Personalized Ventilation to Multiple Patients Using a Single Ventilator: Description and Proof of Concept.

Objectives: To design and test a ventilator circuit that can be used for ventilation of two or more patients with a single ventilator, while allowing individualization of tidal volume, fractional concentration of oxygen, and positive end-expiratory pressure to each patient, irrespective of the other patient's respiratory system mechanics.

Design: Description and proof of concept studies.

Settings: Respiratory therapy laboratory.

Long-term changes in cerebrovascular reactivity following EC-IC bypass for intracranial steno-occlusive disease.

The purpose of this retrospective observational study is to investigate the long-term changes in cerebrovascular reactivity (CVR) as a measure of cerebral hemodynamics in patients with intracranial steno-occlusive disease (IC-SOD) after they have undergone an Extracranial-intracranial (EC-IC) bypass. Twenty-six patients suffering from IC-SOD were selected from our CVR database. Nineteen patients underwent unilateral and 7 underwent bilateral revascularization.

Measurement of Cerebrovascular Reactivity as Blood Oxygen Level-Dependent Magnetic Resonance Imaging Signal Response to a Hypercapnic Stimulus in Mechanically Ventilated Patients.

Background: Impaired cerebrovascular reactivity (CVR) is an important prognostic marker of stroke. Most measures of CVR lack (1) a reproducible vasoactive stimulus and (2) a high time and spatial resolution measure of cerebral blood flow (CBF), particularly for mechanically ventilated patients. The aim of our study was to investigate the feasibility of measuring CVR using sequential gas delivery circuit and gas blender for precise targeting of end-tidal PCO (PetCO), and blood oxygen level-dependent magnetic resonance imaging (BOLD-MRI) signal as a surrogate of CBF, in mechanically ventilated patients.

Assessing the effect of unilateral cerebral revascularisation on the vascular reactivity of the non-intervened hemisphere: a retrospective observational study.

Objectives: Unilateral haemodynamically significant large-vessel intracranial stenosis may be associated with reduced blood-oxygen-level-dependent (BOLD) cerebrovascular reactivity (CVR), an indicator of autoregulatory reserve. Reduced CVR has been associated with ipsilateral cortical thinning and loss in cognitive function. These effects have been shown to be reversible following revascularisation.

Reduced contralateral cerebrovascular reserve in patients with unilateral steno-occlusive disease.

Unlabelled: The purpose of this study was to evaluate cerebrovascular reactivity (CVR) of major arterial vascular territories, particularly in the contralateral hemodynamically unaffected hemisphere, in patients with unilateral internal carotid artery (ICA) steno-occlusive disease compared to control subjects with risk factors for cerebrovascular disease.

Methods: In this retrospective observational study, twenty-seven patients with right-sided unilateral ICA steno-occlusive disease (age range, 25 to 91 years; 17 males) and twenty-one patients with left-sided unilateral ICA steno-occlusive disease (age range, 24 to 83 years; 14 males) and 41 control subjects were studied. CVR was quantitated as the change in blood oxygen level dependent (BOLD) MRI signal (as a surrogate of cerebral blood flow), in response to a consistently applied step change in the arterial partial pressure of carbon dioxide (PaCO2).

BOLD MRI and early impairment of cerebrovascular reserve after aneurysmal subarachnoid hemorrhage.

Currently no biological or radiological marker is available to identify patients at risk of delayed ischemic deficit (DIND) after aneurysmal subarachnoid hemorrhage (aSAH). We hypothesized whether MR-based quantitative assessment of cerebrovascular reserve (CVR) would detect early radiological markers of vasospasm and DIND. This manuscript describes our initial experience with this population.

Vascular steal explains early paradoxical blood oxygen level-dependent cerebrovascular response in brain regions with delayed arterial transit times.

Introduction: Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) during manipulation of inhaled carbon dioxide (CO2) can be used to measure cerebrovascular reactivity (CVR) and map regions of exhausted cerebrovascular reserve. These regions exhibit a reduced or negative BOLD response to inhaled CO2. In this study, we sought to clarify the mechanism behind the negative BOLD response by investigating its time delay (TD).

