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Biomedical subjects

Marek Czosnyka

Publications and source records attributed to Marek Czosnyka.

At least 37 records · Page 2Linked to original sources
PubMed2004

Continuous assessment of cerebral autoregulation in subarachnoid hemorrhage.

UNLABELLED: Cerebral vasospasm remains a leading cause of morbidity and mortality after subarachnoid hemorrhage (SAH). Cerebral ischemia may ensue when autoregulation fails to compensate for spasm. We examined how autoregulation is affected by vasospasm by using transcranial Doppler. The moving correlation coefficient between slow changes of arterial blood pressure and mean or systolic flow velocity (FV), termed "Mx" and "Sx," respectively, was used to characterize cerebral autoregulation. Vasospasm was declared when the mean FV increased to more than 120 cm/s and the Lindegaard ratio was more than 3. This occurred in 15 of 32 SAH patients. On the basis of the bilateral transcranial Doppler recordings of the middle cerebral artery in vasospastic patients, Mx and Sx were calculated for baseline and vasospasm. Mx increased during vasospasm (0.46 +/- 0.32; mean +/- SD) and was significantly higher (P = 0.021) than at baseline (0.21 +/- 0.24). Sx was also increased (0.22 +/- 0.26 vs 0.05 +/- 0.21 at baseline; P = 0.03). Mx correlated with mean FV (r = 0.577; P = 0.025) and the Lindegaard ratio (r = 0.672; P < 0.006). Mx (P = 0.006) and Sx (P = 0.044) were higher on the vasospastic side (Mx, 0.44 +/- 0.27; Sx, 0.24 +/- 0.23) when compared with the contralateral side (Mx, 0.34 +/- 0.29; Sx, 0.16 +/- 0.25). The increased Mx and Sx during cerebral vasospasm demonstrate impaired cerebral autoregulation. Mx and Sx provide additional information on changes in autoregulation in SAH patients. IMPLICATIONS: The moving correlation coefficients between slow changes of arterial blood pressure and mean or systolic flow velocity, termed "Mx" and "Sx," respectively, characterize cerebral autoregulation but have not been applied to subarachnoid hemorrhage. A study in 15 patients revealed that Mx and Sx were significantly increased, indicating impaired autoregulation during vasospasm as compared with baseline, as well as on the side of vasospasm in comparison with the contralateral side.

Adult↗
PubMed2004

Pressure autoregulation and positron emission tomography-derived cerebral blood flow acetazolamide reactivity in patients with carotid artery stenosis.

OBJECTIVE: Testing autoregulation is of importance in predicting risk of stroke and managing patients with occlusive carotid arterial disease. The use of small spontaneous changes in arterial blood pressure and transcranial Doppler (TCD) flow velocity can be used to assess autoregulation noninvasively without the need for a cerebrovascular challenge. We have previously described an index (called "Mx") that achieves this. Negative or low positive values (<0.4) indicate intact pressure autoregulation, whereas an Mx greater than 0.4 indicates diminished autoregulation. The objective of this study was to compare acetazolamide reactivity of positron emission tomography (PET)-derived cerebral blood flow (CBF) with Mx in patients with carotid arterial disease. METHODS: In 40 patients with carotid arterial disease, we used bilateral TCD recordings of the middle cerebral artery to derive Mx and compared this with PET-derived CBF measurements of acetazolamide reactivity. RESULTS: Mx correlated inversely with baseline PET CBF (P = 0.042, R = -0.349) but not with postacetazolamide CBF or cerebrovascular reactivity to acetazolamide. This may reflect discordance between pressure autoregulation and acetazolamide reactivity. Mx correlated significantly with degree of internal carotid artery stenosis (P = 0.022, R = 0.38), whereas CBF reactivity to acetazolamide did not correlate with Mx (P = 0.22). After the administration of acetazolamide, slow-wave activity in blood pressure and TCD flow velocity recordings was seen to diminish, rendering the calculation of Mx unreliable after acetazolamide. CONCLUSION: The measurement of Mx offers a noninvasive, safe technique for assessing abnormalities of pressure autoregulation in patients with carotid arterial disease.

Acetazolamide↗
PubMed2003

Assessment of cerebrovascular autoregulation in head-injured patients: a validation study.

