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Increasing mean airway pressure reduces functional MRI (fMRI) signal in the primary visual cortex
I H Lorenz1, C Kolbitsch, C Hörmann
1Department of Anesthesia and Intensive Care Medicine, University of Innsbruck, Austria.
Abstract:
Changes in both blood flow and blood oxygenation determine the functional MRI (fMRI) signal. In the present study factors responsible for blood oxygenation (e.g., FiO(2)) were held constant so that changes in pixel count would above all reflect changes in regional cerebral blood flow (rCBF). Continuous positive airway pressure (CPAP) breathing at 12 cm H(2)O, which was previously shown to influence rCBF, was applied in human volunteers (n = 19) to investigate the sensitivity of fMRI for changes in rCBF caused by increased mean airway pressure. Increasing the mean airway pressure decreased the pixel count in the primary visual cortex (median (range)): baseline: 219 (58-425) pixels vs. CPAP (12 cm H(2)O): 92 (0-262) pixels). These findings indicate that fMRI is sensitive to detect a reduced rCBF-response in the primary visual cortex. The underlying mechanism is likely to be a reduced basal rCBF due to constriction and/or compression of postcapillary venoles during CPAP breathing. These findings are important for interpreting fMRI results in awake and in artificially respirated patients, in whom positive airway pressure is used to improve pulmonary function during the diagnostic procedure.
Insights
Functional MRI (fMRI) detects reduced regional cerebral blood flow (rCBF) during continuous positive airway pressure (CPAP) breathing. This sensitivity is crucial for interpreting fMRI in patients receiving positive airway pressure therapy.
Area of Science:
- Neuroimaging
- Physiology
- Medical Engineering
Background:
- Functional MRI (fMRI) signal relies on blood flow and oxygenation.
- Previous research indicates continuous positive airway pressure (CPAP) affects regional cerebral blood flow (rCBF).
- Understanding fMRI sensitivity to rCBF changes under positive airway pressure is vital for clinical applications.
Purpose of the Study:
- To assess the sensitivity of fMRI in detecting changes in rCBF.
- To investigate the impact of increased mean airway pressure via CPAP on fMRI signal.
- To explore the physiological mechanisms underlying observed fMRI signal alterations.
Main Methods:
- fMRI was employed in 19 human volunteers under controlled conditions.
- Blood oxygenation factors (e.g., FiO2) were kept constant to isolate rCBF effects.
- Volunteers underwent CPAP breathing at 12 cm H2O to measure changes in visual cortex pixel counts.
Main Results:
- A significant decrease in pixel count was observed in the primary visual cortex during CPAP.
- Baseline pixel count was 219 (58-425), reducing to 92 (0-262) under CPAP.
- These results demonstrate fMRI's capacity to detect reduced rCBF.
Conclusions:
- fMRI is sensitive to detecting reduced rCBF in the primary visual cortex during CPAP.
- The observed reduction in rCBF is likely due to venule constriction or compression.
- Findings are critical for interpreting fMRI in patients undergoing positive airway pressure therapy.