CO2 blood oxygen level-dependent MR mapping of cerebrovascular reserve in a clinical population: safety, tolerability, and technical feasibility.

Purpose: To evaluate the safety, tolerability, and technical feasibility of mapping cerebrovascular reactivity (CVR) in a clinical population by using a precise prospectively targeted CO(2) stimulus and blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging.

Materials And Methods: A chart review was performed of all CVR studies from institutional review board-approved projects at a tertiary care hospital between January 1, 2006, and December 1, 2010. Informed consent was obtained.

The interaction of carbon dioxide and hypoxia in the control of cerebral blood flow.

Both hypoxia and carbon dioxide increase cerebral blood flow (CBF), and their effective interaction is currently thought to be additive. Our objective was to test this hypothesis. Eight healthy subjects breathed a series of progressively hypoxic gases at three levels of carbon dioxide.

Impact of extracranial-intracranial bypass on cerebrovascular reactivity and clinical outcome in patients with symptomatic moyamoya vasculopathy.

Background And Purpose: The purpose of this study was to evaluate in symptomatic moyamoya patients the effect of surgical revascularization on impaired cerebrovascular reactivity (CVR) and its relationship to clinical outcome.

Methods: Brain revascularization was performed using a direct superficial temporal artery to middle cerebral artery bypass or indirect encephalo-dural-arterial synangiosis. CVR was measured pre- and 3 months postoperatively using blood oxygen level-dependent MRI during iso-oxic hypercapnic changes in end-tidal carbon dioxide.

Surgical revascularization reverses cerebral cortical thinning in patients with severe cerebrovascular steno-occlusive disease.

Background And Purpose: Chronic deficiencies in regional blood flow lead to cerebral cortical thinning without evidence of gross tissue loss at the same time as potentially negatively impacting on neurological and cognitive performance. This is most pronounced in patients with severe occlusive cerebrovascular disease in whom affected brain areas exhibit "steal physiology," a paradoxical reduction of cerebral blood flow in response to a global vasodilatory stimulus intended to increase blood flow. We tested whether surgical brain revascularization that eliminates steal physiology can reverse cortical thinning.

Measurement of cerebrovascular reactivity in pediatric patients with cerebral vasculopathy using blood oxygen level-dependent MRI.

Background And Purpose: Cerebrovascular reactivity (CVR) is an indicator of cerebral hemodynamics. In adults with cerebrovascular disease, impaired CVR has been shown to be associated with an increased risk of stroke. In children, however, CVR studies are not common.

The effect of hypercarbia and hyperoxia on the total blood flow to the retina as assessed by magnetic resonance imaging.

Purpose: The feasibility of measuring total blood flow to the retina with Arterial Spin Labeling Magnetic Resonance Imaging (ASL-MRI) has been described previously. In the present study, the hypothesis was that the reactivity that the ASL-MRI detects at the human retina is dominated by the choroidal blood flow, and thus it may serve as a useful tool for quantitative assessment of the choroidal vascular reactivity.

Methods: Before imaging, the intraocular pressure (IOP) was measured in the study eye of nine clinically healthy subjects (four males) while the subject performed the ventilatory protocol subsequently imaged by the scanner.

Impaired peri-nidal cerebrovascular reserve in seizure patients with brain arteriovenous malformations.

Epileptic seizures are a common presentation in patients with newly diagnosed brain arteriovenous malformations, but the pathophysiological mechanisms causing the seizures remain poorly understood. We used magnetic resonance imaging-based quantitative cerebrovascular reactivity mapping and conventional angiography to determine whether seizure-prone patients with brain arteriovenous malformations exhibit impaired cerebrovascular reserve or morphological angiographic features predictive of seizures. Twenty consecutive patients with untreated brain arteriovenous malformations were recruited (10 with and 10 without epileptic seizures) along with 12 age-matched healthy controls.

Exaggerated increase in cardiac output during exercise in patients with peripheral high-flow arteriovenous malformations.

Purpose: To test the hypothesis that cardiac output (Q) in patients with arteriovenous malformations (AVMs) is normal at rest and increases disproportionately during exercise.