BACKGROUND AND PURPOSE: Cerebrovascular autoregulation is frequently measured in head-injured patients. We attempted to validate 4 bedside methods used for assessment of autoregulation. METHODS: PET was performed at a cerebral perfusion pressure (CPP) of 70 and 90 mm Hg in 20 patients. Cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRo2) were determined at each CPP level. Patients were sedated with propofol and fentanyl. Norepinephrine was used to control CPP. During PET scanning, transcranial Doppler (TCD) flow velocity in the middle cerebral artery was monitored, and the arterio-jugular oxygen content difference (AJDo2) was measured at each CPP. Autoregulation was determined as the static rate of autoregulation based on PET (SROR(PET)) and TCD (SROR(TCD)) data, based on changes in AJDo2, and with 2 indexes based on the relationship between slow waves of CPP and flow velocity (mean velocity index, Mx) and between arterial blood pressure and intracranial pressure (pressure reactivity index, PRx) RESULTS: We found significant correlations between SROR(PET) and SROR(TCD) (r2=0.32; P<0.01) and between SROR(PET) and PRx (r2=0.31; P<0.05). There were no significant associations between PET data and autoregulation as assessed by changes in AJDo2. Global CMRo2 was significantly lower at the higher CPP (P<0.01). CONCLUSIONS: Despite some variability, SROR(TCD) and PRx may provide useful approximations of autoregulation in head-injured patients. At least with our methods, CMRo2 changes with the increase in CPP; hence, flow-metabolism coupling may affect the results of autoregulation testing.

Adolescent↗
PubMed2003

Tissue oxygen reactivity and cerebral autoregulation after severe traumatic brain injury.

OBJECTIVE: To study the relationship between arterial blood pressure, intracranial pressure, directly measured brain tissue oxygenation (PtiO2), and middle cerebral artery blood flow velocity in severely head-injured patients. DESIGN: Prospective study. SETTING: Neurosurgical intensive care unit. PATIENTS A total of 14 patients with severe head injury. INTERVENTIONS: Pharmacologic blood pressure manipulations using norepinephrine. MEASUREMENTS AND MAIN RESULTS: We assessed the magnitude of PtiO2 related to changes in cerebral perfusion pressure in 12 of the patients. We calculated in all the static rate of regulation, which is an index to describe the change of cerebrovascular resistance, using cerebral artery blood flow velocity in relation to changing cerebral perfusion pressure. Finally, we calculated the rate of change in PtiO2, which quantifies the percentage of change in PtiO2 divided by the percentage of change in cerebral perfusion pressure. It is a new marker for cerebral tissue oxygen regulation based on direct measurement of PtiO2. There was a plateau phase for the cerebral perfusion pressure-PtiO2 relation that was similar to the autoregulatory plateau seen in the relationship between cerebral perfusion pressure and cerebral artery blood flow velocity. The rate of change in PtiO2 demonstrated a significant correlation with the static rate of regulation (R = -.61, <.05). A decrease in intracranial pressure when arterial blood pressure increased from 70 to 90 mm Hg was strongly correlated with static rate of regulation (R =.79, <.001). CONCLUSIONS Cerebral tissue PO2 demonstrates a plateau phase similar to what is known about cerebral blood flow velocity, which suggests a close link between cerebral blood flow and oxygenation. Static cerebral autoregulation is significantly correlated with cerebral tissue oxygen reactivity.

Adult↗
PubMed2003

Responses of posttraumatic pericontusional cerebral blood flow and blood volume to an increase in cerebral perfusion pressure.

In and around traumatic contusions, cerebral blood flow (CBF) is often near or below the threshold for ischemia. Increasing cerebral perfusion pressure (CPP) in patients with head injuries may improve CBF in these regions. However, the pericontusional response to this intervention has not been studied. Using positron emission tomography (PET), we have quantified the response to an increase in CPP in and around contusions in 18 contusions in 18 patients. Regional CBF and cerebral blood volume (CBV) were measured with PET at CPPs of 70 and 90 mmHg using norepinephrine to control CPP. Based upon computed tomography, regions of interest (ROIs) were placed as two concentric ellipsoids, each of 1-cm width, around the core of the contusions. Measurements were compared with a control ROI in tissue with normal anatomic appearance. Baseline CBF and CBV increased significantly with increasing distance from the core of the lesion. The increase in CPP led to small increases in CBF in all ROIs except the core. The largest absolute CBF increase was found in the control ROI. Relative CBF increases did not differ between ROIs so that ischemic areas remained ischemic. Pericontusional oedema on computed tomography was associated with lower absolute values of CBF and CBV but did not differ from nonoedematous tissue in the relative response to CPP elevation.

