.

Cerebral vasospasm affects arterial critical closing pressure.

The effect of cerebral vasospasm (CVS) after aneurysmal subarachnoid hemorrhage (SAH) on critical closing pressure (CrCP) has not been fully delineated. Using cerebral impedance methodology, we sought to assess the behavior of CrCP during CVS. As CrCP expresses the sum of intracranial pressure (ICP) and vascular wall tension, we also explored its role in reflecting changes in vascular tone occurring in small vessels distal to spasm.

Comparison of frequency and time domain methods of assessment of cerebral autoregulation in traumatic brain injury.

The impulse response (IR)-based autoregulation index (ARI) allows for continuous monitoring of cerebral autoregulation using spontaneous fluctuations of arterial blood pressure (ABP) and cerebral flow velocity (FV). We compared three methods of autoregulation assessment in 288 traumatic brain injury (TBI) patients managed in the Neurocritical Care Unit: (1) IR-based ARI; (2) transfer function (TF) phase, gain, and coherence; and (3) mean flow index (Mx). Autoregulation index was calculated using the TF estimation (Welch method) and classified according to the original Tiecks' model.

Baroreflex and cerebral autoregulation are inversely correlated.

Background: The relative stability of cerebral blood flow is maintained by the baroreflex and cerebral autoregulation (CA). We assessed the relationship between baroreflex sensitivity (BRS) and CA in patients with atherosclerotic carotid stenosis or occlusion.

Methods And Results: Patients referred for assessment of atherosclerotic unilateral >50% carotid stenosis or occlusion were included.

Increased blood glucose is related to disturbed cerebrovascular pressure reactivity after traumatic brain injury.

Background: Increased blood glucose and impaired pressure reactivity (PRx) after traumatic brain injury (TBI) are both known to correlate with unfavorable patient outcome. However, the relationship between these two variables is unknown.

Methods: To test the hypothesis that increased blood glucose leads to increased PRx, we retrospectively analyzed data from 86 traumatic brain injured patients admitted to the Neurocritical Care Unit.

Bilateral failure of cerebral autoregulation is related to unfavorable outcome after subarachnoid hemorrhage.

Backround: The extent of hemodynamic disturbances following subarachnoid hemorrhage (SAH) varies. We aim to determine the prognostic implications of unilateral and bilateral autoregulatory failure on delayed cerebral ischemia (DCI) and outcome.

Methods: Ninety-eight patients with aneurysmal SAH were recruited.

Relationship of vascular wall tension and autoregulation following traumatic brain injury.

Background: The vascular wall tension (WT) of small cerebral vessels can be quantitatively estimated through the concept of critical closing pressure (CrCP), which denotes the lower limit of arterial blood pressure (ABP), below which small cerebral arterial vessels collapse and blood flow ceases. WT can be expressed as the difference between CrCP and intracranial pressure (ICP) and represent active vasomotor tone. In this study, we investigated the association of WT and CrCP with autoregulation and outcome of a large group of patients after traumatic brain injury (TBI).

Cessation of diastolic cerebral blood flow velocity: the role of critical closing pressure.

Background: Reducing cerebral perfusion pressure (CPP) below the lower limit of autoregulation (LLA) causes cerebral blood flow (CBF) to become pressure passive. Further reductions in CPP can cause cessation of CBF during diastole. We hypothesized that zero diastolic flow velocity (FV) occurs when diastolic blood pressure becomes less than the critical closing pressure (CrCP).

Monitoring of spinal cord perfusion pressure in acute spinal cord injury: initial findings of the injured spinal cord pressure evaluation study*.

Objectives: To develop a technique for continuously monitoring intraspinal pressure at the injury site (intraspinal pressure) after traumatic spinal cord injury.

Design: A pressure probe was placed subdurally at the injury site in 18 patients who had isolated severe traumatic spinal cord injury (American Spinal Injuries Association grades A-C). Intraspinal pressure monitoring started within 72 hours of the injury and continued for up to a week.