Materials And Methods: Q was measured in eight patients with large peripheral AVMs and in nine healthy subjects using a noninvasive carbon dioxide (CO₂)-based differential Fick method. Subjects were tested while seated at rest and during mild exercise (repeated leg straightening while sitting).

Impaired cerebrovascular reactivity with steal phenomenon is associated with increased diffusion in white matter of patients with Moyamoya disease.

Background And Purpose: Reduced cerebrovascular reactivity (CVR) with steal phenomenon is an independent predictor for stroke and may indicate tissue exposed to episodic low-grade ischemia. The apparent diffusion coefficient (ADC) calculated using diffusion-weighted MRI is effective in characterizing focal brain ischemia and subtle structural changes in normal-appearing white matter (WM). We hypothesized that regions of steal phenomenon are associated with increased ADC in normal-appearing WM of patients with Moyamoya disease.

Steal physiology is spatially associated with cortical thinning.

Background: The physiological impact of severely impaired cerebral autoregulatory vascular reactivity on cortical integrity is unknown. The purpose of this study is to determine the relationship between severe impairment of autoregulatory flow control associated with steal phenomenon and its impact on cortical thickness.

Methods: 250 blood oxygen level dependent (BOLD) MRI cerebrovascular reactivity (CVR) studies were reviewed in order to identify subjects with severe unilateral exhausted cerebrovascular reserve demonstrating steal physiology but with normal appearing cortex on fluid attenuated inversion recovery imaging.

A simple and portable breathing circuit designed for ventilatory muscle endurance training (VMET).

Background: Ventilatory muscle endurance training (VMET) involves increasing minute ventilation (V (E)) against a low flow resistance at rest to simulate the hyperpnea of exercise. Ideally, VMET must maintain normocapnia over a wide range of V (E). This can be achieved by providing a constant fresh gas flow to a sequential rebreathing circuit.

Ophthalmic injuries from a TASER.

The TASER (TASER International) is an energy-conducting weapon, that is becoming more frequently used by law enforcement officials to subdue combative individuals. Though generally regarded as a safe alternative, the use of such weapons has been reported to cause serious injuries. We describe a case in which ocular injuries were sustained by impalement with a TASER dart.

BOLD-MRI cerebrovascular reactivity findings in cocaine-induced cerebral vasculitis.

Background: An 18-year-old woman presented to a regional stroke center with dysphasia and right hemiparesis 2 days after consuming alcohol and inhaling cannabis and -- for the first time -- cocaine.

Investigations: Physical examination, blood tests for inflammatory markers, vasculitis and toxicology screen, echocardiography, electrocardiography, CT scanning, brain MRI, magnetic resonance angiography, magnetic resonance vessel wall imaging, catheter angiography, and correlation of blood oxygen level-dependent (BOLD)-MRI signal intensity with changes in end-tidal partial pressure of carbon dioxide.

Diagnosis: Cocaine-induced cerebral vasculitis.

Selective reduction of blood flow to white matter during hypercapnia corresponds with leukoaraiosis.

Background And Purpose: Age-related white matter disease (leukoaraiosis) clusters in bands in the centrum semiovale, about the occipital and frontal horns of the lateral ventricles, in the corpus callosum, and internal capsule. Cerebrovascular anatomy suggests that some of these locations represent border zones between arterial supply territories. We hypothesized that there are zones of reduced cerebrovascular reserve (susceptible to selective reductions in blood flow, ie, steal phenomenon) in the white matter of young, healthy subjects, the physiological correlate of these anatomically defined border zones.

Mapping cerebrovascular reactivity using blood oxygen level-dependent MRI in Patients with arterial steno-occlusive disease: comparison with arterial spin labeling MRI.

Background And Purpose: Blood oxygen level-dependent MRI (BOLD MRI) of hypercapnia-induced changes in cerebral blood flow is an emerging technique for mapping cerebrovascular reactivity (CVR). BOLD MRI signal reflects cerebral blood flow, but also depends on cerebral blood volume, cerebral metabolic rate, arterial oxygenation, and hematocrit. The purpose of this study was to determine whether, in patients with stenoocclusive disease, the BOLD MRI signal response to hypercapnia is directly related to changes in cerebral blood flow.