Adolescent↗
PubMed2003

Adaptive noninvasive assessment of intracranial pressure and cerebral autoregulation.

BACKGROUND AND PURPOSE: A mathematical model has previously been introduced to estimate noninvasively intracranial pressure (nICP). In the present multicenter study, we investigated the ability of model to adapt to the state of cerebral autoregulation (SCA). This modification was intended to improve the quality of nICP estimation and noninvasive assessment of pressure reactivity of the cerebrovascular system. METHODS: We studied 145 patients after severe head injuries or stroke. All patients had direct ICP, arterial blood pressure (ABP), and transcranial Doppler middle cerebral artery blood flow velocity (FV) monitored. The SCA was assessed by moving correlation (Mx index) of cerebral perfusion pressure (CPP=ABP-ICP) and cerebral blood flow velocity and correlation of ABP and ICP (PRx index). nICP was calculated from ABP and FV waveforms. When nICP was used instead of ICP, the SCA was continuously estimated, and the model was dynamically adapted to the SCA. RESULTS: High and moderate correlations between invasively (Mx, PRx) and noninvasively (nMx, nPRx) estimated autoregulation indexes were observed (Mx: R=0.90, P<0.001; PRx: R=0.62, P<0.001). Values of Mx and nMx indicated contradictory SCA in 4 of 167 evaluated recordings; values of PRx and nPRx were contradictory in 27 recordings. When the model was adapted to the SCA, the mean error of ICP estimation decreased significantly (P<0.005). CONCLUSIONS: Continuous adaptation of the model to SCA improves the accuracy of noninvasive estimation of ICP and ICP dynamics. The same model provides a noninvasive and continuous assessment of SCA.

Adolescent↗
PubMed2003

The effects of large-dose propofol on cerebrovascular pressure autoregulation in head-injured patients.

UNLABELLED: In healthy individuals, cerebrovascular pressure autoregulation is preserved or even improved when propofol is infused. We examined the effect of an increase in propofol plasma concentration on pressure autoregulation in 10 head-injured patients. Using target-controlled infusions, the static rate of autoregulation was determined at a moderate (2.3 +/- 0.4 microg/mL) and a large (4.3 +/- 0.04 microg/mL) plasma target concentration of propofol. Using norepinephrine to control cerebral perfusion pressure, transcranial Doppler measurements from the middle cerebral artery were made at a cerebral perfusion pressure of 70 and 85 mm Hg at each propofol concentration. Middle cerebral artery flow velocities at the large propofol concentration were significantly lower than at the moderate concentration, without any concurrent increase in arterio-jugular difference in oxygen content, a finding compatible with maintained flow-metabolism coupling. Despite this, static rate of autoregulation decreased significantly from 54% +/- 36% to 28% +/- 35% (P = 0.029). Our data suggest that after head injury, the cerebrovascular effects of propofol are different from those observed in healthy individuals. We propose that large doses of propofol should be used cautiously in head-injured patients, because there is the potential to increase the injured brain's vulnerability to secondary insults. IMPLICATIONS: Propofol is used for sedation and control of intracranial pressure in head-injured patients. In contrast to previous data from healthy individuals, we show a deterioration of cerebrovascular pressure autoregulation with fast propofol infusion rates after head injury. Large propofol doses may increase the injured brain's vulnerability to secondary insults.

Adult↗
PubMed2003

Hydrodynamic properties of extraventricular drainage systems.

