Iterative analysis of cerebrovascular reactivity dynamic response by temporal decomposition.

Objective: To improve quantitative cerebrovascular reactivity (CVR) measurements and CO arrival times, we present an iterative analysis capable of decomposing different temporal components of the dynamic carbon dioxide- Blood Oxygen-Level Dependent (CO -BOLD) relationship.

Experimental Design: Decomposition of the dynamic parameters included a redefinition of the voxel-wise CO arrival time, and a separation from the vascular response to a stepwise increase in CO (Delay to signal Plateau - DTP) and a decrease in CO (Delay to signal Baseline -DTB). Twenty-five (normal) datasets, obtained from BOLD MRI combined with a standardized pseudo-square wave CO change, were co-registered to generate reference atlases for the aforementioned dynamic processes to score the voxel-by-voxel deviation probability from normal range.

The CO2 stimulus for cerebrovascular reactivity: Fixing inspired concentrations vs. targeting end-tidal partial pressures.

Cerebrovascular reactivity (CVR) studies have elucidated the physiology and pathophysiology of cerebral blood flow regulation. A non-invasive, high spatial resolution approach uses carbon dioxide (CO2) as the vasoactive stimulus and magnetic resonance techniques to estimate the cerebral blood flow response. CVR is assessed as the ratio response change to stimulus change.

Sequential gas delivery provides precise control of alveolar gas exchange.

Of the factors determining blood gases, only alveolar ventilation (VA) is amenable to manipulation. However, current physiology text books neither describe how breath-by-breath VA can be measured, nor how it can be precisely controlled in spontaneously breathing subjects. And such control must be effected independent of minute ventilation (VE) and the pattern of breathing.

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.