A5083264968- Neuroscience of respiration and sleep
- Heart Rate Variability and Autonomic Control
- Respiratory Support and Mechanisms
- Advanced MRI Techniques and Applications
- Traumatic Brain Injury and Neurovascular Disturbances
- High Altitude and Hypoxia
- Cardiovascular and exercise physiology
- Neuroendocrine regulation and behavior
- Cardiac Arrest and Resuscitation
- Sleep and Wakefulness Research
- Cerebrovascular and Carotid Artery Diseases
- Obstructive Sleep Apnea Research
- Sports Performance and Training
- Neonatal Respiratory Health Research
- Optical Imaging and Spectroscopy Techniques
- Chronic Obstructive Pulmonary Disease (COPD) Research
- MRI in cancer diagnosis
- Functional Brain Connectivity Studies
- Acute Ischemic Stroke Management
- Infant Health and Development
- Lanthanide and Transition Metal Complexes
- Advanced Neuroimaging Techniques and Applications
- Renal function and acid-base balance
- Thermoregulation and physiological responses
- Mechanical Circulatory Support Devices
University of Toronto
2016-2025
University Health Network
2015-2025
Thornhill Medical (Canada)
2012-2024
Toronto General Hospital
1975-2022
University of Manitoba
2022
Toronto General Hospital Research Institute
2022
St. Michael's Hospital
2022
Canadian Sleep Society
2020
Canadian Thoracic Society
2020
Canadiana.org
2020
Carbon dioxide (CO2) increases cerebral blood flow and arterial pressure. Cerebral not only due to the vasodilating effect of CO2 but also because increased perfusion pressure after autoregulation is exhausted. Our objective was measure responses both middle artery velocity (MCAv) mean (MAP) in human subjects using Duffin-type isoxic rebreathing tests. Comparisons hyperoxic with hypoxic tests enabled oxygen tension be determined. During MCAv response sigmoidal below a discernible threshold...
Current methods of forcing end-tidal PCO2 (PETCO2) and PO2 (PETO2) rely on breath-by-breath adjustment inspired gas concentrations using feedback loop algorithms. Such servo-control mechanisms are complex because they have to anticipate compensate for the respiratory response a given inspiratory concentration basis. In this paper, we introduce low flow method prospectively target control PETCO2 PETO2 independent each other minute ventilation in spontaneously breathing humans. We used change...
1. The incidence of entrainment breathing frequency by the rhythm exercise was detected a cross-correlation two frequencies. 2. During moderate, steady-state on bicycle ergometer at 50 rev/min, eight fifteen volunteers (53%) showed when pedalling speed kept constant with metronome, and three (20%) speedometer. 3. At 70 in second group volunteers, results were nine (60%) five (33%) respectively. 4. steady state treadmill, third 15 while walking, twelve (80%) running. 5. It is concluded that...
We examined the dependence of respiratory rhythm generation on rate CO2 production (VCO2) in six awake sheep using a venous-to-venous extracorporeal perfusion circuit that included two carbon dioxide membrane lungs (CDML) designed to facilitate removal from blood. As progressively greater proportions resting VCO2, were removed venous blood by CDML, there proportional reductions pulmonary excretion and minute volume ventilation (VE); when was CDML at equal its metabolic sheep, VE fell zero,...
Accurate measurements of arterial P(CO(2)) (P(a,CO(2))) currently require blood sampling because the end-tidal (P(ET,CO(2))) expired gas often does not accurately reflect mean alveolar and P(a,CO(2)). Differences between P(ET,CO(2)) P(a,CO(2)) result from regional inhomogeneities in perfusion exchange. We hypothesized that breathing via a sequential delivery circuit would reduce these sufficiently to allow accurate prediction P(ET,CO(2)). tested this hypothesis five healthy middle-aged men...
Objective White matter hyperintensities (WMH) observed on neuroimaging of elderly individuals are associated with cognitive decline and disability. However, the pathogenesis WMH remains poorly understood. We that regions reduced cerebrovascular reactivity (CVR) in white young correspond to most susceptible elderly. This finding prompted us consider CVR may play a role WMH. hypothesized precedes development Methods examined 45 subjects (age range = 50–91 years; 25 males) moderate–severe WMH,...
We define cerebral vascular reactivity (CVR) as the ratio of change in blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) signal (S) to an increase partial pressure CO2 (PCO2): % Δ S/Δ PCO2 mm Hg. Our aim was further characterize CVR into dynamic and static components then study 46 healthy subjects collated a reference atlas 20 patients with unilateral carotid artery stenosis. applied abrupt boxcar monitored S. convolved set first-order exponential functions whose time...
Although sleep apnoea is very common in patients with end-stage renal disease, the physiological mechanisms for this association have not yet been determined. The current authors hypothesised that altered respiratory chemo-responsiveness may play an important role. In total, 58 receiving treatment chronic dialysis were recruited overnight polysomnography. A modified Read rebreathing technique, which used to assess basal ventilation, ventilatory sensitivity and threshold, was completed before...
After defining the current approach to measuring hypoxic ventilatory response this paper explains why method is not appropriate for comparisons between individuals or conditions, and does adequately measure parameters of peripheral chemoreflex. A measurement regime therefore proposed that incorporates three procedures. The first procedure measures chemoreflex responsiveness both hypoxia CO(2) in terms hypoxia's effects on sensitivity recruitment threshold CO(2). second third procedures...
Attribution of vascular pathophysiology to reductions in cerebrovascular reactivity (CVR) is confounded by subjective assessment and the normal variation between anatomic regions. This study aimed develop an objective scoring abnormality. CVR was measured as ratio blood-oxygen-level-dependent magnetic resonance signal response divided increase CO2, standardized eliminate variability. A reference atlas generated coregistering maps from 46 healthy subjects into a standard space calculating...
Central chemoreceptor stimulation, by hypercapnia (acidosis), and peripheral, hypoxia plus hypercapnia, evoke reflex increases in ventilation sympathetic outflow. The assumption that central or peripheral chemoreceptor-mediated activation elicited when PCO2 parallels concurrent ventilatory responses is unproven. Applying a modified rebreathing protocol equilibrates whilst clamping O2 tension at either hypoxic hyperoxic concentrations, the independent muscle stimulus-response properties of...
This paper uses a steady-state modeling approach to describe the effects of changes in acid-base balance on chemoreflex control breathing. First, mathematical model is presented, which describes breathing by respiratory chemoreflexes; equations express dependence pulmonary ventilation Pco2 and Po2 at central peripheral chemoreceptors. These equations, with values as inputs chemoreceptors, are transformed hydrogen ion concentrations [H+] brain interstitial fluid arterial blood inputs, using...
1. The threshold of the ventilatory response to carbon dioxide mediated by peripheral chemoreceptors was determined under mild hypoxic conditions during both rest and exercise in eight volunteers. 2. method used an adaptation Read rebreathing technique, modified for hypoxia with prior hyperventilation. produced values ventilation which, when plotted against each other, exhibited three straight‐line segments differing slopes. break‐points were interpreted as resting peripheral‐...