OBJECTIVE: Extraventricular drains (EVDs) are intended to control intracranial pressure for patients with acute disorders of the cerebrospinal fluid circulation. We tested five commercially available EVDs to assess their fundamental hydrodynamic properties, which determine the quality of this control. METHODS: The five most frequently used drainage systems were tested. The pressure responses to water flow from a computer-controlled infusion pump were studied in the rig constructed in the UK Shunt Evaluation Laboratory (Cambridge, England). EVDs were studied under normal conditions and after brief (20-s) contact of the vent located in the drip chamber with the test reagent. Pure water and water with 10% rat blood content were used for testing. RESULTS: All of the tested EVDs demonstrated low hydrodynamic resistance [<3.5 mm Hg/(ml/min)], indicating their ability to control intracranial pressure. When the drip chamber vents were in brief contact with the reagent, the hydrodynamic properties of two models were unaffected. For the three other EVDs, blockage of the drip chamber was observed, leading to increases in the inlet pressure to more than 150 mm Hg. All three models that demonstrated obstruction have the same vent configuration, which allows cerebrospinal fluid to accumulate close to the filter when the drip chamber is held horizontally. This feature was confirmed to be the cause of the blockage. CONCLUSION: In clinical practice, special care should be taken to avoid contact of the drip chamber vents with cerebrospinal fluid, which causes obstruction and may lead to the development of gross intracranial hypertension. Specific configurations, as identified in this testing program, are safer than others in this respect.

Animals↗
PubMed2003

Asymmetry of pressure autoregulation after traumatic brain injury.

OBJECT: The aim of this study was to assess the asymmetry of autoregulation between the left and right sides of the brain by using bilateral transcranial Doppler ultrasonography in a cohort of patients with head injuries. METHODS: Ninety-six patients with head injuries comprised the study population. All significant intracranial mass lesions were promptly removed. The patients were given medications to induce sedation and paralysis, and artificial ventilation. Arterial blood pressure (ABP) and intracranial pressure (ICP) were monitored in an invasive manner. A strategy based on the patient's cerebral perfusion pressure (CPP = ABP - ICP) was applied: CPP was maintained at a level higher than 70 mm Hg and ICP at a level lower than 25 mm Hg. The left and right middle cerebral arteries were insonated daily, and bilateral flow velocities (FVs) were recorded. The correlation coefficient between the CPP and FV, termed Mx, was calculated and time-averaged over each recording period on both sides. An Mx close to 1 signified that slow fluctuations in CPP produced synchronized slow changes in FV, indicating a defective autoregulation. An Mx close to 0 indicated preserved autoregulation. Computerized tomography scans in all patients were reviewed; the side on which the major brain lesion was located was noted and the extent of the midline shift was determined. Outcome was measured 6 months after discharge. The left-right difference in the Mx between the hemispheres was significantly higher in patients who died than in those who survived (0.16 +/- 0.04 compared with 0.08 +/- 0.01; p = 0.04). The left-right difference in the Mx was correlated with a midline shift (r = -0.42; p = 0.03). Autoregulation was worse on the side of the brain where the lesion was located (p < 0.035). CONCLUSIONS: The left-right difference in autoregulation is significantly associated with a fatal outcome. Autoregulation in the brain is worse on the side ipsilateral to the lesion and on the side of expansion in cases in which there is a midline shift.

Adolescent↗
PubMed2003

Positron emission tomographic cerebral perfusion disturbances and transcranial Doppler findings among patients with neurological deterioration after subarachnoid hemorrhage.

OBJECTIVE: After aneurysmal subarachnoid hemorrhage, approximately 30% of patients experience delayed neurological deficits, related in part to arterial vasospasm and dysautoregulation. Transcranial Doppler (TCD) ultrasonography is commonly used to noninvasively detect arterial vasospasm. We studied cerebral perfusion patterns and associated TCD indices for 25 patients who developed clinical signs of delayed neurological deficits. METHODS: Patients were treated in a neurosurgical intensive care unit and were studied if they exhibited delayed focal or global neurological deterioration. Positron emission tomographic cerebral blood flow (CBF) studies and TCD studies measuring the mean flow velocity (FV) of the middle cerebral artery and the middle cerebral artery FV/internal carotid artery FV ratio (with the internal carotid artery FV being measured extracranially at the cranial base) were performed. Glasgow Outcome Scale scores were assessed at 6 months. RESULTS: A markedly heterogeneous pattern of CBF distribution was observed, with hyperemia, normal CBF values, and reduced flow being observed among patients with delayed neurological deficits. TCD indices were not indicative of the cerebral perfusion findings. The mean CBF value was slightly lower for patients who did not survive (32.3 ml/100 g/min), compared with those who did survive (36.0 ml/100 g/min, P = 0.05). CONCLUSION: Among patients who developed delayed neurological deficits after aneurysmal subarachnoid hemorrhage, a wide range of cerebral perfusion disturbances was observed, calling into question the traditional concept of large-vessel vasospasm. Commonly used TCD indices do not reflect cerebral perfusion values.

Adult↗
PubMed2003

Symmetry of cerebral hemodynamic indices derived from bilateral transcranial Doppler.

OBJECTIVE: The authors evaluated with bilateral transcranial Doppler (TCD) ultrasonography the norm of interhemispheric difference for several cerebrovascular hemodynamic parameters. METHODS: Forty-four volunteers (33 male, 11 female; average age = 21 years; range, 20-23 years) were studied. The authors recorded bilateral systolic, diastolic, and mean flow velocity (FV) and noninvasive systolic, diastolic, and mean arterial blood pressure. Calculated indices included Gosling's pulsatility index (GPI), an index of autoregulation (Mx), critical closing pressure (CCP), and a noninvasive estimator of cerebral perfusion pressure (nCPP). All indices were averaged per side and patient. For each parameter, the left-right correlation coefficient (r2) and the 95% confidence limit of the left-right differences were calculated. RESULTS: All TCD-derived indices displayed significant correlations between the left and right sides: r2 = 0.49 for mean FV (FVm), r2 = 0.66 for GPI, r2 = 0.79 for Mx, r2 = 0.93 for CCP, and r2 = 0.94 for nCPP. The 95% confidence intervals for the left-right differences were 20 cm/s for FVm, 0.16 for GPI, 0.18 for Mx, 13 mm Hg for CCP, and 4.6 mm Hg for nCPP. CONCLUSIONS: This study gives the reference values for the assessment of left-right symmetry of cerebral hemodynamics using various TCD-derived indices. These reference values should be useful for clinical studies assessing the left-right asymmetry of cerebral hemodynamics on a daily basis.

Adult↗
PubMed2002

Clinical applications of a non-invasive ICP monitoring method.

BACKGROUND AND PURPOSE: Until now the assessment of intracranial pressure (ICP) requires invasive methods. A previously introduced mathematical model allowed the non-invasive estimation of ICP (nICP) from arterial blood pressure (ABP) and blood flow velocity (FV). In various studies we have investigated the accuracy of this method and possible clinical applications. METHODS AND RESULTS: Selected hemodynamic parameters, calculated from the cerebral blood FV and the ABP curves, were used to express the relationship between ABP input and ICP output by linear transformation rules. In several clinical studies the accuracy and possible benefits of this method of non-invasive ICP (nICP) assessment were investigated. ASSESSMENT OF ICP PLATEAU WAVES: In 17 severely head injured patients we verified this model by comparison of nICP and measured ICP during generation of plateau waves, recorded in seven of these patients. In all simulations plateau elevations of ICP were well replicated. The correlation coefficient between increase of nICP and real ICP was R=0.98; P<0.001. LUMBAR INFUSION TESTS: Twenty one hydrocephalic patients were studied. Parallel increases in real ICP and nICP during lumbar infusion tests were evidently visible. Resistance of cerebrospinal fluid outflow (Rcsf) was computed using nICP and compared with Rcsf computed from real ICP. The mean error between real and non-invasive Rcsf was 4.1+/-2.2 mmHg min/ml. CEREBRAL AUTOREGULATION: One hundred and forty five patients were studied after severe head injuries. The state of autoregulation was assessed by moving correlation of cerebral perfusion pressure (CPP=ABP-ICP) and FV (Mx index). nICP instead of ICP was used to continuously estimate the state of autoregulation and to dynamically adapt the nICP procedure to this state. A median error between ICP and nICP of 6.0 mmHg was observed. Directly and non-invasively assessed Mx indices correlated highly significantly (R=0.9; P<0.001). CONCLUSIONS: The results demonstrate that the nICP assessment model constitutes a reliable method to monitor ICP and may therefore provide various useful clinical applications.

Blood Flow Velocity↗